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Suspension (motorcycle)
Encyclopedia
A motorcycle's suspension
serves a dual purpose: contributing to the vehicle's handling and braking, and providing safety and comfort by keeping the vehicle's passengers comfortably isolated from road noise, bumps and vibrations.
The typical motorcycle has a pair of fork tubes for the front suspension, and a swingarm with one or two shock absorber
s for the rear suspension.
. Early front suspension designs used frames with springs.
Some British manufacturers (e.g. Greeves) used a version of the swinging arm for front suspension on their motocross designs. A single-sided version of the idea is also used in motor scooters such as the Vespa
.
The Hub-center steering
as developed by Ascanio Rodorigo, on a concept associated to Massimo Tamburini
is a complex front swingarm alternative system that entails suspension and steering, as seen in projects such as Bimota
Tesi and Vyrus motorcycles.
s. They allow the front wheel to react to imperfections in the road while isolating the rest of the motorcycle from that motion.
The top of the forks are connected to the motorcycle's frame in a triple tree clamp (otherwise known to British riders as the top yoke and bottom yoke), which allows the forks to be turned in order to steer the motorcycle.
The bottom of the forks are connected to the front axle around which the front wheel spins.
On typical forks, the upper portion, known as the fork tubes, slide inside the fork bodies, which are the lower part of the forks. As the tubes slide in and out of the body they are telescoping, thus the term telescopic forks. The fork tubes must be smooth to seal the fork oil inside the fork, and typically have a mirrored finish, though some fork tubes, especially those on off-road motorcycles, are enclosed in plastic protective sleeves, known as gaiters.
"Upside-down" (USD) forks, also known as inverted forks, are installed inverted compared to typical forks, with the tubes at the bottom and the bodies at the top. This decreases the unsprung weight
of the motorcycle and improves its handling. USD forks are usually found on sportbikes, though Honda
's large power-cruiser, the Valkyrie
, sported USD forks.
The difference between the fully extended length of the suspension and the length compressed by the weight of the motorcycle and rider is called total sag. Total sag is set to optimize the initial position of the suspension to avoid bottoming out or topping out under normal riding conditions. Bottoming out" occurs when the suspension is compressed to the point where it mechanically cannot compress any more. Topping out occurs when the suspension extends fully and cannot mechanically extend any more. Increasing pre-load increases the initial force on the spring thereby reducing total sag. Decreasing pre-load decreases the initial force in the spring thereby increasing total sag.
A few motorcycles allow adjustment of pre-load by changing the air pressure inside the forks. Valves at the top of the forks allow air to be added or released from the fork. More air pressure gives more preload, and vice versa.
. The adjuster turns a rod inside the fork which brings different sized orifices into alignment with the damping fluid flow path inside the fork. Smaller orifices restrict the flow of the fork oil more and give greater damping.
Since forks act as hydraulic shocks, changing the weight of the fork oil will change the damping.
Cartridge forks use internal cartridges with various leaf springs covering orifices to control the damping of the fork.
Some of the leaf springs lift with little force allow fluid to flow through the orifice. Other springs require greater force to lift and allow flow. This gives the fork digressive damping, allowing it to be stiff over small bumps, but get relatively softer over larger bumps.
Also, the springs only allow flow in one direction, so one set of springs controls compression damping, and another rebound damping. This allows the dampings to be set separately.
Cartridge emulators are aftermarket parts that make non-cartrdige forks behave like cartridge forks.
In 2007 the gas-charged bolt-in cartridge set for modern sportbike forks became available. This kit is legal for supersport styled classes of racing, which regulations do not allow a complete fork replacement, and force competitors to use the stock fork casings.
article.
If the motorcycle is equipped with telescopic forks, the added load on the front wheel is transmitted through the forks, which compress. This shortening of the forks causes the front end of the bike to move lower, and this is called brake dive.
Brake dive can be disconcerting to the rider, who may feel like he or she is about to be thrown over the front of the motorcycle. If the bike dives so far as to bottom out the front forks, it can also cause handling and braking problems. One of the purposes of a suspension is to help maintain contact between the tire and road. If the suspension has bottomed out, it is no longer moving as it should, and is no longer helping to maintain contact.
Brake dive with telescopic forks can be reduced by either increasing the spring rate of the fork springs, or
increasing the compression damping of the forks. However, all of these changes make the motorcycle less pleasant to ride on rough roads, since the front end will feel stiffer, in the 1980s various manufacturers attempted to get round this by methods of anti-dive such as:
Another method to reduce or eliminate brake dive in telescopic forks is to use a reactive link or torque arm to connect the braking components to the motorcycle frame via the triple clamp.
Some fork designs mitigate dive, eliminate it, or even reverse it without affecting the front suspension adversely. The Earles fork is among the latter; when braking the front brake hard, the front end of the motorcycle actually rises. BMW's Telelever fork is designed to nearly eliminate dive, but could have been designed to eliminate it completely if the manufacturer chose to do so. Leading link front forks, such as used on some Ural motorcycles
, can also be designed either to reduce or eliminate dive.
The Saxon-Motodd (marketed as Telelever by BMW
) has an additional swingarm that mounts to the frame and supports the spring. This causes the rake and trail to increase during braking instead of decreasing as with traditional telescopic forks.
) separates completely the suspension from steering forces. It was developed by Norman Hossack though used by Claude Fior and John Britten
on racebikes. Hossack himself described the system as a 'steered upright'. In 2004 BMW announced the K1200S with a new front suspension that is based upon this design.
, introduced in 1993. The GTS used the RADD front suspension designed by James Parker
. A single sided girder fork was use by the German firm Imme between 1949 and 1951, and the Vespa
scooter has a single-sided trailing-link fork. More recently, the ItalJet "Dragster" scooter also uses a single-sided swingarm suspension, though unlike the GTS1000 there is no upper control arm; the upper part of the suspension on the Dragster serves only to transmit steering input.
Single with a swingarm suspended from a leaf spring
and the 1913 Pope with wheels supported on a pair of plungers which were each suspended by a coil spring
.
Notable manufacturers of bikes with plunger suspension include Adler
, Ariel
, BMW
, BSA
, Indian
, MZ
, Norton
, and Zündapp
so that it can pivot. The other short side is the rear axle around which the rear wheel turns. The long sides are connected to the motorcycle's frame or rear sub-frame with one or two shocks with coil-over springs.
In production motorcycles, swingarms are not exactly rectangular, but their function can be more easily understood by thinking of them as such.
When a swingarm is present on only one side of the motorcycle, this is known as a single-sided swingarm. Notable examples include the Honda VFR800
and the BMW
R- and K-series. Single-sided swingarms make rear-wheel removal easier, though they generally increase the unsprung weight
of the rear suspension. This is due to the additional material required to give identical torsional rigidity to a conventional (two-sided) swingarm setup. For this reason sports bikes are rarely seen using the setup. Notable exclusions are the Ducati 916 which was intended to be taken endurance racing, the MV Agusta f4 which has a hollow interior for reducing weight (a magnesium version is also available), and the Ducati 1098, which was given a single sided swingarm purely for styling reasons.
On many shaft-drive motorcycles the drive shaft is contained in one of the long sides of the swingarm. Notable examples include all post-1955 BMW models prior to BMW's use of the single-sided swingarms, Urals
, many Moto Guzzi
twins, the Honda Goldwing
, the Yamaha XS Eleven
, and the Yamaha FJR1300
.
The BMW R- and K-series combine a shaft-drive contained in the swing arm with a single-sided swingarm, and the combination is marketed as the Paralever. Newer Moto Guzzi motorcycles use a similar arrangement marketed as the CA.R.C. ("CArdano Reattivo Compatto" - Compact Reactive Shaft Drive).
For motorcycles with chain drives, the rear axle can be adjusted forward and back in relation to the swingarm, to adjust chain tension.
Motorcycle shocks do differ slightly in that they nearly always use a coil-over spring. In other words, the spring for the rear suspension is a coil spring that is installed over, or around, the shock.
In terms of adjustment, rear shocks span the range from pre-load adjustments only to racing shocks with adjustments for pre-load, and four different kinds of damping. Most shocks have internal oil reservoirs, but some have external ones, and some offer air-assisted damping.
A number of companies offer custom-built rear shocks for motorcycles. These shocks are assembled for a specific motorcycle and rider combination, taking in to account the characteristics of the motorcycle, the weight of the rider, and the rider's preferred riding style/aggressiveness.
During the late 1970s and 1980s, motorcycle rear suspension design and performance underwent tremendous advances. The primary goal and result of these advances were increased rear wheel travel, as measured in the how far the rear wheel could move up and down. Before this period of intense focus on rear suspension performance, most off-road motorcycles had rear wheel travel of about 3.5–4 inch (9–10 cm). At the end of this period, most of these motorcycles had rear wheel travel of approximately 12 inch (30 cm). At the beginning of this period, various rear suspension designs were used to reach this degree of performance. However, by the end of this period, a design consisting of using only one shock absorber (instead of two) was universally accepted and used. Motorcycles with only one shock absorber are called monoshock motorcycles. The performance of monoshock motorcycles was vastly superior to twin shock motorcycles. Accordingly, this design distinction is readily used to categorize motorcycles. Since monoshock motorcycles have been the norm since the 1980s, the term "twinshock" is now used to categorize vintage motorcycles. This distinction is important in that it provides classes used for vintage motorcycle competition. For example, vintage motocross races are held for older motocross motorcycles. To prevent the better-performing monoshock motorcycles from dominating the competition, there are separate competition classes for monoshock and twinshock motorcycles, which prevents them from competing directly against each other.
to connect to the swingarm.
Mono-shocks eliminate torque to the swingarm and provide more consistent handling and braking. They are also easier to adjust, since there's only one shock absorber to adjust, and there is no worry about matching two shocks. Also, the linkages used to connect the shock to the swing-arm are frequently designed to give a rising rate of damping for the rear.
Honda refers to its mono-shock designs as Pro-link suspensions, Kawasaki as Uni-Track, Suzuki as Full-Floater and Yamaha as Monocross.
Suspension (vehicle)
Suspension is the term given to the system of springs, shock absorbers and linkages that connects a vehicle to its wheels. Suspension systems serve a dual purpose — contributing to the car's roadholding/handling and braking for good active safety and driving pleasure, and keeping vehicle occupants...
serves a dual purpose: contributing to the vehicle's handling and braking, and providing safety and comfort by keeping the vehicle's passengers comfortably isolated from road noise, bumps and vibrations.
The typical motorcycle has a pair of fork tubes for the front suspension, and a swingarm with one or two shock absorber
Shock absorber
A shock absorber is a mechanical device designed to smooth out or damp shock impulse, and dissipate kinetic energy. It is a type of dashpot.-Nomenclature:...
s for the rear suspension.
Front suspension
The most common form of front suspension for a motorcycle is the telescopic forkMotorcycle fork
A motorcycle fork connects a motorcycle's front wheel and axle to its frame, typically via a pair of triple clamps. It typically incorporates the front suspension and front brake, and allows the bike to be steered via handlebars attached to the top clamp....
. Early front suspension designs used frames with springs.
Vespa
Vespa is an Italian brand of scooter manufactured by Piaggio. The name means wasp in Italian.The Vespa has evolved from a single model motor scooter manufactured in 1946 by Piaggio & Co. S.p.A...
.
The Hub-center steering
Hub-center steering
Hub-center steering is one of several different types of front end suspension/steering mechanisms used in motorcycles. Hub-center steering is characterized by a swingarm that extends from the bottom of the engine/frame to the centre of the front wheel instead of two forks.The advantages of using a...
as developed by Ascanio Rodorigo, on a concept associated to Massimo Tamburini
Massimo Tamburini
Massimo Tamburini is an Italian motorcycle designer for motorcycle companies including: Cagiva, Ducati, MV Agusta; and Bimota, which he founded, together with Bianchi and Morri ....
is a complex front swingarm alternative system that entails suspension and steering, as seen in projects such as Bimota
Bimota
Bimota is a small, Italian manufacturer of custom and production motorcycles. It was founded in 1973 in Rimini, Italy by Bianchi, Morri and Tamburini. The company name is a portmanteau derived from the first two letters of each of the three founders' surnames, i.e...
Tesi and Vyrus motorcycles.
Telescopic forks
In 1934 Nimbus was the first manufacturer to produce a motorcycle with hydraulically damped telescopic forks. Most motorcycles today use telescopic forks for the front suspension. The forks can be most easily understood as simply large hydraulic shock absorbers with internal coil springCoil spring
A Coil spring, also known as a helical spring, is a mechanical device, which is typically used to store energy and subsequently release it, to absorb shock, or to maintain a force between contacting surfaces...
s. They allow the front wheel to react to imperfections in the road while isolating the rest of the motorcycle from that motion.
The bottom of the forks are connected to the front axle around which the front wheel spins.
On typical forks, the upper portion, known as the fork tubes, slide inside the fork bodies, which are the lower part of the forks. As the tubes slide in and out of the body they are telescoping, thus the term telescopic forks. The fork tubes must be smooth to seal the fork oil inside the fork, and typically have a mirrored finish, though some fork tubes, especially those on off-road motorcycles, are enclosed in plastic protective sleeves, known as gaiters.
"Upside-down" (USD) forks, also known as inverted forks, are installed inverted compared to typical forks, with the tubes at the bottom and the bodies at the top. This decreases the unsprung weight
Unsprung weight
In a ground vehicle with a suspension, the unsprung weight is the mass of the suspension, wheels or tracks , and other components directly connected to them, rather than supported by the suspension...
of the motorcycle and improves its handling. USD forks are usually found on sportbikes, though Honda
Honda
is a Japanese public multinational corporation primarily known as a manufacturer of automobiles and motorcycles.Honda has been the world's largest motorcycle manufacturer since 1959, as well as the world's largest manufacturer of internal combustion engines measured by volume, producing more than...
's large power-cruiser, the Valkyrie
Honda Valkyrie
The Honda Valkyrie is a motorcycle that was manufactured by Honda, from model years 1997 to 2003. It was designated GL1500C in the US market and F6C in other markets....
, sported USD forks.
Pre-load adjustment
Motorcycle suspensions are designed so that the springs are always under compression, even when fully extended. Pre-load is used to adjust the initial position of the suspension with the weight of the motorcycle and rider acting on it.The difference between the fully extended length of the suspension and the length compressed by the weight of the motorcycle and rider is called total sag. Total sag is set to optimize the initial position of the suspension to avoid bottoming out or topping out under normal riding conditions. Bottoming out" occurs when the suspension is compressed to the point where it mechanically cannot compress any more. Topping out occurs when the suspension extends fully and cannot mechanically extend any more. Increasing pre-load increases the initial force on the spring thereby reducing total sag. Decreasing pre-load decreases the initial force in the spring thereby increasing total sag.
A few motorcycles allow adjustment of pre-load by changing the air pressure inside the forks. Valves at the top of the forks allow air to be added or released from the fork. More air pressure gives more preload, and vice versa.
Damping adjustment
Some stock telescopic forks have external adjustments for dampingDamping
In physics, damping is any effect that tends to reduce the amplitude of oscillations in an oscillatory system, particularly the harmonic oscillator.In mechanics, friction is one such damping effect...
. The adjuster turns a rod inside the fork which brings different sized orifices into alignment with the damping fluid flow path inside the fork. Smaller orifices restrict the flow of the fork oil more and give greater damping.
Fork oil
Since forks act as hydraulic shocks, changing the weight of the fork oil will change the damping.
Cartridge forks
Cartridge forks use internal cartridges with various leaf springs covering orifices to control the damping of the fork.
Some of the leaf springs lift with little force allow fluid to flow through the orifice. Other springs require greater force to lift and allow flow. This gives the fork digressive damping, allowing it to be stiff over small bumps, but get relatively softer over larger bumps.
Also, the springs only allow flow in one direction, so one set of springs controls compression damping, and another rebound damping. This allows the dampings to be set separately.
Cartridge emulators are aftermarket parts that make non-cartrdige forks behave like cartridge forks.
Gas-charged cartridge forks
In 2007 the gas-charged bolt-in cartridge set for modern sportbike forks became available. This kit is legal for supersport styled classes of racing, which regulations do not allow a complete fork replacement, and force competitors to use the stock fork casings.
Brake dive
Applying the brakes of a moving motorcycle increases the load borne by the front wheel and decrease the load borne by the rear wheel due to a phenomenon called load transfer. For a detailed explanation and a sample calculation, see the braking section of the Bicycle and motorcycle dynamicsBicycle and motorcycle dynamics
Bicycle and motorcycle dynamics is the science of the motion of bicycles and motorcycles and their components, due to the forces acting on them. Dynamics is a branch of classical mechanics, which in turn is a branch of physics. Bike motions of interest include balancing, steering, braking,...
article.
Brake dive can be disconcerting to the rider, who may feel like he or she is about to be thrown over the front of the motorcycle. If the bike dives so far as to bottom out the front forks, it can also cause handling and braking problems. One of the purposes of a suspension is to help maintain contact between the tire and road. If the suspension has bottomed out, it is no longer moving as it should, and is no longer helping to maintain contact.
Brake dive with telescopic forks can be reduced by either increasing the spring rate of the fork springs, or
increasing the compression damping of the forks. However, all of these changes make the motorcycle less pleasant to ride on rough roads, since the front end will feel stiffer, in the 1980s various manufacturers attempted to get round this by methods of anti-dive such as:
- ACT: Developed by Marzocchi and fitted to Buell motorcycles such as the Buell RR 1200 (1988).
- ANDF (Anti Nose Dive Forks): This was fitted to a number of Suzuki GSX models and the RG250.
- AVDS (Automatic Variable Damping System): This was fitted to a number of Kawasaki motorcycles.
- NEAS (New Electrically Activated Suspension): As fitted to the Suzuki GSX-R 1100 and GSX-R 750 Limited Edition.
- PDF (Posi Damp Fork): This was fitted to the Suzuki RG500 and GSX-R 750 and worked by brake fluid pressure closing a valve in the mechanism when the brakes are applied, restricting the flow of damping oil and slowing fork compression. The valves are spring-loaded so if the wheel hits a bump when the brakes are on, they bounce off their seats and restore the flow of oil for a moment to allow the suspension to absorb the shock.
- TCS (Travel Control System): Anti-dive system with variable damping. TCS was introduced on the FZ 400 R (1984, only for the Japanese market).
- TRAC (Torque Reactive Anti-dive Control): This was fitted to a number of Honda motorcycles such as the CB1100FHonda CB1100FThe CB1100F is a standard motorcycle that was made by Honda, based on their line of DOHC air-cooled inline four engines. It was only available in 1983...
, CB1000C, and VFR750F and worked by utilizing a pivoting caliper that activated a valve in the fork leg.
Another method to reduce or eliminate brake dive in telescopic forks is to use a reactive link or torque arm to connect the braking components to the motorcycle frame via the triple clamp.
Some fork designs mitigate dive, eliminate it, or even reverse it without affecting the front suspension adversely. The Earles fork is among the latter; when braking the front brake hard, the front end of the motorcycle actually rises. BMW's Telelever fork is designed to nearly eliminate dive, but could have been designed to eliminate it completely if the manufacturer chose to do so. Leading link front forks, such as used on some Ural motorcycles
IMZ-Ural
IMZ-Ural is a Russian maker of heavy sidecar motorcycles. Recently the company has developed a solo motorcycle with no sidecar.In 1940, the Soviet Union acquired the design and production techniques for BMW R 71 motorcycles and sidecars. The first M-72 model was finished in 1941...
, can also be designed either to reduce or eliminate dive.
Saxon-Motodd (Telelever) fork
BMW motorcycles
BMW's motorcycle history began in 1921 when the company commenced manufacturing engines for other companies. Motorcycle manufacturing now operates under the BMW Motorrad brand...
) has an additional swingarm that mounts to the frame and supports the spring. This causes the rake and trail to increase during braking instead of decreasing as with traditional telescopic forks.
Hossack/Fior (Duolever) fork
The Hossack/Fior (marketed as Duolever by BMWBMW motorcycles
BMW's motorcycle history began in 1921 when the company commenced manufacturing engines for other companies. Motorcycle manufacturing now operates under the BMW Motorrad brand...
) separates completely the suspension from steering forces. It was developed by Norman Hossack though used by Claude Fior and John Britten
John Britten
John Kenton Britten was a New Zealand mechanical engineer who designed a world-record-setting motorcycle with innovative features which are still ahead of contemporary design.-Biography:...
on racebikes. Hossack himself described the system as a 'steered upright'. In 2004 BMW announced the K1200S with a new front suspension that is based upon this design.
Single-sided
A single-sided front swingarm suspension was used on the Yamaha GTS1000Yamaha GTS1000
The GTS1000 is a sport-touring motorcycle introduced by Yamaha in 1993, sold until 1994 in the United States, and sold elsewhere until 1996. It is notable for its innovative forkless front suspension, specifically a RADD front suspension designed by James Parker...
, introduced in 1993. The GTS used the RADD front suspension designed by James Parker
James Parker
James Parker may refer to:*Jim Parker , founder of Parker College of Chiropractic and Parker Seminars*Jim Parker , British composer*Jim Parker , American professional football player...
. A single sided girder fork was use by the German firm Imme between 1949 and 1951, and the Vespa
Vespa
Vespa is an Italian brand of scooter manufactured by Piaggio. The name means wasp in Italian.The Vespa has evolved from a single model motor scooter manufactured in 1946 by Piaggio & Co. S.p.A...
scooter has a single-sided trailing-link fork. More recently, the ItalJet "Dragster" scooter also uses a single-sided swingarm suspension, though unlike the GTS1000 there is no upper control arm; the upper part of the suspension on the Dragster serves only to transmit steering input.
Rear suspension
Early rear suspensions
While front suspensions were almost universally adopted before World War I, several manufacturers did not use rear suspension on their bikes until after World War II. However, motorcycles with rear suspension were offered to the public before World War I. Notable among these are the 1913 IndianIndian (motorcycle)
Indian is an American brand of motorcycles. Indian motorcycles were manufactured from 1901 to 1953 by a company in Springfield, Massachusetts, USA, initially known as the Hendee Manufacturing Company but which was renamed the Indian Manufacturing Company in 1928. The Indian factory team took the...
Single with a swingarm suspended from a leaf spring
Leaf spring
Originally called laminated or carriage spring, a leaf spring is a simple form of spring, commonly used for the suspension in wheeled vehicles...
and the 1913 Pope with wheels supported on a pair of plungers which were each suspended by a coil spring
Coil spring
A Coil spring, also known as a helical spring, is a mechanical device, which is typically used to store energy and subsequently release it, to absorb shock, or to maintain a force between contacting surfaces...
.
Plunger suspension
Several motorcycles before and immediately after World War II used plunger suspension in which the vertical movement of the rear axle was controlled by plungers suspended by springs.Notable manufacturers of bikes with plunger suspension include Adler
Adler (automobile)
Adler was a German automobile and motorcycle manufacturer from 1900 until 1957. Adler is German for eagle.-History:The Adler factory produced bicycles, typewriters, and motorcycles in addition to cars...
, Ariel
Ariel (vehicle)
Ariel was a bicycle, motorcycle and automobile marque manufacturer based in Bournbrook, Birmingham, England. Car production moved to Coventry in 1911. The company name was reused in 1999 for the formation of Ariel Ltd, a sports car producer.-History:...
, BMW
BMW motorcycles
BMW's motorcycle history began in 1921 when the company commenced manufacturing engines for other companies. Motorcycle manufacturing now operates under the BMW Motorrad brand...
, BSA
Birmingham Small Arms Company
This article is not about Gamo subsidiary BSA Guns Limited of Armoury Road, Small Heath, Birmingham B11 2PP or BSA Company or its successors....
, Indian
Indian (motorcycle)
Indian is an American brand of motorcycles. Indian motorcycles were manufactured from 1901 to 1953 by a company in Springfield, Massachusetts, USA, initially known as the Hendee Manufacturing Company but which was renamed the Indian Manufacturing Company in 1928. The Indian factory team took the...
, MZ
MZ Motorrad- und Zweiradwerk
MZ Motorrad- und Zweiradwerk GmbH is a motorcycle manufacturer located in Zschopau, Germany. MZ an acronym, stands for Motorradwerk Zschopau in the Erzgebirge region of Saxony...
, Norton
Norton (motorcycle)
Norton is a British motorcycle marque, originally from Birmingham, founded in 1898 as a manufacturer of "fittings and parts for the two-wheel trade". By 1902, they had begun manufacturing motorcycles with bought-in engines. In 1908, a Norton-built engine was added to the range...
, and Zündapp
Zündapp
Zündapp was a major German motorcycle manufacturer. The company was founded in 1917 in Nuremberg by Fritz Neumeyer, together with the Friedrich Krupp AG and the machine tool manufacturer Thiel under the name "Zünder- und Apparatebau G.m.b.H." as a producer of detonators...
Swingarms
The basic motorcycle swingarm is a rectangle, with one short side connected to the motorcycle's frame with bearingsBearing (mechanical)
A bearing is a device to allow constrained relative motion between two or more parts, typically rotation or linear movement. Bearings may be classified broadly according to the motions they allow and according to their principle of operation as well as by the directions of applied loads they can...
so that it can pivot. The other short side is the rear axle around which the rear wheel turns. The long sides are connected to the motorcycle's frame or rear sub-frame with one or two shocks with coil-over springs.
In production motorcycles, swingarms are not exactly rectangular, but their function can be more easily understood by thinking of them as such.
Honda VFR800
The Honda VFR800, also known as the Interceptor, is a motorcycle introduced by Honda in 1998. It is a successor to the VFR750F , which was preceded by the VF750.From its first sales in 1986, the VFR750F scored highly on many press reviews...
and the BMW
BMW Motorrad
BMW Motorrad is the motorcycle brand of the German company BMW, part of its Corporate and Brand Development division. The current General Director of the unit is Hendrik von Kuenheim....
R- and K-series. Single-sided swingarms make rear-wheel removal easier, though they generally increase the unsprung weight
Unsprung weight
In a ground vehicle with a suspension, the unsprung weight is the mass of the suspension, wheels or tracks , and other components directly connected to them, rather than supported by the suspension...
of the rear suspension. This is due to the additional material required to give identical torsional rigidity to a conventional (two-sided) swingarm setup. For this reason sports bikes are rarely seen using the setup. Notable exclusions are the Ducati 916 which was intended to be taken endurance racing, the MV Agusta f4 which has a hollow interior for reducing weight (a magnesium version is also available), and the Ducati 1098, which was given a single sided swingarm purely for styling reasons.
On many shaft-drive motorcycles the drive shaft is contained in one of the long sides of the swingarm. Notable examples include all post-1955 BMW models prior to BMW's use of the single-sided swingarms, Urals
IMZ-Ural
IMZ-Ural is a Russian maker of heavy sidecar motorcycles. Recently the company has developed a solo motorcycle with no sidecar.In 1940, the Soviet Union acquired the design and production techniques for BMW R 71 motorcycles and sidecars. The first M-72 model was finished in 1941...
, many Moto Guzzi
Moto Guzzi
Moto Guzzi is an Italian motorcycle manufacturer. It is one of seven brands owned by Piaggio.Established in 1921 in Mandello del Lario, Italy, the company is noted for its central historic role in Italy's motorcycling manufacture, its prominence worldwide in motorcycle racing, and a series of...
twins, the Honda Goldwing
Honda Goldwing
The Honda Gold Wing is a touring motorcycle designed and manufactured by Honda. It was introduced October 1974, and went on to become a popular model in North America, Western Europe and Australia. Over the course of its history, it has had numerous modifications to its design. In 1975 it featured...
, the Yamaha XS Eleven
Yamaha XS Eleven
The Yamaha XS Eleven motorcycle, also called XS11 and XS1100, is a Japanese superbike produced from 1978 to 1981, powered by an air-cooled 1101.6cc 4-stroke, DOHC inline four-cylinder engine mounted transversely in a duplex cradle frame with swingarm rear suspension, shaft drive, and telescopic...
, and the Yamaha FJR1300
Yamaha FJR1300
The Yamaha FJR1300 is the Yamaha Motor Company's largest sport touring motorcycle, currently in production as the FJR1300A and FJR1300AS .-History:...
.
The BMW R- and K-series combine a shaft-drive contained in the swing arm with a single-sided swingarm, and the combination is marketed as the Paralever. Newer Moto Guzzi motorcycles use a similar arrangement marketed as the CA.R.C. ("CArdano Reattivo Compatto" - Compact Reactive Shaft Drive).
For motorcycles with chain drives, the rear axle can be adjusted forward and back in relation to the swingarm, to adjust chain tension.
Shock absorbers
The hydraulic shock absorbers used on the rear suspensions of motorcycles are essentially the same as those used in other vehicle applications.Motorcycle shocks do differ slightly in that they nearly always use a coil-over spring. In other words, the spring for the rear suspension is a coil spring that is installed over, or around, the shock.
In terms of adjustment, rear shocks span the range from pre-load adjustments only to racing shocks with adjustments for pre-load, and four different kinds of damping. Most shocks have internal oil reservoirs, but some have external ones, and some offer air-assisted damping.
A number of companies offer custom-built rear shocks for motorcycles. These shocks are assembled for a specific motorcycle and rider combination, taking in to account the characteristics of the motorcycle, the weight of the rider, and the rider's preferred riding style/aggressiveness.
Twin shock absorbers
Twinshock refers to motorcycles that have two shock absorbers. Generally, this term is used to denote a particular era of motorcycles, and is most frequently used when describing off-road motorcycles.During the late 1970s and 1980s, motorcycle rear suspension design and performance underwent tremendous advances. The primary goal and result of these advances were increased rear wheel travel, as measured in the how far the rear wheel could move up and down. Before this period of intense focus on rear suspension performance, most off-road motorcycles had rear wheel travel of about 3.5–4 inch (9–10 cm). At the end of this period, most of these motorcycles had rear wheel travel of approximately 12 inch (30 cm). At the beginning of this period, various rear suspension designs were used to reach this degree of performance. However, by the end of this period, a design consisting of using only one shock absorber (instead of two) was universally accepted and used. Motorcycles with only one shock absorber are called monoshock motorcycles. The performance of monoshock motorcycles was vastly superior to twin shock motorcycles. Accordingly, this design distinction is readily used to categorize motorcycles. Since monoshock motorcycles have been the norm since the 1980s, the term "twinshock" is now used to categorize vintage motorcycles. This distinction is important in that it provides classes used for vintage motorcycle competition. For example, vintage motocross races are held for older motocross motorcycles. To prevent the better-performing monoshock motorcycles from dominating the competition, there are separate competition classes for monoshock and twinshock motorcycles, which prevents them from competing directly against each other.
Mono-shock
On a motorcycle with a mono-shock rear suspension, there is only one shock that connects the rear swingarm to the motorcycle's frame. Typically this lone shock absorber is in front of the rear wheel, and uses a linkageLinkage (mechanical)
A mechanical linkage is an assembly of bodies connected together to manage forces and movement. The movement of a body, or link, is studied using geometry so the link is considered to be rigid. The connections between links are modeled as providing ideal movement, pure rotation or sliding for...
to connect to the swingarm.
Mono-shocks eliminate torque to the swingarm and provide more consistent handling and braking. They are also easier to adjust, since there's only one shock absorber to adjust, and there is no worry about matching two shocks. Also, the linkages used to connect the shock to the swing-arm are frequently designed to give a rising rate of damping for the rear.
Honda refers to its mono-shock designs as Pro-link suspensions, Kawasaki as Uni-Track, Suzuki as Full-Floater and Yamaha as Monocross.