Wire Wheels

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"The fundamental fact is that the hub, and thus the vehicle borne by the wheels, in fact hangs on the spokes, which thus have to be tensioned not to break. The spokes can only be put under a pulling strain, otherwise they break."

The explanation above illustrates the common misconception that the hub of a wire-spoked wheel "hangs" from the upper spokes. A hub-spoke-rim wheel properly tensioned applies nearly equal force along all spokes in each direction, causing the wheel to act as one unit: force is transmitted between spokes at the rim, at the hub, and at the crossings between spokes. Despite the common misconception that a bicycle wheel "hangs" from its upper spokes, the upper spokes show no significant change in tension. A load on the hub causes the wheel rim to flatten only very slightly against the ground as the lowermost pre-tensioned spoke shortens and compresses, losing some of its pre-tension.

For explanations, computer models, and tests confirming this odd behavior, see this analysis which shows the lower spokes of pre-tensioned bicycle wheels compressing (losing their pre-tension) as they roll under a loaded hub.

Before 1960, sports/racing cars often had laced wire wheels, often equipped with "knock-off" hubs, which could be unscrewed by hitting the end of the hub with a mallet. In the 60's, cast-alloy , or"Mag" wheels, became more common and now predominate. These may have knock-off hubs, but only on racing cars. (Racing teams will gladly spend thousands of dollars to save a few seconds in a race: a few seconds, times two stops, could easily win a race worth millions of dollars in various ways.

Bicycle manufacturers make millions of wheels per year, nearly all of them using the common "three-cross" spoking pattern, in which each spoke crosses three others. Specialized wheelbuilders, found in racing teams and in very good bicycle shops, can build wheels to other patterns (two-cross, one-cross, no-cross or radial). All these patterns were used in the 1970's, but there has been little demand for these patterns since the publication of Jobst Brandt's seminal book, The bicycle Wheel, in 1980. Brandt was a hard-core cyclist, who built and rode racing bikes, touring bikes, and some of the first mountain bikes. as well as a mechanical engineer for Hewlett-Packard. He used an HP minicomputer to do stress analyses of the usual and unusual spoking patterns and concluded that the three-cooss pattern had more strength and stability than the other patterns, even in the more exotic forms of bicycle racing.

In the 1980's, cast wheels with 5 or 6 rigid spokes began to appear in the Olympic Games and professional racing: these have advantages in specialized applications, such as time trials, but wire-spoked wheels are used for most purposes.

Source: Wikipedia