A mountain bike or mountain bicycle (abbreviated MTB) is a bicycle created for off-road cycling.
Mountain bikes are typically ridden on single track trails, fire roads, logging roads, and other unpaved environments. These types of terrain commonly include rocks, washouts, ruts, loose sand, loose gravel, roots, and steep grades (both inclines and declines). Mountain bikes are built to handle this terrain and the obstacles that are found in it like logs, vertical drop offs, and smaller boulders.
Mountain bike construction differs from a typical bicycle in many ways. The most noticeable differences are the inclusion of suspension on the frame and fork, larger knobby tires, more durable heavy duty wheels, more powerful brakes, and lower gear ratios needed for steep grades with poor traction.
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. However, advancements in sprocket design has recently led to the "1 by" trend, simplifying the gearing to one sprocket in the front and 10 or 11 in the rear of the drive train. This allows for lighter component weights while still maintaining a large spread of gearing options. Single speed mountain bikes are also becoming more and more popular. Other developments include disc instead of rim brakes and 29" and 27.5" tires instead of the traditional 26" tires.
Bicycle suspension is the system, or systems, used to suspend the rider and bicycle in order to insulate them from the roughness of the terrain. Bicycle suspension is used primarily on mountain bikes, but is also common on hybrid bicycles.
Bicycle suspension can be implemented in a variety of ways, and any combination thereof:
Bicycles with only front suspension are referred to as hardtail and bicycles with suspension in both the front and rear are referred to asfull suspension bikes. When a bicycle has no suspension it is called rigid. Bicycles with only rear suspension are uncommon.
Even a rigid bicycle has some suspension as the tires, wheels, and even the frame absorb some shocks. Although a stiffer frame is usually preferable, no material is infinitely stiff and therefor any frame will flex a little bit. Some bicycle designers intentionally make frames in such a way that the frame itself can absorb some vibrations.
Besides providing comfort to the rider, suspension systems improve traction and safety by helping to keep one or both wheels in contact with the ground.