unsprung weight

totopo

Unsprung weight is SUPER important.

Basically, bumps apply an acceleration to the unsprung weight, not a force. So lighter unsprung weight means less acceleration, and less perturbation of the chassis on the other end.

The major way of measuring the end effect of springs on a suspension is the wheel frequency. Basically, you have 2 weights separated by a spring, so the wheel frequency is dependent on the weight of both, but more so on the lighter weight (the unsprung weight). The wheel frequency is almost linearly proportional to the minor unsprung weight. So a decrease of weight of 10% iirc is basically like having a 10% stiffer spring. This is where you get where people say xx lbs unsprung weight = xx lbs sprung weight. like shaving 15 or 20 lbs or whatever off a corner weight has the same effects on wheel frequency that shaving 1lb off unsprung weight will have.

but it isn't like exactly true, since shaving off unsprung or sprung weight has the same effect on the normal force on the tire and the lateral force needed to turn the car.

Other benefits of lessening unsprung weight is you usually decrease rotational mass as you do it, since most of the unsprung weight is wheels and rapidly rotating components. decreasing rotational mass effectively improves your braking and acceleration.

spacers are kind of interesting from a vehicle dynamics standpoint. They increase the wheelbase, which is super great for decreasing weight shift, but it changes your scrub angles in the front, and changes your overall suspension geometry (and i think kills bushings). I think the motoiq people actually like running modest spacers for cheap wheelbase increases for more lightly modded projects.