Pull the lever on a motorcycle and you are not flipping a switch. You are peeling apart a stack of spinning discs held together by nothing but spring force and friction. Almost every bike runs a wet multi-plate clutch, and the whole thing lives in an oil bath inside the primary drive. Torque from the crankshaft spins the outer clutch basket. Stacked inside it, alternating like a deck of cards, sit two sets of plates: - Friction plates, tabbed to the outer basket, spinning with the engine - Steel plates, splined to the inner hub, feeding the gearbox Stiff coil or diaphragm springs clamp the stack. Pressed together, friction locks every plate into one rotating unit and drive passes straight through to the rear wheel. Pull the lever and a pushrod lifts the pressure plate a fraction of a millimetre. The stack separates, the surfaces slip, and the engine spins free of the transmission. Torque capacity comes down to one relationship: T = n mu F r, where n is the number of friction faces,...