A hardtail mountain bike.
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 typically used for mountain biking need to be able to withstand off-road use and the surmounting of obstacles such as logs and rocks. Most mountain bikes use 26 inch (590 mm in ISO sizing) bicycle wheels with wide, knobby tires for extra traction and shock absorption. In the current century, 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 to suit them. MTB development has included an increase in gearing, up to 27 speeds, to facilitate climbing and rapid descents. Other developments have included disc instead of cantilever or V-brakes.
[edit] History
A cross country mountain bike race.
The history of the mountain bike includes contributions from cyclo-cross in Europe, the Roughstuff Fellowship in the UK. The name mountain bike first appeared in print in 1966 as "mountain bicycle". The mountain bike was a modified heavy cruiser bicycles used for freewheeling down mountain trails. The sport became popular in the 1970's in Marin county. The 2007 documentary film, *Klunkerz: A Film About Mountain Bikes, looks at this period of off-road cycling in detail. However, it was not until the late 1970s and early 1980s that road bicycle companies started to manufacture mountain bicycles using high-tech lightweight materials. Throughout the 1990s and 2000s, mountain biking moved from a little-known sport to a mainstream activity.
[edit] Designs
Mountain bikes can be classified into four categories based on suspension:
- Fully rigid: A frame with a rigid fork and fixed rear, no suspension.
- Hardtail: A frame with a front suspension fork and no rear suspension.
- Soft tail: A frame with small amount of rear suspension, activated by flex of the frame instead of pivots.
- Dual or full suspension: A front suspension fork and rear suspension with a rear shock and linkage that allow the rear wheel to move on pivots.
[edit] Discipline-oriented designs
There are several different styles of mountain biking, usually defined by the terrain, and therefore bikes employed. All of the bikes in this category fall into one of the above four categories and bikes of each of the above style can be found almost any of the following categories.
Cross country (XC) mountain bikes usually have only a small amount of front and/or rear suspension (usually 65-110 mm) and are relatively light, which is achieved via the use of lightweight materials and construction in both frame and components. As a consequence, XC bikes are often less durable than other types of mountain bikes when used outside of their intended purpose. On full-suspension XC bikes, both front and rear, is typically provided by pneumatic (air) shocks or smaller coil/oil shocks and forks. Some full-suspension XC bikes may weigh as little as 21 pounds (9.5 kg), although they still are not as popular as hardtail XC bikes. Many XC bikes have only front suspension, and are normally referred to as hardtails. This is the most used type in XC competitions. A few XC bike models have no suspension and use a rigid front fork, saving weight but relying more on rider skill to negotiate rough terrain. XC or general riding is the most popular form of mountain biking, focused on climbing and quick turning abilities rather than on the aggressive descent capabilities of freeride or single-purpose downhill mountain bikes. XC bikes reflect this in their lighter weights and steeper geometries. However, due to their lighter frames and suspension, most XC bikes are poor choices for heavy-impact activities such as jumps and high-speed traverse of large obstacles such as rocks and deep washouts.
"Trail" Bikes are a cross between XC bikes and AM bikes. They usually have around 5" (120-140mm) of travel, weigh 25-32 lbs, 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 Gary Fisher HiFi, and others.
Enduro/all-mountain (AM) bikes bridge the gap between cross-country and freeride bikes, typically weighing between 30 and 35 pounds (14 to 16 kg). 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 ascend mild-to-moderate inclines and descend steep declines, though their relatively heavy overall weight limits their utility in all-day rides involving steep climbs.
A Specialized BigHit II entry level
Downhill/
Freeride mountain bike with 180 millimetres (7.1 in) of travel in the front forks 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 30 to 45 pounds (14 to 20 kg). Freeride trails are built using natural terrain features to create stunts such as dropoffs, also known as "hucks", narrow ladder bridges called "North Shores", as well as large ramps built to launch the rider into the air. 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. It is, however, quite common for freeriders to frequent lift accessed riding terrain, offered at ski resorts during the off season, or simply walk their bikes uphill, rather than riding them.
Downhill (DH) races are time trials events where riders ride courses separately, racing the clock. They can have technical sections like rock gardens as well as jumps and drops. Downhill 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.
At ski resorts that have mountain biking in the off-season, riders can get lots of runs in because of chair lifts. Shuttling up to the top of trails is very common as most trails away from ski resorts do not have lift access. When there is no car or truck access to shuttle, riders usually push and/or ride bikes to the top of the trails. 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 drop weight.
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 15 to 25 pounds (6.8 to 11 kg). 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.[1]
North Shore mountain biking originated in the steep, wet, rocky, rooty terrain of Vancouver, Canada's north shore, thus it was coined "north shore" riding. Because of the almost, if not completely impassable terrain, riders began building bridges over muddy areas, rocks, stumps and deadfall. These bridges evolved into complex, often extremely challenging, man-made stunts. Because stunts are often narrow and may require the rider to move very slowly regardless of width, north shore riding requires immense balance and bike handling skills. 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.
[edit] Modern designs
Until the late 1990s, mountain bicycles often had road bicycle style frames and geometry. In the 2000s, mountain bikes often use frames designed for off-road use, which 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.
[edit] Geometry
The critical angles in bicycle geometry are the head angle (the angle of the head tube), and the seat tube angle (the angle of the seat tube). These angles are measured from the horizontal, and drastically affect the rider position and performance characteristics of the bicycle. In general, steeper angles (closer to 90 degrees from the horizontal) are more efficient for pedaling up hills and make for sharper handling. Slacker angles (leaning farther from the vertical) are preferred for high speeds and downhill stability.
[edit] Suspension
A full suspension mountain bike
In the past mountain bikes had a rigid frame and fork. In the early 1990s, the first mountain bikes with suspension forks were introduced. This made riding on rough terrain easier and less physically stressful. The first suspension forks had about 1½ to 2 inches (38 to 50 mm) of suspension travel. Forks are now available with 8 inches (200 mm) of travel or more (see above under "Design.") Bikes with front suspension and rigid, non-suspended rear wheels, or hardtails became popular nearly overnight. While the hardtail design has the benefits of lower cost, less maintenance, and better pedaling efficiency, it is slowly losing popularity due to improvements in full suspension designs.
Many new mountain bikes integrate a "full suspension" design known as Dual Suspension or "full-susser", meaning that both the front and rear tire are fitted with a shock absorber in some form as the wheel attaches to the bike to provide a smoother ride as the front and rear wheels can now travel up and down to absorb the force of obstacles striking the tires. Dual suspension bikes are considerably more expensive, but this price increase brings an enormous performance upgrade as dual suspension bikes are much faster on downhill and technical/rough sections, than other forms of the mountain bike. This is because when the wheel strikes an obstacle its tendency is to bounce up. Due to some forward energy being lost in the upward movement some speed is lost. Dual Suspension bikes solve this problem by absorbing this upward force and transmit it into the shocks of the front and rear wheels, drastically decreasing the translation of forward momentum into useless upward movement. Many bikes have dual suspension including downhill, freeride and mountain, although some bikes are built only to have front suspension e.g. dirt jump, some mountain. This makes them lighter and easier to control while in motion.
The advantages of dual suspension are increased comfort on rough terrain, and improved handling over obstacles. Disadvantages of rear suspension are increased weight, increased price, and with some designs, decreased pedaling efficiency. At first, early rear suspension designs were overly heavy, and susceptible either to pedaling-induced bobbing or lockout at certain points of the suspension arc or travel. One of the most popular rear suspension designs to solve these issues has been the 'Horst Link' which first appeared with the AMP series of bikes, and was later adopted by Specialized and many other mountain bike manufacturers.
[edit] Disc brakes
A front disc brake, mounted to the fork and hub
While inexpensive department store-style mountain bikes often come with V-brakes, most higher-end mountain bikes produced since the mid-2000s use disc brakes. These offer improved stopping power over rim brakes under adverse conditions, because they are located at the centre of the wheel (on the wheel hub) and therefore remain drier and cleaner than wheel rims, which are more readily soiled or damaged. While the traditional cantilever and V-brake style braking system provided ample braking for fully rigid bikes and the earlier, less sophisticated suspension fork-equipped bicycles, as suspension has evolved bicycle speeds have increased. Disc brakes offer the capacity for sustained heavy braking with fewer problems of brake fade than are encountered with rim brakes, allowing greater safety margins with less rider fatigue, greater modulation and therefore control.
The disadvantage of disc brakes is their increased cost and often greater weight. Hydraulic disc brakes, which work by moving brake fluid through a hose or line to squeeze the pads together, require much more technical maintenance but enjoy far more stopping power and much longer service intervals than their mechanical counterparts. Mechanical disc brakes, which are simpler and somewhat less expensive, work in a similar fashion to rim brakes by pulling one pad towards the disc with a cable, however offering around the same amount of braking force as a V-brake, meaning that advantages of such a system over are limited to the general advantages of disc brakes over V-brakes, barring, of course, power - these include better performance in muddy and wet conditions, and ease of removing wheels. The braking power of a disc brake also depends on the size of the rotor. For example, an 8-inch rotor has more stopping power than an 6-inch rotor of the same design (about 33% more). This is because the brake caliper can apply more torque with the same amount of force because the larger disc provides a longer moment arm.
Disk brakes are a good choice for any type of riding, especially on wet and muddy terrain. In just about every form of MTB racing, V-brakes have become obsolete, replaced by hydraulic disc brakes - disc-brakes are a must for Downhill, as V-brakes are unable to provide the necessary stopping power. In pro-level XC racing, V-brakes have also become obsolete due to great weight reductions in hydraulic disc brakes (some sets today can weigh as little as 300 grams) and increasingly technical courses.
[edit] Wheel and tire design
Most mountain bikes use 26 in (660 mm) bicycle wheels, though some models offer 24 or 29 in (520 or 622 mm) wheels. Bicycle wheel sizes are not precise measurements, a 29 inch mountain bike wheel actually has a 622 millimetres (24.5 in)ch) bead seat diameter (the term, bead seat diameter (BSD), is used in the ETRTO tire and rim sizing system). 622 mm wheels are standard on road bikes and are commonly known as 700c. In some countries, mainly in Continental Europe, 700c (622 mm) wheels are commonly called 28 inch wheels.[2] 24 inch wheels are used for dirt jumping bikes and sometimes on freeride bikes, rear wheel only, as this makes the bike more maneuverable. 29 inch wheels were once used for only Cross Country purposes, but are now becoming more commonplace in other disciplines of mountain biking. Wheels come in a variety of widths, ranging from standard rims suitable for use with tires in the 26 in x 1.90 in to 2.10 in (559 x 48 to 53 mm) size, to 2.35 and 3.00 in (60 and 76 mm) widths popular with freeride and downhill bicycles. Although heavier wheelsets are favored in the freeride and downhill disciplines, advances in wheel technology continually shave weight off strong wheels. This is highly advantageous as rolling weight greatly affects handling and control, which are very important to the technical nature of freeride and downhill riding. The widest wheel widths are sometimes used by icebikers who use their mountain bikes for winter-time riding in snowy conditions.
Manufacturers produce a wide variety of tread patterns to suit different needs. Among these styles are: slick street tires, street tires with a center ridge and outer tread, fully knobby, front-specific, rear-specific, and snow studded. Some tires can be specifically designed for use in certain weather (wet or dry) and terrain (hard, soft, muddy, etc) conditions. Other tire designs attempt to be all-around applicable. Within the same intended application, more expensive tires tend to be lighter and have less rolling resistance. Sticky Rubber tires are now available for use on freeride and downhill bikes. While these tires wear down more quickly, they provide greater traction in all conditions, especially during cornering. Tires and rims are available in either tubed or tubeless designs, with tubeless tires recently (2004) gaining favor for their pinch flat resistance. Tubeless tires can also be run at lower air pressures to improve traction and increasing rolling resistance. Popular tire manufacturers include Wilderness Trail Bikes, Schwalbe, Maxxis, Nokian, Michelin, Continental, Tioga, Kenda, Hutchinson and Panaracer.
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