Motorcycle Shock Damping Piston Parts

Your rear shock absorber has a complex thick metal disc with machined passages flowing between both flat sides, and to make sure the suspension fluid can only flow through these holes, a rubber o-ring and a teflon coated bush (or a soft PTFE band) seal around the outer diameter.

Stacked on both sides of this piston are the valving shims, a collection of thin steel washers that flex when pushed by the oil pressure. They come in a huge range of diameters and thicknesses, and are arranged in a very specific order to create the right damping characteristics, with the compression valve stack on one side, and rebound stack on the other. The piston and it's shim stacks are then attached to the end of the shock shaft using a locknut.

When the motorbike's coilover compresses, some of the oil flexes the shims open and pushes through the piston holes to the other side, creating friction and heat. If the damper gets pushed harder, the valving flexes further, allowing more through. After the bump, the coil spring pushes the bike back to it's ride height, and the oil is squeezed back through the piston and rebound shims to the other side, absorbing more energy.

It's all basic science but there are thousands of different variables that change the way it feels - our shim equivalence calculator can help - and that's why experienced tuners test and refine all that data on a suspension dyno. If you want to know more you can check out our suspension mods for your budget article to better understand how to approach tuning based on price vs performance, or watch Teknik's suspension guru Nick rebuild and revalve a shock.

We sell piston assemblies with o-rings & bushing rings or gapless bands already installed, as well as individual parts like lock nuts. For other internal valving components like shims and valve stop washers, please see our Valving Shims section.