Before installation?measure the spring distance (H2) when the car is stationary (no need to use a jack or other tools to lift it). After measuring the data, use a jack to jack up the vehicle to completely relax the spring. Measure the gap between the springs (H2) and select the appropriate size cushion for extra support. Choose Size (C) of the rubber buffer, if the Car Coil Spring Gap (when lifted and unloaded) is between 1.27''-1.47'' Effectively solve problem of springs weakness when heavy load & improve performance of shock absorber. Improve driving comfort and more stable during curve corner. Reduce pumping of absorber when passing through road hump or yellow line. Reduce noise and vibration during traveling.