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File:Suspension stem.jpg

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:

  • Suspension front fork
  • Suspension stem (although these have fallen out of favor)
  • Suspension seatpost
  • Rear suspension
  • Suspension hub

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 suspensionEdit

File:Mountain Bike Fork.jpg

Front 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[1] 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 suspensionEdit

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.[2]

Soft tailEdit

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.

File:SinglePivotMTBSuspension.jpg

Single pivotEdit

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 triangleEdit

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 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 simple design uses only one pivot, which keeps down the number of moving parts. It can be easily modified into a single-speed, and has the benefit of zero chain growth and consistent front shifting. On the other hand, when the URT rider shifts any weight from the seat to the pedals, he or she is essentially standing on the swingarm, resulting in a massive increase in unsprung weight, and as a result the suspension tends to stop working. During braking, riders naturally brace themselves on the pedals,[citation needed] and combined with brake dive leads to more severe pitching, sometimes called "stinkbugging".[citation needed] Because of lockout and pitching, along with persistent suspension bob in low-pivot URTs, and a constantly changing saddle-to-pedal distance, the URT design has fallen out of favor in recent years.[3]

Examples of bike with this kind of suspension include the Castellano Zorro, Catamount MFS, Ibis Szazbo, Klein Mantra, Schwinn S-10, Trek Y, and Voodoo Canzo.

Four bar suspensions and the Horst linkEdit

The four bar active suspension utilizes several linkage points to activate the shock. A Horst link suspension has one pivot behind the bottom bracket, one pivot mounted at the chain stay, in front of the rear wheel drop-out (this pivot being the venerated "Horst Link"[1] ), and one at the top of the seat stay. Some examples of Horst Link four-bar designs include the now-discontinued AMP B-5, the Specialized FSR and related bikes, Ellsworth, KHS, Titus, and Merida.

A four-bar, seat-stay pivot suspension is similar looking, having a pivot above the drop out instead of in front of the drop out (ie no Horst Link and no patent problem). 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 complex arc of the axle path. Placing the pivot on the seat stay (above the drop out) makes the rear axle travel path like that of a single-pivot bike, since the chain stay is the only component that affects the rear axle's arc.

Seat-stay four-link pivot bikes perform exactly like similarly placed monopivots under acceleration and chain forces, which means they aren't as neutral under acceleration as Horst-link, four-bar bikes, dw-link, or Split Pivot bikes. However, when brakes are mounted on the seat stays, dw-link, Split Pivot and FSR four-link bikes have an advantage while braking over rough ground.[4] One manufacturer well known for their long-time use of the seat-stay pivot four-bar link suspension is Kona, who incorporate the design on their entire line-up, along with other manufacturers such as Infiza and Icon.

FSR systemEdit

File:FSR.jpg

The bike company Specialized worked with Leitner to develop a heavier-duty version of the four-bar/Horst Link suspension which was marketed as the Specialized FSR. The popular FSR system works by providing a wheel path that helps prevent the suspension preload or unload (squatting and locking) during acceleration and braking. The design is regarded by someTemplate:Who as superior to single-pivot/four-bar system due to other designs having a wheel path that either squats or "locks", depending on the position of the swingarm. The FSR system uses a wheel path that is in the middle of either squatting and lockout throughout most of the travel (circular, like single pivots). The FSR proved popular, and became a standard for full suspension designs, although recent innovations from competitors have set the company back. Specialized bought several of Leitner's patents in May 1998 and other manufacturers must now pay license fees to Specialized for the use of the 'Horst Link' suspension design. The Horst Link suspension design is the most leased or "borrowed" suspension design. It is very popular with companies such as Norco, Ellsworth, Chumba, KHS, and Fuji.[5]

In 2003 Specialized introduced the Brain, an external inertia valve designed to effectively eliminate pedal bob. The system utilizes a brass weight inside a cylinder situated atop the non-drive-side chainstay, near the rear dropout, and connected to the shock directly or through a hose. The weight closes the shock valving and deactivates the rear shock at rest. Upward force from rough terrain displaces the weight, opening the valve and engaging the suspension. In the original Brain mechanism, when the terrain evens out, the weight returns to its original position through a return spring, and deactivates the shock again. The position of the weight near the rear axle is designed to prevent downward pedaling force from affecting the mechanism while optimizing response from terrain. A newer version of the Brain was developed that utilizes the rebound hydraulic fluid flow to return the weight to its rest position instead of relying on a return spring. This was developed to address a noticeable delay in the shock activation/deactivation.[6]

VPPEdit

Template:Inappropriate tone The VPP (or Virtual Pivot Point) is a linkage designed bike frame that is built to activate the suspension differently depending on what inputs the suspension has received. The "Virtual Pivot" system used in bikes by Santa Cruz and Intense use a specific type of Virtual Pivot design that was originally developed and patented by Outland Bicycles in the late 1990s. The patents cover a specific linkage configuration and rear wheel travel path that is designed to aid the pedalling performance of a rear suspension bike without negatively affecting the overall bump absorption capabilities of the suspension. Yeti Cycles has created a unique rail system to eliminate pedal jacking (aka "bob"). Giant's Maestro is yet another design that works well, and is considered by many to be an attempt to replicate aspects of the dw-link design. Patents have drawn definite lines among the manufacturers.

The VPP family of suspension systems fall into the four bar linkage category. 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 new designs in suspension design have come out. These 'intelligent' shocks always have to compromise between their resistance to bob and performance with smaller bumps. VPP designs typically use shocks that include some sort of platform damping.

However, the four bar linkage may cause pedal bobbing, lockout, and brake jack. With the rise of more complicated shocks and a larger market share for full suspension bikes, mountain bike suspension tuners have now arrived. It is now possible to have shocks tuned to each individual rider's desires.

DW-linkEdit

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Dave Weagle's dw-link suspension is claimed by many cycling media and user reviews at consumer sites like MTBR.com to be the pinnacle of cycling suspension performance today. The dw-link design is protected by patents in the USA and Europe, with patent coverage in more countries than any other bicycle suspension in existence today. The dw-link is licensed to Ibis, Independent Fabrication, Turner Suspension Bicycles, and Pivot Cycles.[7]

Split pivotEdit

DW-Link inventor David Weagle applied for patents on a concentric rear axle pivot rear suspension system called split pivot in 2006.[8] The Split Pivot System was designed to allow the separation of braking and acceleration forces in a bicycle suspension. As with Dave's dw-link design, the Split Pivot design has been licensed within the bicycle industry, with licensing companies releasing new models in 2008, 2009, and 2010. The split pivot suspension is described in patent applications in the USA (US2008/006772 A1 and US 2008/00738 A1) and Europe (WO2008/027277 A2).[9][10]

After Mr. Weagle's patent applications were filed, Trek Bicycle Corporation released a version of the split pivot design called active braking pivot (ABP) in early 2007. In identical fashion to the split pivot design, the ABP system uses a rear pivot concentric to the rear axle. Trek's design allowed their new full suspension system to look very similar to previous models, but dramatically improved their ride quality. ABP reduces brake feedback that is typically felt by the rider as suspension stiffening. This allows the suspension to remain active while braking — hence the term, active braking pivot.

Split pivot patent applications predate all patent applications filed by Trek.[9][10]

Trek also introduced a full floater system to go along with the ABP. The full floater system mounts the rear shock to two moving points in the suspension (rocker link and an extension of the chainstay). Other systems mount the shock to one end on the swing-arm, and the other to a fixed mount on the frame. This means as one part of the suspension compresses the shock, the other end of the shock moves as well. This allows Trek engineers more freedom to more accurately and precisely tune the system's leverage ratio. This functionality is also described in David Weagle's Split Pivot patent applications.[10]

MonolinkEdit

The "Monolink" made by Maverick Bikes uses 3 pivot points and places the bottom bracket on a floating linkage between the front and rear triangle. It was designed by Paul Turner. The monolink design is unique in that is uses a shock body that is 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. Examples are the Maverick ML7/5, ML8, Klein Palomino, and Seven Duo.

File:Stinger.gif

EquilinkEdit

The "Equilink" suspension system was developed by Felt Bicycles for their full suspension line. The system is a "Stephenson-style six-bar" suspension system:[11] the Equilink ties the lower link (between the rear triangle and main frame) to the upper rockers. Felt contends that this system "equalizes" movement of the suspension in response to chain forces by linking the motion of the upper and lower linkages.[12] In actuallity, it works on the same principle of the dw-link; that is it creates a dropping rate of chain growth as it moves through its travel.[citation needed]

Saddle suspensionEdit

File:Gefederte-sattelstuetze.jpg

Suspension may be added at the saddle either with a Suspension saddle or a Suspension seatpost.

This style of suspension is the oldest, cheapest, and simplest, but it is also the least effective as all of the bicycle's weight is unsprung weight.

Suspension hubEdit

Suspension may be provided in the hub of a bicycle wheel.[13] One manufacturer offers 12 mm to 24 mm of travel.

TerminologyEdit

Several terms are commonly used to describe different aspects of a bicycle suspension.

TravelEdit

Travel refers to how much movement a suspension mechanism allows. It usually measures how much the wheel axle moves.

PreloadEdit

Preload refers to the force applied to spring component before external loads, such as rider weight, are applied. More preload makes the suspension sag less and less preload makes the suspension sag more. Adjusting preload affects the ride height of the suspension.

ReboundEdit

Rebound refers to the rate at which the suspension component returns to its original configuration after absorbing a shock. The term also generally refers to rebound damping or rebound damping adjustments on shocks, which vary the rebound speed.

SagEdit

Sag refers to how much a suspension moves under just the static load of the rider. Sag is often used as one parameter when tuning a suspension for a rider. Spring preload is adjusted until the desired amount of sag is measured.

LockoutEdit

Lockout refers to a mechanism to disable a suspension mechanism to render it substantially rigid. This may be desirable during climbing or sprinting to prevent the suspension from absorbing power applied by the rider. Some lockout mechanisms also feature a "blow off" system that deactivates the lockout when an appropriate force is applied to help prevent damage to the shock and rider injury under high unexpected loads.

Bob and squatEdit

Bob and squat refer to how a suspension, usually rear, responds to rider pedalling. Squat usually refers to how the rear end sinks under acceleration, and bob refers to repeated squat and rebound with each pedal stroke. Both are undesirable characteristics as they rob power from pedalling. Many suspension systems incorporate anti-bob, anti-squat, or "platform" damping to help eliminate bob.[14]

Pedal feedbackEdit

Pedal feedback describes torque applied to the crankset by the chain caused by motion of the rear axle relative to the bottom bracket.[14] This can sometimes by felt by the cyclists and can be considered undesirable.

Compression dampingEdit

Compression damping refers to systems that slow the rate of compression in a front fork shock or rear shock. Compression damping is usually accomplished by forcing a hydraulic fluid (such as oil) through a valve when the shock becomes loaded. The amount of damping is determined by the resistance through the valve, a higher amount of damping resulting from greater resistance in the valve. Many shocks have compression damping adjustments which vary the resistance in the valve. Often, lockouts function by allowing no compression.

Unsprung massEdit

Unsprung mass is the mass of the portions of the bicycle that are not supported by the suspension systems. At one extreme we have a road bicycle with no suspension in the frame, very little in the tires, and none in the saddle. By raising themself off the saddle the rider may provide suspension with their knees, making their mass be sprung mass, but all of the mass of the bicycle is unsprung mass. At the other extreme we have the full suspension mountain bike. With front and rear suspension the only parts unsuspended are the wheels and a small part of the fork and rear chain-stay. Even then, as the mountain bike has large low pressure tires which allow much more travel than small high pressure road tires, the wheels are sprung to some extent as well.

In general, bikes are so light compared to their riders that travel is a much bigger motivator than unsprung mass in determining where to put the suspension and how much to use. The exception to this is that on recumbent and tandem bicycles where the rider is either unable to lift themself out of their seat or unable to see in advance when that will be needed, the riders weight can no longer be expected to be supported by their knees over road irregularities. These bicycles generally have some sort of suspension system to keep down unsprung mass.

See also: Unsprung mass

Mountain bikesEdit

File:Mountain Bike Suspension.jpg

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 Manitou, Marzocchi, Fox Racing Shox, Rock Shox, Suntour, RST and (to a lesser extent) Magura, White Brothers, DT Swiss and Maverick. Some Cycle manufacturers (notably Cannondale and Specialized) also make their own suspension systems to fully complement and integrate the bike set-up.

Road bikesEdit

Although much less common, some road bicycles do incorporate suspensions, particularly the Soft Tail variety mentioned above. One example is Trek Bicycle Corporation's s.p.a (Suspension Performance Advantage) rear suspension, offered on some of their Pilot models, but the system was removed for the 2008 model year. Virtually all bicycles produced by Alex Moulton bicycles also have very effective full suspension, due to the low unsuspended mass of the small wheels and high pressure tires, a characteristic of the unconventional design of these bicycles.

Recumbent bikesEdit

Many recumbent bicycles have at least a rear suspension because the rider is usually unable to lift themselves off of the seat while riding. Single pivot is usually adequate when the pedaling thrust is horizontal - that is, forwards rather than downwards. This is usually the case provided the bottom bracket is higher than the seat's base height. Where the bottom bracket is significantly lower than the seat base, there may still be some pedalling-induced bounce.

Short-wheelbase recumbents benefit from front suspension, because the front wheel is often smaller than the rear wheel and bumps are unduly felt without it.

Softride and ZippEdit

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. Softride ceased bicycle production in 2007.[15]

A very closely related suspension design to the Softride is the Zipp 2001, a contemporary competing beam bicycle, where the suspension was in the hinge, rather than in flex of the beam itself.

See alsoEdit

ReferencesEdit

External linksEdit

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