the rear stays. Compact geometry frames with sloping top tubes are less common than on road bicycles due to the need to carry the bicycle easily on the shoulder. Top tube (rather than bottom bracket) routed derailleur cables help combat the build-up of mud. 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 common as clipless pedals have become the norm for cyclo-cross. Typically, the frame geometry is somewhat more relaxed than that of a road bike, not as upright in the seat tube, which allows for more stability in soft ground. Also, the wheelbase can be a bit longer, which provides a more planted feeling when using aft body weighting over rough terrain, and can help keep the rider's feet from contacting the front wheel during a tight turn. Components 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. Gearing is typically lower, with most common setups using a 46-36 (110mm BCD) or 48-38 (130mm BCD) chainring combination with a 12-25 to 12-30 cassette. Some riders opt to use a single chainring in the front (typically a 40-42 tooth chainring) while retaining multiple sprockets 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, a single chainring allows for a tighter chainline, thus reducing the chance of throwing a chain on a bumpy course, and further, racing is psychologically simpler. Wheels are of the normal road racing type fitted with knobby tires (a variety of tread designs in both tubular and clincher types are available), although deeper rim profiles may be preferred for their advantages in thick mud. There are slight geometry differences between road and cyclocross bicycles; cyclo-cross bikes tend to have slightly higher handlebars for a more upright position as aerodynamics have little importance in a cross race. A second set of brake levers on the tops, called "top mount" or "interrupter" brake levers, are favored by some competitors. These are also commonly called "cross levers" due to their popularity in the sport. The top tubes of