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Why do track-racing bicycles use a single fixed gear?

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An African American family of four, all wearing helmets, rides bicycles together on a tree-lined country trail, with two children in front and two adults following behind. — bicycle Family bicycling on a country road.

Track-racing bicycles utilize a single fixed gear because the drivetrain is designed to transmit motion directly from the pedals to the rear wheel hub without a freewheel mechanism. This configuration means the rear wheel sprocket, chain, and pedals move as one, preventing the rider from coasting.1

By eliminating the freewheel, the bicycle ensures a constant, direct connection between the rider's legs and the drivetrain. This setup is essential for track cycling, as it allows the rider to control their speed through pedal resistance and reverse leg force, which is necessary for slowing down or stopping in the absence of traditional braking systems. This mechanical simplicity also minimizes maintenance and provides the immediate power transfer required for high-speed track competition.1