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A cyclo-cross bicycle is a bicycle specifically designed for the rigors of a cyclo-cross race. Cyclo-cross bicycles roughly resemble the racing bicycles used in road racing. The major differences between the two are the geometry and the wider clearances that cyclo-cross bikes have for their larger tires and mud and other debris that is picked up by them.

Design

Frame materials are selected with an aim to produce a lightweight, stiff frame. Lightness is prized for ease of carrying while running, aluminum frames were popular long before they became commonplace on the road. Today the most popular material is aluminum with carbon fibre being popular at a professional level and steel and titanium being favorites amongst those searching for a smoother ride.

Cyclo-cross frames require clearance for slightly fatter (generally 30-34mm) tires and the debris that is picked up by them. They are typically very simple, often eschewing bridges between the rear stays. Other features that combat build up of mud are top tube (rather than bottom bracket) routed derailleur cables. Some specialist cyclo-cross bikes also have a higher bottom bracket to aid clearance over rough ground.

Cantilever brake bosses are mounted with the traditional design of brake preferred to V-brakes, again to prevent clogging with mud. Wheels are of the normal road racing type fitted with knobbie tires (a variety of tread designs in both tubular and clincher types are available), and gearing is a little lower. There are also slight geometry differences between the two; cyclo-cross bikes tend to have slightly higher handlebars for a more upright position. A second set of brake levers on the tops, called top mount brake levers, are favored by some competitors. In general, with a change of tires and gearing a cyclo-cross bike can double as a perfectly adequate road racing machine for riders in the lower ranks. Choices of equipment tend more towards the idiosyncratic than in road racing; for example singlespeed bikes also have some popularity due to the advantage of mechanical simplicity in the often very muddy conditions and the fringe nature of the sport. Some riders opt to use a single chainring in the front while retaining gears in the rear cassette. This has some of the advantages of the single-speed: the weight of the front derailleur and the front shift lever are lost, fewer mechanical problems arise (there is no danger of the chain falling off), and racing is psychologically simpler.

In some countries riders are also permitted to race in cyclo-cross events using mountain bikes (generally without bar ends), at least in low-level competition, but this is not currently allowed in events on the international calendar.

Tires

Tire choice is of great importance in cyclo-cross racing. First of all the use of tubular tires is still very popular, even more so than in road racing. This is, in part, due to their ability to be run at low pressure (35-40psi/2.5-2.75bar) without increasing the risk of pinch flats. Low pressure is desirable due to increased grip with the ground, however this increases the risk of the rim 'bottoming out" on the ground. With clincher tires, this is a problem since the tube becomes pinched by the rim and can be cut open causing a catastrophic flat. A tubular setup also offers a weight saving over its clincher counterpart and has the ability to be ridden on if a flat does occur so a racer can reach the pits for a replacement. Clinchers do have their advantages however. Changing tires is much quicker since it doesn't invlove a lengthy gueing and curing process so a rider can have a large selection of tires at their disposal. Clinchers also generally have more cutting edge tread patterns than the more traditional tubulars.

Because cyclo-cross season spans autumn/fall and winter, conditions can vary quite drastically. Offen racers have at least dry and wet weather tires to choose between. Dry tires tend to have much smaller, closely spaced tread such as the diamond pattern for low rolling resistance. Wet weather tires have larger and more widely spaced knobs to aid in grip and mud shedding. Tires don't usually vary in width a great deal due to the theory that a narrow tire has the least rolling resistance (for dry courses) and that it will also cut through mud to the harder ground underneath (for wet/muddy courses).