Freewheel

Not to be confused with Flywheel.
"Freewheeling" redirects here. For the Italian comedy, see Freewheeling (film).

A freewheel or overrunning clutch is a device in a transmission that disengages the driveshaft from the driven shaft when the driven shaft rotates faster than the driveshaft. An overdrive is sometimes mistakenly called a freewheel, but is otherwise unrelated.

The condition of a driven shaft spinning faster than its driveshaft exists in most chain-driven bicycles when the rider stops pedaling. In a specialized fixed-gear bicycle (that lacks a freewheel) the rear wheel drives the pedals around.

Some automobile transmissions include freewheel mechanisms for reasons ranging from fuel efficiency and noise reduction to preventing damage that some engines incur when driven by the wheels.

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