as required for tubular tires. Not all clincher rim designs allow for tubeless tires as an air tight contact surface is required to prevent the unintended loss of tire pressure. 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 in width. Tire width may not exceed and tires may not feature any kind of studs or spikes. Wheels shall have at least 12 spokes. The weight of the bicycle cannot be less than 6.8 kilograms (15 lb to two significant figures). As of 2010, disc brakes have recently been allowed for UCI races. Non-racing use Some cyclocross bicycles available in the consumer market are supplied with disc brakes as a stock item. Some models include braze-ons to enable the use of cantilever style brakes instead. The growing popularity of disc brakes on cyclocross bicycles has allowed for improved and lighter rim designs due to a lack of brake track on the side of the rim. Mountain bikes in Cyclocross Racing 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 effective. See also Cyclo-cross List of bicycle types Cycle sport Bicycle Outline of cycling All-rounder (cycling) References External links Cycle types Cyclo-cross ja:シクロクロス