How's my numbers?

[Treefrog]

Good afternoon working on the new chassis for the race truck. Haven't played with this since back in the pirate days early versions. Just curious how my numbers look and am I doing something wrong why I'm not getting data. Thank you Keith with Evolve Racing

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[cagcig]

The numbers don't look to bad. But the rear frame lower is extremely high. I don't entirely believe the anti values for the rear. The links are also pretty narrow.

The frame is 23 1/2” on the inside. The frame bracket puts the upper 3” in. I could possibly French it into the frame to get a little more separation. The front lower can probably get an inch lower. The bracket I’m using.

 

[Treefrog]

The frame is 23 1/2” on the inside. The frame bracket puts the upper 3” in. I could possibly French it into the frame to get a little more separation. The front lower can probably get an inch lower. The bracket I’m using.

You should be fine on convergence angle and separation. It was more of a remark than a needs changed. It doesn't seem like narrow links are common. I would double check the rear lower frame Z. Right now you have them at the same height. There also seems to be something wrong with the rear IC location math.

 

[cagcig]

What is the rear ic?

 

[Treefrog]

What is the rear ic?

The side view instant center. I would recommend reading the linked suspension thread linked in post 1 if you have not already.

 

[EVolveRacing]

thanks treefrog fixed it.

 

[cagcig]

Thanks for your help

 

[EVolveRacing]

thanks Treefrog for the fix on the micros. just seeing how the numbers are looking now after I got it all working.

 

[Treefrog]

thanks Treefrog for the fix on the micros. just seeing how the numbers are looking now after I got it all working.

Assuming this is for the electric race car? I think this is my first time saying it, but your antis may be too low. Also your pinion angle change is opposite of what you want. You want it to be negative in positive travel and positive in negative travel.

 

[EVolveRacing]

ok sounds good I'll play withthe numbers more. yep thes is the Ev race truck were preping it to lower it 6in. And start to preep for a new chassis.

 

[Home_brewd]

This is a front 3-link for a rock crawler that will see some highway driving. If I understand correctly (and often I don’t) I want my front anti-lift to be above 50% throughout travel and my roll slope in the negative. What can I do to get my roll slope to the negative? I have moved everything I can think of, within reason, and have not found a sweet spot.

 

[Treefrog]

This is a front 3-link for a rock crawler that will see some highway driving. If I understand correctly (and often I don’t) I want my front anti-lift to be above 50% throughout travel and my roll slope in the negative. What can I do to get my roll slope to the negative? I have moved everything I can think of, within reason, and have not found a sweet spot.

You want anti lift below 50%, otherwise it will ride rough will braking. On a three link the roll slop is between the center of the panhard and the where the lower links cross the centerline. This may require flat lowers or the frame points being lower than the axle points. Moving the panhard up also helps.

Keep an eye on the distance from the lower mounts to the axle tube. It looks like you may have some clearance issues there.

 

[YellowTurtle]

This is with the rear upper frame mount at the top of 3 holes, so lowest AS I have available, and the front upper frame mount at the bottom of 3 holes, so the highest anti-dive. The rear stays were it is, but the front get's adjusted up and down as I try to decide what I like in different situations.

The reason I post these is because I have been fighting a super annoying trait since I built it. It has a strong Roll Oversteer feeling. On smooth roads or perpendicular bumps, it feels find. On roads that pitch it side to side, as soon as it leans one direction it acts like it wants to dart the opposite way. Sometimes it even wobbles a couple of times until it settles. Feels like the right front tire wants to dart to the left and the left front wants to dart to the right and they are always fighting each other. Alignment has been checked and adjusted (caster and toe to try to find the best setting, it can help but never eliminate the feeling).

Ideas on the numbers? Thanks

These numbers are from the V4.0, which is the newest my computer wants to run, so hopefully they are accurate.

 

[Rockchump]

I started this build in2013 when it seemed everyone was subscribed to the 100% anti squat church and I wanted to build a more dual purpose rig. That rig ended up being built to Ultra4 4500 class rules of the day. But here are my numbers.

 

[Treefrog]

This is with the rear upper frame mount at the top of 3 holes, so lowest AS I have available, and the front upper frame mount at the bottom of 3 holes, so the highest anti-dive. The rear stays were it is, but the front get's adjusted up and down as I try to decide what I like in different situations.

The reason I post these is because I have been fighting a super annoying trait since I built it. It has a strong Roll Oversteer feeling. On smooth roads or perpendicular bumps, it feels find. On roads that pitch it side to side, as soon as it leans one direction it acts like it wants to dart the opposite way. Sometimes it even wobbles a couple of times until it settles. Feels like the right front tire wants to dart to the left and the left front wants to dart to the right and they are always fighting each other. Alignment has been checked and adjusted (caster and toe to try to find the best setting, it can help but never eliminate the feeling).

Ideas on the numbers? Thanks

These numbers are from the V4.0, which is the newest my computer wants to run, so hopefully they are accurate.

What is the relation between the panhard and the drag link? Is the oversteer more prevalent when it leans one way over the over?

Based on the link layout screen grabs in the 4 link calc thread, I would guess that the roll issue comes from a mix of the angle of the panhard and very slightly from the downward and converging angles of the lower links.

 

[Treefrog]

I started this build in2013 when it seemed everyone was subscribed to the 100% anti squat church and I wanted to build a more dual purpose rig. That rig ended up being built to Ultra4 4500 class rules of the day. But here are my numbers.

100% anti in the older version of the calculator is on the upper end of what is recommended for more modern general purpose rigs and a bit higher than desert biased U4 rigs normally run.

 

[YellowTurtle]

What is the relation between the panhard and the drag link? Is the oversteer more prevalent when it leans one way over the over?

Based on the link layout screen grabs in the 4 link calc thread, I would guess that the roll issue comes from a mix of the angle of the panhard and very slightly from the downward and converging angles of the lower links.

Thanks for the reply. The panhard and draglink are in the stock TJ location, so stock geometry. No obvious bumpsteer. Before I built this suspension, I was running the same trackbar and the same steering for a few years (same springs and lift height as well), with no issues with steering/sway/body roll. Since then I've upgraded the steering (same geometry though), trackbar joints, balljoints. Originally after the suspension I was running the same wheels and tires, and have had 2 other sets of wheels and tires since then without any change. It's been a few years and I've changed and upgraded a number of things, but initially I was basically running the same setup I had been for years before that, just with the new arms. So, I've kind of ruled out a lot of variables. Acts the same in both directions. Much easier to handle with stiffer sway bar. Seems worse between about 20-50mph, at freeway speed it actually isn't too bad. I've adjusted caster between 4-9deg, seems best around 7-ish. Have adjusted toe from very toed in to very toed out, behaves best with 1/16" toed out. Any toe in at all feels like it drives with 6" of toe in.

Despite the F&R individually in understeer at ride height, the body is overall a little oversteer (just under 1deg oversteer). And the front goes into oversteer with a few inches of compression. I just can't figure out if that's what I'm feeling, or of there's something else going on.

I would love to raise the axle side of the trackbar way up (and match with the draglink of course), but it's on a TJ and the passenger spring is right in the way. Doesn't mean it's impossible but challenging. I'm also considering dropping the axle side of the lower arms down a little and trying to straighten the lowers out some. Not a lot of wiggle room there, but I could squeeze some inches.

When I first built it, I was just running a front antirock (no rear bar), softer shock valving, and I had to stop my friend from driving it cause it behaved so bad, constantly feeling like the front end was trying to tuck under and roll us, swaying back and forth, etc.

I've got it aligned where it is definitely drivable, but still doesn't feel great and it's just a much busier ride than it should be with little side to side jerks on bumps, it's driving me nuts and makes me want to not drive it as much. I do crawling, but I also daily drive it pretty often, and spend a lot of time bombing down desert roads as well; so high speed handling is definitely important.

Really appreciate any help and thoughts.

 

[Treefrog]

Thanks for the reply. The panhard and draglink are in the stock TJ location, so stock geometry. No obvious bumpsteer. Before I built this suspension, I was running the same trackbar and the same steering for a few years (same springs and lift height as well), with no issues with steering/sway/body roll. Since then I've upgraded the steering (same geometry though), trackbar joints, balljoints. Originally after the suspension I was running the same wheels and tires, and have had 2 other sets of wheels and tires since then without any change. It's been a few years and I've changed and upgraded a number of things, but initially I was basically running the same setup I had been for years before that, just with the new arms. So, I've kind of ruled out a lot of variables. Acts the same in both directions. Much easier to handle with stiffer sway bar. Seems worse between about 20-50mph, at freeway speed it actually isn't too bad. I've adjusted caster between 4-9deg, seems best around 7-ish. Have adjusted toe from very toed in to very toed out, behaves best with 1/16" toed out. Any toe in at all feels like it drives with 6" of toe in.

Despite the F&R individually in understeer at ride height, the body is overall a little oversteer (just under 1deg oversteer). And the front goes into oversteer with a few inches of compression. I just can't figure out if that's what I'm feeling, or of there's something else going on.

I would love to raise the axle side of the trackbar way up (and match with the draglink of course), but it's on a TJ and the passenger spring is right in the way. Doesn't mean it's impossible but challenging. I'm also considering dropping the axle side of the lower arms down a little and trying to straighten the lowers out some. Not a lot of wiggle room there, but I could squeeze some inches.

When I first built it, I was just running a front antirock (no rear bar), softer shock valving, and I had to stop my friend from driving it cause it behaved so bad, constantly feeling like the front end was trying to tuck under and roll us, swaying back and forth, etc.

I've got it aligned where it is definitely drivable, but still doesn't feel great and it's just a much busier ride than it should be with little side to side jerks on bumps, it's driving me nuts and makes me want to not drive it as much. I do crawling, but I also daily drive it pretty often, and spend a lot of time bombing down desert roads as well; so high speed handling is definitely important.

Really appreciate any help and thoughts.

I know TJs can have that tendency. Are you running the stock Y style steering or crossover? It may be worth playing with tire pressures some. The TJ I used to have and the current LJ are sensitive to it. Hopefully someone else will chime in.

 

[YellowTurtle]

I know TJs can have that tendency. Are you running the stock Y style steering or crossover? It may be worth playing with tire pressures some. The TJ I used to have and the current LJ are sensitive to it. Hopefully someone else will chime in.

I just have to say, you are awesome for trying to help people out so much, Thanks a ton!

Originally I was running the stock steering with a ZJ tie rod for beef. I ran that for years before I did the links, and for a while after. With the travel I have, I felt like I started to notice some of the inherent bump-steer that can occur when the haltenberger Y style is lifted high enough or cycles far enough (I know I'm gonna take crap for saying that haha). After a few years of the new links, I went to a cross over system that has the draglink in the same location as stock, with a separate tierod that spans knuckle to knuckle. I wanted to keep toe consistent throughout travel, and hoped it might help the darty sensation also. It did improve the steering by eliminating some issue, but the dartiness remained.

I've tried tires from 20psi on the street to the max of 50psi just to see if it made any difference. Hard to say if it did or I imagined it, so not much change. Seems to me likely that it just tramlines on grooves a little more at some pressure vs others.

Do you feel like the numbers I posted would account for what I'm feeling? When I built it I felt like the numbers were decent, and it drives way worse than I would think from the numbers.

Would you say F/R roll axis affects the overall tracking more than the body roll axis, or vice-versa?

Any thoughts on how to get the axle end of the panhard up higher on a TJ with stock style front springs? I've been looking at the steering damper mount location and wondering if that could all be cleared out and the axle mount placed around there. I knew a guy who did the WJ knuckle/brake/steering swap and to match the panhard and draglink he clearanced under the passenger spring as much as possible and had the panhard curve under the spring and then back up and attach near the top of the inner C. Seemed to work well for him and no durability issues after years of running hard trails.

Any other thoughts on how to improve my geo to get it to track neutrally?

Thanks again for the help.

 

[Treefrog]

I just have to say, you are awesome for trying to help people out so much, Thanks a ton!

Originally I was running the stock steering with a ZJ tie rod for beef. I ran that for years before I did the links, and for a while after. With the travel I have, I felt like I started to notice some of the inherent bump-steer that can occur when the haltenberger Y style is lifted high enough or cycles far enough (I know I'm gonna take crap for saying that haha). After a few years of the new links, I went to a cross over system that has the draglink in the same location as stock, with a separate tierod that spans knuckle to knuckle. I wanted to keep toe consistent throughout travel, and hoped it might help the darty sensation also. It did improve the steering by eliminating some issue, but the dartiness remained.

I've tried tires from 20psi on the street to the max of 50psi just to see if it made any difference. Hard to say if it did or I imagined it, so not much change. Seems to me likely that it just tramlines on grooves a little more at some pressure vs others.

Do you feel like the numbers I posted would account for what I'm feeling? When I built it I felt like the numbers were decent, and it drives way worse than I would think from the numbers.

Would you say F/R roll axis affects the overall tracking more than the body roll axis, or vice-versa?

Any thoughts on how to get the axle end of the panhard up higher on a TJ with stock style front springs? I've been looking at the steering damper mount location and wondering if that could all be cleared out and the axle mount placed around there. I knew a guy who did the WJ knuckle/brake/steering swap and to match the panhard and draglink he clearanced under the passenger spring as much as possible and had the panhard curve under the spring and then back up and attach near the top of the inner C. Seemed to work well for him and no durability issues after years of running hard trails.

Any other thoughts on how to improve my geo to get it to track neutrally?

Thanks again for the help.

I have read that the roll axis are not the only factor when it comes to oversteer and understeer. Roll centers and roll axis are predicters, not determining factors.

The geometry numbers do not seem to point to an issue.

It almost sounds like it may be a load transfer issue. I'm wondering if the CG height is higher than believed. That could increase roll oversteer.

Another option is to stretch the front an inch or two using spring mounts behind the axle. Steering geometry can get a bit less optional, but in my experience, bump steer is much better than wandering.

Have you checked for loose rods ends or steering shaft/box yet? Wallowed out holes? Other common TJ things like a drop pitman arm?

 

[YellowTurtle]

I have read that the roll axis are not the only factor when it comes to oversteer and understeer. Roll centers and roll axis are predicters, not determining factors.

The geometry numbers do not seem to point to an issue.

It almost sounds like it may be a load transfer issue. I'm wondering if the CG height is higher than believed. That could increase roll oversteer.

Another option is to stretch the front an inch or two using spring mounts behind the axle. Steering geometry can get a bit less optional, but in my experience, bump steer is much better than wandering.

Have you checked for loose rods ends or steering shaft/box yet? Wallowed out holes? Other common TJ things like a drop pitman arm?

I'll definitely keep searching and reading as well.

An interesting note: I have repeated an experiment to blindly adjust toe (which definitely affects the behavior) and consistently end up with Toe-OUT. I just repeated and ended up at ¼" out. With more tow IN, it darts on bumps, more toe OUT and the toe out issues get annoying.

The thing that always throws me is I only changed the link setup and it definitely didn't drive like this with short arms with the same steering, panhard, springs, lift height, etc.

I remeasured my panhard with better accuracy and it wasnt as bad as the previous numbers showed.

All rod ends have been replaced, link ends changed to different type with less fore-aft deflection, and new ball joints. None of that made any difference. Steering box still tight, very little play in wheel, pitman arm is stock. Definitely a head scratcher for me.

I'm about to do a rear axle swap so I will play with the link positions F&R a little to see if it helps.

Thanks again. Let me know if anything else comes to mind.

 

[Treefrog]

The thing that always throws me is I only changed the link setup and it definitely didn't drive like this with short arms with the same steering, panhard, springs, lift height, etc.

Did you change both front and rear?

 

[YellowTurtle]

Yep, both at same time. I didn't drive it before switching ends because... delayed gratification.

All arms 25-26" (so 1 spare works), 3 link front, double triangulated rear, tried to keep lower arms flat and tucked up for clearance+good numbers. The only unusual aspect is the narrow ends of rear triangles have some horizontal separation because of packaging, but have more than enough triangulation between upper+lower. Only other change was rear spring mount moved.

TJ with about 3-3.5" lift over stock. Outboarded shock in rear end extended shock tower in front, but already had that with short arms.

 

[NDCjeepsmith]

OK, Neb to to the calc!

I'm digging playing around with it but the setup I'm currently working on seems to be not jiving well.

On a CJ7 with 258 straight six and factory frame so things are kinda not entirely moveable for optimal geometrics.

I'm thinking something is off that I'm over looking. Why is rear pinion change so dramatic with equal length uppers and lowers but front isn't with shorter uppers?

What about CG placement? is the only input height? no for/aft placement?

 

[NDCjeepsmith]

Found a goof. Had the rear frame side links at a shared point.

Just not too happy with 45% antisquat. and rear pinion change being almost double front when I thought equal length uppers kept it neutral?

Thoughts?

 

[Treefrog]

OK, Neb to to the calc!

I'm digging playing around with it but the setup I'm currently working on seems to be not jiving well.

On a CJ7 with 258 straight six and factory frame so things are kinda not entirely moveable for optimal geometrics.

I'm thinking something is off that I'm over looking. Why is rear pinion change so dramatic with equal length uppers and lowers but front isn't with shorter uppers?

It's because the rear links share a side view frame point. The pinion rotates about that point. Length isn't the only factor affecting pinion angle change.
Edit: Beat me to it. End edit

What about CG placement? is the only input height? no for/aft placement?

For/aft cg is weight distribution. It does not affect any of the link calc stuff.