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 cyclocross bike frames typically have an ovalized or flattened bottom profile to provide greater comfort when riders need to shoulder and carry their bikes. 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. Additionally, mountain biking shoes provide better traction while running than typical road style shoes thanks to flexibility in the sole and pronounced tread patterns.