Bicycle suspension

From Wikipedia, the free encyclopedia

A full suspension Mountain Bike

1 Mountain bike
- 1.1 Front suspension
- 1.2 Rear suspension
2 Road bikes
3 Recumbent bikes
4 Softride
5 See also
6 References

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 suspension are used primarily on mountain bicycles, 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:

Suspension front fork
Suspension stem (although these have fallen out of favor)
Suspension seat post
Rear suspension

or any combination of the above. Bicycles with suspension front forks and rear suspensions are referred to as full suspension bikes.

Besides providing obvious rider comfort, suspensions and 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.

[edit] Mountain bike

Rear suspension of a Trek Fuel 90

Many newer mountain bikes have a full suspension design. In the past, mountain bikes had a rigid frame and a rigid fork. In the early 1990s, mountain bikes started to have front suspension forks. This made riding on rough terrain easier on a rider's arms. The first suspension forks had about 1½ to 2 inches (38 to 50 mm) of suspension travel. Soon after, some frame designers came out with a full suspension frame which gave riders a smoother ride throughout the ride.

Newer suspension frame and fork designs have reduced weight, increased amount of suspension travel, and improved feel. Many lock out the rear suspension while the rider is pedaling hard or climbing, in order to improve pedaling efficiency. Most suspension frames and forks have about 4 inches (100 mm) of suspension travel. More aggressive suspension frames and forks made for downhill racing and freeriding have as much as 8 or 9 inches (200 or 230 mm) of suspension travel.

Many riders still prefer to ride a hardtail frame, and almost all mountain bicycle riders use a suspension fork. Well-known suspension fork manufacturers include Magura, Manitou, Marzocchi, Fox, Rock Shox, and (to a lesser extent) White Brothers and Maverick. Some Cycle manufacturers also make their own suspension systems to fully complement the bike set-up.

[edit] Front suspension

Main article: Bicycle_fork

On most mountain bicycles, the fork contains a set of shock absorbers. 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, and freeride riding.

The shock absorber usually consists of two parts: a spring and a damper or dashpot. The spring may be implemented with a steel coil, an elastomer, or even compressed air. The damper is usually implemented by forcing oil to pass through a small opening. 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 in one blade 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 blade that has a shock built into it.

[edit] 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. Lawwill's design was hindered because it couldn't use traditional cantilever brakes and had to use disc 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.

In 1991, while working for AMP Research, (owned and run by another motorcycle racer named Horst Leitner) Karl Nicolai designed a bike that utilized the four bar linkage design and accepted a normal cantilever brake. This bike was initially marketed under the AMP brand and a version came to the mass market as the Specialized FSR. It became the standard by which all other full suspension designs were judged for the next decade. Specialized bought several of Leitner's patents in May 1998 and other manufacturers (ironically now including Nicolai himself) must now pay licence fees to Specialized for the use of the 'Horst Link' suspension design.

The amount of travel on full suspension bikes has steadily increased with 100mm now acceptable for XC race designs and up to 150mm on trail or enduro bikes. For freeride and downhill even more suspension travel is the norm. Technological advances have enabled these machines to be of similar weight and cost as high end hardtails of the mid 1990s.

Almost all of the full suspension designs have been able to benefit from advances in new suspension technology. A stable platform shock is the latest design to hit the market and reduces unwanted bob. There are several different designs that have come to market with Fox, Manitou, Rock Shox, and several smaller companies now in the fray.

In 2003, Specialized introduced the Brain^TM, an external inertia valve that effectively eliminates pedal bob completely. Situated atop the drive-side chainstay, near the rear dropout, and connected to the shock directly or through a hose, the Brain^TM boasts an elegant and simple design: a brass weight sits inside a cylinder, closing the valve and deactivating the rear shock. Upward force from rough terrain displaces the weight, opening the valve and engaging the suspension. When the terrain evens out, the weight returns to its original position, and deactivates the shock again. Downward pedaling force has no effect on the brass weight inside the mechanism. The Brain^TM-equipped Specialized Epic became the first full-suspension mountain bike to win a cross-country world championship.^[1]

Several different full suspension designs are now well established in the marketplace.

[edit] Soft tail

The Soft Tail 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 pedalling 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 are the Trek STP or the Moots YBB.

Various manufacturers have used soft tail technology on their road bicycles. One current example is Trek Bicycle Corporation's s.p.a (Suspension Performance Advantage) rear suspension available on some of their Pilot models. It consists only of a sliding linkage in the mono seat stay encased in an elastomer. All of the rear travel comes from flexing of the chain stays.^[2]

A full-suspension mountain bike with a single-pivot suspension.

[edit] Single Pivot

The Single Pivot is one of the simplist types of rear suspension. It simply consists of a pivot around the bottom bracket area and a solid chainstay to the rear axle. The rear axle will always rotate in a circle around the pivot point. Some implementations use linkages to attach the rear triangle to the rear shock for a progressive spring rate (see Faux Bar). An example is the Trek Fuel line which has a solid chainstay, yet uses a rocker link to activate the shock. Other implementations directly attach the rear triangle to the rear shock for a more linear rate. Gary Fisher's Cake line is such an example. Pros are, that it's a simple design. There are few moving parts, relatively easy to design and has good small bump compliance. The cons are that the design suffers from bob, brake jacking, and chain growth. Some other manufacturers that use a single pivot design are bcd, Morewood, Orange, Cannondale, Santa Cruz, Mountain Cycle, and cheap department store bikes.

[edit] Unified Rear Triangle

The "Unified Rear Triangle" or "URT" for short, keeps the bottom braket and rear axle directly connected at all times. The pivot is placed between the rear triangle and the front triangle so that the rear axle and bottom bracket move as one piece, and the saddle and handlebars move as another piece. This design is simple because it again, uses only one pivot keeping moving parts low. It also has the advantage of having a hardtail like drivetrain - zero chain growth, consistent front shifting because the chain angle is always known, and possibly less chain suck. It's one of the rare rear suspension designs that can be turned into a single speed. The URT design has mostly fallen out of favor. One of the reasons is that the saddle to pedal distance would change. An example is the Klein Mantra.

[edit] Four Bar

The Four Bar (and its variant the Faux bar) use several linkage points to activate the shock. A 'true' Four Bar will have a pivot behind the bottom bracket, one in front of the rear wheel drop out (this pivot being the venerated "Horst Link"), and one at the top of the Seatstays. A Faux Bar will be similar but will have a pivot above the drop out instead of in front of the drop out (ie no Horst Link and no patent problem). The importance of this one pivot is heavily debated with supporters on both sides of the debate. Having the pivot in front of the drop out (i.e. on the chain stay) allows the linkage components to affect the path of the rear axle, thereby allowing for a more vertical travel path. Having the pivot on the seat stay (above the drop out) effectively makes the rear axle travel path very similar to that of a single pivot bike, since the chain stay is the only component that affects the rear axle's arc. Four Bar designs include Norco "VPS" bikes, almost all Specialized bikes, Ellsworth, KHS, Turner (although their new 06 Flux has lost the Horst link), and Ventana. A manufacturer that makes use of the 'Faux Bar' is Kona, who use it on their entire line-up.

Faux bar suspension designs are in fact single pivots. The rear axle rotates around a single fixed point near the bottom bracket that it is connected to with a single link. The seatstays and rocker only serve to activate the shock and have no effect on the path of travel that the rear axle takes. The term "Faux bar" is used because they look similar to four bars.

[edit] Virtual Pivot Point

The VPP (or Virtual Pivot Point) is a linkage designed bike that is built to activate the suspension differently depending on what inputs the suspension has received. The VPP design is currently owned by Santa Cruz who also licenses the design to Intense. Yeti Cycles have created a unique rail system to eliminate pedal jacking The DW-Link is another design licensed to Iron Horse and Independent Fabrications. Giant's Maestro is yet another design. Patents have drawn definite lines among the manufacturers.

To define a VPP/DW-link/Maestro suspension design, imagine a line that follows the path the rear axle takes as it moves through its travel. Continue it into a complete circle. The center of the circle will be the pivot point. It will be a virtual point in space and not an actual pivot on the bicycle. It can either be a fix point or one that moves around as the suspension compresses (floating), depending on the design.

The VPP family of suspension systems are in fact four bar designs. They have short links instead of the longer links on a conventional four bar (chainstay and rocker).

The VPP (Virtual Pivot Point) system used by Santa Cruz and Intense, also claims to have reduced the problem of pedal bob. Soon after the VPP was introduced, the creation of the Progressive Suspension 5th Element rear shock (based on Currnut's platform damper) near the beginning of the Millennium allowed riders to adjust almost any frame, regardless of design, to be pedaled without the pedal bob that plagued earlier designs. Other companies have followed Progressive's lead (mainly Manitou with its SPV system based on the 5th Element and Fox's ProPedal which uses a shim stack rather than an air pressurized valve) and a revolution in suspension design is underway. However, these 'intelligent' shocks always have to compromise between their resistance to bob and performance with small bumps.

Many think the tried and trusted technology of the four bar linkage with a comparatively simple shock still offers the best performance. Ironically, as shock manufacturers compete to have the latest 'pedal platform' technology four bar riders are pushed to the most expensive dampers on which it is possible to switch off the pedal platform. With the rise of more complicated shocks and a larger market share of full suspension bikes mountain bike suspension tuners have now arrived. It is now possible to have shocks tuned to individual rider's desires.

[edit] Monolink

The "Monolink" made by Maverick Bikes uses 3 pivot points and place the bottom bracket on a floating linkage between the front and rear triangle. It was designed by suspension guru Paul Turner, formerly of RockShox. The monolink design is unique in that is uses an shock body that's integrated into the rear triangle, and that the saddle to bottom bracket distance changes as the suspension is compressed, although not as large as a URT design. The suspension is more active when in the saddle, as pressure on the cranks actively works against the suspension. However, because of this property, there is less bob in out of the saddle sprints. The monolink design is also unique in having a rearward axle path, which is similar to the angle of attack of the front suspension. Unfortunately, the monolink suffers from horrible front shifting and long chainstays. Examples are the Maverick ML7/5, ML8, Klein Palomino, and Seven Duo.

The Optima Stinger recumbent with rear suspension

[edit] Road bikes

Although much less common, some road bicycles do incorporate suspensions, particularly the Soft Tail variety mentioned above. One current example is Trek Bicycle Corporation's s.p.a (Suspension Performance Advantage) rear suspension available on some of their Pilot models.

[edit] Recumbent bikes

Many recumbent bicycles have at least a rear suspension because the rider is usually unable to lift themselves off of the seat while riding.

[edit] Softride

The Softride Suspension System was launched at the Interbike 1989 bike show. The original SRS systems consisted of two foam filled fiberglass boxes bonded together with a viscoelastic layer. Originally intended for the use in mountain bikes, Softride produced its first full-fledged mountain bike, the PowerCurve, in 1991. During 1996 Softride released its first aluminum frame road bike, the Classic TT. The Softride Suspension System is used almost exclusively for triathlon racing.^[3]