A Slipper Clutch is a special type of clutch used in performance bikes to mitigate the effects of engine braking during aggressive down shifting.
Let’s assume a situation in which a rider approaches a corner at speed. The rider, in order to slow down, downshifts aggressively. As a result, the engine revs dramatically increases. The engine cannot accept this sudden change in revs. The difference is made up by the bike’s rear wheel’s excess inertia. This excess inertia is absorbed by the powertrain. The roles are now reversed. The rear wheel of the bike tries to drive the engine quicker to match road speed with engine speed. As a result, the piston is forced to reciprocate quicker and the cams are forced to open and close quicker. This puts a lot of unwanted force on the powertrain. This is known as back torque. Due to this, the rear wheel emits an audible squeal as it locks due to the transfer of back torque and it comes to a stop.
A Slipper clutch tries to avoid this situation. A Slipper Clutch is a device which allows the clutch to freewheel in one direction. Imagine riding a cycle. When you stop pedalling, you hear a whirring sound from the sprocket. This is precisely what the slipper clutch aims to do for motorcycles. Now consider the same situation. You are about to take a corner and speed and you downshift aggressively. The rear wheel tries to drive the power train. Due to the Slipper Clutch partially disengages the clutch. Thus, the gearbox and the engine are spared from catastrophic damage.
Another use for the slipper clutch is that in case of transmission lock or engine seizure, the rear wheel is prevented from locking up, which could be fatal at times.