- Location
- Indiana-Missouri
you haven't seen it after the 2nd chop, its almost hard to look at.
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Front suspension geometry...lets get in depth...
- Thread starter Willis
- Start date
Willis
NAXJA Forum User
- Location
- Hoquiam, WA
Beezil said:Kacz.
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
outings, that's going to add weight. Until you do so, you are banned. 
Steve
Willis
NAXJA Forum User
- Location
- Hoquiam, WA
Ed A. Stevens said:
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
- Location
- Indiana-Missouri
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.
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.
- Location
- Foresthill, CA
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
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
NAXJA Forum User
- Location
- Hoquiam, WA
Goatman said:
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
NAXJA Forum User
- Location
- Hoquiam, WA
Link price just went up huh?Beezil said:
Ya, he'll be on you like rice on a Honda.
Trailer tire, steal one off of one of those great single wides in SlickRock?
Great idea. I think I'll hit the can. That's where I do my best thinking.
Been there, done that. That's what got me thinking about the 'correct' geometry of the front. Yes, it's all your fault.
Steve
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
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
- Location
- Bakersfield, CA
Willis said:
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.
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.
- Location
- Indiana-Missouri
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.
- Location
- Redstone Canyon, Nor CO.
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.
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.
- Location
- Redstone Canyon, Nor CO.
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
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
- Location
- Indiana-Missouri
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.
- Location
- Brighton, CO
Beezil said:Kacz.
here's a quick drawing....
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).
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
- Location
- Desert Beach So Cal
Grant said: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).
- Location
- Redstone Canyon, Nor CO.
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.
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
NAXJA Forum User
- Location
- Hoquiam, WA
Beezil said:
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
Last edited:
- Location
- Indiana-Missouri
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.
- Location
- Bakersfield, CA
Beezil said:
I couldn't have said it better myself.
