Bicycle wheel: Encyclopedia II - Bicycle wheel - Road/racing bicycle wheels

Bicycle wheel - Road/racing bicycle wheels

For road bicycle racing performance there are several factors which are generally considered the most important:

• weight (for this article equivalent to mass)
• rotational inertia
• aerodynamics
• hub/bearing smoothness
• stiffness

Semi-aerodynamic and aerodynamic wheelsets are now commonplace for road bicycles. Aluminum rims are still the most prevalent, but carbon fiber is also becoming popular. Carbon fiber is also finding use in hub shells to reduce weight, although some argue that its proximity to the center of rotation means that it is less useful than reducing rim weight.

Semi-aerodynamic and aerodynamic wheelsets are characterized by greater rim depth, which is the distance between the outermost and the innermost surfaces of the rim, a triangular or pyramidal cross-section and by fewer numbers of spokes, or no spokes at all--with blades molded of composite material supporting the rim. The spokes are also often flattened in the rotational direction to reduce wind drag. These are called bladed spokes. However, semi-aerodynamic and aerodynamic wheelsets tend to be heavier than more traditional spoked wheelsets due to the extra shapings of the rims and spokes. More importantly, the rims must be heavier when there are fewer spokes, as the unsupported span between spokes is greater. While the increase in weight is somewhat important, it is the increased rotating inertia which is the greatest problem for "aero" wheels, as the rim, being farther from the axis of rotation, has the largest effect on rotational inertia, or in other words, moving 20 grams from the spokes (fewer spokes) to the rim will keep the weight the same, but will increase the rotational inertia. They are also more difficult to control in a "cross-wind" condition due to the larger projected lateral area. The tradeoff between rim depth, weight and spoke count is still under debate. However a number of wheel manufacturers are now producing wheels with roughly half the spokes of a top of the line traditional wheel from the 1980's, with approximately the same rotational inertia and less total weight. These improvements have been made possible primarily through improved aluminum alloys for the rims.

Almost all clincher carbon fiber wheelsets, such as those made by Zipp and Mavic, still use aluminum parts at the clinching part of the rim. One exception to this is the Campagnolo Hyperon Ultra clincher wheelset, in which the rims are entirely made from carbon fiber.

Adapted from the Wikipedia article "Road/racing bicycle wheels", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki