Rebound Separator Valves replace the Shock Shaft Nut with an asymmetric valve (it has a different flow rate in each direction). On standard shocks testing shows that when rebound dampening is quick enough to get good traction, the compression is too mushy. In Dirt this causes a vague feeling and bottoming on long duration hits like big dips or gullies. For pavement, Rebound Separators Valve’s have the added benefit of pitch control (front to back movement during acceleration and braking).