Interactive crossovers use a shim diameter larger than the shim stack clamp. The larger crossover diameter transfers force from the face shims directly into the high speed stack forcing the high speed stack to deflect before the crossover closes. Interaction with the high speed stack softens the crossover closure event (more).

Valving Logic on Thumper Talk demonstrated the performance of an interactive crossover. The damping force data shows no evidence of the crossover closing.

However, Shim ReStackor calculations of the shim stack deflection and stack flow area make it easy to spot the crossover closure velocity at 20 in/sec,

Soft closures of interactive crossover with a soft high speed stack often do not produce any specific “event” in the damping force curve. The data at 20 in/sec where the crossover closes shows that.

Interactive crossover configuration produces a "soft" crossover closure event

Interactive crossovers use a shim diameter larger than the shim stack clamp. The larger crossover diameter transfers force from the face shims directly into the high speed stack forcing high speed stack deflection before the crossover closes. Requiring the face shims to chase down a moving high speed stack softens the crossover closure event.

Shim ReStackor analysis of the interactive crossover tested by MXScandinavia on Thumper Talk produces a crossover closure velocity of 60 in/sec. However, the MXScandinavia dyno could only test to shaft speeds of 40 in/sec.

The test illustrates a typical frustration of dyno testing. At the velocity limit of the dyno no unusual behavior is observed. However, the crossover gap has not closed creating uncertainties in the high speed damping performance of the shock.

Shim ReStackor helps relive those uncertainties with the capability to compute high speed performance, evaluate crossover closure velocities and the effect of valve port flow restrictions that kick in at velocities beyond the limits of conventional dyno testing.

Crossover closes at shaft velocities beyond the dyno test speed capability

A faux crossover gap never closes. Faux gaps are created by large crossover shim diameters, stiff low speed stacks or soft high speed stacks that do not produce enough force to close the crossover gap.

Valving logic tests of an rmz450 shock on Thumper Talk demonstrate the operation of a faux crossover.

Shim ReStackor analysis of the configuration shows the crossover gap eventually closes at a shaft velocity of 180 in/sec. However, the soft high speed stack used in the configuration produces virtually no change in damping force at the crossover closure. In that sense, the configuration demonstrates “faux” over the range tested.

Faux crossover gap never closes creating confusion in operation of the shim stack

Two stage crossovers have a similarity to split crossovers in spreading out the bend radius of the crossover shim shoulder. Valving Logic dyno testing of an rmz250 shock demonstrates performance of a two stage crossover.

Shim ReStackor analysis of the configuration shows the upper crossover gap closes first followed by closure of the lower crossover gap at shaft velocities near 37 in/sec.

The soft high speed stack used in the configuration produces little increase in damping force when the crossover gap closes.

Two stage crossover spreads out the crossover closure event