Bicycle suspension refers to the system or systems used to suspend the rider and all or part of the bicycle in order to protect them from the roughness of the terrain over which they travel. Bicycle suspensions are used primarily on mountain bikes, but are also common on hybrid bicycles, and can even be found on some road bicycles.
Bicycle suspension can be implemented in a variety of ways:
or any combination of the above. Bicycles with suspension front forks and rear suspensions are referred to as full suspension bikes . Additionally, suspension mechanisms can be incorporated in the seat or saddle, or the hubs.
Besides providing obvious rider comfort, suspensions improve both safety and efficiency by keeping one or both wheels in contact with the ground and allowing the rider's mass to move over the ground in a flatter trajectory.
Front suspension
Main article: Bicycle forkFront suspension is often implemented with a set of shock absorbers in the front fork. The suspension travel and handling characteristics vary depending on the type of mountain biking the fork is designed for. For instance, manufacturers produce different forks for cross-country (XC), downhill (DH), and freeride riding.
Suspension fork design has advanced in recent years with suspension forks becoming increasingly sophisticated. The amount of travel available has typically increased. When suspension forks were introduced 80–100 mm of travel was deemed sufficient for a downhill mountain bike. Typically this amount of travel is now more normal for cross country disciplines. Downhill forks can now offer in the region of 170 to 203 mm of travel for handling the most extreme terrain.
Other advances in design include adjustable travel allowing riders to adapt the forks travel to the specific terrain profile. eg less travel for uphill sections more travel for downhill sections. Advanced designs also often feature the ability to lockout the fork to completely eliminate or drastically reduce the fork's travel for more efficient riding over smooth sections of terrain. This lockout can sometime be activated remotely by a cable and lever on the handlebars.
The shock absorber usually consists of two parts: a spring and a damper or dashpot. The spring may be implemented with a steel or titanium coil, an elastomer, or even compressed air. The choice of spring material has a fundamental effect on the characteristics of the fork as a whole. Coil spring forks are often heavier than designs which use compressed air springs, however they are more easily designed to keep a linear spring rate throughout their travel. Substituting titanium coils in favor of steel coils in a design can decrease the weight of the design but leads to an increase in expense. Air springs work by utilizing the characteristic of compressed air to resist further compression. As the "spring" is provided by the compressed air rather than a coil of metal they can often be made lighter; this makes their use more common in cross country designs. Another advantage of this type of fork design is that the spring rate can easily be adjusted by adjusting the pressure of the air in the spring. This allows a fork to be effectively tuned to a rider's weight. One disadvantage of this design is the difficulty in achieving a linear spring rate throughout the fork's action. As the fork compresses, the air held inside the air spring also compresses; towards the end of the fork's travel, further compression of the fork requires ever increasing compression of the compressed air with the spring. This results in an increase in spring rate. Increasing the volume of the air inside the spring can reduce this effect but the volume of the spring is ultimately limited as it needs to be contained within the dimension of the fork leg.
The damper is usually implemented by forcing oil to pass through one or more small openings or shim stacks. On some models, the spring, the damper, or both may be adjusted for rider weight, riding style, terrain, or any combination of these or other factors. The two components may be separated with the spring mechanism in one leg and the damper in the other.
Some manufacturers, especially Cannondale, have tried other variations including a single shock built into the steering tube above the crown and a fork with just a single leg that has a shock built into it. Others have marketed suspension forks that employ linkages to provide the mechanical action instead of relying upon telescoping elements.
Rear suspension
Perhaps because front suspension has been easier to implement and more readily adopted, it is often assumed, and rear suspension is sometimes synonymous with full suspension.
Full suspension mountain bike technology has made great advances since first appearing in the early 1990s. Early full suspension frames were heavy and tended to bounce up and down while a rider pedaled. This movement was called pedal bob, kickback, or monkey motion and took power out of a rider's pedal stoke — especially during climbs up steep hills. Input from hard braking efforts (known as brake jack) also negatively affected early full suspension designs. When a rider hit the brakes, these early designs lost some of their ability to absorb bumps — and this happened in situations where the rear suspension was needed most.
The problems of pedal bob and brake jack began to be solved in the early 1990s. One of the first successful full suspension bikes was designed by Mert Lawwill, a former motorcycle champion. His bike, the Gary Fisher RS-1, was released in 1990. It adapted the A-arm suspension design from sports car racing, and was the first four bar linkage in mountain biking. This design solved the twin problems of unwanted braking and pedaling input to the rear wheel, but the design wasn't flawless. Problems remained with suspension action under acceleration, and the RS-1 couldn't use traditional cantilever brakes. A lightweight, powerful disc brake wasn't developed until the mid 1990s, and the disc brake used on the RS-1 was its downfall.
Horst Leitner began working on the problem of chain torque and its effect on suspension in the mid 1970's with motorcycles. In 1985 Leitner built a prototype mountain bike incorporating what became known later as the "Horst Link". Leitner formed a mountain bike and research company, AMP research, that began building full-suspension mountain bikes. In 1990, AMP introduced the Horst link as a feature of a fully independent linkage rear suspension for mountain bikes. The AMP B-3 and B-4 XC full-suspension bikes featured active Horst Link/Macpherson strut rear suspensions and optional disc brakes. A later model, the B-5, was equipped with both the Horst link and a four-bar active link suspension featuring up to 125 mm (5 inches) of travel on a bicycle weighing around 10.5 kg (23 pounds). For 10 years AMP Research manufactured their full-suspension bikes in small quantities in Laguna Beach, California, including the manufacture of their own cable-actuated-hydraulic disc brakes, hubs, shocks and front suspension forks.
Soft tail
The Soft tail (also Softail) relies on the flexing of the rear triangle and a rear shock or elastomer placed in line with the seat stays. Soft tails are a variation of the original Amp Research Mac-Strut design (technically a 3 bar suspension design). Soft tails have no moving parts, besides the shock/elastomer, making it extremely simple. It maintains pedaling efficiency and power delivery because of the solid chainstays. They tend to be extremely light compared to other rear suspension types. Soft tails are out of favor now because of the limited rear axle travel of these designs - typically around 1 inch. Some examples include the KHS Team Soft Tail, Trek STP and the Moots YBB. The Cannondale Scalpel is an exception with 4 inches of travel.
Single pivot
The Single pivot is the simplest type of rear suspension. It simply consists of a pivot near the bottom bracket and a single swingarm to the rear axle. The rear axle will always rotate in a part-circle around the pivot point. Some implementations use linkages to attach the rear triangle to the rear shock for a progressive spring rate. Other implementations directly attach the rear triangle to the rear shock for a more linear rate. Santa Cruz's Superlight is such an example. The main benefit of this design is its simplicity. There are few moving parts, relatively easy to design and has good small bump compliance. Challenges with this design are brake jacking, and chain growth.
Manufacturers that use a single pivot design are Trek, K2, Morewood, Orange, Cannondale, Mountain Cycle, Haro, small boutique frame builders such as bcd and, due to its simplicity, many inexpensive department store bikes.
Unified rear triangle
The "Unified rear triangle" or "URT" for short, keeps the bottom bracket and rear axle directly connected at all times. The pivot is placed between the
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