| The most common form of front suspension for | | | | longer longer helping to maintain contact. |
| a motorcycle is the telescopic fork. Early | | | | |
| front suspension designs used frames with | | | | Brake dive can be reduced by: |
| springs. | | | | |
| | | | Increasing the spring rate of the fork |
| Some British manufacturers (eg Greeves) used | | | | springs |
| a version of the swinging arm for front | | | | |
| suspension on their motocross designs. A | | | | Increasing the pre-load |
| single-sided version of the idea was also | | | | |
| used in motor scooters such as the Vespa | | | | Increasing the compression damping of the |
| | | | forks |
| Telescopic forks | | | | |
| | | | However, all of these changes make make the |
| In 1935 BMW was the first manufacturer to | | | | motorcycle less pleasant to ride on rough |
| produce a motorcycle, the R12, with | | | | roads, since the front end will feel stiffer. |
| hydraulically damped telescopic forks. Most | | | | |
| motorcycles today use telescopic forks for | | | | Telelever |
| the front suspension. The forks can be most | | | | |
| easily understood as simply large hydraulic | | | | BMW introduced its Telelever Front Suspension |
| shock absorbers with internal coil springs. | | | | in 1993. The Telelever uses a linkage and |
| They allow the front wheel to react to | | | | single hydraulic shock with external spring |
| imperfections in the road while isolating the | | | | to replace the more common telescopic front |
| rest of the motorcycle from that motion. | | | | fork suspension. |
| | | | |
| The top of the forks are connect to the | | | | The Telelever, according to BMW, "separates |
| motorcycle's frame in a triple tree clamp | | | | suspension and steering." It is most commonly |
| (otherwise known to British riders as the top | | | | praised for virtually eliminating braking |
| yoke and bottom yoke), which allows the forks | | | | dive. It is standard on BMW's R-series |
| to be turned in order to steer the | | | | motorcycles and was standard on all the |
| motorcycle. | | | | K-series bikes until the introduction of the |
| | | | K1200S. |
| The bottom of the forks are connected to the | | | | |
| front axle around which the front wheel | | | | BMW introduced a copy of a front suspension |
| turns. The front brakes are also connected to | | | | system designed by Norman Hossakfor the |
| the forks, and act against a rotor or drum | | | | K1200S, naming it Duolever. |
| attached to the front wheel. | | | | |
| | | | Single-sided |
| On typical forks, the upper portion, known as | | | | |
| the fork tubes, slide inside the fork bodies, | | | | The only production motorcycle to use a |
| which are the lower part of the forks. As the | | | | single-sided front swingarm suspension was |
| tubes slide in and out of the body they are | | | | Yamaha's GTS1000, introduced in 1993. The GTS |
| telescoping, thus the term telescopic forks. | | | | used the RADD front suspension designed by |
| The fork tubes must be smooth to seal the | | | | James Parker. |
| fork oil inside the fork, and typically have | | | | |
| a mirrored finish, though some fork tubes, | | | | Rear suspension |
| especially those on off-road motorcycles, are | | | | |
| enclosed in plastic protective sleeves, known | | | | Swingarms |
| as gaiters. | | | | |
| | | | The basic motorcycle swingarm is a rectangle, |
| "Upside-down" (USD) forks are installed | | | | with one short side connected to the |
| inverted compared to typical forks, with the | | | | motorcycle's frame with bearings so that it |
| tubes at the bottom and the bodies at the | | | | can pivot. The other short side is the rear |
| top. This decreases the unsprung weight of | | | | axle around which the rear wheel turns. The |
| the motorcycle and improves its handling. USD | | | | long sides are connected to the motorcycle's |
| forks are usually found on sportbikes, though | | | | frame or rear sub-frame with one or two |
| Honda's large power-cruiser, the Valkyrie, | | | | shocks with coil-over springs. |
| sported USD forks. | | | | |
| | | | In production motorcycles, swingarms are not |
| Pre-load adjustment | | | | exactly rectangular, but their function can |
| | | | be more easily understood by thinking of them |
| When a motorcycle's forks are compressed or | | | | as such. |
| extended, the fork springs inside them are | | | | |
| under compression or tension, respectively. | | | | Some swing arms have only one long-side, and |
| | | | are know as single-sided swingarms. Notable |
| Pre-load is an amount of additional | | | | examples include the Honda VFR800 and the BMW |
| compression force the springs experience when | | | | R- and K-series of motorcycles. Single-sided |
| the forks are at a given position. When you | | | | swingarms make rear-wheel removal easier and |
| adjust the pre-load, you are either | | | | reduce the unsprung weight of the rear |
| increasing or decreasing the amount of that | | | | suspension. |
| force. | | | | |
| | | | On many shaft-drive motorcycles the drive |
| When you increase the pre-load, you increase | | | | shaft is contained in one of the long sides |
| the additional force at any given position of | | | | of the swingarm. Notable examples include the |
| the forks under compression. This causes the | | | | Honda Goldwing and the Yamaha FJR1300. |
| forks to extend more under any given external | | | | |
| force than they would at a lower pre-load | | | | The BMW R- and K-series combine a shaft-drive |
| setting. Therefore, the forks have to | | | | contained in the swing arm with a |
| experience greater external force before they | | | | single-sided swingarm, and the combination is |
| bottom out, or reach the maximum compression | | | | marketed as the Paralever. Newer Moto Guzzi |
| travel. The pre-load can be used for | | | | motorcycles use a similar arrangement |
| suspension tuning (see below). | | | | marketed as the CA.R.C. ("CArdano Reattivo |
| | | | Compatto" - Compact Reactive Shaft Drive). |
| Some motorcycles have externally accessible | | | | |
| pre-load adjustments. Typically, this is a | | | | For motorcycles with chain drives, the rear |
| screw-type adjustment that moves a backing | | | | axle can be adjusted forward and back in |
| plate inside the fork against the top of the | | | | relation to the swingarm, to adjust chain |
| fork spring. The farther down the adjuster is | | | | tension. |
| screwed, the more force is applied to the | | | | |
| spring, and the higher the preload. | | | | Shock absorbers |
| | | | |
| A few motorcycles allow adjustment of | | | | The hydraulic shock absorbers used on the |
| pre-load by changing the air pressure inside | | | | rear suspensions of motorcycles are |
| the forks. Valves at the top of the forks | | | | essentially the same as those used in other |
| allow air to be added or released from the | | | | vehicle applications. For more detail, see |
| fork. More air pressue gives more preload, | | | | the article on shock absorbers. |
| and vice versa. | | | | |
| | | | Motorcycle shocks do differ slightly in that |
| Preload on bikes without adjusters can be | | | | they nearly always use a coil-over spring. In |
| changed by disassembling the fork and | | | | other words, the spring for the rear |
| changing the length of the spacer between the | | | | suspension is a coil spring that is installed |
| top of the fork spring and the fork cap. A | | | | over, or around, the shock. |
| longer spacer gives higher pre-load, and | | | | |
| vice-versa. | | | | In terms of adjustment, rear shocks span the |
| | | | range from pre-load adjustments only to |
| The pre-load on both forks should always be | | | | racing shocks with adjustments for pre-load, |
| the same. Dangerous handling characteristics | | | | and four different kinds of damping. Most |
| and possible mechanical damage can result | | | | shocks have internal oil resevoirs, but some |
| otherwise. | | | | have external ones, and some offer |
| | | | air-assisted damping. |
| Damping adjustment | | | | |
| | | | A number of companies offer custom-built rear |
| Some stock telescopic forks have external | | | | shocks for motorcycles. These shocks are |
| adjustments for damping. The adjuster is | | | | assembled for a specific motorcycle and rider |
| either a dial or a knob slotted for a | | | | combination, taking in to account the |
| screwdriver. Turning the adjuster turns a rod | | | | characteristics of the motorcycle, the weight |
| inside the fork which brings different sized | | | | of the rider, and the rider's preferred |
| orifices into alignment with the damping | | | | riding style/aggressiveness. |
| fluid flow path inside the fork. Smaller | | | | |
| orifices restrict the flow of the fork oil | | | | Twin shocks |
| more and give greater damping, and vice | | | | |
| versa. | | | | On motorcycles with twin-shock rear |
| | | | suspensions, there is a shock on each side of |
| This adjustment is either for compression | | | | the swingarm, which connects to its |
| damping alone, or for both compression and | | | | respective side of the motorcycle's frame or |
| rebound damping. | | | | subframe. There are no linkages between the |
| | | | shocks and the swingarm or frame. |
| Fork oil | | | | |
| | | | It is important on twin-shock motorcycles |
| Since forks act as hydraulic shocks, changing | | | | that both shocks be the same, and that if |
| the weight of the fork oil will change the | | | | they are adjustable, that the adjustments on |
| damping. Higher weight fork oil will give | | | | both sides be the same. Otherwise, there can |
| more damping, and vice versa. | | | | be a torque to the swingarm which may cause |
| | | | dangerous handling and braking |
| Fork oil collects impurities over time and | | | | characteristics. |
| should be changed periodically. A | | | | |
| motorcycle's manual will give guidelines on | | | | Mono-shocks |
| how often the oil should be changed. Decades | | | | |
| ago, it was often recommended to use ATF | | | | On a motorcycle with a mono-shock rear |
| (automatic transmission fluid) as fork oil. | | | | suspension, there is only one shock that |
| Currently most sources recommend using an oil | | | | connects the rear swingarm to the |
| specifically designed to be used as fork oil, | | | | motorcycle's frame. Typically this lone shock |
| such as Bel Ray's. | | | | is in front of the rear wheel, and uses a |
| | | | linkage to connect to the swingarm. |
| Cartridge forks | | | | |
| | | | Mono-shocks eliminate torque to the swingarm |
| Cartridge forks use internal cartridges with | | | | and provide more consistent handling and |
| various leaf springs covering orifices to | | | | braking. They are also easier to adjust, |
| control the damping of the fork. | | | | since there's only one shock to adjust, and |
| | | | there is no worry about matching two shocks. |
| Some of the leaf springs lift with little | | | | |
| force allow fluid to flow through the | | | | Honda refers to its mono-shock designs as |
| orifice. Other springs require greater force | | | | Pro-link suspensions. |
| to lift and allow flow. This gives the fork | | | | |
| progressive damping, allowing it to be stiff | | | | Pre-load adjustment |
| over small bumps, but get softer over larger | | | | |
| bumps. | | | | The pre-load on a rear shock is typically |
| | | | adjusted via a threaded or notched collar on |
| Also, the springs only allow flow in one | | | | the shock. As the collar is rotated, the |
| direction, so one set of springs controls | | | | coil-over spring is compressed more or less. |
| compression damping, and another rebound | | | | The more the spring is compressed, the higher |
| damping. This allows the dampings to be set | | | | the pre-load, and vice versa. |
| separately. However, changing the settings | | | | |
| requires disassembly of the forks. | | | | Some shocks, known as air-assist shocks, |
| | | | allow adjustment of preload by changing the |
| Cartridge emulators are aftermarket parts | | | | air pressure inside the shock. A valve on the |
| that make non-cartrdige forks behave like | | | | shock allows air to be introduced or released |
| cartridge forks. | | | | from the shock. More air pressure gives more |
| | | | preload, and vice versa. |
| Brake Dive | | | | |
| | | | On motorcycles with twin shocks it is very |
| When a motorcycle brakes, weight is | | | | important that both shocks have the same |
| transferred to the front wheel, just like in | | | | pre-load. Dangerous handling and braking |
| any vehicle with a suspension. This is | | | | characteristics can result from dissimilar |
| similar to the feeling of leaning forward | | | | pre-load adjustments. |
| when you brake hard in a car. | | | | |
| | | | Damping adjustment |
| That added weight to the front wheel is | | | | |
| transmitted through the forks, which compress | | | | Stock rear shocks typically offer no damping |
| under the additional force. Since the wheel | | | | adjustment, or a single adjustment for both |
| is at the same level (the road hasn't gone | | | | compression and rebound damping. This |
| down), the shortening of the forks causes the | | | | adjustment is usually made by a dial at the |
| front end of the bike to move lower. This is | | | | very top or very bottom of the shock. The |
| brake dive. | | | | dial selects one of a few different orifice |
| | | | sizes for the damping fluid flow path. The |
| Brake dive can be disconcerting to the rider, | | | | larger the orifice, the less the damping, and |
| who may feel like he or she is about to be | | | | vice versa. |
| thrown over the front the motorcycle. If the | | | | |
| bike dives so far as to bottom out the front | | | | On motorcycles with two rear shocks, it is |
| forks, it can also cause handling and braking | | | | very important that the damping on both |
| problems. One of the purposes of a suspension | | | | shocks be set the same. Dangerous handling |
| is to help maintain contact between the tire | | | | and braking characteristics can result from |
| and road. If the suspension has bottomed out, | | | | dissimilar damping on the rear shocks. |
| it is no longer moving as it should, and no | | | | |