GSpeedR wrote:In my experience, kinematic roll centers are directionally correct at best and completely dangerous at worst. Roll-center analysis invariably implies the creation of a 'pin joint' at the roll center location, where forces are transmitted between the sprung and unsprung bodies; this aspect of RCs is true of kinematically determined roll-centers and force-based methods (Mitchell, Ortiz, etc). Force-based roll center's advantage over its kinematic cousin is that distribution of lateral tire load is accounted for. Creation of a singular joint is especially suspicious for independent suspensions. The notion of a "roll moment arm" between the CG and roll center is a nice thought, but is a gross oversimplification.
However, regarding independent suspension, the instant center is a much more valid approximation of a pin joint and is a much better location to apply suspension forces. So a better option for the original poster is to determine a jacking coefficient at each corner independently (using instant centers), which is based in mechanical statics. The concept can be visualized in a Free Body Diagram. Without tire data, you may be unwilling to assume a distribution of tire force, in which case you will stop at the jacking coefficients.
As an aside, it is important not to confuse the "roll center" you read about in Carrol Smith books with a modal center located between the trackwidth, which is derived from a 2 DoF (roll & heave) modal analysis of a vehicle. It is a more common engineering exercise to investigate modal analysis in the pitch plane, but it is equally valid in the roll plane.
I've toyed with the idea of what I think you stated, where you apply your contact patch loads at the instant center. I've never done it that way only merely played with it in my head, which I assume you are then able to generate your jacking forces no? This is what bothers me about that, wouldn't you then after finding jacking forces be able to calculate your tire load distribution which is basically what finding your FBRC is giving you also? Thus the whole concept of doing the instant center method twice would be pointless and we wouldn't even need a roll center...
And not sure what you're on about with the modal center idea?
GSpeedR wrote:I think simply determining jacking coefficients for each side is more valid and more informative. Others may disagree.
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