Editing Freewheel (section)

==Mechanics==
The simplest freewheel device consists of two saw-toothed, [[Spring (device)|spring]]-loaded discs pressing against each other axially with the toothed sides together, like a [[ratchet (device)|ratchet]] but with the usual stationary part also rotating. Rotating in one direction, the saw teeth of the drive disc lock with the teeth of the driven disc, making it rotate at the same speed. If the drive disc slows down or stops rotating, the teeth of the driven disc slip over the drive disc teeth and continue rotating, producing a characteristic clicking sound proportionate to the speed difference of the driven gear relative to that of the (slower) driving gear.

A more sophisticated and rugged design has spring-loaded steel [[roller (disambiguation)|rollers]] inside a driven cylinder. Rotating in one direction, the rollers lock with the cylinder making it rotate in unison. Rotating slower, or in the other direction, the steel rollers just slip inside the cylinder.

Bicycles use freewheels to allow the cyclist to coast without pedaling. Rotating either the wheel or [[Cogset#Cassettes|cassette]] in the direction that produces the clicking sound causes the pawl to easily slide up and over the gently sloped edges of the teeth. This process is sometimes informally referred to as "slipping." In this scenario, the cassette rotates independently of the rear wheel. When the cyclist stops pedaling, the ratchet slips as the wheel continues to rotate while the cassette stops, producing the clicking noise. Consequently, a bicycle will not move in reverse if the cyclist pedals backwards. When the cassette or wheel is rotated in the opposite direction, the pawl catches against the steeper-sloped edges of the teeth, creating a lock. As the cyclist pedals forward, the cassette spins forward causing the pawl to catch against the steep slope of the teeth and drive the rear wheel in the forward direction. This also explains why pushing the bicycle forward causes the pedals to rotate in the forward direction. 

Most bicycle freewheels use an internally step-toothed drum with two or more spring-loaded, hardened steel [[Ratchet (device)|pawls]] to transmit the load. More pawls help spread the wear and give greater reliability although, unless the device is made to tolerances not normally found in bicycle components, simultaneous engagement of more than two pawls is rarely achieved.