RedShift Sports Replacement Spring Kit - Fits 27.2mm ShockStop Endurance SeatPost +25% StiffnessRedShift Sports Replacement Spring Kit Fits 27. 2mm ShockStop Endurance SeatPost +25% Stiffness. Replacement springs are an ideal upgrade if you need a bit more stiffness from your ShockStop Suspension Seatpost. The stiffer springs provide a more topped out feel or if youre at the upper end of the weight range and want more support. Approximately 25% more stiffness than the standard spring set Includes two steel springs (one outer and one inner