motion ratio on leaf springs

[High Plains Mopars]

On an independant suspensions, wheel rate can be calculated by squaring the motion ratio then multiplying the spring rate. Motion ratio can be calculated by dividing the distance from the coil spring to the pivot point by the length of the control arm.

Can the same be done on a leaf spring suspension and where is the cacluation points orginated at? Is it the drum face to roll center, drum face to opposite side spring, drum face to same side spring?



If my leaf is 120#, how much of that is being applied at the wheel?

[David Pozzi]

According to my old Steve Smith book, "Advanced Race Car Suspension Development":

The std formula is D1 divided by D2.

For A arms:
D1 is from A arm pivot to spring
D2 is from A arm pivot to LBJ (lower ball joint)

For a leaf spring rear axle:
D1 is distance from center of left spring, to center of right spring.
D2 is the tread width - center of tire to center of tire.
Divide D1 by D2 and square to arrive at wheel rate.

David

[High Plains Mopars]

For a leaf spring rear axle:
D1 is distance from center of left spring, to center of right spring.
D2 is the tread width - center of tire to center of tire.
Divide D1 by D2 and square and multiple by the spring rate to arrive at wheel rate.

David

Just a small piece of the formula you forgot, but it all works out. Thanks David!

[David Pozzi]

Duh! Yeah, sorry about that!
I can tell you that on a Camaro, a 120 is pretty stock, 175 is tuner street rate, and 250 is a race rate. I can't even MOVE the rear by jumping on it with the 250 rate! But driving on a track or autocross, it's fine, kinda rough on the road, but street tires ease the ride a lot. I wouldn't want to go far on race rubber though.
David