A Wheel Is what allows a Bicycle to roll. A pair is called a wheelset, especially in the context of performance-oriented wheels. A wheel consists of a rim connected to the hub by spokes. In the case of traditional wire spoke wheel, the end of each wheel spoke is a nut, called a nipple. Bicycle wheels connect to the frame and fork via dropouts.
The hub uses bearings to reduce friction with the axle. Except in fixed gear bicycles, the rear hub is connected to the freewheel and the rear sprockets. Some bicycle wheels are attached using a quick release for ease of removal from the bicycle.
Bicycle wheels come in many different sizes. Most road and racing bicycles use 700C wheels (approximately 700 mm diameter with a tire mounted) due to regulation, while many mountain bikes use 26 inch wheels. Some mountain bikes use 24 inch or 29 inch wheels (29 inch wheels are in fact identical in diameter to 700C road wheels). Some bicycles designed for triathlon or time trial purposes use 650c wheels, which are roughly 26 inch.
Bicycle wheels can also be categorized according to the way in which the tire attaches to the wheel. A tubular wheelset has a round profile on its rims and uses adhesive to attach the tubular tire onto the wheel. A clincher wheelset uses a metal hook around the rims that clinches the tire with the tube inside of the tire. While tubular wheels are lighter, and can be made to operate in a wider range of tire pressures, clincher wheels are easier to service, for example in the case of a flat tire. However, tubulars are popular for bicycle road racing applications and it is argued that it is safer than clinchers in the case of flatting while the bicycle is traveling at high speeds.
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
- hub/bearing smoothness
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 triangualr or pyramidal cross-section and by fewer numbers of spokes, or blade like spokes 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 importatnly, the rims must be heavier when there are fewer spokes, as the unsupported span between spokes is greater. While the increase in weight is smewhat 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.
Mountain bike wheels
26inch tubular tires are the most popular. One maunfacturer has introduced 27inch. Tubeless tires (UST) are also becoming popular as they can run very low pressures.
Bicycle Wheel was also a readymade sculpture by Marcel Duchamp consisting of a bicycle wheel mounted upside-down on a wooden stool. The original from 1913 was lost, and Duchamp recreated the sculpture in 1951.