Friday, July 27, 2012

Friday Writings for Randos - Tension and Compression

{Friday Writings for Randos - A weekly post that features pieces from other writers that touch some facet of the Randonneuring experience, even if that was not the author's intent. It's stuff that's best read out loud - slowly.} This week it's:...
An excerpt from:

The Bicycle Wheel

3rd edition

by Jobst Brandt

Bicycle wheels don't work the way people think they do.Wire wheels are pre-stressed structures, with built in stresses that are reduced when they are subjected to loads.

Tension and compression

In the bicycle wheel, wires replace the rigid spokes of wooden wheels. Although wires are strong, they cannot directly replace wooden spokes that carry loads in compression. 

In order to work, wires must be tensioned to prevent their bucking under load. With tension, wires can support compression loads up to the point where they become slack. The same loads that increase compression in wooden spokes reduce tension in wires. As in algebra, where negative and positive numbers are combined to give algebraic sums, in spokes tension and compression are the negative and positive forces whose sums depend on built in tension and the carried load.

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