Motorcycle fork

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1968 BMW R60US with conventional telescopic fork

Yamaha's inverted telescopic fork

The world's first oil-damped telescopic fork, on a 1939 BMW R12

Trailing link fork on a 1928 BMW R57

Unusual "trailing bottom link" on a Honda Rune

Earles front forks on three BMWs

BMW Telelever fork on an R1200GS

Ural's variant of the leading link fork

Duolever front fork

A motorcycle fork is the portion of a motorcycle that holds the front wheel, usually incorporates the front suspension, and allows one to steer. A fork may consist of two fork tubes (sometimes also refered to as forks) which hold the front wheel axle and a triple tree which connects the fork tubes and the handlebars to the frame with a pivot that allows for steering.

The fork, along with its attachment points on the frame establish the critical motorcycle geometry parameters of rake and trail, which in turn contribute to wheelbase.

The front brakes are connected to the fork, and act against a rotor or drum attached to the front wheel. The front fender is also usually attached to the front fork.

The fork, how it is implemented and adjusted, plays a major role in defining how a motorcycle handles, especially how much it dives during braking.^[1]

1 Variations
2 See also
3 References

[edit] Variations

Over the more than one hundred years of motorcycle development, several variations of front forks have been tried. Several are commercially available today.

[edit] Telescopic fork

A telescopic fork uses fork tubes which contain the suspension components internally. This is the most common form of fork commercially available.

[edit] Trailing Link Fork

A trailing link fork suspends the wheel on a link (or links) with a pivot point forward of the wheel axle. Most famously used by Indian Motorcycles, it was also used by BMW for its early bikes.

[edit] Leading Link Fork

A leading link fork suspends the wheel on a link (or links) with a pivot point aft of the wheel axle. Russian Ural motorcycles still use leading link forks on sidecar equipped motorcycles, and aftermarket leading link forks are often installed today on motorcycles when they are outfitted with sidecars.

[edit] Springer fork

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 tree. This style of fork may be found on antique motorcycles or choppers, and is available today on Harley-Davidson's Softail Springer.

[edit] Earles fork

The Earles fork was a variety of leading link fork where the pivot point was aft of the rear of the wheel ─ this was the basis of the Earle's patent. Designed by Englishman Ernest Earles, this triangulated fork actually caused the front end of a motorcycle to rise when braking hard — the reverse of the action of a telescopic fork. It was designed to accommodate sidecars, and from 1955 to 1969, BMW used the fork even though most of its motorcycles were sold as solo bikes.

[edit] BMW Telelever fork

The BMW Telelever fork has an additional swingarm that mounts to the frame and supports the spring. This causes the trail and castor angle (rake) to increase during braking instead of decreasing as with traditional telescopic forks.^[2] In the 21st century, most BMW twins are equipped with Telelever forks.

[edit] Duolever fork

In 2003 BMW announced the K1200S with a new front suspension that appears to be based upon a design by Norman Hossack. BMW named its new front suspension the Duolever, and it separates completely the suspension from steering forces. As of 2006, the Duolever is on the K1200S, K1200R, and K1200GT.

[edit] Non forks

There have been several attempts to implement front steering and suspension without using anything that could be described as a "fork". An example is Hub-center steering as implemented on the Bimota Tesi^[3] or the RADD by James Parker implemented on the Yamaha GTS-1000^[4].