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A track bicycle or track bike is a bicycle optimized for racing at a velodrome or outdoor track. Unlike road bicycles, the track bike is a fixed-gear bicycle; thus, it has only a single gear ratio and has neither a freewheel nor brakes. Tires are narrow and inflated to high pressure to reduce rolling resistance. Tubular tires are most often used in track racing and training, though advances in clincher tire design have seen them being used somewhat more often.
A track frame is specific to its intended use, with emphasis on rigidity and lightness. Frames for sprinting seek to maximize rigidity, while those for general racing seek to reduce aerodynamic drag.
A track bicycle differs from one used on the road by having:
- higher bottom bracket so the pedals do not touch a steeply banked track
- steeper seat tube for a more aerodynamic position and a shorter wheelbase
- steeper head tube for more responsive steering,
- less fork rake.
Typical track frames use 120mm spacing for the rear hub. The dropouts or track ends face rearwards to facilitate chain tension adjustment.
Frames are typically made of steel, aluminium, or titanium alloys, carbon fiber, or a combination of these materials. Carbon fiber frames are most common at the professional level. Frames are assembled from tubular elements (typically with round or elliptical cross sections), or cast in a mould for "one-piece" type models. The UCI permits special exceptions for the construction and geometry of track bikes.
Track bicycles have only one drive sprocket (or cog) and one chainring, so the size ratio is relevant. A lower gear ratio allows quicker acceleration or 'jump' but can limit top speed. A larger gear ratio makes sustained speed easier, important in pursuit racing, time trial and bunched races such as points or scratch events. Without a good jump, the rider risks opponents accelerating away; without good sustained speed, the rider will be unable to keep up with a fast race. Track cyclists practice fast pedalling (cadence) as a compromise.
There are two common widths of single speed and fixed gear bicycle chains: 1⁄8 inch and 3⁄32 inch. The chainring, sprocket and chain should all be the same width. Although an 1⁄8 inch chain will work on a 3⁄32 inch chainring or sprocket, it is not ideal. A 3⁄32 inch chain will not work on a 1⁄8 inch chainring or sprocket. Because they do not need to shift between sprockets, track chains use a full bushing to reduce flex and increase strength. Newer bicycles with derailleur gears use bushingless chains which flex, making gear changing possible.