A mountain bike or mountain bicycle (abbreviated MTB or ATB (all terrain bicycle)) is a bicycle designed for off-road cycling, including jumps, and traversing of rocks and washouts, and steep declines, either on dirt trails, logging roads, or other unpaved environments. Bicycles used for mountain biking are different from road bikes and racing bikes, because mountain bikes need to be able to withstand the impacts of off-road use and the frame geometry needs to allows for the surmounting of obstacles such as logs and rocks. Most mountain bikes use 26 inch (559 mm) bicycle wheels with wide, knobby tires for extra traction and shock absorption. Since the 2000s, front wheel suspension has become the norm and full front and rear suspension has become increasingly common. Some mountain bikes are also fitted with bar ends on the handlebars to give extra leverage for hill-climbing.
Since the sport’s development in the 1970s, many new subtypes of mountain biking have developed, such as cross-country (XC) biking, all-day endurance biking, Freeride-biking, downhill mountain biking, and a variety of track and slalom competitions. Each of these subtypes places different demands on the bike and the cyclist, and so high-end mountain bike companies make different designs to suit these different sports. MTBs produced in the 2000s often have a wide range of gears, giving 21 to 27 speeds, to facilitate steep hill climbing and rapid descents. Most higher-end mountain bikes produced since the mid-2000s use disc brakes instead of cantilever or V-brakes, because disc brakes offer better stopping power under extreme conditions.
The risk of injury is inherent in the sport of mountain biking, especially in the more extreme disciplines such as downhill biking, which can include drops and jumps over rocky terrain. To reduce the risk of injuries such as concussions, abrasions, and cuts, mountain bikers often wear protective equipment such as helmets, gloves, and padding. The amount of protective gear depends on the type of mountain biking and the difficulty of the course. While a cross-country rider on a flat dirt trail might only wear a road biking helmet and gloves, a downhill biker or dirt jumper will typically wear a full-face BMX-style helmet and plastic “armor” pads on the knees, elbows, chest, and back.