Bicycle wheel
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A bicycle wheel is a wheel designed for a bicycle. 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. At 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. Most 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 due to regulation, while many mountain bikes also use 26in wheels. Others use 24in or 29in wheels. Some bicycles designed for triathlon or time trial purposes use 650c wheels.
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:
- rotating weight
- 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 then 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, and by fewer numbers of spokes. 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 non-aerodynamic wheelsets due to the extra shapings of the rims and spokes. They are also more difficult to control in a "cross-wind" condition due to the larger areas. The tradeoff between rim depth, weight and spoke count is still under debate.
Almost all clincher carbon 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, which rims are entirely made from carbon fiber.
Mountain bike wheels
Tubular tires and 29in wheels are now starting to become popular in mountain bikes, especially for racing applications.