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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.

Frame design

Frame materials are selected with an aim to produce a lightweight, stiff frame. Lightness is prized for ease of carrying while running. A cyclo-cross racer may have lifted or carried his bike as many as 30 times in one 60 minute race, inceasing the need for a lightweight bicycle. 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 and a longer lasting frame.

Cyclo-cross frames require clearance for slightly fatter (generally 30-34 mm) tires and the debris and mud 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; extra clearance could prevent toe clips from dragging while re-mounting after an obstacle. This is less and less common as clipless pedals have become the norm for cyclo-cross.

Components

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 as aerodynamics has little importance in a cross race. 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. However, most cyclo-cross racers prefer clipless mountain bike pedals for their easy dual-sided entry and mud-shedding abilities. Also, the mountain bike shoes used with them provide better traction whilst running than a typical road style shoe thanks to grip and flexibility in the sole. Gearing is typically lower, with most common setups using a 46-38 chainring combination with a 12-27 cassette cluster.

Choices of equipment tend more towards the idiosyncratic than in road racing; for example single-speed bicycles 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 (typically a 40-42 tooth chainring) 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 less danger of the chain falling off), and racing is psychologically simpler.

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 (22-40psi/1.5-2.75bar) without increasing the risk of pinch flats. Low pressure is desirable due to increased amount of contact with the ground giving the tire more "grip". 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. On the other hand, with a tubular set up, this is not a problem as they cannot pinchflat thus the only concern is damage to the rim. 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 glueing and curing process so a rider can have a large selection of tires at their disposal. Until recently, clinchers also generally have more cutting edge tread patterns than the more traditional tubulars. Some enthusiasts even went as far as to send Michelin Mud tires (a popular clincher tire) to Dugast (a manufacturer of high end tubular tires) to have a modern tread pattern incorporated into a traditional tubular. However, since 2005 several tubular manufacturers have designed more modern style tread patterns, namely Dugast with its Rhino and Tufo with its Flexus. Lastly, clinchers cost less than a tubular. For the serious age group cyclo-cross racer, tubulars are the more popular option.

Because cyclo-cross season spans autumn/fall and winter, conditions can vary quite drastically. Often 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). Although widths below 30c were popular in the past, current tires tend to be available from 30-35c with 32 and 34 being the most common.

Equipment choice

Since ground conditions can vary so much, equipment choices are extremely important. Add to this the fact that the races are relatively short and that equipment changes are allowed during races and you can imagine that equipment selection can get fanatical. Since tubulars are so common and tires cannot easily be removed from the rim, collections of wheels, not tires, are required for the varying conditions. It is common for racers even at an amateur level to have a pair of race bikes (one to ride and one in the pits) and several wheels to choose from. At the professional level it is essential to have several bikes and wheel collections.

Rules

The following are rules that have been put in place by the UCI that are either specific to or have particular effect on cyclo-cross bicycles. Bear in mind that these rules are not exhaustive, are only for UCI sanctioned events and may not be enforced at all cyclo-cross events.

• Handlebars must not measure more than 50 cm (19.5 inches) in width.
• Tire width may not exceed 35 mm and tires may not feature any kind of studs or spikes.
• Wheels shall have at least 12 spokes.
• The bicycle must not weigh less that 6.8 kg (15 lb).
• Disc brakes are forbidden.

In recent years, some cyclo-cross bicycles available in the consumer market have come stock with disk brakes which violate UCI regulations. In general these bicycles also have the ability to use cantilever style brakes instead. In the United States, disk brakes are now allowed for non-UCI events.

Mountain bikes

In some countries (including the United States, so long as it is not a UCI event) 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. It has been known for local races to be won on mountain bikes, particularly if the course is technical with little road or fast sections. However, for a traditional cyclo-cross course a cyclo-cross bicycle is the most suitable tool for the job.

References

UCI (05.12.05). "Cycling Regulations : Part I, General Organisation Of Cycling As A Sport". Union Cycliste Internationale. Retrieved April 21, 2006

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