High Speed Stack Enough theory, lets look at some dyno data for practical suspension tuning problems “Loosen up high speed damping by pulling the even number shims from the high speed stack, unless you be fast – then pull the odd.” That statement is spread all over suspension forums. Others say shim stacks don't work that way, the high speed stack effects damping force everywhere, not just at high speed. So whats the deal? Do high speed stack changes make a difference or not? MXScandinavia posted some dyno data on TT showing what modification to the high speed stack do in terms of changing the shape of the damping force curve. This first example keeps the same low speed stack and replaces five 0.25 mm shims in the high speed stack with softer 0.20 mm thick shims. That mod keeps the same number of shims in the stack so the shim surface area and friction should be the same for both stacks. By the thickness cubed rule 0.20 mm shims have 51% of the stiffness of a 0.25 mm shim. The stack has ten shims in the stack taper and this mod replaces five of them with 51% softer shims. So half of the shims in the stack taper were replaced with shims that were half as stiff. So maybe that loosens up the high speed stack by 25% or so? Does softening the high speed stack loosen up high speed damping or not?