Front suspension geometry...lets get in depth...

[Willis]

Almost every suspension geometry thread I can find is in reference to the rear. I'd like to talk about the front. With track-bar, without track bar, parabolic uppers, 3 mid-length arms, etc, etc...

The information I am looking for is in reference to the geometry involved in properly building a front suspension. The specific questions I have would be this:

Anti-dive, how is it calculated, and what effect does it have on road, and offroad? Where would the optimal anti-dive be set?

Instant Center. This is commonly talked about when building a rear 4 link suspension. This convergence point between the upper and lower control arms have a lot to do with anti-squat in rear application. However, in many situations in the front suspension, the instant center would be located just inches rear of the front links, usually under the front seats. How does the IC effect a front suspension, or is it only in reference to rears? And, what if the lower arm mounted higher than the upper arm, the arms would cross and the IC would end up somewhere around the front floor boards or even forward of that?

What about front steer (like rear steer, as in fore and aft movement of the axle during articulation). Is this as noticeable in a front application since you can easily correct it with steering input?

The reason I want to get in depth with this is that it seems a lot of people just build a front suspension and don't think about the geometry at hand. There are a lot of long arms fabricated at home, where the only paper used was the paper used to wipe their :moon: .

I have a bunch of designs on paper, from Beez's parabola, to Goat's 3 mid arm, to a 33" 'J' arm that mounts outside, but next to the frame rail. I want to build it right the first time, or at least get it close :D

Thanks,
Steve

[MaXJohnson]

Front and rear instance centers are derived by using the same method. Project the upper and lower arms out to a point where they converge. The front is no more likely to have a short virtual link than the rear. The rear IC locates where braking and acceleration torque react with the chassis; pushing up to counter-act the rearward pitching of the body during acceleration and pulling down to counter-act the forward pitching of the body during braking. With the front suspension the reverse happens. The virtual link, acting at the front IC pushes upward to counter-act the forward pithing of the body during braking and, in the case of 4WD, pulling down to counter-act the rearward pitching of the body acceleration. In both cases, the slope of a line drawn from the tire contact patch through the IC is used to determine the percentage of anti-squat, lift or dive.

For anti-squat considerations you will typically see the IC compared to a line extending from the rear tire contact patch forward to a point directly above the front axle centerline at the height of the CG. This is valid for rear wheel drive. When in 4-wheel drive, part of the available torque is sent to each axle. In the case of a part-time transfercase, this is usually a 50/50 split. In my opinion, to correctly calculate anti-squat & anti-lift in 4WD, a line should be extended from the contact patch of each wheel to a vertical line midway between each axle centerline. Compare the intersection of the front and rear lines with the height of the CG at this mid-point to calculate the percent contribution of each axle. Take an average of these two forces for a total anti-pitch calculation.

For braking anti-dive in front and anti-lift in the rear, use the above method, but the vertical line of comparison is based on the amount of braking force available to each axle. If the front brakes provide 65% of the braking force, the vertical line should be drawn 65% rearward of the total wheelbase length. Once again, the combined anti-dive and anti-lift force of both axles is used to determine the total anti-pitching force available.

The problem with anti-dive is that it increases the effective spring rate of the front suspension. For street use, you want enough anti-dive to minimize, but not eliminate front end dive under braking without a noticable increase in front end harshness. Lifting an XJ with short 4-link suspension arms will result in a very steep virtual arm. This creates way too much anti-dive. The end result is a harsh hiway ride. Off-road, the dramatic increase in spring rate makes it difficult to maintain tire contact which can reduce traction on downhill decents under braking.

Longer control arms, drop brackets and radius arm designs tend to reduce the virtual arm angle which lessens the amount of anti-dive. In virtually any link design the kind of lift needed for off-road use will result in more anti-dive than you would normally want. At the same time, the virtual arm angle will dictate the amount of anti-lift available when climbing. Anti-lift pulls the front end (sprung weight) down which is a good thing, but lessens the amount of traction available to the front tires which is a bad thing. I have yet to see any discussion of this topic recommend an optimal percentage for these anti-pitching forces. In most cases, it seems that minimizing anti-pitch percentage in the front is desirable.

Your example of mounting (at the chassis) the lower arms higher than the uppers would cause the pinion to angle downward in droop and upward in compression of the suspension. This is opposite of what you would want. It would also create an extremely short virtual link and result in extreme movement of the IC through the range of suspension travel. None of these traits are good.

Short suspension links and steep link angles increase axle steer; front or rear. Since the front axel also has steerable wheels with the potential for bump steer, axle steer can either work with or against bump steer. The two could actually cancel each other out under the right circumstances. Conversely, these two characteristics could be additive, making unwanted steering movement even worse. A vehicle is more sensitive to rear steering imput than front. A forklift is a good example. With this in mind, rear axle steer should be more noticable to the driver than front.

The advantage of Beezil's parabola is in the clearance it provides, not in the geometry of the suspension. An upper link shaped like an "A", a parabola or a horseshoe would all perform the same from a suspension dynamics point of view. The advantage of all three is the elimination of axle housing rotation with one side in droop and the other in compression. The disadvantage is increased bump steer and a single point of failure.

Richard,s 4-link is slightly longer than stock with modest changes in mounting points at the chassis and axle to help level out the arm angles. He has ended up with a design that lessons the amount of anti-pitch without the loss off clearance associated with longer radius arms. Based on his success, you have to agree that it's a pretty good compromise.

J-arms increase the effective length of a comparable rear (relative to the axle tube) mounted link. Longer links result in lesser amounts of longitudinal movement of the link pivot for a given amount of suspensin travel. This means less axle steer and less torsional stress on the axle tube when articulated.

Your questions open up a very broad discussion. I hope this helps.

[Willis]

Ok, so you're saying, in 4wd, you'd want the IC front and rear to be on a 50/50 center line on the chassis? The rear IC is usually projected to a point above the front axle. This point is usually between 50-80% of the CG, you want more lift, make it closer to the 80% mark, more squat, closer to the 50% mark.

So, what effect does the position, front to rear, of the IC have to do with suspension characteristics? Normally, one would project the rear tire contact patch forward to where the upper and lower links converge (like you said), and that line from the contact patch goes through the front tire. If that line is no longer going through the front tire, and is much steeper, say terminating at a point close to the transfer case, yet still between the 50-80% CG marks, you'd have to change your links to converge at that axle center point. I'd think this would create a steeper lower link.

You have helped a ton, and I need to hit the graph paper a little harder now. I understand more about the rear than front, and I think once I completely understand the rear, I can start transferring that information to front use. I plan on sticking with leaf springs in the rear for now, that may be a future project.

Thanks,
Steve

[MaXJohnson]

Ok, so you're saying, in 4wd, you'd want the IC front and rear to be on a 50/50 center line on the chassis?

No, what I'm saying is that the usual diagrams that you see on here, PBB, etc is correct for calculating anti-squat for a 2WD vehicle, but not for 4WD. This is not a difference is how you determine the placement of your instance centers, but rather how you compare IC reaction with the CG.

Look at it this way. You can draw a diagram of your rear suspension links in the side view to determine where your IC is. Compare the IC location with the anti-squat neutral line (rear contact patch to CG height above front axle) to determine AS%. Now do the same for the front suspension links to determine front anti-lift. Here's the problem. The values you get assumes that each axle get 100% of the engine torque available.

This is wrong. In a part-time transfercase (no center differential) each axle only recieves 50% of the torque. This means that your calculated AS% and AL% are double their actual value. Some fulltime transfercases split torque on an uneven basis, front to rear, say 60%-40%. This would have to be factored in as well.

If, for example, you calculated 80% anti-squat for the rear axle and 60% anti-lift for the front; the total anti-pitch force available through a 50-50 transfercase would be 1/2 the sum of these two values. My previous post indicated that the total anti-pitch force available would be the average of the front and rear percentages

(80%+60%)/2 = 70%.

This application of calculating the TOTAL 4WD anti-squat/lift values is derrived from an example in one of Forbe's Aird's books for determining total anti-dive/lift under braking. The method of determining the individual values is correct, but I am having trouble with his interpretation of the total force acting on the chassis being an average of the two individual values.

What all this means is that if you have a significant difference in the link design between the front and rear suspensions (most do) then the common method being tosses about will produce a significant error.

[Beezil]

just remember only a portion of this theoretical masterbatory nonsense applies to a big, trail-only vehicle getting put through the motions.....

plotting "lines and stuff" in a static 3-view renderings is a good start to design, but the physical limitations of your vehicle, and the methods that are available to you when you go to fabricate your design will be deciding factors...

applying a working f&r link suspension system to an xj can be maddening!

starting with a blank canvass (tube buggy) would be the most ideal obviously, but you wil learn a shitload using your xj as a beginning platform.

[XJJPR]

applying a working f&r link suspension system to an xj can be maddening!


Just check out how much Beezil has changed since he did his, and it wasn't for the better either. :D

[MaXJohnson]

just remember only a portion of this theoretical masterbatory nonsense applies to a big, trail-only vehicle getting put through the motions.....


Sounds like you think he should enter into the design phase wearing a blindfold. Seems like I recall some drawings you worked from in the beginnings of your golden arches. Which portion of this "theoretical masterbatory nonsnese" doesn't apply?

[Beezil]

yeah, read it.

I said "only a portion"....

all that stuff I worked on didn't exactly translate well to the ACTUAL VEHICLE when I began building.

and you missed this one:

"plotting "lines and stuff" in a static 3-view renderings is a good start to design"

where exactly, do you see me launching willis into building without a PLAN?

I'm just saying, IN MY EXPERIENCE, plotting lines and stuff is fine.....actually trying to adapt your design to an xj platform SUCKS. You end up compromising most important aspects of your design (or the platform, the XJ) in the process....

if we were building tube buggies from scratch, more of this shit could apply, and we could hold to our designs better, since we'd have a chance to build our rigs AROUND the suspension, if that's your priority.

the point I'm trying to make, since I've been there, is to not get hung up on paper planning too much. Try not to assume you have to post ten-thousand word inquiries on the jeep boards (like I did) and waste vaulable time NOT strategizing the actual CONSTRUCTION on the vehicle. i feel I wasted at least 4 weeks blabbing about it, and desgning something on paper I couldn't fit on my jeep.

[XJJPR]

He blabbed so long WE finished his designing in Moab. :D

right Sean?

hinkley

[Beezil]

hey, all it needed was some schedule 40!

get yo pipe, and yo nalgene

[MaXJohnson]

yeah, read it.

I said "only a portion"....


I asked "which portion doesn't apply"...

http://home.everestkc.net/alynloya/McDonalds_Arch.jpg

Willis started this post wanting to discuss front link design. I didn't get the impression he was ready to go full buggy.

[Beezil]

I didn't get the impression he was ready to go full buggy

now I know yer just fawkin with me....

nope, never pushed him into a buggy either...

just trying to give him a little advice that he doesn't waste his valuable time getting too hung up on every little detail.

*some* of it doesn't matter

*some* of it can't be applied due to the limitations of the xj platform.

when you actually build one of your own someday, you'll see what I'm talking about.

until then, keep posting the info, I'm still reading, and I'm still learning

[MaXJohnson]

...still wondering which *some* of it you think doesn't matter.

I've built plenty of my own junk, but will probably never build a buggy. It's not on my list.

Whether Willis or you or me or anyone else is building a buggy, an XJ or a bar-b-que grill that plugs into a hitch receiver, it's still a good idea to define constraints and build within them. You chose to change the constraints on your project. You end up with new constraints and built within them.

Thinking things through and schetching ideas out on paper is a good way to eliminate some bad design ideas before commiting to steel. Tossing around ideas on the internet, schetches on a garage floor, string on plywood; it's all good.

[XJJPR]

...still wondering which *some* of it you think doesn't matter.

I've built plenty of my own junk, but will probably never build a buggy. It's not on my list.

Whether Willis or you or me or anyone else is building a buggy, an XJ or a bar-b-que grill that plugs into a hitch receiver, it's still a good idea to define constraints and build within them. You chose to change the constraints on your project. You end up with new constraints and built within them.

Thinking things through and schetching ideas out on paper is a good way to eliminate some bad design ideas before commiting to steel. Tossing around ideas on the internet, schetches on a garage floor, string on plywood; it's all good.


I think what Beezil trying say, which I'm a beleiver in, is *some* times you just need to actaully get your hands dirty and *do it* to learn it. You might need the grinder a little more at first but in the end you might just learn something you will never see on paper or the floor.

mark

[Beezil]

yeah, okay, that's great.....don't know why you keep debating this......

never told him to "forget everything he read here and start building". Its all about the plan. yer making it sound like I want him to scratch his plan, and "to hell" with everything that's been discussed so far.....

once again, for the non-absorbant...

all I'm saying is, *some* of the things you will read and learn about in this thread, cannot be applied to the xj platform due to real physical and/or mechanical limitations.

*some* of these limitations can be overcome by compromising the platform (sawing the shit out of it).

*some* limitations will end up not being overcome due to cost/feasibility issues, or the inability to fabricate everything the design calls for.

I only brought up a tube buggy as a comparison to illustrate that a "blank canvass" is about the only way to employ *almost all* of the lessons learned here.

I'm wanting willis to learn everything he can which is why I'm not trying to add to the information you are already posting. I'm only giving him a "heads up" so that he understands, once he figured things out, and the light bulb goes off, he still has to deal with the realities, and be ready to make a ton of compromises. That process is frustrating, disappointing and time consuming. All thos evehicle dynamics books don't talk about that process when it comes to messing with xjs do they?

relax max, no one is calling your credibility into question. I'm just giving willis a heads up.....ya know, since I've actually done this....

Get back to the discussion at hand, I'm not trying to steal the thread, I'm enjoying it, and still learning.

since you asked, one of the things I think that isn't worth worrying about is anti-dive, for many reasons....I'm assuming on a trail rig, since I'm pretty sure thats what willis is building. There are a few things that prevent a theoretically "perfect" design, dialed in for the desired anti-dive....

pesky things like:

oil pan
axle location
frame rail dimensions
front driveshaft
tire clearance at full lock and stuff (locating links)
exhaust
steering linkages

these are realities, and most of them are a permanant part of the platform. All those groovey suspension dynamics (racecar) books assume that these are secondary features. Try to deal with those things on a cherokee, and treat them all as if they were secondary.

"anti dive".....thats just *one* of the things I didn't worry so much about once I began BUILDING.

I know you've done an excellent job explaining what it is, and I'm sure willis is thankful for the tech. I know I STILL am appreciative of the time spent by a few of you that know how to write about this stuff.....But how can you tell Wilis what to *DO* with this info? If I'm somehow getting in your way, or killing the buzz of the thread by sharing the realities, I'll hit the bench, and take a breather for four weeks until wilis comes back from laying on his back staring at the underside of his XJ for hours wondering what his next move is.

[Willis]

I am of course not going buggy, or even close. Infact, I plan on sticking with a rear leaf setup, and I have yet to figure out rear anti-squat with leaf springs. That's probably my next step, so I have a comparison and between the front and rear and can figure out total anti-pitch. I am still in the design stage, trying to figure out link placement and why others have place links where they have. I was originally thinking of placing my lower link (33") outboard of the frame-rail, and my upper link (30") inboard of the frame-rail. The upper link ends up near parallel with the ground. This also puts my IC right at the point where the lower link mounts to the frame-rail. It does give me a 66% anti-dive though.

Ok, now I completely understand what you are saying about anti-pitch proportions front to rear and why the full percentages are not actual.

I also realize that not all designs can be adapted to the XJ, I am not even looking at 4 link. I'm not up for the challenge given my limited experience customizing suspensions. I'm just looking at options, ideas, and answers to 'why'. Mostly I want to know why anyone can just fab up a set of radius style long-arms and they work. I wanted to know why. It seems that the biggest reason is that they move the anti-dive down into an acceptable range.

The only question that has not been answered is: What happens if my IC is at my transfer case? Not extended over the rear axle. I can adjust the links to project the IC further rearward, but I start compromising ground clearance under the axle and the frame-rail. The only information I can find on the location of the IC is in reference to the vertical placement, and the anti-pitch forces that placement creates. I can't find information on the fore/aft placement of the IC.

To the graph paper.

Steve

[Willis]

Of course, all information in this thread has, so far, been very informative. What my goal here is, to design a close to perfect suspension, whatever design I go with, then modify to fit (if need be), taking into consideration what I have learned in the design process and attempting to keep the characteristics where I want them.

And, a trail rig is what I am looking for. Not all rocks or sand, but multi-duty trails and of course, Moab every year. It will be street legal (or as close as we get) and will most likely be driven to Moab and all trails. Reliability, street-ability, and offroad-ability are all concerns I am trying to take into consideration.

Thanks all!
Steve

[Beezil]

Mostly I want to know why anyone can just fab up a set of radius style long-arms and they work

welp, I have a little bit of understanding why my long, radius arm set-up didn't work, From an operators point of view, I actually thought mine sucked, compared to my new set-up.....

I can't blame it on the geometry totally, it had more to do with excessive lift hieght.

My long radius arms unloaded HORRIBLY. sure, a centered limiting strap worked WONDERS.

It was really interesting to see dozens of xjs with long arms attempt mickeys hot tub, one right after the other, with an occasional "standard" suspension system thrown in here and there making it look easy. Goatmans joking around and poking fun of long arms all the while suddenly became accurate observation, which made it more humorous (except when my turn came up) There were long arms systems on tall rigs that were having a hard time, and some lesser lifted rigs you could tell were still unloading.

Max and Ed know how to explain why this is the case, all I can tell you is, if you think people are just bolting on these things and cleaning up every obstacle out there like it aint no thang, that hasn't been my experience.

the guys with centered limiting straps will be able to hide it well!

:)

[MaXJohnson]

"just remember only a portion of this theoretical masterbatory nonsense applies"

"actually trying to adapt your design to an xj platform SUCKS."

"if we were building tube buggies from scratch, more of this shit could apply,"

"when you actually build one of your own someday, you'll see what I'm talking about."


don't know why you keep debating this......

As you might guess, inflammatory statements like the above fuel debate. They also tend to turn a thread off-topic.

Even though you stated that designing to an XJ platform sucks, that is what he and many others plan to do.Willis' ultimate goal, as far as I can tell, isn't to end up with a buggy.

I doubt that Willis is worrying about anti-dive. I gather he wants to understand it and determine if and how it may apply to his design goals. Anti-dive is pertinent on a trail rig because it has an impact on effective spring rate and suspension jacking. Spring rate has an effect on traction. Steep decents on the trail depend on front wheel traction. Anti-dive is also closely related to anti-lift. Changes in front link design that affect anti-dive will also affect anti-lift. If you wonder about radius arm XJ's struggling with front-end unloading problems, front suspension anti-lift is one of the factors.These things apply to discussions on trail rigs, race cars, steet cars, drag racers, and any other form of automotive chassis design. It's how you apply them that differs. You don't have to manufacture tires to know that "round" is a good design goal.

".....But how can you tell Wilis what to *DO* with this info?"
"All those groovey suspension dynamics (racecar) books"

I suggested some changes to Willis' initial design based on this info. Widen the upper chassis mounts to increase lateral location strength. Decrease the width of the lower chassis mounts to flatten the roll axis. Raise the lower arm axle mount to lower the side view IC. This reduces anti-dive.

Regarding the longitudinal location of the front IC; virtual link length, as defined by the IC, has a direct impact on anti-forces. A longer virtual link lowers the amount of anti-dive and anti-lift. With the exception of radius arm designs, your IC is constantly changing position as the wheels cycle up and down. A longer virtual link lessens the rate of change which provides a more stable, predictable performance. A longer virtual link lessens the change in pinion and castor gain as well.

[Beezil]

what is your real problem max?

I say the word "buggy" and you just can't seem to get off of it....

I'm so sorry "theoretical masterbatory nonsense" hurt your feelings and destroyed your inner being.

I was trying to be silly.

hey, if you wanna mess the thread up, go ahead and keep spinning my words.

I think I made my point clear already

[MaXJohnson]

... go ahead and keep spinning my words.

no spin required. Just responing to your comments.

Suck it up, man. It's only the internet...

[Beezil]

Suck it up, man. It's only the internet...

I already sucked.

[Bob Sheaves]

Max,

I have been lurking on this board for a bit and have found your postings to be quite accurate. As a dynamics engineer, your description of the geometry and how it works is spot on. Congratulations!

Too bad others do not realize the importance of a balanced approach to suspension design. When an engineer makes a mistake, people die- a fact of life that too many dismiss because of ignorance or supposition.

Best regards,

Bob Sheaves

ADDENDUM:

FYI- the stock MJ & XJ have a bit over 18% A/D on the OE base tires...

[Beezil]

okay max and bob....

for the last time, I never told willis to throw away his playbook and wing it.

quit making it look like thats what I was trying to do.

I would be interested in seeing your designs for something like wilis wants to do that addresses all the difficulties of the xj platform. Since you seem threatened by my realistic and practical "heads up" approach, and don't seem to understand the value of what I'm trying to do on this thread, show me how it can be done. lets see a couple versions.

I think research is extremely important. Learning new things is very cool. There is plenty to be learned on this thread, and the infomation posted is fantastic.

To my knowledge, neither of you have ever made an attempt to incorporate the theoretical "PERFECT" link suspension set-up on a cherokee platform. I've never seen your rig bob, but max, isn't your rig a variety of various bolt-ons and possibly some non-exotic diy modifications? For someone that has such an excellent grasp on theoretical suspension geometry, why aren't you trying to incorporate any of this on your own rig?

[Bob Sheaves]

Ummmm....actually, I did on my 1990 XJ when I was at JTE-that car was used as a chase car for several "test sessions" including one out to Moab in the summer of 1991.

Have you ever driven a Dodge Ram of 1994 to 2000 vintage with the 4 link over constrained front suspension?

Best regards,

Bob Sheaves

PS- I never mentioned any specific names in my comments about people. I was making an observation about MOST people here and their collectively cavelier attitude about modifying suspensions-particularly the XJ/MJ. I am not saying it cannot be done-just that there are tradeoffs that should be accounted for that most people here demonstrate a distinct lack of awareness and distain for.

[Willis]

My long radius arms unloaded HORRIBLY. sure, a centered limiting strap worked WONDERS.

So does your parabola system unload at all? Did you have the need or desire for a limiting strap at all?

Also, is there a need to angle the lowers (as viewed from the top) with the parabolic link? Can they be completely straight? In a standard rear 4 link, the distance the mounting points are apart at the chassis is commonly around 50-70% what they are at the axle. This is to help combat rear steer. What would be the benefit of angling the lowers using a parabolic upper?

Steve

[Beezil]

bob, tell me why a dodge ram is at all relevant?

willis, no, it doesn't seem to....

btw, have you made any decisions yet?

do you have an idea of tire size, or which axles you are going to use, or maybe lift hieght?

how comfortable are you in loosing some sheet metal?

would you consider taking metal out of the floor?

what kind of boingers are you going to use?

[Willis]

Too bad others do not realize the importance of a balanced approach to suspension design. When an engineer makes a mistake, people die- a fact of life that too many dismiss because of ignorance or supposition.


It's true, many do go and just build a setup with no regard to geometry and characteristics. I, and others, who are trying to incorporate a link setup to the XJ do see that you may start with a balanced approach, but given the XJ chassis as your canvas, balance can not always be attained. Just because that balance is not attained, does not mean a mistake has been made, it just means that compromises have been made. You just have to choose your compromises and calculate them to achieve a result close to what you set out to build.

Of course we are building trail rigs, and not bridges or carnival rides here, so please leave out the whole death issue. Can some moron build a very unsafe suspension? Of course, but the majority of us here have enough common sense to build enough safety into our systems. Just because the lower links end up 3* off of perfect does not mean anyone is going to die.

Given the safety factor we build into our vehicles like cages, the safety factor is pretty high. We are not engineers here, but the proper design and execution of a link type suspension is what this thread is about. The proper design may differ from the execution given the platform, and that's what Beezil is saying. He never said throw out all your designs and put your links wherever you want.

[Bob Sheaves]

The Dodge pickup suspension fixes a lot of the inherent limitations of the XJ/MJ design. How do I know....I was responsible for all the 4x4 BR suspension design and parameters at JTE in the old PreProgram group. There is a distinct difference between the two in perfromance of the suspension. As it relates to the anti-dive discussion, the XJ has 18% and the Dodge has 36%. The Dodge has far less non-symetrical axle steer due to linkage compound ratios when co,mpared to the XJ/MJ.

Best regards...

Bob

[Beezil]

"balance" is a compromise between what you want and can to do, and what you CAN'T do.

that's great bob.

but that doesn't help willis now does it.

[Willis]

willis, no, it doesn't seem to....

btw, have you made any decisions yet?

do you have an idea of tire size, or which axles you are going to use, or maybe lift hieght?

how comfortable are you in loosing some sheet metal?

would you consider taking metal out of the floor?

what kind of boingers are you going to use?

Ya, 64" HP D44 front (already have), 35" MTRs (already have), hoping to keep lift as low as possible, I have 7" planned in my sketches. The parabola is perfectly parallel with the ground but 8" above the lower link. I need to check oil pan clearance though.

Looks like I may not have to remove metal from the floor for the front, but it depends on where it would be. This will not be daily driver, and I already have my MJ cab to do a chop, plus dovetail the rear is planned. Front fenders are already trimmed to rear TJ flares.

And, what are boinger? Ya lost me there. :confused:

[Beezil]

And, what are boinger? Ya lost me there. :confused:

springs!

:)

[Willis]

Gotcha! Coils front, unsure on brand. Maybe 5.5 REs with spacers? Using leaves rear. I've got some 4.5" RE leaves I plan on taking apart and using some stock waggy front springs in the pack. The waggys have 7 thin leaves per pack and flex well. I'll combine the leaves until I get the flex and lift I desire. That's first, custom leaves come second if I can not make what I have work first.

[Bob Sheaves]

That kind of comment Beezil, is what I would expect of someone that caused of the demise of the CJ's . Too bad...

Let me spell it out for you in simple terms....

A. By directly comparing the BR to the XJ, in stock form, you can see how the compromises made improved the design to where it had greater travel potential, less driveline change (leading to improved joint durability), greater driver control under extreme travel positions, less suspension induced uncontrolable dynamics, and less lateral axle movement relative to vehicle centerline. All of these things are what is striven for in the off road community.

B. "Balance" has nothing to do with what "you" (as an individual) can or cannot do-anything can be done, given time, money, and understanding- but rather, the balanced compromise between street legal drivability and off road capability.

Willis....dying is something that you had best be concerned with, if not for yourself, than be VERY concerned with the responsibility towards others if you take your vehicle on a public road or highway. If you EVER take a modified vehicle on public roads-YOU are responsible for the results of those changes in an accident. A good lawyer will take you to the cleaners for the rest of your life if you make a mistake. Good intentions don't mean a damn thing in a court.

That being said, I wholeheartedly approve of your thought in asking the questions you have. I would only hope you listen to the advice given by Max. You have to make the decisions on how to do the modifications, but thinking before cutting and welding is far more productive than simply dismissing as irrelavent, comments that you disagree with.

Best regards,

Bob

[Bob Sheaves]

Additional thought Willis...

You may be interested in looking for some old pictures of Mike Leslie's MJ and XJ off road race cars from the late 1980's and early 1990's. The 7's (MJ's) has 19 inches of travel from jounce to rebound (don't ever say "droop" or "bump" to a real engineer...LOL!) in the rear and, as I remember, 22" in the front...all with the equivelent of a 6" ride heigth increase relative to axle centerlines (means discounting tire related increases).

Check out the boards at racedezert.com-there are some of the old guys there that may have some.

Best regards,

Bob

[Willis]

Willis....dying is something that you had best be concerned with, if not for yourself, than be VERY concerned with the responsibility towards others if you take your vehicle on a public road or highway. If you EVER take a modified vehicle on public roads-YOU are responsible for the results of those changes in an accident. A good lawyer will take you to the cleaners for the rest of your life if you make a mistake. Good intentions don't mean a damn thing in a court.

That being said, I wholeheartedly approve of your thought in asking the questions you have. I would only hope you listen to the advice given by Max. You have to make the decisions on how to do the modifications, but thinking before cutting and welding is far more productive than simply dismissing as irrelavent, comments that you disagree with.



For the record, I don't want to die, and don't want to kill anyone. Of course that is a concern, but that chance everyone takes when making modifications to the XJ. The guy who lifts it 2" and removes the rear sway-bar can be held liable if some lawyer decides to pursue that avenue during prosecution of an accident where death was the result. Sure some XJs came with a 1" lift and no rear sway bar, but that extra inch has added anti-dive to the suspension dynamics. Some aggressive lawyer can argue that extra anti-dive did not allow enough weight transfer during braking and caused the accident. Does that mean the custom linked suspension I build will be more dangerous than his? No. That's what I mean my leave the whole death issue alone. Since this will be used on road, safety will be my #1 concern. I plan on building a suspension with better road characteristics than a 4" lifted XJ with 4 short arms.

Max has provided a great basis for building a suspension. If the 'perfect' suspension can not be adapted to the XJ, it does not mean it is unsafe. I am listening to Max, his knowledge on this subject is much appreciated and his advise is heeded. But from a real world standpoint, which Beezil has been, some of the ideal positioning may have to be changed. Again, with safety in mind. I have yet to dismiss anything as being irrelevant.

Steve

[Willis]

Additional thought Willis...

You may be interested in looking for some old pictures of Mike Leslie's MJ and XJ off road race cars from the late 1980's and early 1990's. The 7's (MJ's) has 19 inches of travel from jounce to rebound (don't ever say "droop" or "bump" to a real engineer...LOL!) in the rear and, as I remember, 22" in the front...all with the equivelent of a 6" ride heigth increase relative to axle centerlines (means discounting tire related increases).

Check out the boards at racedezert.com-there are some of the old guys there that may have some.

Best regards,

Bob

I'll check into that out of curiosity. His suspension will be miles away from what I plan to build. There is no way I need that much 'jounce'. This thing will never (intentionally) get airborne.

Thanks

[XJJPR]

The Dodge pickup suspension fixes a lot of the inherent limitations of the XJ/MJ design. How do I know....I was responsible for all the 4x4 BR suspension design and parameters at JTE in the old PreProgram group. There is a distinct difference between the two in perfromance of the suspension. As it relates to the anti-dive discussion, the XJ has 18% and the Dodge has 36%. The Dodge has far less non-symetrical axle steer due to linkage compound ratios when co,mpared to the XJ/MJ.

Best regards...

Bob

Bob,

Seeing your saying you're a Dodge engineer, working for Dodge either directly or indirectly thru a subcontractor, if I'm wrong please let me know. If I'm not where do you work?

Couple questions on the Dodge.

First off I truley hated my 95 dodge 4x4 2500hd quad cab long bed suspension/braking system.

What was it in the suspension that allowed for massive side pull during braking with oversized tires verses stock size tires. All the people who have explained it to me have never done a great job on this.

With all the beef in that front suspension why was such a crummy track bar used. It's gotta be one of the most under engineered things on any truck suspension in the last 10 + years.

I'm no where close to understanding all the suspension design you guys are talking about but have messed with the XJ/MJ suspension in it's relative stock/modified forms. Staying with basic stock type mounting. I do know what works on and off road, maybe not by design stats but by what it does.

BTW I always love when engineers boast about if things aren't engineered right people die. Do you realize how many people have died from engineers making mistakes? All engineered or DYI aren't perfect but most try to be as good as they can be, because noone wants to see anyone die from a mistake.

I will say I'm always amazed at how many DYIs do do such hugh suspension changes and what they get away with. But then some of the big suspension manufacturing companies blow me away with what they get away with too.

mark

[Bob Sheaves]

I'll add my comments inline, if you do not mind....

Bob,

Seeing your saying you're a Dodge engineer, working for Dodge either directly or indirectly thru a subcontractor, if I'm wrong please let me know. If I'm not where do you work?

At the time, I was a direct employee of Chrysler Corporation in the PreProgram Engineering Group (R&D-we set the parameters for vehicles then handed off the designs to the various production groups). Currently I am consulting with DCX as an independent on "business process analysis".

Couple questions on the Dodge.

First off I truley hated my 95 dodge 4x4 2500hd quad cab long bed suspension/braking system.

Sorry to hear that-over 90 percent of those that bought the truck initially bought another.

What was it in the suspension that allowed for massive side pull during braking with oversized tires verses stock size tires. All the people who have explained it to me have never done a great job on this.

While I cannot comment on other people's hearsay, I am afraid you have not given me enough information to determine what was "wrong", if anything. Oversize tires change the response geometry due to a greater didtance from the center of the hub to the ground contact patch-greater leverage means increased loading from braking transferred to the pivot axis (the hub centerline). Changing the load in the vehicle will alos make a difference-as little as 3/4" change in the relative height of the frame mounts for the control arms and the frame end of the panhard rod will alter this reaction to braking.

Under your circumstances, what was the loading of the truck? (The design point is called BPL-Body Part Loaded- and is an SAE and industry standardized design process.) How many passengers? How much fuel? All of these things alter the geometry as they are changed. In some cases, as little as 2% weight shift can cause drastic changes in the manner a car responds to steering and braking input.

With all the beef in that front suspension why was such a crummy track bar used. It's gotta be one of the most under engineered things on any truck suspension in the last 10 + years.

What makes you say the problem lies with the panhard rod? That bar is far stiffer than anything the XJ has, proportionally. Perhards the fault lies elsewhere.....like the frame bracket loading???

I'm no where close to understanding all the suspension design you guys are talking about but have messed with the XJ/MJ suspension in it's relative stock/modified forms. Staying with basic stock type mounting. I do know what works on and off road, maybe not by design stats but by what it does.

BTW I always love when engineers boast about if things aren't engineered right people die. Do you realize how many people have died from engineers making mistakes?

Yes, as a matter of fact I do, since I deal with this stuff everyday, and have for over 28 years.

All engineered or DYI aren't perfect but most try to be as good as they can be, because noone wants to see anyone die from a mistake.

I will say I'm always amazed at how many DYIs do do such hugh suspension changes and what they get away with. But then some of the big suspension manufacturing companies blow me away with what they get away with too.

mark

You are exactly right-"THEY GET AWAY WITH IT"...for a while. Does anyone here remember Jackman Wheels? Enough said...

Best regards,

Bob

[XJJPR]

Bob,

Sorry to hear that-over 90 percent of those that bought the truck initially bought another.

That's hard to believe unless you meant "another brand" I bought a GMC sold that now too.

While I cannot comment on other people's hearsay, I am afraid you have not given me enough information to determine what was "wrong", if anything. Oversize tires change the response geometry due to a greater didtance from the center of the hub to the ground contact patch-greater leverage means increased loading from braking transferred to the pivot axis (the hub centerline). Changing the load in the vehicle will alos make a difference-as little as 3/4" change in the relative height of the frame mounts for the control arms and the frame end of the panhard rod will alter this reaction to braking.

My basic believe that the whole thing had problems as a suspension system. The braking problem was wide spread from all I could ever reaserch on it. DC ofcourse denied everything.

What makes you say the problem lies with the panhard rod? That bar is far stiffer than anything the XJ has, proportionally. Perhards the fault lies elsewhere.....like the frame bracket loading???

The joint fails way to soon for the socalled HD the truck was supposed to be.

Yes, as a matter of fact I do, since I deal with this stuff everyday, and have for over 28 years.

It's nice to see a real engineer here, because the wana bes would have argued that one until the cows came home :D

Does anyone here remember Jackman Wheels?

Yes I do!!!!!!! They weren't DYIers...

thanks for your info :D

mark

[Bob Sheaves]

Thanks for the vote of confidence... :) Too bad about the Jackman guys-there was an excellent product and they were victil to0dxactly what I was referring to-someone that thought they knew more than the engineer that originally designed the wheels. A lot of people got hurt (both literally and figuratively speaking) on that mess.....

Bit of trivia on the Dodges-during the first 6 years, over 90 percent that bought or leased a 94 or up pickup returned to get another one after their lease was up, or 3 to 5 years of ownership.

The "braking pBlblem" was not bh much that the vehicle would not stop- but rather the brakes felt "mushy". This was caused by the type of ABS and RWAL used, in my opinion-I am not speaking as a rep of DCX (I cannot!) but as one that worked on a friend's vehicle to repair the problem. I fixed his by replacing the RWAL entirely and converting to 4WD's 13" front and 12" in the rear, with a GM Hydroboost master cylinder and p/s fluid booster with fluid cooler.

Since I left the corp before the introduction of the truck, I cannot verify that there were any issues with the balljoint used at the frame end of the panhard rod. On the one I worked on, I noticed no unusual wear, BUT it never saw the extreme, high speed, desert duty that my XJ did. I have heard reports of these failures and exces2ave wear before, but to determine a cause, I'd have to measure one to see what changes, if any, were made to the original design by the production group.

Best regards,

Bob

[XJJPR]

The "braking problem" was not so much that the vehicle would not stop- but rather the brakes felt "mushy". This was caused by the type of ABS and RWAL used, in my opinion-I am not speaking as a rep of DCX (I cannot!) but as one that worked on a friend's vehicle to repair the problem. I fixed his by replacing the RWAL entirely and converting to 4WD's 13" front and 12" in the rear, with a GM Hydroboost master cylinder and p/s fluid booster with fluid cooler.


Best regards,

Bob

Hydroboost master was the only thing I could find that did fix the problem for others. I just replaced mine by buying truck with one on it. :D Seems like I'm in that top (bottom :D )5% thing like normal!


Man good hijacking here!

hinkley

[RCP Phx]

Two quick things,(I dont want to interupt your discussion but).One,to answer part of Willis's question about why long arms work,EASY-Its a 40 year old tried and proven design.Sure there is a little tweaking to each vehicle(as Beezil has already pointed out) but its been around the block a few times.Second,as a side note,there is a very nice rod end conversion out for the Dodge!

[Kaczman]

Beezil- Do you have any photos or sketches of the profile for your front suspension? I've looked for some pics, but they all seem to be from the front, rear, or action shots. And, do you know what A/D and roll axis you have with the 3 link? Ballpark value are close enough for me. I just want to see if I'm getting close with my 4 link design.

Bob- Did you say the stock XJ/MJ's have 18% A/D? It seems lifting the vehicles (with aftermarket or custom designs) puts the A/D percentages WAY higher than that. I thought the anti-dive would be a bit higher stock-- but I guess I haven't looked at a stock XJ suspension for a while.

-Jon

[MaXJohnson]

WARNING!I have never made an attempt to incorporate the theoretical "PERFECT " link suspension set-up on a cherokee platform. If the following information offends you, please disregard the content and move on.

Beezil, you're right. I am not attempting to incorporate the perfect link suspension on my Jeep. In fact, I still run leafs in the rear. Most of the parts I have built have, in fact, been bolted on.

I built my front bumper, and then bolted it on.
I built my rear bumper, and then bolted it on.
I built my tire carrier, and then bolted it on.
I built my roof top rack, and then bolted it on.
I built my air tube, and then bolted it on.
I built my "A" hoop, and then bolted it on.
I built my "B" hoop, and then bolted it on.
I built my skid plate, and then bolted it on.
I built my rock rails, and then bolted them on.
I built my traction bar, and then bolted it on.
I built other junk, and probably bolted it on too.
I built lots more junk and bolted it on to other vehicles.

As you can see, most every thing is bolted on. It would fall off otherwise. I'm sure your list is longer, bigger and more impressive so I don't need to see it

Thankyou for thinking that I have an excellent grasp on theoretical suspension geometry, but I have no plans, facilities, money or desire to incorporate the theoretical perfect link suspension on my XJ. I can appreciate and admire yours instead.

There; the truth is out.

[MaXJohnson]

Bob, nice to hear from someone with some inside info on the XJ and Dodge link designs. Someday, I'd like to chat and pick your brain a little.

If I were you, I would have claimed to have worked on "an unspecified vehicle for a domestic manufacturer" There's always going to be a disatisfied customer in the crowd. I remember doing a search on "Death Wobble" a few months ago and was surprised at the large number of hits returned on Dodge trucks. I wondered if the steeper control arm angles had anything to do with it.

Do you happen to remember the anti-squat percentage on the XJ and Dodge at factory specs?

[Bob Sheaves]

Bob, nice to hear from someone with some inside info on the XJ and Dodge link designs. Someday, I'd like to chat and pick your brain a little.

If I were you, I would have claimed to have worked on "an unspecified vehicle for a domestic manufacturer" There's always going to be a disatisfied customer in the crowd. I remember doing a search on "Death Wobble" a few months ago and was surprised at the large number of hits returned on Dodge trucks. I wondered if the steeper control arm angles had anything to do with it.

Do you happen to remember the anti-squat percentage on the XJ and Dodge at factory specs?

Thanks for the kind words Max.

I am used to (and have made my living) by accepting personal responsibility for my work-I just can't dodge a direct question, unless it involves info from a confidentiality agreement... :) .

If you would like to chat-please feel free to email me at my yahoo address... rwsheaves@yahoo.com ....at your convenience. Unfortunately, I do not rememebr the anti squat numbers off the top of my head-I'd have to do some digging in some old notes I have somewhere....

The "Death wobble" you mentioned has been researched a lot, I'll admit. Many vehicles are suseptable, to varying degrees, especially when the panhard rod (when equipped) is at too steep an angle relative to the axle centerline (or commonly called "horizontal"). I worked on an old style C/K 1/2 ton that had terminal shake from a set of 38" tall Mudders on it with a Rancho 6" lift. The driver ended up climbing the steps of a bank and entered the lobby. Unfortunately, he was still in the truck doing 35mph at the time. Fortunately there were no casualties, except for the driver's drawers.....

Best regards,

Bob

[Beezil]

WARNING!I have never made an attempt to incorporate the theoretical "PERFECT " link suspension set-up on a cherokee platform. If the following information offends you, please disregard the content and move on


Oh my Gawd!!!

with lines like that, me thinks you and rich should go on a comedy cruise vacation together!

"WARNING ! The contents of this post may include references to competition related products, if you feel this is inappropriate or offensive please disregard."

you jackass!

:laugh3:

[RCP Phx]

I am used to (and have made my living) by accepting personal responsibility for my work-I just can't dodge a direct question, unless it involves info from a confidentiality agreement... :) .

If you would like to chat-please feel free to email me at my yahoo address... rwsheaves@yahoo.com ....at your convenience. Unfortunately, I do not rememebr the anti squat numbers off the top of my head-I'd have to do some digging in some old notes I have somewhere....

The "Death wobble" you mentioned has been researched a lot, I'll admit. Many vehicles are suseptable, to varying degrees, especially when the panhard rod (when equipped) is at too steep an angle relative to the axle centerline (or commonly called "horizontal"). I worked on an old style C/K 1/2 ton that had terminal shake from a set of 38" tall Mudders on it with a Rancho 6" lift. The driver ended up climbing the steps of a bank and entered the lobby. Unfortunately, he was still in the truck doing 35mph at the time. Fortunately there were no casualties, except for the driver's drawers.....

Best regards,

Bob

You where doing great up to this post! Ive had DW on 3 "stock" DC products,all with less than 5K miles on them.Your credibility just "took a major Sh!t"!

[MaXJohnson]

Oh my Gawd!!!

with lines like that, me thinks you and rich should go on a comedy cruise vacation together!

"WARNING ! The contents of this post may include references to competition related products, if you feel this is inappropriate or offensive please disregard."

you jackass!

:laugh3:

They ought to look similar. Rich stole that out of one of my posts. :doh:

[Bob Sheaves]

You where doing great up to this post! Ive had DW on 3 "stock" DC products,all with less than 5K miles on them.Your credibility just "took a major Sh!t"!

Excuse me????????

[RCP Phx]

DC has known about "death wobble" since the day they bought Jeep.Did they ever re-design anything to cure it, "No".What they did do is build a larger version and stuck it under the Dodge so now we have another vehicle thats dangerous to drive!I feel 10k times better with my modified rig than I ever did in a stocker w/ DW!

[Goatman]

DC has known about "death wobble" since the day they bought Jeep.Did they ever re-design anything to cure it, "No".What they did do is build a larger version and stuck it under the Dodge so now we have another vehicle thats dangerous to drive!I feel 10k times better with my modified rig than I ever did in a stocker w/ DW!

I don't understand the heat. Here we have a guy with real inside info on some important topics, plus a thorough understanding of complicated suspension issues, and you're picking on him over some DW issues? :rolleyes:

Do you think DW only happens on Jeeps? Or on Chrysler vehicles? DW is something that can show up on almost anything with a straight axle, depending on the circumstances. The discussions on the subject, and the opinions, are nearly endless.

This has been a really weird thread. I put off reading it for a few days because I figured there would be too much info to digest, and plenty of opinions. I finally have time to read it, and while there has been some good info and discussions, I'm amazed at how much offense has been taken and how many shots have been fired. Weird.......

[Ed A. Stevens]

No, what I'm saying is that the usual diagrams that you see on here, PBB, etc is correct for calculating anti-squat for a 2WD vehicle, but not for 4WD. This is not a difference is how you determine the placement of your instance centers, but rather how you compare IC reaction with the CG.

Look at it this way. You can draw a diagram of your rear suspension links in the side view to determine where your IC is. Compare the IC location with the anti-squat neutral line (rear contact patch to CG height above front axle) to determine AS%. Now do the same for the front suspension links to determine front anti-lift. Here's the problem. The values you get assumes that each axle get 100% of the engine torque available.

This is wrong. In a part-time transfercase (no center differential) each axle only recieves 50% of the torque. This means thatpyour calculated AS% and AL% are double their actual value. Some fulltime transfercases split torque on an uneven basis, front to rear, say 60%-40%. This would have to be f`ctobmd in as well.

If, for example, you calculated 80% anti-squat for the rear axle and 60% `ntihift for the front; the total anti-pitch force available through a 50-50 transfercase would be 1/2 the sum of these two values. My previous post indicated that the total anti-pitch force available would be the average of the front and rear percentages

(80%+60%)/2 = 70%.

This application of calculating the TOTAL 4WD anti-squat/lift values is derrived from an example in one of Forbe's Aird's books for determining total anti-dive/lift under braking. The method of determining the individual values is correct, but I am having trouble with his interpretation of the total force acting on the chassis being an average of the two individual values.

What all this means is that if you have a significant difference in the link design between the front and rear suspensions (most do) then the common method being tosses about will produce a significant error.


Max (Willis),

The 70% answer (something less than 100%) is not to be discounted because the forces at the two IC's that define AL and AS superimpose and appear to cancel out the vertical force component on the GC. I imagine you are uncomfortable with the missing resistance to the total mass acting through the CG and gravity? (I am)

Drawing the FBD for the two suspensions allows us to identify the CG contribution acting on each system, and when the respective portion of the mass applied to each IC is calculated the total mass acting on both axles does work out (rather than 70% it totals 100%). The forward IC (the rear axle) is resisting (working against) it's portion of the weight, and the rearward IC (the front axle) is complementing (working in the same direction as) the weight (and interestingly enough, against anti-squat).

If we look at the vertical forces, the rear axle system torque force pushes up against 80% of the vehicle weight, and the front axle system torque force is pulling the vehicle weight down 10% (80-10=70%), but the actual vehicle weight applied at each IC is not an 80/20 or 80/-10 split (it's not a function of the available torque, we have 100% of the vehicle weight). The actual weight applied at each IC is the percentage of total vehicle weight defined by the distance away from the CG, and the portion of weight resistance applied to each suspension system is the limit on how much each contributes to the chassis pitch. The imbalance between the available torque and the appied resistance (weight on the IC lever arm) provides the motivation for the dynamic movement between the suspension and the chassis. 80% front IC lift, acting on 60% of the mass about the CG, will get the front lifting more than the rear when it has -10% lift (anti-lift) on the 40% of the mass that is acting on the IC that is rear of the CG. Move the IC closer or farther away from the CG and the imbalance between the two suspension systems contribution to the chassis pitch can be equalized or made more diverse.

In your example the front of the vehicle would pitch up faster than the rear (somewhat like what is observed on radius arm XJ's). The difference in feel the driver experiences (chassis rotation about a location near the drivers seat or the rear bumper) has a lot to do with the confidance to be had when challenging a climb like the dump bump. If the front pitch is significantly faster than the rear, moving the instant chassis rotation center back, the movement of the CG is accelerated and the throttle induced pitch control becomes sensitive (and much more sensitive when the seat is also being lifted more with each throttle touch). What the radius arms guys feel is the accelerated front chassis pitch moving the CG back in addition to placing the AS% in an unstable position (well past 100% and growing with more throttle application). Fix a limit strap and you place a limit on the throttle induced pitch acceleration (the contribution of the front suspension IC about the CG is removed from the two force moment that pitches the chassis).

The short arm guys have the same AS% for the approach angle, but the front of the chassis is not pitching as fast. It feels more stable because the front suspension is contributing to chassis rotation on the rear of the chassis, moving the instant center of the chassis rotation forward. The front axle torque reaction on the short arm chassis (anti-lift) resists the growth of rear AS% (it slows the rapid acceleration of the AS%). The total chassis lifts, not just the front end of the chassis. The tires on both axles lose traction rather than accelerate the tip-over feeling (or the XJ climbs).

The two IC's are acting on the chassis as a two force moment about the CG. The instant chassis pitch moment (in a perfect traction world) is a factor of the IC distance away from the CG and imbalance with the torque split between the axles. The AS & AL of each system provides a factor to compare the percentage of force working on the springs and links, but all the vehicle weight and resistance is still applied through the IC of each suspension system.

The IC location defines the leverage of the suspension system acting on the chassis in a horizontal plain (how leverage about the axle is used to lift the chassis weight). Raising or lowering the IC on a vertical line without changing it's horizontal distance away from the CG changes the AS%/AL%, or the efficiency of the system to convert the applied vertical force to horizontal motion (how much is stored in the suspension springs compared to directly transferred to the links for the rest angle of the vehicle), but is will not change the share of force rotating the chassis (other than that being applied at the spring tower mount rather than the IC, something that complicates analysis).

This independence between the IC and AS% is one reason why one vehicle will climb without jacking and wheelhop, and another will become very unstable, even when both have the same relative IC leverage. We have PBB folks calculating AS% recommendations without regard to the IC length or height, and IC location (forward or rear of the front axle) without reference to the IC height (the factor changing the AS%). There is no reliable rule of thumb for IC distance from the axle and CG, or AS%, and to quote one parameter without the other is ignoring the independence of the two. Quoting answers for the front and rear, is just as much of a swag (but I know you understand this well).

Bob,

I am pleased to have the input of someone who has reverse engineered the dynamics of the XJ (I assume) to advise DC on what was required to build a better evolution of the four link (the RAM truck). I can see the improvement in axle steer, pinion angle gain, and bumpsteer, but all improve with longer arms and the wider track that a full size chassis allows. We are confined by the XJ track and wheelbase.

"There is a distinct difference between the two in perfromance of the suspension. As it relates to the anti-dive discussion, the XJ has 18% and the Dodge has 36%. The Dodge has far less non-symetrical axle steer due to linkage compound ratios when co,mpared to the XJ/MJ."

The later design has more equal length arms reducing the non-symmetrical action, and longer arms working a longer wheelbase that allows acceptable suspension compliance with the steeper anti-dive. The vehicles are different in wheelbase, CG & weight distribution, and we have to accept the suspension performance will be different. What I want to know is what (in your opinion) improved the performance of the later design the most, and if it can be applied to a modified XJ system?

Were more equal length controls arms a significant benefit (reducing the non-symmetrical axle steer)?
Was raising the front system IC or shortening the IC distance from the CG (the two factors that can raise the AD%) a benefit (and what, IYO, was the more beneficial change)?
Anything else (I am always willing to share opinion and learn something new)?

I have photos of many of the late 80's and early 90's XJ/MJ that were in SCORE competition (and still know a few of the people who wrenched and rode in them as well) as I was involved in Class 11 and 1/2-1600 at the time and used my XJ for chase and prerunning (with me always looking and asking for applicable improvements). I find the comparison of what worked for the long arm systems for off-road racing, systems that did not worry as much about ground clearance, to be helpful but not the answer for a dual purpose rockcrawler and street runner. Was there any system improvement (or design) that you saw as a benefit that did not rob ground clearance or require the chassis and fender tubs to be highly modified (a design change that can be easily applied to the XJ chassis)?

Willis,

Take Max's advice to heart, as the stability and pinion angle gain improvements will provide a good initial platform if the design is to be cut and rehashed on the XJ or on paper (welded or web-welded). There is a point where the XJ frame and axle (and all the stuff in the way) will limit the design (lets call it the BezzWall), and it will likely dictate the final design compromise.

If you read (and agree with) the above description of the front suspension and the impact of the front IC on the chassis pitch rotation, then it makes sense to locate the front system IC well behind the transfercase crossmember and CG. You would certainly not want it find it ahead of the CG on an incline (IMO) as it would make the chassis pitch very throttle sensitive. I have not played with a modified XJ on rocks as much as others on this board, and do not have feedback other than that expressed in the long and short arm debates, so I am as eager to listen to advice on what works as much as you.

FWIW, I see no reason to delete the panhard rod and draglink steering as long as it is designed to be relatively level at rest. The fixed three link (the wishbone, rather than the assymetrical upper link Goatman runs) deletes the need for the panhard bar, but invites complicated steering (hydro, electric fixed rack, or some other axle mounted steering actuation). I am not that comfortable with full hydro steering on the street, at speed, and I have not seen a good axle mounted electric rack & pinion system.

I have a family birthday, a funeral, and a wedding anniversary to tie up my week so I leave you folks to hash all this out.

[Willis]

I'm amazed at how much offense has been taken and how many shots have been fired. Weird.......

Ya, maybe we are like women. We've all been together too long and now we are on on our man-stration cycle. :confused:

I do agree, we need not jump on anyone's back about DW. It's not DC's doing. Like Goatman said. It can happen on any solid axle rig. I'll add, it can happen on IFS rigs too. I worked on a 92 1500 Chev with 38s and DW at 30mph. It is strange how big tires change DW. I had it twice with 3" and 30s, very violent and uncontrollable. The Chev w/ 38s was still DW, but much slower. The oscillations were much less frequent.

I also saw a 78ish Chevy Blazer cruising down Glendale Ave (Glendale, AZ) doing around 35mph with the front tires bouncing back and forth from what looked like lock to lock. He just kept driving. :rolleyes: Blatant disregard for safety.

Steve

[Goatman]

Since this will be used on road, safety will be my #1 concern. I plan on building a suspension with better road characteristics than a 4" lifted XJ with 4 short arms.

Max has provided a great basis for building a suspension. If the 'perfect' suspension can not be adapted to the XJ, it does not mean it is unsafe. I am listening to Max, his knowledge on this subject is much appreciated and his advise is heeded. But from a real world standpoint, which Beezil has been, some of the ideal positioning may have to be changed. Again, with safety in mind. I have yet to dismiss anything as being irrelevant.

Steve

Steve, what do you figure is a perfect suspension? I guess that would have to depend on what you want it to do for you. I always figure that since we're not building rock buggies, our suspensions need to do many things well. Good on the street, good at a reasonable speed on rough roads, decent flex, good climbing ability, and stable in off camber situations. Perfect will be at least some compromise between the various things that you want it to do for you, leaning towards your own personal priorities. I'm curious about what you're after so I can watch as it comes together for you.

I'd love to add something to the discussion, but you guys are beyond what I can intelligently discuss. I'm getting a better handle on anti-dive, anti-squat, etc, but have a long way to go to talk much about it. Mine does work well, and handles well on the street, and has great ground clearance, but it was built using as much common sense as I could muster without a lot of technical information. Now I'm working on the right shocks so I can go faster on the way to and from the trail. :D

[FarmerMatt]

Where the heck did this thread go & why did it get here...? I started reading expecting people to throw out ideas about different linked suspensions & instead we get this? You guys are having problems focusing. There is medication for this you know.

Matt

[CRASH]

When an engineer makes a mistake, people die

I'm a biologist. When biologist's fawk up, beavers die.

CRASH

P.S. Not a bad so far, other than the pecker measuring contest and some high and mighty stuff. Oh well. At least we're not in the Den yet.

[Beezil]

Kacz.

here's a quick drawing....

understand that I have not lowered the rear to where it USED to be before I cut the back off, which weighed close to 325 lbs. I gained at least an inch, maybe two. I'm running around 7 to 7 1/2 of lift for my 37's.

my rear links have adjustment on 1" centers. I haven't gotten a chance to play with them yet.

I'll try to plot the top view tomorrow.

http://users.rcn.com/beezil/public/drawing2.JPG

edit:

also, I am having trouble determining where the CG is.....my rig is WAY lighter in the rear, has heavy fullwidth axles, big tires, and no a ton of lift relatively speaking. I'm not sure if I can use the theoretical CG that everyone puts right behind the top bellhousing bolts.

[XJJPR]

Kacz.

here's a quick drawing....

understand that I have not lowered the rear to where it USED to be before I cut the back off, which weighed close to 325 lbs. I gained at least an inch, maybe two. I'm running around 7 to 7 1/2 of lift for my 37's.

my rear links have adjustment on 1" centers. I haven't gotten a chance to play with them yet.

I'll try to plot the top view tomorrow.

http://users.rcn.com/beezil/public/drawing2.JPG

Beezil, atleast that picture looks better than your junk does. :D

hinkley

Helping with the straying from the point part.

[Beezil]

you haven't seen it after the 2nd chop, its almost hard to look at.

[XJJPR]

you haven't seen it after the 2nd chop, its almost hard to look at.

I hope you're gona add some steel dimond plate to make it better looking. :D

email me some pic you .....

hinkley

[Willis]

Kacz.


http://users.rcn.com/beezil/public/drawing2.JPG

edit:

also, I am having trouble determining where the CG is.....my rig is WAY lighter in the rear, has heavy fullwidth axles, big tires, and no a ton of lift relatively speaking. I'm not sure if I can use the theoretical CG that everyone puts right behind the top bellhousing bolts.

Wow! Your rear anti-squat is upto or over 100%. I'd say your front AD is close to 80% too. I, so far have built mine lower with my AD around 65-70%.

As far as you CG, you may move it forward some because of your loss of rear weight. Up and down, I'd say bellhousing bolt level still, maybe a couple inches lower, but not much. You've added suspension and axle junk, but also added cage up top, and moved that fuel up higher too. That swirly mark 45* behind the front axle should get you close.

Oh ya, you need to carry a spare for NAXJA outings, that's going to add weight. Until you do so, you are banned. :D

Steve

[Willis]

The 70% answer.....(insert lots of kick ass tech)... rack & pinion system.

Damn Ed, some great tech there. I understand most of it, just need to re-read it a few times once my head stops spinning from the first two times I've read it.

Thanks!
Steve

[Beezil]

willis you jackazz!!!!

we were trying not to let eagle find out, remember?

besides, didn't I make it clear that I had an "adequate spare"?

never mind the fact that it was a trailer tire, I considered it "adequate", just like the bylaws state.

BTW, what I do with ed's posts, is I print them out, I leave the computer room and sit on the couch, and begin to read.....slowly.....rinse and repeat.

if you do a search on 4-links, you'll find a long one I started a while back, and there's some really great info there....

have a look.

[CRASH]

That's it, after this thread, I'm going for front leaf springs.

They're like links for dummies. Two flexible links.

Look at the advantages:

Ride quality. Let's be serious, anyone that's ever ridden in leaf sprung vehicle all day on the trail knows that nothing will fix up your kidney's faster than 2 or 3 thousand bone jarring hits.

Anti-dive, anti-squat. Forget about it. You don't like the way it handles? Add another leaf.

Clearance? Oil pans, links, coil springs, frame? Doesn't matter. Still won't clear? Add another leaf.

Last one: Sex Appeal. Nothing says "I'm your huckleberry" like an XJ on some big azz swampers bouncing it's way to the mud bogs in an old school, Colt Seavers kind of way.


CRASH

[Willis]

Steve, what do you figure is a perfect suspension? I guess that would have to depend on what you want it to do for you. I always figure that since we're not building rock buggies, our suspensions need to do many things well. Good on the street, good at a reasonable speed on rough roads, decent flex, good climbing ability, and stable in off camber situations. Perfect will be at least some compromise between the various things that you want it to do for you, leaning towards your own personal priorities. I'm curious about what you're after so I can watch as it comes together for you.



The theoretical perfect suspension would be the best at all above mentioned characteristics. Of course, the best suspension for speeds on rough roads, may not give good on-road or climbing characteristics.

Stability off-camber is a big one. I need to feel comfortable, and have confidence in my vehicle (those side hills make me nervous).

Climbing and hill descent would be up there too, after seeing Stephanie's and Leds vehicles unload in the rear at Moab, I'm convinced I do not want to go that route, however, they said they work well in Colorado, and would probably work well in most flat rocky areas.

The NorthWest is hilly, muddy, rocky and narrow. Maneuverability and control are my biggest concerns.

I also need good street-ability, as it will not be daily driven, but will drive to and from Moab, no trailer in my immediate future.

The more I learn about a link system, the harder it is to plan one out. So far, I'm looking mostly at anti-dive. Keeping that anti-dive% low (60-70%), is proving to be harder than I thought. I just re-sketched a few min ago after realizing a mistake. I am trying to keep my upper completely level and at 70% as long as the lower. From what I gather, I am trying to keep my control arm separation at the axle at 25% of my tire size (35"). That puts my separation at 8.75". I want my lower to mount directly behind my axle, but 8.75" above that, puts my upper pretty close to my pan, if not into it at full compression. So, the lower needs to be mounted lower, so the uppers are not so high. I want my lower arms at around 7*. Well, with a 33" long arm, at 7*, my arm is around 3" below my framerail, which I suppose is not too bad, I just wanted more clearance. Now, the separation of the links at the frame end should be close to 1/2 the distance apart they are at the axle end (vertically). This puts my upper arm around 1* downward from the axle to the frame (good enough), and my IC at around 72* (located front to rear just under the middle of my rear door). It's pretty good on paper, and this would be taking into considerations mounting points. I could execute this design using a parabolic upper. I still need to play with my pinion change and re-read Ed's post, because I know there are many more variables involved, and more changes that will come. I have not even gotten into roll axis. I'm trying to sketch the geometries as I learn and understand them. If I come away with anything from this thread, it will at least be more than what I started with.

My brain hurts,
Steve

[Willis]

willis you jackazz!!!!
Link price just went up huh? :D


we were trying not to let eagle find out, remember?
Ya, he'll be on you like rice on a Honda.


besides, didn't I make it clear that I had an "adequate spare"?

never mind the fact that it was a trailer tire, I considered it "adequate", just like the bylaws state.
Trailer tire, steal one off of one of those great single wides in SlickRock?


BTW, what I do with ed's posts, is I print them out, I leave the computer room and sit on the couch, and begin to read.....slowly.....rinse and repeat.
Great idea. I think I'll hit the can. That's where I do my best thinking.


if you do a search on 4-links, you'll find a long one I started a while back, and there's some really great info there....

have a look.
Been there, done that. That's what got me thinking about the 'correct' geometry of the front. Yes, it's all your fault.

Steve

[XJguy]

Bob, Ed and or Max,

What do you gentlemen think, as far as geometery, of the long arm suspension by Rockcrawler (I think), that locates the control arms (body side) basically inline to one another, inside the frame rails, with the lowers at the forward face of the crossmember and the uppers 30%~ shorter, and retains the stock axle-side mounts?

XJguy

[Goatman]

The NorthWest is hilly, muddy, rocky and narrow. Maneuverability and control are my biggest concerns. I also need good street-ability, as it will not be daily driven, but will drive to and from Moab, no trailer in my immediate future.

I want my lower to mount directly behind my axle, but 8.75" above that, puts my upper pretty close to my pan, if not into it at full compression. So, the lower needs to be mounted lower, so the uppers are not so high. I want my lower arms at around 7*. Well, with a 33" long arm, at 7*, my arm is around 3" below my framerail, which I suppose is not too bad, I just wanted more clearance.

Steve

Well, you lost me with the lower arm mounting point 3" below the frame on a 33" long arm. You and I are different, but for me no other design parameter would be more important than that. In my experience, loss of ground clearance stops us more often than lack of traction. The reduced breakover angle of a long arm hanging below the frame is unacceptable to me. We build these things to be capable wheelers, and that amount of compromised ground clearance nullifies a whole bunch of other performance attributes. No sense in going through that much planning and work to make that much of a compromise in that serious of an area.

That will get you a picture (of you hung up) in my "hung up long arm" scrapbook. :D

OK, now just for fun, consider that ground clearance cannot be compromised. Now go do some more drawings and calculations and see what you come up with. :)

[Beezil]

That puts my separation at 8.75

I don't know how playing with that number changes your design, or if this helps to know, and depending on how "hard" your mounting points are on the front axle, you can run 7" if you wanted to...8" has been considered the "rule of thumb" amongst in the offroad crowd.

see, this is what I'm saying....

first off, where are you trying to locate your lower links at the axle end?

if you say "behind the axle at the center-line" and still want 8.75" of vertical seperation, that puts you upper link point 7.25 above the top of the axle tube. what did you say you wanted for lift height 7" right? I don't know how many inches you figured for compression, but with an upper link mounting point 7.25 inches above the axle tube, that doesn't leave a ton of room for you to compress without punching a really serious, and buzz-killing hole in the bottom of your oil pan....but, maybe your design allows for this?

you need to spend a couple hours under your rig on a comfortable creeper, with some sage incense buring, candles lit as mood lighting, a pot of green tea going, and some mystical ambient music playing in the backround.


btw goatman, I'm wondering if you have a SEPEARTE scrapbook for "frontend unloaded and lost momentum on the ledge" scrapbook, or are all the pictures in the same scrapbook? I have some pictures to send you.

[Grant]

Just a word or two. Tried in vain to resist.

If you think a buggy is a blank sheet, think again. The new buggy is a PITA and it started as a clean sheet.

"Attempting" to keep front and rear links and driveshafts the same length, less spares to carry. also a buggy makes an XJ look wide, not easy to get the triangulation required.

From the competition buggies I've studied, I would say most engineers would doom it to failure before the first tube was cut. AS %'s over 200, which means most of the top guys are running limiting straps (or winching the front axle) front and rear. But does it work for climbing? Like nothing you've ever seen. How many of the current buggies were professionally engineered and designed? How many were built using experience learned in previous vehicles? How many were built and the AS and RC calculated after fabrication?

Not to be mean to the real engineers on this board, but this thread is typical of an "engineer vs Engineer" discussion. Too many of the Engineers (studied at fancy school for a piece of paper to hang on the wall) of recent years are seriously lacking in any hands on knowledge. They can pull fancy figures out of their laptop (or out of their arse) all day long, but until you have practical hands on experience those figures are hardly valid.

The old school engineers (studied at the school of hard knocks, no fancy piece of paper, plenty of experience) know if something is possible or not largely through experience. An example - desperately attempting to get qualified at Indy in 98. New Engineer on the team, fancy $$$ laptop computer. So instead of referring to previous year's notes, we are relying on Mr Engineer to come up with the set up. I knew he was full of BS when the ride height change requests were being done in THOUSANDTHS of an inch. Sure he (or the laptop) could show us how 3 thou would improve down force by 35 lbs. So the car is on the setup pads, and he (or the laptop) says that a further reduction in the ride height of 5thou was needed. Being the angry South African (or Australian) I shoved the wrenches in his hands and told him to lower the car. He had NEVER actually used wrenches before. Just how the hell do you get through 4,5,or 6 years of engineering without using wrenches? or a lathe? or a welder?

My point being - if he had any PRACTICAL experience he would have known that ride height adjustments in the thou's is a dream, 1/32 is possible if you have a good mechanic, 1/8 more practical. Fired his ass (a pleasure firing someone who was making three times what my deal was), returned to the previous year's notes, adjusted, pulled some figures out of MY arse, and got the car in the field, barely.

Call me a Luddite (sp?) if you will, but in a way all this tech info and data today, is actually hurting things. A young driver today comes into the pits and waits for the Engineer or data aquisition tech to tell him how the car is handling, rather than storming into the pits and telling the crew what the car is doing. They can barely tell the difference between "loose" and "push" without an Engineer there to tell them what to say.

I would class 90% of the Engineers (big three related) I have worked with, into the same category. Dreams of designing what you wish fall to the wayside when the first college loans are due, and you end up working for Detroit engineering door locks, cup holders, and seat heaters. Half of the time is spent justifying your design to the bean counters. True engineering will never again be seen in mass auto manufacture, the bean counters are holding the reigns.

Now after that little rant, let me express my appreciation for all things engineering. Sure engineering improves the product, but at what cost? Take NASCAR for example. In 1994 when I worked in the South I was offered a job at Hendrick motorsports. The crew chief on one of the cars was my boss early on in south african racing circles. Ken was one of the first engineers to make it in NASCAR, and partially as a result of him winning the Winston Cup as crew chief, the doors opened and engineers came flooding down south. As a result the cost of fielding an competitive ride in Winston Nextel Cup has tripled in 10 years, from $5 mill to around $15 mil. Have the cars got any quicker? Are the races three times as exciting? Has the spectacle improved?

Beezil - real world engineer
Max - real world Engineer

All the figures in the world are not going to be helpful until you actually crawl under an XJ and start building. Theory has to stop somewhere, and building and using and evaluating has to start sometime.

[Grant]

A quick question for the real Engineer's now.

Front suspension only. Buggy not XJ.

What roll center differences are there between the following?
Example 1 - Double triangulated 4 link, upper links narrow to a common point on the top of the front axle, lowers slightly splayed outwards from frame to axle

vs

Example 2 - Same setup but lower links converge, and upper links splay out.

Basically if you used Beezil's existing setup, and compared it to the same setup, but with the parabolic link located low and splayed links located high (ignore packaging problems)

Am I correct that AS stays constant, as upper and lower link angles remain unchanged? Am I correct that RC is now lower? Why?

Typical damn South African's - bash the Engineers in one post and then ask their advice in the next. Hypocrite :)

[Beezil]

If you think a buggy is a blank sheet, think again. The new buggy is a PITA and it started as a clean sheet

thanks a whole lot for wrecking my buzz grant!!!!

i was looking foreward to one day starting my own buggy, and was under the impression the "blank canvass" would make things easier!!!!

I hate you.

[Kaczman]

[QUOTE=Beezil]Kacz.

here's a quick drawing....



http://users.rcn.com/beezil/public/drawing2.JPG

Sweet, back on topic!

B-Thanks for the pic. I'm suprised to see the profile of our rear links looks very similar. It will be interesting to see how much more body roll and rear steer I get by only triangulating the uppers (assuming the rig ever gets some action).

http://www.crawltech.com/albums/Front-4-link/Jeep_Scan_001_2.jpg

Did you ever consider shortening the wishbone in order to help clear any of the obstacles underneath? Right now, mine may end up being a mid-arm (~26-28") four link.

-Jon

[Ed A. Stevens]

A quick question for the real Engineer's now.

Front suspension only. Buggy not XJ.

What roll center differences are there between the following?
Example 1 - Double triangulated 4 link, upper links narrow to a common point on the top of the front axle, lowers slightly splayed outwards from frame to axle

vs

Example 2 - Same setup but lower links converge, and upper links splay out.

Basically if you used Beezil's existing setup, and compared it to the same setup, but with the parabolic link located low and splayed links located high (ignore packaging problems)

Am I correct that AS stays constant, as upper and lower link angles remain unchanged? Am I correct that RC is now lower? Why?

Typical damn South African's - bash the Engineers in one post and then ask their advice in the next. Hypocrite :)


If the IC locations are the same in the elevation view, the AS is the same.

The roll axis for the axle system (front or rear) is a line between the convergent points of the upper and lower link intersections. The tightly convergent links (upper in E1, lower in E2) locate one end of the roll axis, the end closest to the axle centerline. It will anchor one end of the roll axis near the axle, and because the convergent point does not move vertically much as the suspension cycles (as the virtual extension of the convergent links is short). The tight link spacing keeps the roll axis close to the link height at the axle centerline (where the Roll Center is located).

The problem with comparing the Roll Centers only, is that you do not consider the impact the non-convergent links have on the angle change in the roll axis. Small defelections in the non-convergent links (minimal wheel travel) can significantly relocate this distant end intersection that defines the roll axis.

In your comparison you are correct, the RC is lower, but it is wise to identify the roll axis, because leveling it is one of the improvements that Bob mentioned as a gain in ride quality between the XJ and later RAM factory 4-links (if I read his comments correctly).

Roll Center is tossed out a lot in road racing comparisons because the rake of the roll axis does not change when the inboard pins of the A-arms fix the roll axis. The roll axis is at a fixed rake with a parallel frame mount A-arm independent system, and it is not with a four link.

The best we can do with a four link is to make both sets of paired arms convergent, locating opposite ends of the roll axis close to the link ends to minimize the elevation change in each as the suspension cycles.

BTW, if any Engineer is offended by your rant I would expect they have not spent much time actually building or fabricating (or testing, including racing). Where the Engineering does help, if applied, is to predict how much to expect as the result of changes in a design. Will it fail, will the road feel be better or worse. Will it push or oversteer if this or that is changed, and how much. The fallacy is in believing the numbers come from pure theory, and not the experience of non-Engineers. The numbers model only what is communicated and try to quantify subjective input from drivers and others (tire manufactures, etc., some is quantative data, but the advice is subjective).

What is difficult to do, for many Engineers, is to listen to the subjective responses when they do not match the numbers and admit the theory does not apply. This has been common in off-road racing, where the long travel suspension systems exaggerate the movement of the normal parameters tossed out in suspensions design manuals (low roll center, moderate anti-dive & squat, etc.). I am always interested in reading what others have experienced in any conversation with traditional suspension Engineers who have dabbled in off-road racing, because the feedback for the drivers and owners I listened to point to the lack of an open mind (the Engineers responses were more along the line of "don't drive it that way if you don't like the way it handles" rather than actually discussing why the driver did not like the performance. Ten or twenty years ago few off-road drivers (rally or endurance racing ) advanced to successful paved track racing. The Engineers used to walk away and criticise the drivers. The Engineers should not be able to do that today (with names like Gorden and Johnson winning in both arenas).

[Grant]

I should have known I would get an excellent reply to this, many thanks Ed. I have been driving myself crazy with front 4-link packaging problems, and sometimes, it's a case of not seeing the forest because the trees are in the way. Going back to the basics has made it clear again.

Moving from open wheel racing to offroad has been quite the challenge. I almost find open wheel competition boring in comparison, very little changing year to year, mostly due to rules strangulation in the quest for safety. But it's 12 years since I worked in F1, and almost 3 since I've been seriously involved with Indy stuff. I like the wide open rules in rock crawling, or total lack of rules in building my own junk.

Eloquent reply to my rant Ed, great. :)

[Willis]

if you say "behind the axle at the center-line" and still want 8.75" of vertical seperation.....that doesn't leave a ton of room for you to compress without punching a really serious, and buzz-killing hole in the bottom of your oil pan....but, maybe your design allows for this?

you need to spend a couple hours under your rig on a comfortable creeper, with some sage incense buring, candles lit as mood lighting, a pot of green tea going, and some mystical ambient music playing in the backround.



Ya, I spent about an hour under there on Sunday with my hi-lift making my 4" lift 7". I quickly found out that 8.75" will not cut it. I have not re-sketched since that, but do plan to re-design.

Also, the 3" under the framerail mount that Goatman describes is a spot I plan on playing with, once I decipher all of Ed's wisdom. The steeper the angle of the lower arm, the more axle steer, but as we have proved, not nearly the issue with the front as the rear.

Steve

[Beezil]

Also, the 3" under the framerail mount that Goatman describes is a spot I plan on playing with

I really really really really really think this is a bad idea.

I'm 1.75" under the frame rail at my lowest point, with 37" tires.

You are gonna HANG like a horse theif with a 3" rock snagger on 35's....

Doing so might make the numbers look good, but at the cost of getting DENIED on trail.....

once you hear the terrifying sound of goatmans evil snicker as he's lifting your jeep by your rockrails with the highlift and throwing you tow straps, you'll never get it out of your head, and you'll have the nightmares to look forward to.

[Goatman]

I really really really really really think this is a bad idea.

I'm 1.75" under the frame rail at my lowest point, with 37" tires.

You are gonna HANG like a horse theif with a 3" rock snagger on 35's....

Doing so might make the numbers look good, but at the cost of getting DENIED on trail.....

once you hear the terrifying sound of goatmans evil snicker as he's lifting your jeep by your rockrails with the highlift and throwing you tow straps, you'll never get it out of your head, and you'll have the nightmares to look forward to.

I couldn't have said it better myself. :D :D :D

http://fototime.com/558E53F821D6669/standard.jpg

[Beezil]

The steeper the angle of the lower arm, the more axle steer

You may one day, experience driving your rig home, with ONE rear axleshaft operating......

I can guarantee you won't worry about the effects of a little "axle steer" in a maladjusted 4-link after that!

[XJJPR]

http://fototime.com/558E53F821D6669/standard.jpg

Gee, I recognize that jeep, I knew he plowed fields but ROCKS? :D

hinkley

[Beezil]

Oh, I get it now...

no wonder he painted his rig "john deere green".....

[Willis]

You are gonna HANG like a horse theif with a 3" rock snagger on 35's....


Ya, that's why I plan on playing with it, to see if I can make it better. You are right, it makes my numbers look good, and will probably give me good road characteristics, but at the cost of offroad-ability. Guess the compromising begins.

[Beezil]

Guess the compromising begins.

isn't it a bitch???

have fun!

remember, its supposed to be fun!

best of luck.

don't forget to keep watering this thread.

[FarmerMatt]

One day goat herder... you will pay for that pic. I'll have you all know the mounts sit up flush with the cross member now. I haven't been hung on the cross member since raising the mounts. On road handleing was better with the mounts lower, but raising the mounts so as not to have anymore pics like this one is worth the compramise.

"remember, its supposed to be fun!"

I think you should have remembered this in the begining of this thread beaver butt.

Matt

[Goatman]

Ya, that's why I plan on playing with it, to see if I can make it better. You are right, it makes my numbers look good, and will probably give me good road characteristics, but at the cost of offroad-ability. Guess the compromising begins.

That's why you need good design priorities, at least to me it means that. What you are willing to compromise and what you aren't willing to compromise, and how much. Priorities.........

I do think you can make an XJ suspension do everything well, but it won't be the absolute best at anything, and you can always keep fine tuning it. I really do drive mine from CA to Moab and CO and wheel it hard, and it handles and rides reasonably well. Plus, it can be loaded up with people and camping gear. Many of us have rigs that work well in most situations, something that is really nice about a well built XJ.

[Goatman]

One day goat herder... you will pay for that pic. I'll have you all know the mounts sit up flush with the cross member now. I haven't been hung on the cross member since raising the mounts. On road handleing was better with the mounts lower, but raising the mounts so as not to have anymore pics like this one is worth the compramise.

Matt

Hey Matt, just think about that pic as a contribution to the education process. You have enlightened many people. ;)

:D :D

[Bob Sheaves]

For your viewing pleasure (along the discussion here).....an extreme design that could be used in certain conditions:


http://www.race-dezert.com/wwwthreads/files/6-22397-00000003.jpg



I go away for a day and the thread explodes!!! OK, hope I get everyone that asked in here...

Ed- I did not have to reverse engineer the XJ system- I had all that info, plus the testing, analysis, and issue reports available to work from. That makes the job a LOT easier.

As a sidebar, you must remember Walter Voss then from that time period-I was wroking for him at the time. I did all the simulation and dynamics approvals and rework when necessary. I also did "field support"... :)

http://www.race-dezert.com/wwwthreads/files/6-22398-00000004.jpg

Goatman- Thanks for the support! I agree that IFS (as well as IRS) can get the shakes as bad as a 4link overconstrained system.

http://www.race-dezert.com/wwwthreads/files/6-22399-00000005.jpg

Beezil- Nice work so far on your sketches. Please accept my apologies for my comments earlier.

http://www.race-dezert.com/wwwthreads/files/6-22401-00000007.jpg

Willis- I know there is a lot of info to be understood about these overconstrained systems, but hang in there-it just takes time (and a really BIG bottle of asprin).

http://www.race-dezert.com/wwwthreads/files/6-19861-00000003.jpg

XJguy-I am not familiar with the design you mentioned (it's heck being the newbie at times) so I cannot comment. I'd need to see it and get a few measurements to form an opinion. Sorry.

http://www.race-dezert.com/wwwthreads/files/6-20110-ga.jpg

Grant- I could not agree more. When I got out of the military, I started as a liasiaon engineer for IH on the Scout Group (that ought to tell you how crotchity I can be...LOL). My supervisor was an old fart that made me spend the first 6 months of my work there working in the plant, learning how to build the vehicles, and their problems, from the bare frame, to body assembly, paint, building seats and engines, wiring (I STILL have nightmares about chasing down shorts)..etc. I do not understand how the "engineering schools" can turn out a "qualidied engineer" that doesn't know which end of a screwdriver to use....

Best regards to all,

Bob

[Beezil]

Bob, I can appreciate your education, your experience, and your presence on the board, but seriously, what *is* your purpose on this thread, except for maybe impressing some of us?

I'll admit, I'm impressed, but so far, you haven't really done anything except, list some credentials, post some cool looking CAD, and take part in some engineer-SPEAK.

If you could have done any of those things WHILE MAKING AN ATTEMPT to help willis design a suspension system that incorporates 35" tires with 7" of lift on a JEEP CHEROKEE, you would have impressed me even more.

[FarmerMatt]

Ok... Explain what we're looking at here. It seems like we're looking at a swing arm assembly with a built in IRS system suspended by a cross mounted leaf spring, driven by hyd. or electric motors on gear reduction boxes? Although the last pic seems to show a drive shaft. You can't drop a bomb like this & not splain what's going on to us common folk.

Matt

[Bob Sheaves]

Ok... Explain what we're looking at here. It seems like we're looking at a swing arm assembly with a built in IRS system suspended by a cross mounted leaf spring, driven by hyd. or electric motors on gear reduction boxes? Although the last pic seems to show a drive shaft. You can't drop a bomb like this & not splain what's going on to us common folk.

Matt

Hi Matt,

My intention was not to drop a bomb, but rather show by design how some of the problems in wheel travel and the control arm length can be corrected. I prefer to allow people to ask questions, as some of the ideas presented in this design are rather unorthodox and esoteric.

If you follow the pix url back to race-dezert.com, you will see that this design was in response to a question on how to design a high travel suspension for the desert, without going to a fully independent desigh, as is currently common in the truggys and trophy trucks. This thread is 10 pages long, but contains a LOT more detail on the hows and whys....

In the application of Willis', meaning the +7" height and 35" tall tires, the common approach in these trucks (which DO require a great deal of articulation, as well as vehicle speed) is the "Jeepspeed approach" (for the time being-I will assume you understand this approach). One of the changes made between this design and the OE suspension on the XJ is a lack of a track bar. The shown pix demonstrate how to delete this item and still maintain control over the motion of the axle. (BTW- do NOT be impressed-this is just the application of basic "book larnin' ".)

The overall design is an application of a DeDion type suspension. If you have never seen one-look under the rear of a Chrysler AWD minivan. The primary benifit of the DeDion is a lower unsprung weight of an independent syspension (good for high speed and reducing the "death wobble" mentioned earlier), with the grund contact patch control of a hotchkiss ( a leaf sprung live axle). Follow the explaination so far?

Best as always,

Bob

[Bob Sheaves]

I will continue....

The DeDion tube is supported by 2 inverted struts, rigidly mounted to the engine cage structure in the chassis (not shown for clarity). In a common XJ-these struts would be supported by bracketry on either wheelhouse on the Z axis and tied together across the top of the engine, and then tied back from each strut to the dash panel (common term is the firewall) and under dash cross car beam that should be installed in the front cage section.

The DeDion tube itself is no different in concept than the dead axle on the front of a 2WD XJ. This tube supports the knuckle yokes, Steering knuckles, brakes (altho this design uses, as you surmised, hydrostatic drive and braking), wheels, tire, beadlocks, and CTIS. At the outer ends of the tube, facing rear, are a pair of brackets not unlike the existing lower control arm brackets, that pick up the tringular, tubular construction, lower control arm and voided bushings. The reason for voided bushings is to control the deflection of the control arm arc by utilizing the elastomer in the bushing to allow deflection on one plane but not either of the 2 other pivot planes. In one of the pictures, you can see that the "top and bottom" of the bushing has no elastomer, but the fore and aft positions do have the rubber. This is what allows the pivot location to vary (increasing and decreasing the active length (as opposed to static length) of the lower control arms as the axle moves from full rebound (commonly called "droop") through design (static load height-where the truck sits at rest), up to the full jounce (commonly called "bump") position.

More in a bit....

Best as always,

Bob

[Willis]

The overall design is an application of a DeDion type suspension. If you have never seen one-look under the rear of a Chrysler AWD minivan. The primary benifit of the DeDion is a lower unsprung weight of an independent syspension (good for high speed and reducing the "death wobble" mentioned earlier), with the grund contact patch control of a hotchkiss ( a leaf sprung live axle). Follow the explaination so far?

I know the DeDion very well actually. The rear axle in my Alfa Romeo Milano is of the DeDion design with an IRS transaxle. It handles great! On my list is to change out the rubber bushing at the front mount to a factory race spherical bearing for additional axle control. Down side is it transfers more road noise and vibration to the chassis.


Damnit! I'm contributing to the hi-jacking of my own thread.
*edit* Not complete hi-jacking, but I don't see how a DeDion can be used in the front or rear of an XJ. If you know otherwise, please elaborate *edit*

[Bob Sheaves]

I know the DeDion very well actually. The rear axle in my Alfa Romeo Milano is of the DeDion design with an IRS transaxle. It handles great! On my list is to change out the rubber bushing at the front mount to a factory race spherical bearing for additional axle control. Down side is it transfers more road noise and vibration to the chassis.


Damnit! I'm contributing to the hi-jacking of my own thread.


Willis, if you bear with me for a bit-you will see how that applies (especially the comment you made about the axle). Actually, I do not think this constitutes hijacking, does it? It has direct applicability to your original application question.

Best as always,

Bob

[Beezil]

do any specs exist on this type of set-up in terms of articulation or suspension travel?

[Bob Sheaves]

do any specs exist on this type of set-up in terms of articulation or suspension travel?

Yes, and I will get to them shortly. If you are in a hurry-go tothe original thread on race-dezert.com.

Bob

[Willis]

Actually, I do not think this constitutes hijacking, does it? It has direct applicability to your original application question.

Hehe, you were posting while I was editing. No not really hi-jacking, I just don't quite understand how this all relates to the XJ, or how to make it relate. It may help us understand the geometry, but I don't know about the direct application of the design. I personally don't think the DeDion flexes well (articulation), and if it were usable, it would have to be mounted very high on the axle, or have a pretty extreme angle to work well. In that case, it would have similar characteristics to radius arms, where they have very high anti-dive percentages. Correct me if I am wrong.

[Bob Sheaves]

Hehe, you were posting while I was editing. No not really hi-jacking, I just don't quite understand how this all relates to the XJ, or how to make it relate. It may help us understand the geometry, but I don't know about the direct application of the design. I personally don't think the DeDion flexes well (articulation), and if it were usable, it would have to be mounted very high on the axle, or have a pretty extreme angle to work well. In that case, it would have similar characteristics to radius arms, where they have very high anti-dive percentages. Correct me if I am wrong.


This design has controls there in the form of motion design that compensates. I will get in more depth shortly. If you guys do not mind-it's 1:15am here and I have to be in the office at 6:30 for a 7am review meeting. I'd like to continue this tomorrow afternoon when I get home. OK????

Best as always,

Bob

PS: One final research "assignment" look up the Morgan "sliding pillar" front suspension design and compare it to the "struts" shown....

ADDENDUM: think what the primary purpose of a suspension and drive axle is-forget the "type" of suspension used for the time being...just concentrate on what it is you are trying to accomplish (NOT in terms of components, but in performance).

[Beezil]

willis, screw the 4-link.

just build one of these instead:

http://www.starwarsnet.co.uk/lukeslandspeeder.jpg

[XJJPR]

willis, screw the 4-link.

just build one of these instead:

http://www.starwarsnet.co.uk/lukeslandspeeder.jpg

B,
I think you finally hit the nail on the head of where this thread is going! :D

hinkley

[Willis]

willis, screw the 4-link.

just build one of these instead:

http://www.starwarsnet.co.uk/lukeslandspeeder.jpg

I just can't find the parts. ORGS, and URF don't carry them. Guess I need to open up the Grainger Catalog.

[Beezil]

the only thing wrong with this set-up, is you won't be allowed to run any trail that woody is on.

he hates magnet kids.

[Goatman]

Hey, Woody likes anything that uses magnets.....he'd dig it!

Back to the subject matter. Steve, what are your thoughts on wanting a triangulated upper link/links so you get rid if the track bar? I realize it's something different, but I just don't see anything negative about a front track bar, and there are definitely some things that are positive especially if you'll drive it fast off road and on the street.

Forgive me for bringing this up, but some people do mods purely for the fun and cool factor, rather than because they'll actually work better. Cracks me up sometimes when pics are posted and a bunch of people go oooh and aaahh, but the only thing I want to see is what it does in real life, on the road and on the trail. I appreciate new ideas and good fabrication, and some of us really enjoy the fabrication part of it, but in the end it should be to improve performance or we're just fooling ourselves.

[CRASH]

URF is only interested in mods that work well on-road, as Richard is always quick to point out.

I dig track bars, I think they are the only way to keep a drag link and not have some funny handling characteristics at high speed (commonly referred to as "bump steer"). If you're going fully hydro steer, I'm all for triangulation of links to lose the track bar, but otherwise, they are the best way to go for a rig driven in different kinds of conditions.

The best solution other than leaf springs, that is. ;)

CRASH

[Beezil]

go watts linkage or go home

[Willis]

Back to the subject matter. Steve, what are your thoughts on wanting a triangulated upper link/links so you get rid if the track bar? I realize it's something different, but I just don't see anything negative about a front track bar, and there are definitely some things that are positive especially if you'll drive it fast off road and on the street.

My goal with this thread was not necessarily to cover one or another front suspension design, but to learn some of the geometry that effects the characteristics of any front suspension, to aid in making a good decision on what type I desire.

That said, I have seen long arms (radius arms) at work, and was not overly impressed with the unloading. I have not learned yet how to calculate the AD% for radius arms (Ford, Rover, Clayton's), but I'd imagine it must be pretty high. For that reason, I chose to investigate alternatives.

3 mid arms like your's intrigue me (or any asymmetrical system for that matter). The issue I see with this design, is that when drawn from the side with 2 arms (left side), you can calculate an AD%, and make that a respectable number. When drawn from the side with only one lower arm (right side), you can not calculate AD% because of the missing link (I don't know if the AD% would be infinite or not). What does this have to do with handling? Well, the way I see it, the AD% for the front, as a whole, will be what the AD is on the left. However, when in a hard braking situation with high traction, that left anti-dive is going to keep the left side of the frame rail from diving. The right side does not have any upward force from the upper control arm, and will dive more than the left. When the right dives more, it may reduce the angle of the lower control arm. By doing so, may push the right side of the front axle forward inducing a leftward brake pull which may be exactly what you want to avoid in a panic situation. Of course, this is my postulation on what could happen. Have you experienced this yet?

4 mid arms with track-bar. This option really has not been explored (Kinda by Tomkin, but not really what I'd want), and would probably net a fairly good suspension. I would love to try something new, but will be using family tools and workspace to do any serious work that needs to be done. Some things can be done in my single car garage, but I just don't have the room or tools for design after design like some people **coughBeezilcough**. Someday though. The problem I see with this type suspension, is the fact that it creates a twisting bind upon full flex where all 4 mounts are fighting each other.I am thinking Rock Ready, no compliance arms that break the front axle bridge. This idea is still on the back burner, I may explore it some more. Rubber joints on the axle end would be a must.

And finally, the track-bar-less parabola, wishbone, 4 link, whatever the design, still functions similar. I plan on running the inverted T steering setup, hydro is not an option at this time. I know I will here all kinds of "what about bump-steer" comments. The thing I see, is the fact that the suspension moves similar to a leaf sprung vehicle. CJs did not have track-bars, but YJs did. I plan on running hi steer, with a dropped pitman arm on a HD saginaw 4 bolt box (not the weak XJ box). The flatter the drag link, the less likelihood for bump-steer. What I like about this type suspension is, equal, and good AD numbers from side to side, excellent, bind-free flex, and the cool factor doesn't hurt either.

Steve

[Goatman]

3 mid arms like your's intrigue me (or any asymmetrical system for that matter). The issue I see with this design, is that when drawn from the side with 2 arms (left side), you can calculate an AD%, and make that a respectable number. When drawn from the side with only one lower arm (right side), you can not calculate AD% because of the missing link (I don't know if the AD% would be infinite or not). What does this have to do with handling? Well, the way I see it, the AD% for the front, as a whole, will be what the AD is on the left. However, when in a hard braking situation with high traction, that left anti-dive is going to keep the left side of the frame rail from diving. The right side does not have any upward force from the upper control arm, and will dive more than the left. When the right dives more, it may reduce the angle of the lower control arm. By doing so, may push the right side of the front axle forward inducing a leftward brake pull which may be exactly what you want to avoid in a panic situation. Of course, this is my postulation on what could happen. Have you experienced this yet?

4 mid arms with track-bar. This option really has not been explored (Kinda by Tomkin, but not really what I'd want), and would probably net a fairly good suspension. The problem I see with this type suspension, is the fact that it creates a twisting bind upon full flex where all 4 mounts are fighting each other.I am thinking Rock Ready, no compliance arms that break the front axle bridge. This idea is still on the back burner, I may explore it some more. Rubber joints on the axle end would be a must.
Steve

I didn't answer earlier because I wanted a little seat time before I did. We had this discussion once before about there being different anti-dive amounts on each side. This is theory, and I don't think it bears out in reality. My rig goes perfectly straight under braking, even hard braking. I had some pulling to the right when braking initially after putting in this suspension, but it's been gone for quite some time, and had something to do with alignment, a weak track bar mount, or something, but it's long gone. I didn't remember any pulling for a long time, but just to make sure I went out and drove it around tonight. I can hit the brakes hard or soft without holding the wheel and it stays straight. The front end does not dip more to one side, but as far as I can tell dips evenly. BTW, my upper arm is on the right side and attaches to the axle on the same mount as the track bar does.

Initially, I built a four link on this axle. My original concept was the three link, but I put a mount on the drivers side just to try it. It didn't work. Like you said, it needs rubber somewhere, and I had johnny joints on both ends of the lower links and JJ's on the axle end and heims on the frame ends of the upper links. Trying to cycle the suspension with no springs or shocks hooked up wouldn't happen. A floor jack on one side of the axle would just start to lift the vehicle rather than raise the axle any more. In the real world, with tires on and on the trail, it probably would have flexed, but only by extreme presure on the JJ's and something would eventually have to give. So, I never ran it with both upper arms.

A mid arm four link would work well, even without rubber bushings, but the lower and upper arms would need to be close to equal length and parallel. When the upper and lower arms are equal length and parallel there is no castor change as the suspension cycles, so even when articulating there would be no binding in the bushings. Work on that a little....... :)

Or just go three link........very simple. The only issue is that it has to be strong, but clearance is much easier to deal with.

[XJJPR]

3 mid arms like your's intrigue me (or any asymmetrical system for that matter). The issue I see with this design, is that when drawn from the side with 2 arms (left side), you can calculate an AD%, and make that a respectable number. When drawn from the side with only one lower arm (right side), you can not calculate AD% because of the missing link (I don't know if the AD% would be infinite or not). What does this have to do with handling? Well, the way I see it, the AD% for the front, as a whole, will be what the AD is on the left. However, when in a hard braking situation with high traction, that left anti-dive is going to keep the left side of the frame rail from diving. The right side does not have any upward force from the upper control arm, and will dive more than the left. When the right dives more, it may reduce the angle of the lower control arm. By doing so, may push the right side of the front axle forward inducing a leftward brake pull which may be exactly what you want to avoid in a panic situation. Of course, this is my postulation on what could happen. Have you experienced this yet?

Steve

Here I can give you some real world experience. I have the 3 link like Goats but I put my upper on the correct side, the driver's side (Goat :D ) .

There isn't anything different here than when it had four arms in it's driving and braking charateristics. I can lock up my 35" tires on dry pavment and not have a bit of pull. (other than the normal sliding from being locked up) Turning either right or left is exactly the same. No more or less dive or under or over steer. This Jeep handles better than any other XJ I've ever built! I drive 3 different XJs and MJs (2 four link and one 3 link) and can't tell a difference between the setups on the street, but off road the three link just articulates over obsticals much better!

My upper arm is made the same as a lower arm using 2.5" JJ with 9/16" cross bolts. Both mounts, axle and frame have been redone accordingly. So alot of extra strength has been built into my upper arm setup.

mark

[Willis]

Thanks guys for the real world experience. That is definitely an option. For some reason I thought Goat's was on the drivers side as well.

I sketched the 4 mid arms. You are right about the caster change on articulation/compression/droop. I drew them at 24" each. The lower just below the framerail, but with 7" separation at the axle end, equal length arms, being parallel, that puts the uppers above and behind the existing upper arm mount (read, inside the cab where your left foot rests while driving). Now, I don't have a problem cutting and modifying the floor, but it seems like more work than it may be worth. Also, when the upper and lower arms do not form an imaginary intersection, I don't see how to calculate AD. It looks though, that it may end up performing much like long arms, where they will unload when climbing. Sure, a limit strap would help, but then I might as well go with long arms.

I'll really look close to the 3 arm thing. Just out of curiosity, how long are your upper and lower arms (both Mark and Richard)?

Steve

[Goatman]

Thanks guys for the real world experience. That is definitely an option. For some reason I thought Goat's was on the drivers side as well.

I'll really look close to the 3 arm thing. Just out of curiosity, how long are your upper and lower arms (both Mark and Richard)?

Steve

Nope, my UCA is on the RIGHT side. :D

My lowers are 19.5" and my upper is 16.5".

http://fototime.com/57DB3D9CCCFDE96/standard.jpg

http://fototime.com/9427A3F95831BF9/standard.jpg

[Beezil]

Goatman, why right side?

someone pointed out to me the drastic pinion angle that would result with the drivers side at full droop with running only a pass side upper. I didn't think it was a big deal when I was in the building process until I forklift tested it....

I've run single uppers on both sides, never had a problem, but I was just interested in front driveshaft u-joint life and ran the upper on the drivers side for the remainder of that set-ups life.

what's your excuse?

[Willis]

My lowers are 19.5" and my upper is 16.5".


I thought your arms were longer, at least in the 20s (for the lowers). I was clearly :confused:. Mark runs 'J' arms right? I'll have to play with the designs a bit, but a mid arm 3 link with 'J' lowers should work pretty good. I have a bit of time before I actually tear into my suspension (lots of time to change my mind again, and again, and....). I still think Beezil's design is a good one that we all know works, and I'm still leaning that way.

Thanks all!
Steve

[Goatman]

Goatman, why right side?

someone pointed out to me the drastic pinion angle that would result with the drivers side at full droop with running only a pass side upper. I didn't think it was a big deal when I was in the building process until I forklift tested it....

I've run single uppers on both sides, never had a problem, but I was just interested in front driveshaft u-joint life and ran the upper on the drivers side for the remainder of that set-ups life.

what's your excuse?

Never even considered it. I've had the thing twisted up to the max many times while crawling underneath checking clearances and measureing stuff, and I've never noticed any excess pinion angle in that situation. One reason may be that when I shortened the housing I set the pinion angle to point straight at the t-case with 5* of castor, plus it's high pinion.

[PapaPump]

ha! ressurection...this is a good one, why'd y'all have to go and scare off the engineers?

people are always saying search this and search that so i did...

a lot of the pics here have since expired...so...

what the heck is a j-link suspension?

how well does tomken's long arm setup work and does it retain the upper arms? how would that work

how well would you guess the full traction setup perfornms in regard to these concerns? i don't think it was out at the time this was written.

btw before anyone rips on me for pulling this one out...it was written about a month before i got my xj, i missed out, sounds like it was a good time

thanks,
mike