A mountain bike or mountain bicycle (abbreviated MTB or ATB (all-terrain bicycle)) is a bicycle created for off-road cycling. This activity includes traversing of rocks and washouts, and steep declines, on dirt trails, logging roads, and other unpaved environments — activities usually called mountain biking. These bicycles need to be able to withstand the stresses of off-road use with obstacles such as logs and rocks. Most mountain bikes use wheels with rims which are 559mm in ISO sizing, colloquially referred to as "26-inch", although the term is inaccurate as it covers too many rim and tire sizes to be meaningful. Wheels used on mountain bikes usually use wide, knobby tires for good traction on uneven terrain and shock absorption. Since 2000, 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 development of the sport 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 place different demands on the bike requiring different designs for optimal performance. MTB development has included an increase in gearing, up to 30 speeds, to facilitate both climbing and rapid descents. Other developments include disc instead of cantilever or V-brakes.