A fixed-gear bicycle (or fixed-wheel bicycle, sometimes known as a fixie) is a bicycle that has no freewheel, meaning it cannot coast, because the pedals are always moving when the bicycle is in motion.
The sprocket, or cog, is threaded or bolted directly to a fixed rear hub. When the rear wheel turns, the pedals turn in the same direction. This allows a cyclist to stop without using a brake, by resisting the rotation of the cranks, and also to ride in reverse.
As a rule, fixed-gear bicycles are also single-speed bicycles—bicycles without derailleurs, with a single sprocket attached to the rear hub, and a single sprocket attached to the crank. Most fixed-gear bicycles only have a front brake, and some have no brakes at all. Exceptions do exist: for example,Sturmey-Archer produces 3-speed fixed rear hubs for multispeed fixed-gear bicycles.