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A bicycle fork is the portion of a bicycle that holds the front wheel and allows one to steer. A fork consists of two dropouts which hold the front wheel axle, two blades which join at a fork crown, and a steerer to which the handlebars attach allowing the user to steer the bicycle. The steerer of the fork interfaces with the frame via a headset.
On most mountain bicycles, the fork contains a set of shock absorbers. The suspension travel and handling characteristics vary depending on the type of mountain biking the fork is designed for. For instance, manufacturers produce different forks for cross-country (XC), downhill, and freeride riding.
Bicycle forks usually have an offset, or rake (not to be confused with a different use of the word rake in the motorcycle world *), that places the dropouts forward of the steering axis. This is achieved by curving the blades forward, angling straight blades forward, or by placing the dropouts forward of the centerline of the blades. The latter is used in suspension forks that must have straight blades in order for the suspension mechanism to work. Curved fork blades can also provide some shock absorption.
The purpose of this offset is to reduce 'trail', the distance that the front wheel ground contact point trails behind the point where the steering axis intersects the ground. Too much trail makes a bicycle feel difficult to turn. Virtually all racing bicycle forks have an offset of 43-45mm due to the almost-standard frame geometry and 700c wheels, so racing forks are widely interchangeable. For touring bicycles and other designs, the frame's head angle and wheel size must be taken into account when determining offset, and there is a narrow range of acceptable offsets to give good handling characteristics. The general rule is that a slacker head angle requires a fork with more offset, and small wheels require less offset than large wheels.
In shockless forks the material of fork can noticably affect the feel of the bicycle, with aluminum offering the stiffest ride. Carbon fibre forks are popular in road bicycles because they are light, and also because they lessen the stiffness and absorb vibrations.
When sizing a fork to a frame, the diameter of the fork (1" or 1 1/8") should fit the frame, and the length of the steerer tube should be greater than but approximately equal to the head tube length plus the stack height of the headset.
See also
External links
- Adapter for bicycle forks, article
"Bicycle fork"