Suspension

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 of a similar quality are considerably more expensive, but this price increase brings an enormous off-road 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.
Disadvantages of rear suspension are increased weight, increased price, and with some designs, decreased pedaling efficiency, this is especially noticable when cycling on roads and hard trails. 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, this is still the case of many bottom end bikes. 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.



A front disc brake, mounted to the fork and hub

For further information see Bicycle brake systems. For general information see Disc brake.
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 been created for higher bicycle speeds. 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 the advantages of such a system 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.

Wheel and tire design

Most mountain bikes use 26-inch (559 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)) 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.[3] 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. A mountain bike with 29" wheels is often referred to as a 29er. 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 bicycle tires with 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.