Roll Center; Exactly what is it???

[K-fab]

Dump!,
Thanks for that booklet - covers just about all of it.

In the last suspension setup that I designed, I took into account pretty much everything you've described - and let the RC end up where ever it ended up. I designed for camber and caster changes, scrub issues and scrub radius around the kingpin inclination.

Getting rid of bump steer was probably the hardest part of the design - single seat car with a very wide a-arm setup - front of the a-arms mounted almost together at the nose of the car while the rear of them mounted out near my knees. I had to make a pretty complicated set of bell cranks to get the motions all working together w/o inducing toe changes as the suspension cycled.

I also addressed scrub by making the a-arms as long as possible, so the travel I was getting (about 11") worked closer to the horizontal aspect of the arc that it traveled. - as you're aware, the more your suspension moves downward (on the arc), the more horizontal movement you get. - 45 degrees = the same amount of verticle and horizontal travel in the X-Y plane (x would be parallel to the bottom of the chassis, y would be parallel to the plane of the motion of the arcs the suspension moves).

I know of a five link design that actually induces quite a bit of camber as the suspension gets to the bottom of it's travel and makes the contact patch move outward. The top of the tire will tilt inward near the bottom of the travel, keeping the contact patches of the rear wheels fairly constant in distance thru the suspension's movement. - makes for a pretty stable car.

I guess, in retrospect, the questions about the RC of the car have been answered for me. - Don't really worry about it... Make the suspension work to it's best ability - camber, caster, toe, scrub radius around the kingpin inclination, bump steer and the likes and let the roll center end up where it ends up!

Thanks for the info.

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