Sam Chappell on tough bikes

HAVE you ever thought about your bike's wheels and what they put up with? Clothed in a tyre and gripped in a bike frame, all cyclists expect their wheels to carry them along their chosen path. They receive very few words of encouragement but they always come off the worst when met with a pothole, kerbstone or drunkenly placed foot.

The Broken Spoke Bike Co-op, Oxford's community workshop, works with all bike components including the long-suffering wheels, four days per week, servicing, straightening, replacing and consoling, and also running a wheel-building course every couple of months, introducing people to the complexities of their hoops.

The ingredients of a bicycle wheel: 1x rim: a narrow metal trough, drilled with typically 32 holes, bent into a hoop 1x hub: a sleeve of metal with 16 holes cut into a flange at either end and a spinning metal rod held within 32x spokes: lengths of wire threaded at one end, with a 90 degree corner and a head like a nail at the other 32x spoke nipples: small threaded beads that screw onto the threaded end of the spokes The lacing together and tuning of these components by hand is both a complex activity and a skill that professional bicycle mechanics pride themselves on. That said, the majority of wheels doing the rounds in Oxford are machine built and machine tuned, cheaper than the hand-built wheels but sadly inferior.

Machine built bicycle wheels’ spokes are often twisted and weakened by the tightening process, the rim is thin with minimal reinforcement and the hub is made of flexible steel rather than stiffer aluminium. When ridden repeatedly over the patchy road outside the Old Music Hall (on Cowley Road), the crumbling manhole covers at the bottom of the High Street (travelling westbound), or the disfigured surface at the top of Woodstock Road, that wheel will become warped, rattly and reluctant.

Have you ever thought about what happens when your bike drops into one of these treacherous chasms? The impact from the pothole travels from road to rider through the tyre and rim at the bottom of the wheel and then into the spokes. The jolt will then be passed into the hub and up through the fork to the handlebars. Most of the shock is absorbed by the spokes. On impact, the tension in the spokes at the bottom of the wheel is reduced considerably. Then, as the wheel turns, the spokes spring back into tension. The better built the wheel is, the more times these spokes can relax and spring back without impairing the wheel's roundness.

This flexibility in tension is a big part of why cycling is so popular. It was only when the rigid wooden wheels of the bone-shaker bicycles of old were replaced with wire wheels, that cycling started becoming a more mainstream, everyday activity.

So next time you cleanly bounce over that not-very-lowered-curb on Turl Street, spare a thought for your wheels. And when your spokes ping or your rim buckles, the Broken Spoke Bike Co-op can help!

Go to http://bsbcoop.org/what-we-do/mechanics-courses/postgraduate-courses/#WheelBuilding