Hi. I've done a search on here and on the net and I cant find any referance as to how you calculate roll centre height on a car. A diagram would be much appreciated! Thanks, Danny.

Here you go, second hit on google:

http://www.stockcarproducts.com/pstech3.htm

Nice and simple, and saves me doing a doodle for you...

David

Thanks! I did a search on google and all I could find was something on wkipedia that just confused me.

To the drawing board!

Danny.

Looking at that diagram it seems to asume that the top wishbone is angled, but what if they are parallel?

Danny.

If the wishbones are parallel then the roll height is zero i.e. at ground level.

Where it goes from there depends upon what the lengths of the wishbones are.

Be aware what looks like a parallel arm may not actually be parallel as the true line of the geometry goes from the chassis pivot point through the upright pivot point, which depending on the ball joint arrangement may be a decent distance from the actual end of the wishbone.

I know the arms are parallel, its my own design. I kept them parallel because the top wishbones are shortish so I thought if I angled them I might get too much camber change.
So is a roll centre at ground level a good thing or not?

There is no "perfect" place to have the roll center.
What is widely accepted is that the roll center movement (relative to the car). Through the rage of motion of the suspension is a bad thing.
Typically the roll center is lower at the front by 1" - 2" than that at the rear.

There are entire books on this subject, so i don't think my feeble explanations here will get you where you need to be.

[Edited on 26/1/07 by Doug68]

[Edited on 26/1/07 by Doug68]