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.

[steveshawjr]

heres some stats for yeh

Points Championship 1994, 1998, 2001, 2004
Mid Season Championship race winner 1994, 1995 Ridgetown 1996 1998 1999 2002 2007
Season champion race 1996, 1998, 2001, 2004, 2007, 2011
Most Checkerd Flags 1994 1995 1996 1997 1998 2001 2002 2004 2007 2010 2011
Fan Favourite 1998 2001 2002 2004 2007
total 311 wins... 100 a-main wins
updated Sept.11th 2011
Did not race in 2003, 2008, 2009

Steve Shaw Sr.

[stock car driver]

heres some stats for yeh

Points Championship 1994, 1998, 2001, 2004
Mid Season Championship race winner 1994, 1995 Ridgetown 1996 1998 1999 2002 2007
Season champion race 1996, 1998, 2001, 2004, 2007, 2011
Most Checkerd Flags 1994 1995 1996 1997 1998 2001 2002 2004 2007 2010 2011
Fan Favourite 1998 2001 2002 2004 2007
total 311 wins... 100 a-main wins
updated Sept.11th 2011
Did not race in 2003, 2008, 2009

Steve Shaw Sr.

Whats a fan favourite? Is that like coopitition that Larry McReynolds says?

So you set your car up on a shaker or pull down machine? None of those stats make sense Jimmy Johnson was the champion most of those years.

[steveshawjr]

you must have some timers lol you asked where we where winning at i put up our stats

Fan Favorite Driver award lol


32 years of this crap without any fancy equipment here dont even own a set of scales .... Never once did centers or anything like that ...

Steve Shaw Sr

[4bangerhotrod]

so have you raced at the same track every week for 20 yrs. thats what your stats are showing

[stock car driver]

you must have some timers lol you asked where we where winning at i put up our stats



I asked WHERE you were winning?

You didnt answer that. lol..

Still not sure now why your posting in this thread at all, now you claim to have never used scales or measured anything. But earlier in this thread you were saying we needed pull down machines, lol.

You must be buddys with Ego, he never answers anything directly and most of his posts are useless.

[steveshawjr]

now if you noticed he put steve shaw sr because my dad is the on that put them posts on .

now i never did claim i used a pull down rig for that matter you better go reread what is posted . i simply said that is what the big thing is now..

[stock car driver]

now if you noticed he put steve shaw sr because my dad is the on that put them posts on .

now i never did claim i used a pull down rig for that matter you better go reread what is posted . i simply said that is what the big thing is now..

Yeah on tv Nascar shows, lol...

[hogracer3d]

I wanna see a pic of JJ's wife, if there is one (which I doubt), but I'd accept a cancelled child support check.....

[stock car driver]

I wanna see a pic of JJ's wife, if there is one (which I doubt), but I'd accept a cancelled child support check.....

Man your a loser.

Join my fan page on face book and like the 1150 others on there youll know what Im up to most of the time, including some of the family vacations we take each year.

[sportmod224]

Hey Jeff, I have a couple questions I would like to ask you if you have time about the front spring set. Is there any chance we can talk on the phone instead of messaging back and forth on here? Thanks

[stock car driver]

Still nobody explaining how they get below ground when your last lines go to the tire centerline on the opposite side at ground level.

I guess Im the only one who manually lays out things to confirm my $300 dollar program is correct.

[petermanbuilt]

Alright, I guess I will set this straight for Jeff, since no one else will.

When plotting roll centers, project a line through the control arm pivot and the ball joint pivot for each control arm.

The intersection of the lines through the left upper and left lower defines the instant center for the left side suspension.

A line is then projected from this instant center to the center of the left tire contact patch. I will call this line the "left side swing arm" for future reference.

Repeat the 2 above steps for the right side.

Finally, the Moment center is determined by the intersection of the left and right side "swing arms"

Where you are WRONG Jeff is in saying that "swing arm" line goes to the opposite side. The left instant center will always project through the left side contact patch, and the right instant center always projects through the right side contact patch.

Anytime that the instant center lies outside of the tires, the moment center will be "underground" for lack of a better term.

See this link as I have drawn it out. I exaggerated the angles to make it fit on a sheet of paper.
If that is not enough I will keep proving you wrong with multiple vehicle dynamics textbooks.

http://s823.photobucket.com/albums/zz158/petermanbuilt/Moment%20Center/?action=view&current=momentcenterbelowground.jpg

Nathan Peterman
Penn State Mechanical Engineering Alumni


Still nobody explaining how they get below ground when your last lines go to the tire centerline on the opposite side at ground level.

I guess Im the only one who manually lays out things to confirm my $300 dollar program is correct.

[stock car driver]

Your drawing is based on the upper a arm angle forcing the instant center outside the tire centerlines, is that the deciding factor that changes your next point from the opposite tire to the cl of the tire on that same side?

Maybe thats correct I dont know thats why Ive been asking.

[stock car driver]

Where you are WRONG Jeff is in saying that "swing arm" line goes to the opposite side. The left instant center will always project through the left side contact patch, and the right instant center always projects through the right side contact patch.


If that is not enough I will keep proving you wrong with multiple vehicle dynamics textbooks.

http://s823.photobucket.com/albums/zz158/petermanbuilt/Moment%20Center/?action=view&current=momentcenterbelowground.jpg

Nathan Peterman
Penn State Mechanical Engineering Alumni

Go ahead and keep proving me wrong if thats what makes you feel good about yourself. I asked this question how many times?? obviously I dont know the answer or I wouldnt be asking, I dont see how ASKING for explanation can be proven wrong but whatever floats your boat...

I read your post again and I see you say ALWAYS, I look forward to many more posts from you backing up your ALWAYS since I can post many that say it isnt ALWAYS as you have said. I believe your ALWAYS only pertains to when the instant center is OUTSIDE the wheel base.

[stock car driver]

http://i642.photobucket.com/albums/uu150/jnjfab/101_0113.jpg

So this book is wrong?

[petermanbuilt]

Your drawing is based on the upper a arm angle forcing the instant center outside the tire centerlines, is that the deciding factor that changes your next point from the opposite tire to the cl of the tire on that same side?

Maybe thats correct I dont know thats why Ive been asking.

Yes the instant should should project to the contact patch of the tire on the same side!

A metric is suspension is considered an independent type suspension, simply meaning that the actions of one wheel do not have a direct effect on the other. Because of this, the IC of the left does not correlate to right side contact patch.

In contrast, when one side of a solid axle suspension hits a bump, the opposite side is forced the opposite direction because the two wheels are connected by essentially a beam.

Check out Chapter 17 of "Race Car Vehicle Dynamics" by the Millikens. It lays it all out. This book is widely considered a "bible" for vehicle dynamics as the authors spent their entire life researching the subject before writing.

I don't want to get into a pissing match, just trying to keep you from telling everyone that they are wrong when in fact, your the one that incorrect.

[stockcar5]

peters pic of right for below ground roll centers and jeff yours is correct for the ic being inside the tire contact patch.

saying the ic is always within the wheelbase is as wrong as saying there is no way the roll center can be below ground with lowers level.

[petermanbuilt]

http://i642.photobucket.com/albums/uu150/jnjfab/101_0113.jpg

So this book is wrong?


Nope, that drawing is correct. The instant center on the left is drawn to the left side contact patch and visa versa

I added some color to the picture you posted to show that they too are using what i said above

http://s823.photobucket.com/albums/zz158/petermanbuilt/Moment%20Center/

[stock car driver]

Nope, that drawing is correct. The instant center on the left is drawn to the left side contact patch and visa versa

I added some color to the picture you posted to show that they too are using what i said above

http://s823.photobucket.com/albums/zz158/petermanbuilt/Moment%20Center/

Step 10 in your color pic is the instant center going to the opposite tires centerline.. Thats what Ive said all along. I see what your saying that the instant center of the left suspension which is actaully located on the right comes back to the left tires centerline. That is the tire opposite the instant center point isnt it? lol.. just like Ive said all along.

What youve explained which nobody else explained was what to do when the instant center is outside the tire, your drawing makes sense. thanks.

It does appear you want some sort of pissing match.



Stockcar5, you might as well shut up, Ive asked you to explain how you get below ground repeatedly you had nothing to offer.. This guy explained it. Scroll back I asked point blank before how the roll center was plotted when the instant center is outside the tire.. YOU didnt know your just put the number in your program, lol..

[stockcar5]

if i explained it to you you'd piss and moan anyway like always. i drew it out back in 2003 then bought a program. you'd be retarded to try and draw one out now if you own software.
i figured we were long past explanation when you clowns started comparing stats and asking each other for pics of your wives...lol

[stock car driver]

if i explained it to you you'd piss and moan anyway like always. i drew it out back in 2003 then bought a program. you'd be retarded to try and draw one out now if you own software.
i figured we were long past explanation when you clowns started comparing stats and asking each other for pics of your wives...lol

What have I pissed and moaned about ever? I cant even think of another topic on here where I ASKED a question or for help off the top of my head.


retarded would be the geometry on that chassis of yours I just worked on two weeks ago, lol.

[stockcar5]

yea i hope you get it fixed so chad can win races in it like i did. should be bad fast. he seems like a decent guy so treat him good. he said your jackass sometimes but you know it and your trying to improve yourself. seems like hes willing to give you chances most people wont.

where is he gonna race it?

[petermanbuilt]

[QUOTE=stock car driver;1502905]Step 10 in your color pic is the instant center going to the opposite tires centerline.. Thats what Ive said all along. I see what your saying that the instant center of the left suspension which is actaully located on the right comes back to the left tires centerline. That is the tire opposite the instant center point isnt it? lol.. just like Ive said all along.

Alright, It was just a confusion of wording.

When you say that the instant center goes to the opposite tires centerline I was assuming that you meant the left suspension IC went the right side tire contact patch. If you did that the moment center would be above the ground, which you stated numerous times was the case....But its not

[stock car driver]

seems like hes willing to give you chances most people wont.


Yeah thats why Im turning people away all the time.

I could build a dozen motors and chassis a year if I wanted too, but being retired theres no sense in doing more than is fun!

2011, 37 3rd members, 11 floaters, 3 nine inches. 3 motors. I know fwd cars dont count in your book so no numbers on them.
2010, 29 3rd members, re jigged 18 floaters, sold 9 floaters, 2 nine inches.

Ive removed my floaters from my website and also stopped re jigging any floaters about the middle off 2011.

[stock car driver]

[QUOTE=stock car driver;1502905]Step 10 in your color pic is the instant center going to the opposite tires centerline.. Thats what Ive said all along. I see what your saying that the instant center of the left suspension which is actaully located on the right comes back to the left tires centerline. That is the tire opposite the instant center point isnt it? lol.. just like Ive said all along.

Alright, It was just a confusion of wording.

When you say that the instant center goes to the opposite tires centerline I was assuming that you meant the left suspension IC went the right side tire contact patch. If you did that the moment center would be above the ground, which you stated numerous times was the case....But its not

Like I said thanks.

I was wondering how it was laid out the old fashioned way when the uppers angle forces the ic outside the tire as in your drawing.. my computer program doesnt explain things and nobody else seemed to know either on here. Clearly many in this thread would JUMP at the chance to TEACH me something! I had no idea how to lay that out nothing in any books I have explains when the ic is outside like that.

[racingford]

im with sockcardriver, if ya believe that roll centers can exsist below the ground than you are truely MISSING somthing

[Extreme Race Cars]

Your roll center could be below ground but I doubt it would handle much better than a Mack truck...

[dirt2]

im with sockcardriver, if ya believe that roll centers can exsist below the ground than you are truely MISSING somthing

I understood the question to be about a stock chassis. So in stock form the lower balljoint
will be a little heigher than the bolt center where the arm mounts to the chassis An the upper
balljoint will be a good bit lower than the inner cgassis mount.With these angles the lines drawn
through them will intersect outside of the chassis & then will go back through the tire center line
to the center of the chassis. Where the lines cross the center line of the chassis will be below the ground.This will give you a roll center below the ground. Now lower the chassis so the lower arm will be level from the balljoint pivet point to the center of the bolt then do what you need to level out the top arm from balljoint center to the inner mount center. With both arms level the lines through the pivet points will not intersect & this is refered to as ground level roll center.
Lower the chassis so you have like two deg. from the balljoint center to the bolt center at the chassis
lower the upper arm inner mount so you will have lets say twelve down angle to the chassis.With
this the lines will pass through the pivet points toward the center of the chassis & out to the other side intersecting there & back through the tire center past the center line of the chassis. Where the lines cross at the chassis center will be the roll center.Just measure from the floor up to the cross point to see how high the roll center is abgve the ground. In stock form with a very low roll center & a high center of gravity the car wants to roll a lot & will need stiff springs to control this.
With a heigher roll center & lower center of gravity the car will use softer springs.

dirt2
Ground Effects Suspension Control

[dirt2]

Correcting the stock form on chassis.
In stock form the lower balljoint center pivet will be a little lower than the inner
bolt where the arm mounts to the chassis. Just jumped the keys a bit, sorry about that.
dirt2

[petermanbuilt]

Well Said Dirt2, I agree 100%

[chevy370lsx]

Dumb question. Were is the ideal place for your roll center to be. What affects does it have moving it up and down, side to side?

[stock car driver]

Im gonna try and get mine 12 below ground, I want all the body roll I can get!

[Extreme Race Cars]

Im gonna try and get mine 12 below ground, I want all the body roll I can get!

LMAO... I hear 12" below ground will cause ya to roll over... I'd start with 6"

[really?]

i will chime in just to say that sounds like stkcar5 is on track with whats going on now days with frnt ends i will also agree that the jacking affect is very important as is dynamic measurements but you must have static in the garage before you get dynamic measurments and without a good 3dimensional software stockcardriver jeff your lines on the floor and paper we quit that 20 years ago ,rollcenters below ground level is very easy to obtain. and also 4 whls are faster then 3 thats also something we figured out 20 yrs ago and thats when you need to take alook at the rear rollcntr not the frnt. sounds like your on the right track stockcar5