Manufactures spend millions perfecting the suspension response, “feel” and behavior. Getting it right is critical for sales, especially when the magazines rave about the performance.
However, the stock setup damping is specific to the spring rate the bike was designed for. Changing springs to match rider weight and the suspension performance gets messed up.
Spring-mass-damper theory defines the specific relationship between suspension response and the rider weight, spring rate and damping.
Suspension weight scaling (Physics linky) computes the damping needed to compensate for spring rate changes and restore the suspension response, “feel” and behavior the manufacturer intended for the original suspension setup.
Shim ReStackor spreadsheets make weight scaling easy. Correcting damping for a spring rate change simply requires hacking around on the shock shim stack configuration to hit the target damping curve required for the specified spring rate change (more).
Weight scaling spreadsheet
Inputs of the original and modified spring rate specifies the damping correction needed to scale a known good setup to the spring rate and rider weight of a new setup. The weight scaled damping correction specifies two targets: The broad dashed line, shown in the screen shot, specifies the low speed damping needed for chassis control; the thin dashed line shows the damping needed for high speed wheel motion control.
Weight scaling the baseline, from stock damping or a custom tuned shock, to the damping required for a new spring rate simply requires hacking around on the shim stacks to hit the target damping curve.