MXScandinavia dyno tested shim factor equivalent stacks on Thumper Talk to determine the accuracy of shim factors in scaling suspension setups. The test replaced all of the 0.20 mm shims in the shim stack taper with a pair of 0.15 mm thick shims. By shim factor theory a pair of 0.15 mm thick shims should be 16% softer than a single 0.20 mm shim.
Dyno testing the shim stack configurations shows the theoretically softer stack actually produces 5% more damping force as shown by the MXScandinavia dyno data points. Shim ReStackor calculations shown by the lines in the figure below verify the dyno test results and the 5% damping force increase for the theoretically softer stack expected by shim factors.
The difference in damping force is caused by shim friction. Replacing the stack taper shims with a softer pair of shims doubles the shim interface area and the resulting friction. The friction increase results in the theoretically softer shim stack producing a higher stiffness and damping force.
Shim ReStackor FEA calculations compute the forces acting on the top and bottom surface of each shim allowing the calculations to accurately determine the interface friction and its effect on stack stiffness.
MXScandinavia dyno tests demonstrate shim friction makes a theoretically softer shim stack dyno test 5% stiffer due to the difference in shim interface friction.
