Fork tube

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 front wheel to rotate about the steering axis so that the bike may be steered. Handlebars attach to the top clamp.

The fork and its attachment points on the frame establish the critical geometric parameters of rake and trail, which play a major role in defining how a motorcycle handles and dives during braking.

A variety of front fork arrangements have been tried during more than one hundred years of motorcycle development, several of which remain available today.

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 bikers find attractive.

Conventionally, the fork stanchions are at the top, clamped to a triple tree (also called a triple clamp or a yoke), and the sliders are at the bottom, attached to the front wheel spindle. On some modern sport bikes and most off-road bikes, 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.

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