Skyjacker Hydro Shocks offers you a high quality shock absorber with true velocity sensitive valving. Shock absorbers, or spring dampers, control the rate at which suspension springs compress and rebound. As the shock is pushed together, this is called bump or compression. As the shock expands, this is called rebound or extension. Absorbing the shock of bumps and suspension loading is actually performed by the springs in the suspension. The shocks real job is controlling the energy stored in the springs.