Bicycle suspension
A bicycle suspension is 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 comfort to the rider, suspensions improve both safety and efficiency by keeping one or both wheels in contact with the ground and allowing the rider's body mass to move over the ground in a flatter trajectory.
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[edit] Suspension categories
No Suspension, also called rigid, is no suspension at all.
Hardtail is front suspension but no rear suspension.
Full suspension is front and rear suspension.
[edit] Front suspension
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 fork's travel to the specific terrain profile (e.g. less travel for uphill sections, more travel for downhill sections). Advanced designs also often feature the ability to lock out 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 place of steel coils in a design can decrease the weight of the design but leads to an increase in expense.
Air springs work by using 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. To achieve this in a coil sprung fork the spring constant of the coil would need to be changed. 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 greater force. This results in an increase in spring rate (stiffness). Increasing the volume of the air inside the spring can reduce this effect but the volume of the spring is ultimately limited by the need to be contained within the dimension of the fork leg. The use of dual chambers within the air chamber system has allowed a more linear feel to air suspension, this is achieved by having a 'reserve' chamber that is activated when the main chamber reaches a certain amount of compression; once achieved a valve opens and effectively makes the chamber larger. By linking the two, this reduces the force needed to compress the air in the chamber and reduces the exponential spring rate feel traditionally experienced with air systems when approaching the end of the travel (movement).[2]
A 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. Without a damper unit, the suspension system would rebound excesively and control would be lessened.
Some manufacturers, Cannondale for example, have tried other variations including a single shock built into the steerer tube above the crown (also called a "HeadShok"), and a fork with just a single leg (also called a Lefty). Both of these systems claim to offer greater rigidity and better feel, with lighter weight - by having only one leg, and using Needle Bearings instead of bushings, as well as special forging techniques. Others, namely Proflex (Girvin), Whyte and BMW, have made bikes that utilize suspension forks that employ linkages to provide the mechanical action instead of relying upon telescopic fork legs.[citation needed]
To prevent damage to the suspension mechanism, gaiters have been used to cover the spring cylinder (stanchions), however, it was quickly realised that these acted as a trap for grit and actually wore down the stanchions quicker.
[edit] Rear suspension
Perhaps because front suspension has been easier to implement and more readily adopted, it is often assumed that a bicycle with rear suspension has 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 suspensions compressed into their travel and lost some of their ability to absorb bumps. 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 1970s 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.[3]
[edit] 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.
[edit] Single pivot
The single pivot is the simplest type of rear suspension. It simply consists of a pivot near the bottom bracket or higher up on the down tube and a single swingarm to the rear axle. The rear axle will always rotate in an arc 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. 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, GT, Commencal, K2, Morewood, Transition, Orange, Cannondale, Mountain Cycle, Santa Cruz, Haro, small boutique frame builders such as BCD and, due to its simplicity, many inexpensive department store bikes.
[edit] High single pivot
This kind of a single pivot suspension places it in front and above the bottom bracket. Notable trait of this suspension is that it compresses when pedaled in a small forward ring. Notable examples are Santa Cruz Superlight and Heckler frames.
[edit] Linkage driven low single pivot
This is kind of monopivot suspension with additional pivot on the seat stay (above the drop out). This suspension utilizes several linkage points to activate the shock. Because of a visual similarity with US patented Horst link design, this popular design is often derisively referred to as a "faux-bar".[4] Manufacturer well known for their long-time use of this suspension is Kona, Jamis, Yeti, Ventana, and many others.
[edit] Four-bar
A Horst link suspension has one pivot behind the bottom bracket, with one pivot mounted at each of the chain stays, in front of the rear wheel drop-out (this pivot being the venerated "Horst link"[1] ), and one at the top of the leveraged shock linkage that connects to 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.
The Horst Link patent system proved popular since its debut, becoming a standard for rear suspension designs using an 'active' model. Specialized bought several of Leitner's patents in May 1998, and other manufacturers in U.S. now license the Horst link design from Specialized for the use of the 'Horst link' or FSR suspension patent. It is used by companies such as Norco, Ellsworth, Titus, KHS, and Fuji. European manufacturers, such as Nicolai, Rotwild, Cube and others do use the same suspension design, but can not import it to the United States.[5]. The FSR patent system uses a wheel path that attempts to position suspension compression between a preloaded and an unloaded condition throughout most of its travel.
[edit] Split pivot
A variation of a single pivot design that places a rear pivot concentric with the rear axle. It behaves similar to a low single pivot suspension under acceleration while retaining four-bar design advantages for isolating braking forces, that is typically felt by the rider as suspension stiffening ("brake jack"). Trek Bicycle Corporation released a version of the Split Pivot design called active braking pivot (ABP) in early 2007. Dave Weagle, designer of DW-Link suspension was awarded it's first patent in the USA on May 18, 2010, US Patent 7,717,212. Cycles Devinci has released a licensed implementation of Dave Weagle design.
[edit] 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 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 one end of the swingarm, resulting in an increase in unsprung weight which varies according to the length of the swing-arm and distance between the bottom bracket and the pivot, and as a result the suspensions effectiveness is reduced to some extent. 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.[6]
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.
[edit] Virtual Pivot Point
The Virtual Pivot Point or VPP, 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 Point" system owned by Santa Cruz Bicycles, Inc is protected by four US patents, three of which were originally issued to Outland Bicycles. The four patents cover a specific linkage configurations that are designed to aid the pedaling performance of a rear suspension bike without negatively affecting the overall bump absorption capabilities. The Santa Cruz Blur and V-10 models introduced in 2001 popularized "dual short link" type suspension systems, but have the unique characteristic of having links that rotate in opposite directions. VPP suspension is also licensed to Intense Cycles.
[edit] DW-link
Dave Weagle's dw-link uses two co-rotating short links - unlike counter-rotating links in the VPP design - configured to optimize suspension behavior to avoid compression under acceleration (anti-squat). 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]
[edit] Switch link
Another variation of two short links design is a Dave Earle designed Yeti SB-66 and SB-95 "Switch" link. It is uses an eccentric upper pivot. Upper link switches its rotation direction mid-travel, which is contrasted with co-rotating and contr-rotating links of VPP and DW-link designs. Patent application for this design is pending. Santa Cruz Bicycles is suing Yeti Cycles over aspects of this design in relation to VPP patent.[8][non-primary source needed]
[edit] Independent Drivetrain
The Independent Drivetrain (AKA IDrive) Pat # 6,099,010 / 6,073,950, was the 4th commercialized suspension design developed by pioneering MTB suspension designer Jim Busby Jr. The independent drivetrain system was a direct result of the limitations encountered with the GT LTS (links tuned suspension) 4 bar linkage design used by GT Bicycles from 1993 to 1998. The defining feature of Independent Drivetrain is the isolation of the bottom bracket (crank) from the front or rear triangle. This isolation allows the BB to move in such a manner as to neutralize the unwanted characteristics of chain growth at the pedal. Some may call this a "modified URT" but in reality it is a highly reconfigured 4 bar if examined theoretically. By using this isolated BB construction, pedal forces do not induce undesired suspension compression or extension nor does suspension activity produce pedal actuation through chain growth.
[edit] Monolink
The "Monolink" made by Maverick Bikes, is a variation of a MacPherson strut. It uses three pivot points and the sliding action of the shock to provide the fourth degree of freedom. Monolink is unique in placing the bottom bracket on a floating linkage between the front and rear triangle. While this increases unsprung weight and reduces cushioning on the feet, it also minimizes chain growth, allowing for more efficient pedaling. It was designed by Paul Turner. It is a licensed variant of the Independent Drivetrain suspension system Pat # 6,099,010 / 6,073,950. The monolink design varies from the Independent Drivetrain original design in that it 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.
[edit] Equilink
The "Equilink" suspension system was developed by Felt Bicycles for their full suspension line. The system is a "Stephenson-style six-bar" suspension system:[9] 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.[10] Some, however, argue 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]
[edit] Saddle suspension
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.
[edit] Suspension hub
Suspension may be provided in the hub of a bicycle wheel.[11] One manufacturer offers 12 mm to 24 mm of travel.
[edit] Terminology
Several terms are commonly used to describe different aspects of a bicycle suspension.
[edit] Travel
Travel refers to how much movement a suspension mechanism allows. It usually measures how much the wheel axle moves.
[edit] Preload
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.
[edit] Rebound
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. More rebound damping will cause the shock to return at a slower rate.
[edit] Sag
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.
[edit] Lockout
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.
[edit] Bob and squat
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.[12]
[edit] Pedal feedback
Pedal feedback describes torque applied to the crankset by the chain caused by motion of the rear axle relative to the bottom bracket.[12] Pedal feedback is caused by an increase in the distance between the chainring and rear cog, and it can be felt as a torque on the crankset opposite to forward pedalling.
[edit] Compression damping
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.
[edit] Unsprung mass
Unsprung mass is the mass of the portions of bicycles that is not supported by the suspension systems. At one extreme are road bicycles with no suspension in the frames, very little in the tires, and none in the saddles. By raising themselves off their saddles, riders may provide suspension with their knees, making their mass be sprung mass, but all of the mass of the bicycles remains unsprung mass. At the other extreme are full suspension mountain bikes. With front and rear suspensions the only parts unsuspended are the wheels and small parts of the front forks and rear chain-stays. Even then, as mountain bikes have 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 riders are either unable to lift themself out of their seat or unable to see in advance when that will be needed, the riders' mass can no longer be expected to be supported by their knees over road irregularities. These bicycles generally have some sort of suspension system to reduce unsprung mass.
[edit] Mountain bikes
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 4-6 inches (100-150 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, and (to a lesser extent) Suntour, RST, 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.
[edit] Road bikes
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.
[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. 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 more than long wheelbase recumbents because the front wheel (often small diameter which further magnifies the need for suspension) is taking a much larger portion of the loads than in a long wheelbase recumbent.
[edit] Softride and Zipp
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 after the design was banned from racing.[13]
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.
[edit] See also
- Bicycle
- Bicycle and motorcycle dynamics
- Bicycle fork
- Bicycle frame
- Hybrid bicycle
- Motorcycle fork
- Mountain bike
- Recumbent bicycle
- Road bicycle
- Suspension (motorcycle)
- Suspension (vehicle)
- Swingarm
[edit] References
- ^ "SUPER MONSTER 2003". http://www.marzocchi.com/Template/detailSPAForksMTB.asp?IDFolder=208&LN=UK&Sito=usa%2Dmtb&IDAnno=2147&IDOggetto=56226. Retrieved 2008-12-23.
- ^ "DRCV Benefits". Trek Bicycles. http://fisherbikes.com/bike/series/roscoe. Retrieved 2011-04-21.
- ^ AMP Research > History
- ^ Everything Bicycling - Suspension – the inns and outs
- ^ "Scott USA Genius". http://www.bikemag.com/news/newsarchive/012406_scott/. Retrieved 2009-03-15.
- ^ "Mountain Bike Rear Suspension Design: High Pivot URTs". http://www.rdrop.com/~/twest/mtb/index.html#HighPivotURTs. Retrieved 2008-03-14.
- ^ "dw-Link". http://www.dw-link.com. Retrieved 2009-03-15.
- ^ "Santa Cruz Bicycles, Inc. v. Yeti Cycles Inc. et al". http://www.rfcexpress.com/lawsuits/patent-lawsuits/california-northern-district-court/80389/santa-cruz-bicycles-inc-v-yeti-cycles-inc/summary/. Retrieved 2012-01-09.
- ^ Huang, James (September 25-29, 2006). "Felt Equilink design offers another viable rear suspension alternative". http://autobus.cyclingnews.com/tech/2006/shows/interbike06/?id=results/interbike064. Retrieved 2009-04-17.
- ^ "Equilink Suspension Overview". http://www.feltracing.com/09/content.aspx?catid=1540,1730&pageid=809. Retrieved 2009-04-17.
- ^ "VeloVision Issue 10". http://www.velovision.co.uk/cgi-bin/show_comments.pl?storynum=507. Retrieved 2009-10-06.
- ^ a b Phillips, Matt (April 2009). "You Don't Know Squat". Mountain Bike (Rodale): 39–45.
- ^ "ABOUT SOFTRIDE". Archived from the original on 2007-01-01. http://web.archive.org/web/20070101020935/http://www.softride.com/about_softride.asp. Retrieved 2007-01-18.
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