Rear shock placement

[Norm Peterson]

You don't want much shock angle because with more initial angle comes more variability over suspension motion (the angle becomes larger as the chassis drops, and its cosine becomes smaller at an ever-increasing rate). And since this effect decreases the effectiveness of the shock as travels further into bump, the least amount of damping would occur as you approach the bump stops. Conversely, the greatest damping effectiveness would occur about when the suspension is all but fully extended in droop and the tire is about to leave the ground. That just sounds backward, and the simple fix is to minimize the angle in the beginning.

It's somewhat more important with coil-overs, as wheel rate is a cosine^2 function of spring angle, which is now concentric with the shock.

For the street, mounting the lower end of the shock 8" below axle centerline height is too low for 16" wheels (17's are OK, but only barely) since the shock bracket needs to extend at least an inch or so below the shock mounting bolt center to keep the bolt from tearing out the hole.

You'd run 15" wheels if the racing class rules specified them, as I think most of the roundy-round sanctioning bodies do. Under those circumstances, everybody on the track accepts a good deal more risk with far greater understanding of the possibilities and consequences of things going wrong than does the driving public at large.



On edit - in roll there is rotation of the chassis, so the motion at the chassis side of the shocks is not purely vertical like it is in two-wheel bump. I suppose that you could force roll response to be very close to vertical at the shock mounts, but that would involve a very high rear roll center (strictly enforced by a Watts link or similar direct mechanical constraint), but that would create far worse problems than the bit of nonlinearity in the damping that it's eliminating.

Norm