Roll Centers on G-Body

[7uptruckracer]

I figured this is where I will get the best response. I'm looking to raise my Roll Center and shift it laterally as well. The car does have drop spindles and we have a minimum ride height of 6". I can get Upper Ball Joints with taller studs in a few increments as well. I have also been told different things as to how the lowers should be angled. Should the lower outer ball joint be higher or lower then the inner pivot point if its anything other then level and what happens if its both ways being I have slotted lowers and not sure where to start with ride heights. Please help!

[steveshawjr]

roll centers on a metric G body are below ground ... look in to jacking force and wheel load its the best way to do thes things now.

[stock car driver]

How can it possibly go below ground??

Ive seen stockcar5 say that on here for years. It seems a few believe him?

The only way for it to be below ground is if the line thru the upper pivot points and lower pivot points interesected BELOW ground. Where those lines intersect is the instant center, then you take a line from that point to the centerline off the opposite tire. You do this on both sides and where these lines cross is the roll center.

If your lower a arms are LEVEL or near it theres no way to get your instant center below ground.

Maybe Im missing something??

[stockcar5]

yes my roll center was below ground when we had to run stock a arms, mounts ect. all stock with lower control arms level it was -.3 below ground. my upper a arm pivot points sloped .125 inches down to the spindles so that is what put it below ground level with lowers level. some cars are worse than other due to the factory mounts seem to be all over the place.

[stock car driver]

yes my roll center was below ground when we had to run stock a arms, mounts ect. all stock with lower control arms level it was -.3 below ground. my upper a arm pivot points sloped .125 inches down to the spindles so that is what put it below ground level with lowers level. some cars are worse than other due to the factory mounts seem to be all over the place.

I think you made an error. If your lowers are LEVEL there is no way for the instant center to be below ground. Much less the actual roll center which is the next step of calculating the roll center.

If your uppers sloped that way youll never get the uppers and lower to intersect not sure what you would even do then? I can drop some spindles on the frame Im putting on the jig tuesday and input the all oem numbers into my steve smith front end program, but I dare say last time I did it all oem it wasnt underground.

The oem uppers and the uppers we run now are only 1/4 difference in length.

[Dirtrunner35]

Years ago My metric front roll center was also below the ground. I put these numbers in my program to see where the roll center below ground is true. Lowers and ball joints at 8.25 inches, upper arm frame mount at 21 and ball joint at 20, roll center is 1.85 inches below ground. So it's possible.

[Dirtrunner35]

I think you made an error. If your lowers are LEVEL there is no way for the instant center to be below ground. Much less the actual roll center which is the next step of calculating the roll center.

If your uppers sloped that way youll never get the uppers and lower to intersect not sure what you would even do then? I can drop some spindles on the frame Im putting on the jig tuesday and input the all oem numbers into my steve smith front end program, but I dare say last time I did it all oem it wasnt underground.

The oem uppers and the uppers we run now are only 1/4 difference in length.

Jeff, give me your numbers and I'll put them in my program and see if the programs are close, lol.

[stockcar5]

i use performance trends software. if you make the uppers level with no slope it will put the roll center at .3 inches above ground.

dirtrunner: your numbers are very close to mine. my lower pivot and ball joint pivot were 8.5"

[stock car driver]

Still not sure how you guys are getting below.

draw a line on a paper

draw another under it

those represent the lowers level and the ground

When a line thru your upper a arms intersects with the top line that is your instant center. then you take that point and draw a line from it to the cl of the other tire on ground LEVEL. theres no way to end up below ground.

Unless Im missing something because your point is supposedly outside the wheel base of the car?

Its not science enough to figure roll center to need a computer program. Mine takes all the numbers from the front end from the ground and from a line fwd of all suspension and plots everything at once, bump steer, camber gain, rc etc.

[Dirtrunner35]

A 3-d program, that's what I have.

[steveshawjr]

what dose it matter what everything is a static anyways its just a guessing game anyhow lol ... now with pull down rigs and things like that anyone i know uses wheel loads and jacking force.. Im going to school down in NC as wee speek on this and my teach worked for a few cup teams .. was joey lagonos crew cheif in hootors and so on... he can make a car have its roll center in the center of the infield or 10 rows up in the grand stands its not hard lol ...

[stockcar5]

what dose it matter what everything is a static anyways its just a guessing game anyhow lol ... now with pull down rigs and things like that anyone i know uses wheel loads and jacking force.. Im going to school down in NC as wee speek on this and my teach worked for a few cup teams .. was joey lagonos crew cheif in hootors and so on... he can make a car have its roll center in the center of the infield or 10 rows up in the grand stands its not hard lol ...

do you think youre the only one that knows about jacking forces and wheel loads? i've noticed anytime someone mentions roll center you chime in about jacking forces. fwiw i learned about jacking forces, wheel loads and some areo stuff from a guy that used to build assphalt cars around here..sharp dude. he's now the shop foreman in r&d at roush.

ps: i hope youre not attending nascar school...that place is a big of a ripoff as wyotech!

[steveshawjr]

no its not Nascars School . all i said is guys should look into jacking force and wheel loads instead of what the car is a static load you don't win races with the car static in the pits

[stock car driver]

no its not Nascars School . all i said is guys should look into jacking force and wheel loads instead of what the car is a static load you don't win races with the car static in the pits

Really? I win and run top 4 almost ALL the time no matter where I go now and I set my car up in the garage static....

Where are you winning at?

I ran 12 traveling series special events last year and lost only 2 positions in all those races from where I started on the track. and those two were from fouled plugs from a ignition issue.

[4bangerhotrod]

stockcar im still tryin to figure out how there getting rc below ground. from what i know about rc's it would be impossible with the lowers level. maybe i dont figure it right cause i never use it, since i work with LM's and we pay big money for chassis thats already had all this figured.

[stock car driver]

stockcar im still tryin to figure out how there getting rc below ground. from what i know about rc's it would be impossible with the lowers level. maybe i dont figure it right cause i never use it, since i work with LM's and we pay big money for chassis thats already had all this figured.

I cant figure it out either. Unless their lowers have a lot of angle its impossible...

But apparently they dont want to discuss it. Whatever, maybe its why my cars handle so well Im doing everything different, lol..

[stockcar5]

jeff..if your lower a arms are level and your uppers slope 1/8" down where does you roll center end up?

[stock car driver]

jeff..if your lower a arms are level and your uppers slope 1/8" down where does you roll center end up?

1\8 towards the tire like your saying yours were? Ive said twice not sure if you just go out away from the car with the upper line until it intersects or what??

My program takes all the front end numbers and I dont have oem like I said. Ill have a frame on the jig this week and might measure it up, Im burried with cars to build, garage addition on my house, bathroom remodel upstairs, my jeepster is torn apart in my racing stall so Ive gotta get 4 link rear 3 link front and my new axles struts in it etc. BUSY..

If you want me to lay it out your way and just run it way out till it hit I could lay it out on my shop floor in 5 minutes tomorrow.

I just worked on your old chassis that chad bought and Ill say this, I havent got a lot of faith in your car modification techniques. He couldnt get as much camber on the rf with your a arm mounts to get near what I run on the left front!

The whole construction of that car defies logic, reason and triangulation.

Youve always got some really nice looking alum and bodys though!

[stockcar5]

i dont lay anything out except for the car centerline. then measure all points and input them into the program and it calculates it. same way all roll center software works.

[stock car driver]

i dont lay anything out except for the car centerline. then measure all points and input them into the program and it calculates it. same way all roll center software works.

Yours obviously isnt working. Simple layout proves that for ya. Try it some time its really easy.