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Author Topic:   How to find roll center?
racecrew2
Dirt Newbie

Total posts: 2
posted August 31, 2005 11:09 AM  
How do you find the roll center? For the front and rear.

wfoondirt
Dirt Forum Champ
Total posts: 505
posted August 31, 2005 01:43 PM  
You have to measure all the points of the the front suspension and either use graphpaper or a computer program to find the roll center.

To do it on graph paper you extend a line through the upper and lower control arms individually and find the point they converge (Instant center). You then make a line from the instant center to the center of the contact patch of the tire. where those 2 lines intersect is the roll center.

Heres a picture to help.


Rear roll center is less of an exact science. The most simplistic way is to assume the center point between the panhard bar mounts as being the roll center. Search on here or 4m for jbar if you want more detailed ways to find it, its been discussed quite in depth.

[This message has been edited by wfoondirt (edited August 31, 2005).]

donslink1
Dirt Freak

Total posts: 318
posted August 31, 2005 05:57 PM  
actualy, the rear roll center is not even on the bar when you run a shorty and it may be at the end of a j-bar depends on the angle.
There are so many things that come in to play with the rear roll center.
I use to think it was in the center of the the bar too but it is not.
that is why with a shorty bar raising the bar on the chassis on the left side you are still lowering your roll center but not as much as if you lowered it on the pinion.
hard to explain with out diagrams

racecrew2
Dirt Newbie

Total posts: 2
posted August 31, 2005 07:48 PM  
Thanks guys that is what I needed, does anybody know how to move the front roll center?

wfoondirt
Dirt Forum Champ
Total posts: 505
posted September 01, 2005 07:25 AM  
Don, You're correct, thats why I told him to do a search, its quite lengthy to explain and its been discussed on here and 4m before.


Kromulous
Dirt Forum Champ
Total posts: 796
posted September 01, 2005 07:26 AM  
quote:
that is why with a shorty bar raising the bar on the chassis on the left side you are still lowering your roll center but not as much as if you lowered it on the pinion.
hard to explain with out diagrams [/B]

I'll argue this one till they put me in a hole.

I beleive it may not lower or raise the rear RC at all, its just increases the mechanical leverage over the left side of the chassis.

Most think when they made this change they got more body roll, no the body roll is the same, only thing different is you gave the panhard bar more leverage to pick up on the left side of the car, basicly you created more left side lift, not true body roll.

Lowering both ends at once will give you more true body roll, and less "scotch" or mechanical lift thru the panhard bar. Because you truly did lower the rear RC.

Anyway, dont mean to Hi-jack your thread.

Racecrew2, play with the graph paper or find a program for computer, there are some out there cheap and you will see how to raise or lower it. Easiest way is the upper A-arm angle.

madnik18
Dirt Full Roller

Total posts: 40
posted September 01, 2005 12:10 PM  
would it be possible to get the r/c program in the toolbox?

Kromulous
Dirt Forum Champ
Total posts: 796
posted September 01, 2005 12:49 PM  
I got one, i'll see if i can zip or something to send out. It was freeware made by somebody.

There are a few places you can get them online fairly cheap, and there ultra nice. Once you get your measurements, you can manipulate things from there to see where you need to move things.

donslink1
Dirt Freak

Total posts: 318
posted September 01, 2005 04:39 PM  
hey kromulous, you can call what ever you like, But it is still lowering your roll center.
your panhard bar is the biggest factor of roll center in the rear!!!!!

Chad
Dirt Freak

Total posts: 269
posted September 01, 2005 05:54 PM  
I know the argument continues on rear roll centers. The attached is a link to AFCO's Tech website. Notice that on a J-bar, the roll center is projected beyond the end of the pinion mount. IT IS NOT LOCATED BETWEEN THE FRAME AND PINION MOUNTS. Read the article to understand. This one confuses many racers.
http://www.afcoracing.com/tech_pages/panhard.shtml


donslink1
Dirt Freak

Total posts: 318
posted September 01, 2005 06:31 PM  
Thank you chad!!!!

Mr. Badboy
Dirt Full Roller

Total posts: 29
posted September 04, 2005 08:51 PM  
quote:
Originally posted by racecrew2:
Thanks guys that is what I needed, does anybody know how to move the front roll center?

Depending on if you want to move it up or down, there are different methods. If you race IMCA, check the rules first. To raise front roll center, Coleman makes a special ball joint that is longer than normal and has spacers which help raise the roll center. Using pinto/mustang 2 spindles to replace chevelle, or metric spindles can alter the roll center depending on where you drill the ball joint spindle holes to locate the spindle in relation to the former position it was in. I have tried the chassis height game on front roll center modification, and it helps in a pinch, but throws off front end alignment and bump steer, and anti dive too much. Hope this helps you.

[This message has been edited by Mr. Badboy (edited September 04, 2005).]

CRC
Dirt Newbie

Total posts: 2
posted September 05, 2005 05:49 PM  
Southwest speed makes a adjustable ball joint for there screw-in upper A arm. I have one on my car. Price is around 50.00 for the kit and replacment pin is 10.00 they do bend easy up that high.

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