bottom brackets, in fact many have a lower bottom bracket than road racing bicycles; this is favorable since the lower seat height makes for easier remounting, and a lower center of gravity increases stability. Many cyclo-cross bicycles are now set up with a single chainring and chain "drop" guards. A single chainring setup simplifies mechanics and reduces the chance of the chain derailing on a bumpy course. People who do run a double chain-ring set up on their bicycles generally use a 36–46 gearing. Many professional-level cyclo-cross bikes are set up with deep-section carbon tubular wheels, not for the purpose of aerodynamics, but to keep the wheel from being entrapped in deep sand or mud sections. Tubular tires are used to avoid pinch flats, decrease rolling resistance and increase grip with lower tire pressures. In addition, single speed cyclo-cross bikes are becoming increasingly popular for a variety of reasons, including lower initial cost of setup, ease of use and maintenance, and decreased likelihood of mechanical failure on the course. Clothing Clothing is similar to that of road racing. However, since cyclo-cross is a cold-weather sport there is an emphasis toward warmer clothing such as long sleeves, tights, knickers and arm and leg warmers. While many racers will use standard two-piece road kits, there is a very strong preference to wear one piece skinsuits to maximize freedom of movement. The other advantage of skinsuits is that they are tighter, preventing the jersey from getting caught on stray tree branches during some singletrack sections of the race course. The one piece construction of the skinsuit also prevents it from exposing the torso while the rider shoulders the bike. Mountain bike shoes are adopted, as they allow the competitors to run, unlike their road racing counterparts, and due to their degree of traction (compared to smooth bottoms found on road racing shoes). Toe spikes are used to aid in running up steep muddy slopes and in the adverse underfoot conditions. Full-finger gloves are optional but generally recommended for hand protection and for grip in muddy/wet situations. Experienced riders racing in dry conditions may eschew gloves, presumably for better tractional feedback though the handlebar, and more natural bike portage. Courses Races usually consist of many laps over a short course, ending when a time limit is reached, rather than after a specific number of laps or certain distance; the typical length for senior events