roll center?

[Racedude_5]

I am building a new modified chassis for next year and am confused about roll centers. I basicly know what they are and I have a chart on how to determine your roll center, What i'm confused about is everybody says you need to know where your roll center is but nobody seems to be able to tell me where you want it to be.
Any help would be apreciated!! as now is the time to build it into the car instead of about late march.

[340king]

Roll center preference is just that, a preference. Some drivers like it way low, while others like it higher. Car class does seem to have a little bit to do with this also. The stock class cars are limited on the components they can use and must rely on OEM parts with a little race tweaking.

Roll centers and ride height go hand in hand also. When you change the ride height, you are also changing the geometry that composes the roll center. Most modifieds use a roll center that is very near ground level for the front suspension.

There is another train of thought that you can put your heavier spring on the left front and the softer one on the right front and influence the way the roll center acts. In effect, you are making the left front contact area of the tire the roll center. This causess the car to pivot on left side and lean on the right side springs and is generally a little softer and less dramactic with changing track conditions.

In the rear, you will want to make the roll center adjustable to follow track conditions. Most cars use a track bar/panhard bar for this. Leaf cars can also be manipulated using lowering blocks.

I always try to think of the two roll centers as the roll axis. This is key in understanding the effects of changing the height of weights and their location in the car. The roll axis can run in line with the chassis or can be skewed to one side or the other depending on the springs, sway bar, etc.

I realize you have more experience than my reply might indicate, but there are others here that do not have your experience and I always want to include all levels of experience in my posts. I haven't done much with RC calcs lately, so this will be a good reason to refresh my memory. I do have a couple of computer programs that calculate the roll center of a given suspension. I haven't spent much time with them lately either.

[Racedude_5]

Thanks for your reply!
I just checked roll center as I first put everything in the car and with the car at ride hight it is 2" above the ground and 18" left, that would definitly work for rolling around the left front. I also done some variations and it would be easy to bring it closer to the center and still be 2" above ground.
The car I ran last yoer was junk but the front end stuck like it was glued. there isnt enough left of the car to measure and copy the mounting points though

[sanborn]

Don't know what you need for roll centers for an open wheel modified. A late model generally wants roll centers in the center of tread width or more to the right for a tacky track, as the track gets slicker the roll center needs to move to the left. And, the rear roll center generally moves more than the front. Height of roll center depends somewhat on driver preference but again the slicker the track, the lower the roll center.