ABSTRACT
In its simplest form a cycle wheel comprises a simple wooden disc with a hole through its center. The hubs of all spoked wheels have an axle, wheel bearings and a rotating shell to which the spokes are attached. Hubs may also contain mechanisms involved in the drive system, braking and lighting. Cycle wheels were originally hand-made by wheelwrights, in the same way as wagon wheels. The hub, spokes and rim were made of wood and held together by an iron tire shrunk onto the rim. Hubs were also made of wood and held together by a pair of small iron hoops. Hub shells are usually made from pressed steel or cast aluminum alloy. Except where front-wheel drive is used, the rear hub must accept drive input from a chain, toothed belt or driveshaft. On cheap derailleur-geared bikes, the hub will usually have a screw-on multi-sprocket freewheel with about six sprockets, with the hub axle extending well past the bearing.
