A shaft-driven bicycle is a bicycle that uses a drive shaft instead of a chain to transmit power from the pedals to the wheel. Shaft drives were introduced over a century ago, but were mostly supplanted by chain-driven bicycles due to the gear ranges possible with sprockets and derailleurs. Recently, due to advancements in internal gear technology, a small number of modern shaft-driven bicycles have been introduced.
Shaft-driven bikes have a large bevel gear where a conventional bike would have its chain ring. This meshes with another bevel gear mounted on the drive shaft. The use of bevel gears allows the axis of the drive torque from the pedals to be turned through 90 degrees. The drive shaft then has another bevel gear near the rear wheel hub which meshes with a bevel gear on the hub where the rear sprocket would be on a conventional bike, and canceling out the first drive torque change of axis.
The 90-degree change of the drive plane that occurs at the bottom bracket and again at the rear hub requires the use of bevel gears. Bevel gears are the most efficient way of turning drives 90 degrees as compared to worm gears or crossed helical gears. The drive shaft is often mated to a hub gear which is an internal gear system housed inside the rear hub. Today, there are four significant manufacturers of internal hubs suitable for use with shaft drive systems, including Shimano Nexus, SRAM, Sturmey-Archer and now NuVinci.
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“Newspapers are unable, seemingly, to discriminate between a bicycle accident and the collapse of civilisation.”
—George Bernard Shaw (18561950)