In a motorcycle, the mechanism that allows the rear wheel to rotate at a different speed from the crankshaft is called the "final drive." The final drive transfers power from the transmission to the rear wheel while accommodating the speed difference between the two. There are two main types of final drive mechanisms used in motorcycles: chain drive and shaft drive.
Chain Drive: Chain drive is the most common type of final drive in motorcycles. It consists of a sprocket attached to the output shaft of the transmission and another sprocket attached to the rear wheel. A chain connects the two sprockets, transmitting power from the engine to the rear wheel. The sprocket sizes are chosen to create a specific gear ratio, allowing the rear wheel to rotate at a different speed from the engine.
Shaft Drive: Some motorcycles, particularly larger cruisers and touring bikes, use a shaft drive system. A shaft drive consists of a driveshaft, bevel gears, and a final drive gear assembly. The driveshaft transfers power from the transmission to the rear wheel through a set of bevel gears. The bevel gears change the direction of rotation, allowing the rear wheel to rotate at a different speed than the crankshaft.
Regardless of whether it's a chain drive or shaft drive, the final drive mechanism in a motorcycle accommodates the speed difference between the engine and the rear wheel. This allows the motorcycle to transfer power efficiently to the rear wheel while maintaining control and preventing damage to the engine.