motion ratio help

[element180]

FOund this at the Atlas F1 board

a, I must love to argue or somethin. Now the subject is on motion ratio's, always been taught, disregarding angles at the moment

a = dist from lower arm axis to ball joint
b = dist from lower arm axis to spring mount

MR = b/a

While reading over Milliken on the subject it becomes pivot point to wheel, not ball joint, which makes sense as the torque is reacted at the wheel and we are tryin to find wheel rate, not ball joint rate, that thing is just along for the ride. But then I figure that the wheel doesn't actuallt rotate around the lower arm axis, but the IC.

Then I come across Herb Adams in Chassis Engineering with his equation of



a = dist from lower arm axis to spring mount
b = dist from lower arm axis to ball joint
c = dist from IC to ball joint
d = dist from IC to wheel center

MR = (a/b)^2 * (c/d)^2

Sounds about right, but something still doesn't seem to be clickin on all cylinders, anyone have any insight? I've got some MR numbers from Bill Mitchell's program for our car, but Mr. Mitchell is tight lipped at the moment over the subject. But I have seen many a program use the first equation to figure out motion ratio's, and that seems scary.