MXScandinavia on Thumper Talk demonstrated operation of a trapped crossover (linky sample apps) and compared performance to a simple single shim crossover. The two shim stacks are identical with the single difference of replacing the crossover with a 34.1/28.1 split shim pair.
By the thickness cubed rule (shim fac), the replacement shim pair should be 40% softer than the single 28.15 crossover shim. In addition, the split shim pair forms a 0.2 mm crossover gap making the shim stack softer than the single shim 0.15 mm crossover gap.
However, dyno testing shows the opposite effect with the split shim pair producing 3% more damping force. The reason for the difference is the larger 34.1 crossover shim becomes trapped in the closing crossover gap reducing the “effective” crossover gap to 0.1 mm instead of the expected 0.2 mm crossover gap.
Shim ReStackor closely follows the dyno test data and confirms the occurrence of the trapped crossover shim increasing the damping force of the theoretically softer stack.
