A mountain bike (MTB) or mountain bicycle is a bicycle designed for off-road cycling. Mountain bikes share some similarities with other bicycles, but incorporate features designed to enhance durability and performance in rough terrain. These typically include a suspension fork, large knobby tires, more durable wheels, more powerful brakes, straight handlebars, lower gear-ratios for climbing steep grades and sometimes rear suspension to really smooth out the trail.Mountain bikes are generally specialized for use on mountain trails, single track, fire roads, and other unpaved surfaces, although perhaps the majority based on "mountain-bike" frames for sale. Mountain biking terrain commonly has rocks, roots, loose dirt, and steep grades. Many trails have additional TTFs (Technical Trail Features) such as log piles, log rides, rock gardens, skinnies, gap jumps, and wall-rides. Mountain bikes are built to handle these types of terrain and features. The heavy-duty construction combined with stronger rims and wider tires has also made this style of bicycle popular with urban riders and couriers who must navigate through potholes and over curbs.Since the development of the sport of mountain biking in the 1970s, many new subtypes of mountain biking have developed, such as cross-country (XC), enduro/all mountain, freeride, downhill, and a variety of track and slalom types. Each of these place different demands on the bike, requiring different designs for optimal performance. MTB development has led to an increase in suspension travel, now often up to 8 inches (200 mm), and gearing up to 27 speeds, to facilitate both climbing and rapid descents. Advances in gearing have also led to a "1x" (pronounced "one-by") trend, simplifying the gearing to one chainring in the front and a cassette at the rear, typically with 9 to 12 sprockets.
The expressions "all terrain bicycle", "all terrain bike", and the acronym "ATB" are used as synonyms for "mountain bike", but some authors consider them passé.