Wheelbuilding
From Wikipedia, the free encyclopedia
Wheelbuilding is the art and science of assembling a wheel (generally a bicycle wheel, although such wheels are also used on wheelchairs, motorcycles, and some cars, and known as wire wheels) from its component rim, spokes, nipples and hub.
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[edit] Goals
A good wheelwright will ensure that the wheel is "true" in three ways: "runout" (sideways wobble), "dish" (accurate centering of the rim between the hub locknuts) and "hop" (roundness). Ideally spokes have similar tension (although the two sides will be different if a wheel is dished) with tension high enough to give a rigid wheel and retain some tension under all loads but not so high as to lead to failure of spokes or the rim. Spokes should have no residual twist from tightening the nipples. The spokes may be "stress relieved", i.e. subjected to a greater tension during building than they are ever likely to encounter in use - usually by squeezing pairs of spokes together very hard. This is said to yield the spokes (and/or the hub) into a permanent shape where they bend around the hub flanges and each other.
[edit] Lacing
Spoking patterns may be radial or semi-tangential. Only the latter is suitable for a wheel that has to transmit torque from the hub to the rim, as with rear wheels or hub brakes. Rear wheels may also incorporate radial spoking on the non-drive side and semi-tangential spoking on the drive side. The most common spoking pattern is "three-cross" where each spoke crosses three others on the same flange of the hub before meeting the rim. The last cross is normally "interlaced" by wrapping the spoke around the one from the other side of the flange. Radial-spoked wheels, where the spokes do not cross each other, saves roughly the weight of two spokes (because the spokes are shorter) compared to a three-cross wheel but run the risk of tearing hub flanges apart, unless the hub is specifically designed for this pattern.
[edit] Bicycle wheels
Most conventional bicycle wheels now use 32 or 36 spokes front and rear, although the asymmetry of the rear wheel (to allow for the cluster of sprockets), and the additional weight it carries, means it benefits from having more spokes than the front. Commonly used models vary from 18 spokes (for racing bikes and cross-country bikes) to 48 spokes on heavily abused BMX bikes. Common rim diameters are 700c (sometimes 650c) for road/racing bikes, 27" or even 28" on older road bikes, 26" for most mountain bikes and 20" on BMXs. More recently a 24" wheel has found favour as a MTB/BMX cross for dirt jumping and street riding.
Wheels can be built by machine instead of by hand. However, machine-built wheels are rarely as satisfactory as handbuilt wheels, partly because it is uneconomic to allow the machine to spend long enough on each wheel for a perfect result but also because most machines leave spokes with some residual twist. Machine-built wheels can be identified by their lacing pattern (if it is not radial), as the spokes are laced the same on each side, rather than mirrored as on hand-built wheels. More modern "factory built" wheels such as Mavic's Ksyrium series are of quite different construction from that of a conventional wheel, trading a deeper and stronger rim for fewer spokes. They are popular, being aerodynamic and quite light (in the more expensive models) but not as durable, readily repairable or maintainable as a conventional wheel.
The canonical text on building conventional bicycle wheels is "The Bicycle Wheel" by Jobst Brandt, published by Avocet.
[edit] Motorcycle wheels
Motorcycle wheels or wire wheels typically use 36 or 40 spokes, of much heavier gauge than those on a bicycle. They are never "interlaced" in the manner described above, nor are "radial" builds recommended (except on wheels without brakes, which are not themselves a good idea). Adequate spoke tension is very important with motorcycle wheels, because of the greater torque applied to the wheel by an engine or disc brake. Loose spokes on a wheel fatigue rapidly and break, usually at the bend where they attach to the hub. When this happens, the wheel must be rebuilt using all new spokes, because even unbroken spokes in such a wheel are fatigued, and will usually break when tightened during the truing operation.
[edit] Spoke length
Selecting spokes of the correct length requires a calculation based on rim diameter, hub diameter, hub width, lacing pattern, number of spokes, etc. See [1] and [2].
[edit] References
- ^ Sheldon Brown. Wheelbuilding. self-published. Retrieved on July 28, 2006.
- ^ Robert Torre. Spoke Length Formula with Wheel Lacing and Building Information. self-published. Retrieved on July 28, 2006.
