Join Date: Jul 2005
Bikes: 1984 Trek 520; 1990s Peugeot (Canadian-made) rigid mountain bike; 2007 Bike Friday NWT; misc others
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The centre structure of the wheel, that the spokes attach to, is called the hub. It is a hollow metal tube, flared open like horn at each end. The axle is the straight rod that goes through the hub and is bolted to the fork. Hidden between the axle and the inside of the hub, at each end, are about ten small metal balls that are coated in grease and roll between the hub and axle. They 'bear' the weight of the bike,so this kind of setup is called a "ball bearing" and it ensures smooth, low friction wheel rotation.