What is a Slipper Clutch?
Under power the engine has a rev limiter to stop it getting over revved and in turn damaging its internals. However, when the rear wheel is turning the engine there is no rev limiter – which is where the slipper clutch comes in.
Inside a slipper clutch is a center piece that lifts up on a series of ramps. These ramps lock in one direction (when the engine is turning the rear wheel) but not in the other and so when the back-torque is too much the clutch's center piece lifts and releases some of the pressure on the clutch plates – effectively pulling the clutch lever.
When the pressure reduces the center piece drop down, reengaging the clutch at a set rate until the back-torque is once again too high. On track, a slipper clutch is a wise investment.