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Design, geometry and functionality of tracbar-less suspension

B

Beezil

Member #Nay
NAXJA Member
Location
Indiana-Missouri
I would like to start a conversation and debate on tracbarless front link suspensions.....

in order to avoid this topic being ruined there's some rules:

Leaf spring discussions are irrelevant
"Why?" is irrelevant
Daily driving, on-road situations irrelevant
JNJ's opinions are irrelevant and unfounded.

let's hear something about link geometry and lengths, and mounting locations....

anti-squat / rollcenter info would be great.
 
I won't answer "why?"

I don't know the answer to "what kind?" yet......

was thinking about a four link........before i did my radius arm set-up, I was going to do a upper wishbone similar to one-tons but decided to do the radius because it was fast and easy, and I was pushing to have my rig ready for moab.....Now I have time to re-explore my options.

I was to figure out the geometry and paramters first in order to see how difficult it will be to build with clearance issues with the exhaust and oil pan in the way.....if this was a rear 4 link question, it wouldn't be an issue as much....

I'm trying to figure out link lengths and placements that will make the most sense in regards to anti-dive and articulation......

Or maybe someone can't point me to a POR discussion that has reliable info, and that ISN'T the "god of suspension" thread.....
 
TPIJeep on pirate has been doing a lot of link calculations. there are a number of threads that he has started that seem to have some pretty good solid real world calcs.

if you're into calcs that is.

if you triangulate the uppers and bring them together towards the center you'd either be above the diff or next to it but I can't see how one would get around the oil pan/driveline clearance issues very easily.

wanderingwillys (i think Matt is his name) built a 3 link with a WIDE 'U' for the upper so that it would clear the oil pan etc.

I keep thinking about it in my head because i have a real disdain for the tracbar (just don't like it for some reason) but haven't come up with anything great yet. I'll certainly be curious to hear more from others that have fabed or worked on linked fronts with no tracbar.
 
What about a triangulated 4 link where the lowers come from the center of the crossmember to the outside of the axle end and then do the uppers straight (relatively) front to back?

I believe the give away avalanche buggy is done this way.

Dan
 
Beezil,

Here's one to think on, but it does have a TB but only one upper.

I know Goatman is running one, but the one on the MJ is on the driverside. It articulates really well and can still be used with normal steering so keeping it so you can drive around on the street still works. I know what you said, but... (Options) Check out the MJ page on the site you'll see the setup I'm talking about.

As for a 4 link no TB you'll really want to do a inverted 3 link. Wish bone on the bottom, single center link on axle end, 2 arms on top. This gives you big time clearance and has been proven in Comp buggy. (Ron's at ORGStore). He has a two ended ram to make it steerable at high speeds. His new buggy has this front and rear. The lower wishbone is plated across the whole thing so it works as a big stid plate also.

mark
orgs mfg
 
A front suspension without a trackbar is hard to do with conventional steering. The latest failed attempt I've personally seen used what looked like a traction bar on one side of the axle to control pinion wrap with another forked, traction bar-looking link turned on its side to try and keep the axle centered. Needless to say, that setup didn't work too well with conventional steering. You need alot of lateral confinement (for lack of a better term) to withstand the side-to-side leverage placed on the front end by the draglink. Otherwise, the Jeep will just want to "walk" over top of the axle when you steer. But I'm sure you've already considered that. Are you willing to go full hydro?
 
Beezil. having said that daily driving is not relevent. Might I suggest a full hydro steering, no linkage to the frame might make the design easier.

Rev
 
eh, my heart's not in it at the moment, but try to keep in mind the correct terminology. So far, every time someone has said the term "3-link", they've gone on to describe a triangulated four link. A 3-link only has 3 attachment points on the frame. That's how suspension link systems are defined. All of the proposed systems above have 4 frame attachment points (oddly enough, a track bar does not count as a link for some reason).

Unfortunately, I don't have much else to contribute to this. I really like track bars. I like the way the axle shifts when articulated - it'll push to the high side more than most of the non-track bar systems I've seen and I like how it grabs when it does this. My only complaint about my track bar is how short mine is. If I could get it about 33% longer, I'd be extremely happy. I wish you much luck in getting proper geometry and still clearing the oil pan and exhaust. The triangulated 4-link off that giveaway Avalanche rig may actually be your best bet as far as fitting, but I have yet to see enough info on it to get any sort handling impression of it.
 
Use leaf springs.

Why?

You wont be able to use it as a daily driver or on road.

Beez, the trackbar is not a big bad monster. really, deal with it you wimp. Do a triangulated upper (want to see that work on an XJ (no response from you Matt)) and some form of hydro or hydro assist steering.

You should just got leafs, you know you want to.

Oh ya, check out the POR thread "God of Suspension". Loser :rolleyes:
 
Cresso said:
eh, my heart's not in it at the moment, but try to keep in mind the correct terminology. So far, every time someone has said the term "3-link", they've gone on to describe a triangulated four link. A 3-link only has 3 attachment points on the frame. That's how suspension link systems are defined. All of the proposed systems above have 4 frame attachment points (oddly enough, a track bar does not count as a link for some reason).
Click to expand...

So since my "Y" arms only attach to the frame (Lowers from frame to axle, one upper from lower to axle), this would mean I have a 2 link system............
 
Exactly. Ford named their two-link system "radius arms" and that term seems to be pretty popular. EIther way, that's what you have.
 
Cresso said:
but try to keep in mind the correct terminology. So far, every time someone has said the term "3-link", they've gone on to describe a triangulated four link. A 3-link only has 3 attachment points on the frame. That's how suspension link systems are defined. All of the proposed systems above have 4 frame attachment points (oddly enough, a track bar does not count as a link for some reason).

Click to expand...

Well, Not sure of your terminology but what is on the MJ, mentioned above, is a 3-link per your terminology. But it has a 4th link holding the axle in place called a track bar. Why is a wish bone called a 4 link. The axle is only held in by 3 points. Yes it attaches to the frame in 2 places, so who/what makes it a 4 link? The wish bone is also just one arm even though it has 3 mounting points, total. What would keep the front end stable if there isn't a TB link in your 3 link? Jeep calls the XJ front end a 5 link, by definision. Not sure how a wish bone is a 4 link. Which would never use a TB being a 4th link. Why isn't a TB a link? Could you clearify your thoughts for me so I can undersand your terminology a little better, because I must be missing something in your explination.

mark
orgs mfg
 
It's not my terminology, it's real old school terminology used in suspension design. It's what you'll find in literature about designing race suspensions, from F1 to dirt track. I have no idea why they don't count the track bar as a link, but the general rule is that links that play no part in fore-aft location and ONLY provide lateral location (like a track bar or Watts linkage) are not to be counted when naming the system. I'm not familiar with the MJ system - does it differ from the stock 4-link system on an XJ? As for Jeep calling their system a 5-link, this is merely an example of a company trying to differentiate what they use at the sacrifice of strict correctness. Technically, the front suspension of a TJ/XJ is a 4-link with a track bar. The link system described in JnJ's post is still a 2-link. There are only two mount points on the frame. The third member of the suspension(that upper link) goes from the axle to the lower link. Since it does not go to a distinct point on the frame, it does not count as another link in the naming convention.
 
Your not familar with the my MJ suspension because you didn't look at it you just said it was all being talk about incorrectly.

I'm not sure of Old School suspension design, I'm not formally trained, just 20 yrs of dealing with suspension guys and race truck guys, not familar with F1 never seen one with a straight axle on one, all refer to links as what is attached to the axles, not what is attached to the frame. Maybe just real world instead of old world. I'm not stating I'm a suspension expert, but certian things just arn't quite clear about that terminology.

mark
orgs mfg
 
I was under the impression it was determined by where it mounts to the axle. If the upper link is jointed and has one mount it's a 3 link. 4 link is seperat mounts for upper.

Beezil, you might want to get some books. I would recommend Carroll Smith Tune To Win and Herb Adams Chassis Engineering (I belive is the title)

This should give you all the info you need and weed out the opinion of those that don't know what they are talking about. Not pointing fingers at anyone.
 
Beezil, I see the only practical way to go about this is with triangulated top and lower CAs, similar to what is used on solid axle GM cars, but I would take the NASCAR approach and extend them like a long arm system; I believe they are then called trailing arms. I too have contemplated ditching the track bar because to me it just seems like a patch for a badly engineered system. If you need that extra inch of clearance for the CAs..no one said modifying the oil pan is out of the question.

XJguy
 
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