Discipline-oriented designs
There are several different styles of mountain biking, usually defined by the terrain, and therefore bikes employed. Styles of mountain bike riding and mountain bikes have evolved rapidly in recent years leading to terms such as Freeride and "Trail bike" being used to categorise mountain bikes. Definitions for the most widely used terms are listed below.


Hardtail cross country mountain bike with carbon frame and disc brakes
Cross country (XC) mountain bikes are designed primarily around the discipline of cross country racing. Cross country racing with its emphasis on climbing as well as speed and endurance demands bikes that are both lightweight and efficient. In the 1980's and early 1990's XC mountain bikes typically consisted of a lightweight steel hardtail frame with rigid forks. Throughout the 90's XC bikes evolved to incorporate lightweight aluminium frames and short travel (65 to 110mm) front suspension forks. Recently full suspension designs have become more prevalent, the use of advanced carbon fibre composites has allowed bike designers to produce full suspension designs under 10kg. Full suspension bikes such as the Specialized Epic and the Merida Ninety Two have been successfully used to win the World Cross Country Championships. The geometry of Cross Country bikes favours climbing ability and fast responses over descending and stability and as a result typical head angles are 70-71o

Although intended for off-road use, Cross Country mountain bikes with their emphasis on lightweight construction are not designed for use on the most steep or severe terrain.

"Trail" Bikes are a development of XC bikes that are generally used by recreational mountain bikers either at purpose built "Trail centres" or on natural off-road trails. They usually have around 5" (120-140mm) of travel, weigh 11 to 15 kilograms (24 to 33 lb) , and have geometries slightly slacker than XC bikes, though not as slack as AM bikes. Examples include The Giant Trance, the Trek Fuel EX series, the Specialized Stumpjumper FSR, and others. With less of an emphasis on weight, Trail Bikes are typically built to handle rougher terrain than dedicated XC bikes while having slacker head angles (69-680) which provides greater stability while descending.

Enduro/all-mountain (AM) bikes bridge the gap between cross-country and freeride bikes, typically weighing between 13 to 16 kilograms (29 to 35 lb). These bikes tend to feature greater suspension travel, frequently as much as 6 inches (150 mm) or 7" of front and rear travel, often adjustable on newer mid- and high-end bikes. They are designed to be able to climb and descend well, these bikes are intended to be ridden on all-day rides involving steep climbs and steep descents, hence the term 'all-mountain'.


A Specialized BigHit II entry level Downhill/Freeride mountain bike with 180 millimetres (7.1 in) of travel in the front fork and 190 millimetres (7.5 in) in the rear shock.
Freeride (FR) mountain bikes are similar to downhill bikes, but with less emphasis on weight and more on strength.

Freeride bikes tend to have ample suspension and typically have at least 6 inches (150 mm) of travel. The components are built from stronger, consequently heavier, materials. They can be ridden uphill, but are inefficient and their moderately slack head tube angles make them difficult to maneuver while angled up a hill or traveling at a low speed. They are effective on technical downhill trails. Frame angles are typically steeper than those found in downhill bikes. This enhances maneuverability over and around small objects. Freeride bikes typically range in weight from 14 to 20 kilograms (31 to 44 lb). The most durable freeride bikes are often too heavy and have too much suspension to be ridden uphill as comfortably as other less-sturdy models, although newer, more expensive bikes come with suspension specifically designed to make them easier to ride uphill.

Downhill (DH) bikes typically have seven or more inches (178 mm) of suspension travel. They are built with frames that are strong, yet light, which often requires the use of more expensive alloys. In the past few years, lighter downhill bikes have been getting below the 40lbs mark (18 kg). Due to their typically large or high gears, long, plush travel and slack geometry angles, Downhill bikes are ideal only for riding down dedicated downhill trails and race courses. Downhill bikes have the most sag of Mountain Bikes to get ample traction to go fast over bumpy trails. Head Angles are often as slack as 64 degrees. Several types of bicycle speed records have been registered downhill.
Due to the high-speed nature of downhill riding most bikes only have one chain ring in the front, a large bash guard and a chain guide, though many racers are now using chain guides without bash guards to reduce weight. Some of the most up to date designs feature internal gearboxes built directly into the frame construction, this modification eliminates the need for the rear derailleur mechanism, although this design has not been widely embraced yet.

Trials bikes are set up very specifically for the purpose of bicycle trials. Two varieties of trials bike exist, those with 26" wheels (referred to as 'stock') and those with 20" wheels (referred to as 'mod' - because historically they were modified BMX bikes). They typically have no suspension at all, though some still make use of some form of it. Competition rules require stock bikes to have multiple gears for competition, but most riders never use their shifters. Competition rules do not require mod bikes to have any gears. Many non-competitive riders run single-speed, choosing a fairly low-speed, high-torque gear. Most modern trials bikes have no seat at all, as the rider spends all of his time out of the saddle. These bikes are significantly lighter than almost all other mountain bikes, ranging from 7 to 11 kilograms (15 to 24 lb). This makes maneuvering the bike much easier.


Dirt jumping, urban and street mountain bikes lie somewhere in between a BMX bike and a freeride bike. They are typically very strong bikes, with 4 to 6 inches (100 to 150 mm) of front suspension, and rarely any rear suspension (3 to 4 inches, 76 to 100 mm, if any), with as many as nine gears or as few as one. Tires on these bikes are usually fast-rolling, slick or semi-slicks. Dirt Jumpers usually sport a geometry of 24-26" tires, as well as a bashring (a type of bashguard) replacing the largest ring on the crankset. Dirt jumpers usually have low seatposts and oversized handlebars. Most dirt jumpers have an extended rear brake cable installed and have no front brake, which allows the rider to spin the handle bars without tangling the brake cables.
Single-speed (SS) mountain bikes have one set gear ratio. The gear ratio chosen depends on the terrain being ridden, the strength and skill of the rider, and the size of the bike (a bike with 29" wheels often requires a different gearing than a bike with standard 26" wheels). Often single-speeds are fully rigid, steel-framed bikes. These are typically ridden by very fit individuals on mild to moderate cross country terrain.

Mountain cross or "4-cross racing" (4X) is a relatively new style of riding where four bikers race downhill on a prepared, BMX like, track, simply trying to get down first. These bikes are generally either full suspension with 3 to 4 inches (76 to 100 mm) of travel, or hardtails, and have, typically, quite strong frames. They run a chainguide on front and gears on the back. They have slack head angles, short chainstays and low bottom brackets to aid in cornering and acceleration.
Dual slalom (DS) is similar to mountain cross, but instead of four bikers competing together, there are just two. Courses usually have a lane for each rider, though some combine to a single lane in places or even for much of the course. The courses are in general more technical with smaller jumps compared to Mountain Cross courses and have gates. Dual Slalom races originally took place on grass slopes with gates and minimal jumps. The same bikes used in Mountain Cross are used.

Short cross or speed cross (SC) is the newest form of mountain biking. The idea is to ride short, narrow forest paths with rocks and roots, but not necessarily any ramps on them. The optimal length of the paths are from a few tens to hundreds of meters. The shortness is to provide extreme speed and thrill to get through the hindrances as fast as possible without crashing. The altitude of each path does not have to vary much. The ultimate direction of each path from vertical aspect can be either up or down. The transitions between these essential parts are to be taken lightly and stopping at the beginning of every path is to provide maximum amount of thrilling action gained through the speed. The best fitting bicycle for SC is probably lightweight, but long travel full suspension bike.

Indycross (IX) is essentially a Mountain Cross event featuring a wide variety of features run by one competitor per time.[2]
North Shore bikes are much like freeride bikes in their geometry and downhill bikes in their component makeup. Because north shore stunts have evolved to not only include simple and complex bridges but also large drops and high-speed descents through a series of stunts north shore bikes commonly have as much travel as downhill and freeride bikes, however with much more nimble and maneuverable frame designs, and often lighter weight.
Circle dirt track racing In this class of racing any kind of bikes are used, most commonly a hard tail mountain bike with front suspension. Many different modifications are made to track racing bikes, such as reducing bike weight, increasing brake power, trying different cambers (so that when the bike leans the tire is more level with the track thus creating more grip), and trying different gear ratios.

Modern designs
In the 2000s, mountain bikes often use frames designed for off-road use, which are strengthened to withstand jumps and impacts and which use a geometry that allows for much more spirited riding over obstacles like logs, rocks, and ramps. In the 2000s, mountain bikes often have either 21, 24, or 27 speeds, with 3 gears in the front and 7, 8, or 9 gears at the rear wheel. Thirty-speed mountain bikes have previously been unworkable, as the mud-shedding capabilities of a ten-speed cassette, and the intricacies of a ten-speed rear derailleur have never been suitable. However, many pro-level mountain bikers have taken to using a narrower 10-speed road chain with a 9-speed setup in an effort to reduce the weight of their bike. In early 2009, component group SRAM announced their release of their XX groupset, which uses a two-speed front derailleur, and a ten-speed rear derailleur and cassette, similar to that of a road bike. Mud-shedding capabilities of their ten-speed XX cassette are made suitable for MTB use by extensive CNC machining of the cassette. Due to the time and cost involved in such a product, they are only aimed at top-end XC-racers.