The 8100 series shocks are a 7400 aluminum shock with a remote reservoir. The reservoir improves the performance of the Penske shock with an increase in nitrogen volume and the addition of a floating piston that separates the gas from the fluid. A "separator" piston greatly reduces aeration of the fluid. In addition the reservoir provides for compression adjustment with six settings to fine tune the compression. Shocks with rebound adjusters allow you to make small adjustments externally by turning a small nut located behind the shaft end eye.