A variety of fork arrangements have been tried during more than one hundred years of motorcycle development, several of which remain available today.
Telescopic A
telescopic fork uses
fork tubes which contain the suspension components (coil springs and damper) internally. This is the most common form of fork commercially available. It may or may not include gaiters for protection against abrasive elements on the suspension cylinders. The main advantages of the telescopic fork are that (i) it is simple in design and relatively cheap to manufacture and assemble; (ii) it is lighter than older designs using external components and linkage systems; and (iii) it has a clean and simple appearance that riders find attractive. Conventionally, the fork
stanchions are at the top, secured by a
yoke (also called a triple tree or a triple clamp), and the sliders are at the bottom, attached to the front wheel spindle. On some modern sport motorcycles and most off-road motorcycles, this system is inverted, with "sliders" (complete with the spring/damper unit) at the top, clamped to the yoke, while the stanchions are at the bottom. This is done (i) to reduce unsprung weight by having the heavier components suspended, and (ii) to improve the strength and rigidity of the assembly by having the strong large-diameter "sliders" clamped in the yokes. The inverted system is referred to as an
upside-down fork, or "USD" for short. A disadvantage of this USD design is that the entire reservoir of damping oil is above the slider seal so that, if the slider seal were to leak, the oil could drain out, rendering any damping ineffective.
Trailing link A trailing link fork suspends the wheel on a link (or links) with a pivot point forward of the wheel axle. It has been used by
Indian; by BMW on early models such as the
R32, and in the USSR on the
PMZ-A-750.
Leading link A leading link fork suspends the wheel on a link (or links) with a pivot point aft of the wheel axle. Russian
Ural motorcycles used leading link forks on
sidecar equipped motorcycles, and aftermarket leading link forks are often installed today on motorcycles when they are outfitted with sidecars. They are also very popular with
trikes, improving the handling while steering or braking. The most common example of a leading link fork is that found on the
Honda Super Cub.
Springer The
springer fork is an early type of leading link fork. A springer fork does not have the suspension built into the fork tubes, but instead has it mounted externally, where it may be integrated into the triple clamp. This style of fork may be found on antique motorcycles or
choppers, and is available today on
Harley-Davidson's Softail Springer. While it may have an exposed spring near the triple clamp, a springer fork is distinguishable from a
girder fork by its two parallel sets of legs. The rear is firmly fixed to the bottom triple clamp (usually brazed or welded). A short leading link holds the wheel and the forward leg which actuates the springs (usually mounted on the triple clamp).
Earles The
Earles fork is a variety of leading link fork where the pivot point is behind the front wheel, which is the basis of the Earles' patent. Patented by
Englishman Ernest Earles in 1953, the design is constructed of light tubing, with conventional 'shock absorbers' mounted near the front axle. The Earles fork has a very small wheelbase change under braking or under compression, unlike telescopic forks. Their construction is much stronger than teleforks, especially against lateral deflection caused by hard cornering (as when racing), or when cornering with a
sidecar. While both may have an exposed spring near the triple clamp, a girder fork is distinguishable from a
springer fork by the wheel being fixed firmly to the (usually a long diamond shape) upright. The pivot points are short links mounted to the top and bottom triple clamps. The spring is usually mounted to the girder and compressed against the upper triple clamp. Although girder forks are associated with early motorcycles, the British
Ariel Ace, a modern
sports motorcycle, has an alloy space frame and a matching girder fork. This Ariel girder fork is just as prone to brake dive as any telescopic fork, but is claimed to be more resistant to torsional twisting.
Saxon-Motodd (Telelever) The Saxon-Motodd fork (marketed as Telelever by
BMW) has a wishbone that mounts to the frame and supports the
monoshock unit. This relieves the forks of any braking and suspension forces. With a Saxon-Motodd fork, the trail and
caster angle (
rake) increases during braking instead of decreasing as with traditional telescopic forks. BMW's boxer twins have been equipped with Telelever forks since 1994, but some newer boxers like the
BMW R nineT have reverted to conventional telescopic forks for aesthetic and packaging reasons.
Hossack/Fior (Duolever) The Hossack/Fior fork (marketed as Duolever by
BMW) completely separates the suspension from steering forces. Developed by
Norman Hossack and used by Claude Fior and
John Britten on racing motorcycles, Hossack described the system as a 'steered upright'. In 2004 BMW announced the K1200S with a new front suspension that appears to be based upon the design. As of 2024, the Duolever is on the BMW K models: K1200R,
K1300R, K1200S,
K1300S,
K1200GT,
K1300GT and
K1600.
Coaxial steering front suspension Developed by
MotoCzysz for their C1 and awarded United States Patent 7111700 on September 26, 2006. Defined as a motorcycle or bicycle front end having coaxial steering and suspension components, and having telescopic forks. Swing weight of the forks is dramatically reduced by removing their suspension components to the central location, coaxially within the steering tube. Ride height can be adjusted without loosening the forks in the triple clamps. This particular fork, as implemented on the MotoCzysz C1, also has adjustable trail, from 89 mm to 101 mm.
Non-forks suspension There have been several attempts to implement front steering and suspension without using anything that could be described as a "fork". Examples include
hub-center steering, used as early as 1920 on the
Ner-a-Car, and implemented in the 1990s on the
Bimota Tesi between 1949 and 1951. ==See also==