Wondering if some of you would give me your opinions on these numbers.
What's good.
What's bad.
What to change.

Vehicle is a 03 TJ.

Thanks in advance.


Wheelbase 94.0 in
Tire Diameter 36.00 in
Tire Rolling Radius 17.00 in
Vehicle CG Height 36.00 in
Vehicle Mass 4,000 lb
Front Unsprung Mass 800 lb
Rear Unsprung Mass 700 lb


Upper Links x y z
Frame End 26.00 15.00 26.00 in
Axle End 0.00 0.00 25.50 in
Lower Links x y z
Frame End 26.00 5.00 21.50 in
Axle End 3.50 23.50 19.00 in


Anti-Squat 84.380 %
Roll Axis Slope -0.1036 in/in (Roll Understeer)
Roll Center Height 25.500 in
Roll Axis Angle -5.916 degrees (Roll Understeer)
Instant Center X-Axis 74.977 in
Instant Center Z-Axis 26.942 in

J/W but are you shooting for the rear to squat under throttle?

Shooting for very little wheel hop on climbs. So yes a little squat I think. Still learning all this stuff. Spent over 80hrs on the search button. It's hard though because I don't know who is talking out of their a$$ and who I can beleive.

Instant Center X-Axis- was wondering if this was too low. Thought I read it should be 1.5x your wheelbase.


Roll Axis Angle- and I had a lot of trouble finding any info on this and what it meens exactly.

Thanks a ton for the help. Wanna keep working on it. But wanna do it right.
By the way I live in Alberta Canada, heart of the Rocky Mtns. So it's a real all around rig. We do lots of climbs, and a lot of mud. Want it to perform well all around. Not just as a rock crawler. Not sure how much differenc any of that makes.

My 4-link setup has %167.4 and i love it

not near enough AS IMO. I've run b/t 100% and 220% and now have settled on 163% and am the most happy so far. anything under 100% is silly, especially if you do many climbs. think of it this way, AS over 100% pushes the tires into the ground creating traction, this is a great way to counteract gravity increases by steepness of a hill b/c while the suspension geometry is trying to push the body of the vehicle away from the axle the weight shift to the rear will prevent that which will force more grabbing power to your tires. an elementary explanation but you should get the idea...

Some posts have scared me into thinking over 100 makes you hop. I'm sick of breaking sh!t this way. Is this not accurate?

no, not accurate at all! it sounds as if those were the people "talking out of their a$$". you can take a look at how I 4-linked my TJ for the second time when I dropped in the D60's HERE (http://www.pirate4x4.com/forum/showthread.php?t=274444&page=1&pp=25), it'll give you an idea of how the links laid out & such...

OK. So would this be better in your opinion?

Upper Links x y z
Frame End 36.00 15.00 25.00 in
Axle End 0.00 0.00 27.00 in
Lower Links x y z
Frame End 26.00 5.00 21.50 in
Axle End 3.50 26.50 18.50 in

Anti-Squat 123 %
Roll Center Height 27 in
Roll Axis Angle -9 degrees (Roll Understeer)
Instant Center X-Axis 47 in
Instant Center Z-Axis 24 in

What are the Roll axis angle and the Instand center stuff all about? They are really hard to find any posts on in the searches. I still don't understand what to look for with them. :confused:

Did more searching, and it still seems like the beleif is that over 150 you should be hopping really bad. Just so sick if destroying stuff with wheel hop. Took 3 days to get off a trail last October because one thing went after another after another.

Want the Jeep to not hop(hopefully staying more in one piece)and be really stable on sidehills and other off camber stuff.

Am I on the right track with either example above?

What sort of stuff are you breaking? If you're not running a tough enough drive train, trying to baby it via suspension design is a bit of a backwards approach, IMO.
(If you're going to the trouble of 4-linking the thing, it's worth the trouble.. and cost.. of components that are up to serious wheeling.)

I have about 150% AS and love it, I have never felt it hop. But, you can't really compare AS numbers because they depend on the weight distribution of your jeep. Why not make your mounts adjustable and try what is best for you.

Im by no means an expert, but your Instant Center x-axis should be in front of the vehicle, also try to make it at least as tall as your COG.

I could be wrong, search about it...

What sort of stuff are you breaking? If you're not running a tough enough drive train, trying to baby it via suspension design is a bit of a backwards approach, IMO.
(If you're going to the trouble of 4-linking the thing, it's worth the trouble.. and cost.. of components that are up to serious wheeling.)


I agree. I'm putting in a 9" right now, that's what led me to redo the suspesion. Should be less breakage now that the turd is out.

Why not make your mounts adjustable and try what is best for you.

That's the plan. Just wanting to know I'm in the ball park one way or another. Some are saying as low as 50% some are thinking over 150%. That's a big swing for adjustability isn't it?

your Instant Center x-axis should be in front of the vehicle, also try to make it at least as tall as your COG.

This is what my understanding was also. Can anyone confirm or dismiss this?

The guys with high AS %, how accurate are your weights and COG locations?

More important than anything I think is to shoot for a range rather than a specific AS %. Change your CoG from 30-36" for example to see where it falls. I have also used higher than 100% but wonder how accurate it was given my estimations of cog. For a street driven rig, your numbers look great. Anything you can do to get the roll axis flater would help but it looks much better than most suspensions out there. 85% is still a good amount of anti-squat and will go along way towards traction, I think you'd be very happy with it.

The axle articulates perpendicular to the roll axis, this is what determines if you have "steer from the links". With a flat axis the axle will droop straight down, and with with an angled axis the tire will move forward or back as it droops.

Your instant center location is really driven by your anti-squat. X is purely front to back location. You can't really control the IC independent of anti-squat so it sorta is what it is. I'd like to hear other opinions on general rules of thumbs.

Try making the frame and axle mounts on the uppers adjustable. I just made my axle end uppers adjustable and I can get either about 60,100 or 130ish depending on the accuracy of the COG measurement. I am considering adding an additional set to the frame side upper mounts to be able to split these numbers. Then you don't have to get it right, you just adjust it. One other thing to consider is the spring rate and how it adds up. As your suspension cycles, the antisquat values will change. This is in relation to the links only and does not consider how the springs rate changes. I was shooting to try to get the AS to closely match the change in spring rate of my coils to give a neutral feel, or a similar resonse at any given articulation. Don't know how close I got, but as my axle droops, the AS goes up and as it stuffs, it goes down. This is inverse, but probably not proprtional to the coil spring rate. Still a few months out of completion, or I'd give you more input.

Might also want to look into the roll over/understeer. Although it might not matter on the trail, it could be important on the road. The rear end may want to push past the front, or not track correctly if this number is wrong. My research says close to zero, but just a bit negative for good street manners, but I have not tried multiple configurations to test it out.

I'm sure you saw these in your research, but if not, here are a couple links to some good reading:

God of Suspension thread (http://www.pirate4x4.com/forum/showthread.php?s=&threadid=7503&highlight=antisquat)
Antisquat Hurts my Brain thread (http://www.pirate4x4.com/forum/showthread.php?s=&threadid=212765&highlight=antisquat)

This is what I would do...not exactly the 'right' answer (like there even is one). This is just my opinion. It might not be popular (or even work well :flipoff2: ) but it is how I would do it.

AS from 50-100% and make it adjustable. The only reason I say 50% as the lower limit is that the lower links will be a rock magnet any lower. I don't think lower would hurt performance much otherwise.

Make the IC 'X' somewhere between half of the wheelbase and 1.5* the wheelbase. The length of the upper links will change how the IC changes with suspension travel.

Put the RC height between axle centerline and tire diameter.
Closer to centerline = good at high speed
Closer to tire diameter = good at low speed and sidehills

If you drive it on the street I would shoot for 0 or roll understeer for the roll axis. At any rate it should be less then 5deg pos. or neg.

Don't forget that you can't just change one thing when making adjustments. You might like the roll center/axis with the AS at your 100% setting but it might climb better at your 50% AS setting for example. Knowing what changing each of the variables feals like (AKA a calibrated ass) I think is a God given gift and will be very helpfull in making it 'right' the 2nd time :grinpimp: