What does a slipper clutch do?

During rapid downshifting, a slipper clutch temporarily reduces the amount of friction in a clutch, which disconnects (to a degree) the final drive and transmission of a motorcycle. The result is a decrease in engine braking and an increase in rear wheel freewheeling.

What are the benefits of using a slipper clutch?

Performance: Decreasing engine braking leads to increasing the amount of rear wheel freewheeling. When rear wheel freewheeling is increased, cornering speed is also greatly increased. An increase in cornering speed directly leads to lower lap times! Also, the slipper clutch frees up the rider’s attention so they can focus it on other aspects of riding like reference points, body position, lean angel, braking, etc. Safety: The engine is spinning at one speed, the rear wheel typically is spinning at a higher rate of speed. When engine speed is NOT properly matched to rear wheel speed during rapid downshifting, this results in a situation called “Rear Wheel Hop”. What this means is that the rear wheel starts to hop up and down violently until the two speeds are equalized. Slipper clutches eliminate rear wheel ‘hop’, which ultimately increases the control of a motorcycle. Once the rear wheel starts to hop, it has lost contact with the ground… which means the rider has lost control of the motorcycle! If the rear wheel is hopping and loses contact with the surface, a rider may be able to slow the motorcycle, however the bike can not be turned. This can lead to an accident. If the rear wheel is allowed to freewheel, it can remain in contact with the ground and the bike can be turned. Basically, through use of a slipper clutch rea wheel hop is eliminated, control is increased which could be the difference between going through a corner and leaving the road surface.

Why use a slipper clutch off road?
Performance: It is a common misconception that a slipper clutch will have no benefit in off road conditions because the dirt will give way and the felt engine brake will be minimized. This is not true, engine braking will always be felt and more importantly it can upset the handling of the motorcycle. A slipper clutch allows the rear wheel to freewheel under rapid downshifting conditions… which leads to increased corner speed and lower lap times. Stability: Consider that every time the face of a bump or whoop section is hit, the rear wheel is torqued and opposing force is applied to the engine. This typically results in the rear of the bike being thrusted upward. This throws the front of the bike down and the result is a ‘sea-saw’ effect, or bucking back and forth. Usually the only way to combat this is to get off the gas. However, when using a slipper clutch through a difficult whoop section, as the rear tire hits the face of each whoop, the clutch is allowed to open up and keep the rear wheel spinning… this increases stability and leads directly to the bike staying level; which allows the rider to stay on the throttle. The same is true when landing a jump. As the bike flies through the air, the rear wheel may slow down. Upon landing, the rear wheel is rapidly accelerated again and opposing torque is applied to the rear wheel and subsequently the engine. The result is increased downward force on the front end. With a slipper clutch, the rear wheel is permitted to freewheel upon landing. This leads to increased stability on landing, being able to ride out of the jump faster, and often in many cases enables the rider to use softer front suspension settings for increased feel and control in other parts of the track. In addition to increasing riding benefits, STM slipper clutch systems prevent engine over-revving. Reducing engine over-rev preserves the function of engine components and leads to increased engine life.