Bicycle Fork
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A bicycle fork is the part of a
bicycle A bicycle, also called a pedal cycle, bike or cycle, is a human-powered or motor-powered assisted, pedal-driven, single-track vehicle, having two wheels attached to a frame, one behind the other. A is called a cyclist, or bicyclist. Bic ...
that holds the front wheel. A fork typically consists of two ''blades'' which are joined at the top by a fork ''crown.'' The crown is often at the front. Most suspension forks have an arch connecting the two side of the lowers (the part connected to the axle.) It is often in front of the stanchions (shaft the lowers slide on) but not always. Above the crown, a ''steerer tube'' attaches the fork to the bicycle and the handlebars (via a
stem Stem or STEM may refer to: Plant structures * Plant stem, a plant's aboveground axis, made of vascular tissue, off which leaves and flowers hang * Stipe (botany), a stalk to support some other structure * Stipe (mycology), the stem of a mushro ...
) allowing the rider to steer the bicycle. The steerer tube of the fork interfaces with the
frame A frame is often a structural system that supports other components of a physical construction and/or steel frame that limits the construction's extent. Frame and FRAME may also refer to: Physical objects In building construction *Framing (con ...
via bearings called a headset mounted in the
head tube The head tube is the part of a cycle's tubular frame within which the front fork steerer tube is mounted. On a motorcycle, the "head tube" is normally called the steering head. On bicycles the manufacturer's brand located on the head tube is kno ...
. At the bottom of the fork, ''
fork end A fork end, fork-end, or forkend is a slot in a bicycle frame or bicycle fork where the axle of a bicycle wheel is attached. A dropout is a type of fork end that allows the rear wheel to be removed without first derailing the chain. Track bicycl ...
s'' hold the wheel. Usually, either the axle is bolted to the fork, or a ''
quick release skewer A quick release skewer is a mechanism for attaching a wheel to a bicycle. It consists of a rod threaded on one end and with a lever operated cam assembly on the other. The rod is inserted into the hollow axle of the wheel, a special nut is thr ...
'' passes through a hollow axle, clamping the axle to the fork. The term ''fork'' is sometimes also used to describe the part of a bicycle that holds the rear wheel, which on 19th century ''ordinary'' or ''penny-farthing'' bicycles was also a bladed fork. On most modern bicycle designs the rear wheel is now attached to a rear triangle comprising the
seat tube A bicycle frame is the main component of a bicycle, onto which wheels and other components are fitted. The modern and most common frame design for an upright bicycle is based on the safety bicycle, and consists of two triangles: a main triangle ...
, a pair of seat stays, and a pair of chain stays, rather than an actual fork, but the ''rear fork'' usage persists.


Dimensions

Forks have several key dimensions which include: offset, length, width, steerer tube length, and steerer tube diameter.


Offset

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 fork ends forward of the steering axis. This is achieved by curving the blades forward, angling straight blades forward, or by placing the fork ends 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 A trail, also known as a path or track, is an unpaved lane or small road usually passing through a natural area. In the United Kingdom and the Republic of Ireland, a path or footpath is the preferred term for a pedestrian or hiking trail. Th ...
', 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. Road racing bicycle forks have an offset of 40-55mm. For
touring bicycle A touring bicycle is a bicycle designed or modified to handle bicycle touring. To make the bikes sufficiently robust, comfortable and capable of carrying heavy loads, special features may include a long wheelbase (for ride comfort and to avoid p ...
s 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.


Length

The length of the fork is usually measured parallel to the steerer tube from the bottom of the lower bearing race to the center of the front wheel axle. A 1996 survey of 13 700c road forks found a maximum length of 374.7 mm and a minimum of 363.5 mm.


Width

The width of the fork, also called spacing, is measured colinear with the front wheel axle between the inside edges of the two fork ends. Most modern adult sized forks have 100 mm spacing.
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mountain bike forks designed for through axles have 110 mm spacing.


Steerer tube length

The steerer tube is sized either to just accommodate the headset bearings, in the case of a threaded headset, or to contribute to the desired handlebar height, in the case of a threadless headset.


Steerer tube diameter

When sizing a fork to a
frame A frame is often a structural system that supports other components of a physical construction and/or steel frame that limits the construction's extent. Frame and FRAME may also refer to: Physical objects In building construction *Framing (con ...
, the diameter of the fork steerer or steer tube (1" or 1⅛" or 1½") must not be larger than that of 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. Adapter kits are available to enable use of a 1" fork in a frame designed for a 1⅛" steerer tube or a 1⅛" fork in a 1½" frame. Manufacturers of high-end bikes, both road and mountain, have adopted tapered steerer tubes as the de facto standard, with a 1⅛" OD at the top and a 1½" OD at the bottom.


General sizing issues

The blades must be the proper length to both accommodate the desired wheel and have the correct amount of rake to provide the approximate steering geometry intended by the frame designer. The functional length of the fork is typically expressed in terms of Axle-to-Crown race length (A-C). Also, the axle on the wheel must fit in the fork ends (usually either a 9mm solid or hollow axle, or a 20mm thru-axle). Some manufacturers have introduced forks and matching hubs with proprietary standards, such as Maverick's 24mm axle, Specialized 25mm thru-axle and Cannondale's Lefty system.


Threading

Fork steerer tubes may be threaded or unthreaded, depending on the headset used to attach the fork to the rest of the
bicycle frame A bicycle frame is the main component of a bicycle, onto which wheels and other components are fitted. The modern and most common frame design for an upright bicycle is based on the safety bicycle, and consists of two triangles: a main triangl ...
. An unthreaded steel steerer tube may be threaded with an appropriate
die Die, as a verb, refers to death, the cessation of life. Die may also refer to: Games * Die, singular of dice, small throwable objects used for producing random numbers Manufacturing * Die (integrated circuit), a rectangular piece of a semicondu ...
if necessary. The thread pitch is usually 24 threads per inch except for some old
Raleigh Raleigh (; ) is the capital city of the state of North Carolina and the seat of Wake County in the United States. It is the second-most populous city in North Carolina, after Charlotte. Raleigh is the tenth-most populous city in the Southeas ...
s which use 26.


Suspension

On most mountain bicycles, the fork contains a set of shock absorbers, in which case the blades typically consist of upper and lower telescoping tubes and are called "legs." The suspension travel and handling characteristics vary depending on the type of
mountain biking Mountain biking is a sport of riding bicycles off-road, often over rough terrain, usually using specially designed mountain bikes. Mountain bikes share similarities with other bikes but incorporate features designed to enhance durability and pe ...
the fork is designed for. For instance, manufacturers produce different forks for cross-country (XC), downhill, and freeride riding. Forks designed for XC racing are typically lighter, less robust and have less suspension travel than those designed for rougher terrain and more extreme conditions. Popular makers of suspension forks include Cannondale, Fox, SR Suntour, Manitou, Marzocchi, and RockShox. Suspension fork design has advanced in recent years with suspension forks becoming increasingly sophisticated and diverse in design. The amount of suspension travel available has increased over time. When suspension forks were introduced, 80–100 mm of travel was deemed sufficient for a downhill mountain bike. Typically this amount of travel is now used in XC disciplines, with downhill forks now offering 150 to 200 mm of travel for handling extreme terrain. This is not the limit of suspension fork travel; for example, the Marzocchi Super Monster T offers 300 mm (12 inches) of travel. Other advances in design include adjustable travel allowing riders to adapt the fork's travel to the specific terrain profile. Typically, less suspension travel is needed for uphill or flat terrain than for downhill terrain. Advanced designs also often feature the ability to lock out the fork to eliminate or drastically reduce the fork's travel for more efficient riding over smooth sections of terrain. This lockout can sometimes be activated remotely by a cable and lever on the handlebars. The shock absorber usually consists of two parts: a
spring Spring(s) may refer to: Common uses * Spring (season) Spring, also known as springtime, is one of the four temperate seasons, succeeding winter and preceding summer. There are various technical definitions of spring, but local usage of ...
and a damper or
dashpot A dashpot, also known as a damper, is a mechanical device that resists motion via viscous friction. The resulting force is proportional to the velocity, but acts in the opposite direction, slowing the motion and absorbing energy. It is commonly us ...
. The spring may be implemented with a steel or titanium coil, an
elastomer An elastomer is a polymer with viscoelasticity (i.e. both viscosity and elasticity) and with weak intermolecular forces, generally low Young's modulus and high failure strain compared with other materials. The term, a portmanteau of ''elastic p ...
, or even compressed air. The choice of spring material has a fundamental effect on the characteristics of the fork as a whole. Coil spring forks are often heavier than designs which use compressed air springs, but they are more easily designed to exhibit a linear,
Hookean In physics, Hooke's law is an empirical law which states that the force () needed to extend or compress a spring by some distance () scales linearly with respect to that distance—that is, where is a constant factor characteristic of ...
response throughout their travel. Replacing steel coils with titanium coils in a design can decrease the weight of the design but leads to an increase in expense. Air springs utilize the thermodynamic property of gases that their pressures increase as they are compressed adiabatically. As the "spring" is provided by air rather than a coil of metal, forks with air springs are often lighter. This makes their use more common in XC designs. Another advantage of this type of fork design is that the spring constant can be adjusted by adjusting the air pressure. This allows a fork to be tuned to a rider's weight. One disadvantage of this design is the difficulty in achieving a linear response, as pressure varies approximately inversely (not linearly) with volume in a gas. As the fork compresses, the effective spring constant of the fork increases. Increasing the volume of the air inside the spring can reduce this effect, but the volume of the spring is ultimately limited, as it needs to be contained within the dimension of the fork blade. The damper usually forces oil to pass through one or more small openings or shim stacks in the suspension fork. On some models, the spring, the damper, or both may be adjusted for rider weight, riding style, terrain, or any combination of these or other factors. The two components may be separated with the spring mechanism in one blade and the damper in the other.


Variations

There have been many fork design variations tried over the years. Several are still in use today.


Suspension

Some have employed linkages to provide the mechanical action instead of relying upon telescoping elements. Others, notably
Cannondale The Cannondale Bicycle Corporation is an American division of Dutch conglomerate Pon Holdings that supplies bicycles. Its headquarters are in Wilton, Connecticut with engineering offices in Freiburg, Germany. Frames are manufactured in Taiwan ...
use a single shock built into the steerer tube above the crown. Another notable recent development in fork technology is the Lauf Spring which utilises composite leaf springs to provide mechanical shock absorption and damping, whilst offering a sizable weight reduction compared to conventional designs


Single blade

Some manufacturers, such as
Cannondale The Cannondale Bicycle Corporation is an American division of Dutch conglomerate Pon Holdings that supplies bicycles. Its headquarters are in Wilton, Connecticut with engineering offices in Freiburg, Germany. Frames are manufactured in Taiwan ...
and
Strida Strida is a portable belt-driven folding bicycle with a distinctive 'A'-shaped collapsible frame, designed by British engineer and designer Mark Sanders. The first model, Strida 1, was released in 1987 and the latest, Strida 5.2, in 2009. ...
, offer a fork with a single leg. Many of Cannondale's single bladed forks, called Lefty, are suspension forks, in either conventional or inverted configurations. These forks use linear needle roller bearings on octagonal races to transmit the steering torque to the wheel, while conventional two bladed suspension forks use tubular linear plain bearings. Use of a Lefty fork requires a special Lefty hub, which attaches to the fork end by means of a screw that presses the hub onto the axle that is fixed to the fork.


Track bikes

Track forks traditionally have round-section blades rather than the oval section used on road bikes, partly because a round section is stiffer under the lateral forces imposed by frequent sprinting but mainly because track racing tyres are always narrow and do not require the additional clearance afforded by oval blades. Round blades necessitate a special fork crown with matching round sockets. Track forks may not be drilled for a front brake if the bicycle is intended to be used only on a velodrome. The clearance between the tyre and the underside of the fork crown is often less than 5mm.


Attachment to the frame

Not all forks steer on bearings installed in a head tube. The forks on
Strida Strida is a portable belt-driven folding bicycle with a distinctive 'A'-shaped collapsible frame, designed by British engineer and designer Mark Sanders. The first model, Strida 1, was released in 1987 and the latest, Strida 5.2, in 2009. ...
s and Pedersen bicycles pivot about an axis external to the fork, supported at two different points on the frame. A new trend in
triathlon A triathlon is an endurance multisport race consisting of Swimming (sport), swimming, Cycle sport, cycling, and running over various distances. Triathletes compete for fastest overall completion time, racing each segment sequentially with the t ...
bikes is similar, called a bayonet or external-steerer fork, but the pivot bearings are at the top and bottom of something that still resembles a head tube.


Materials

Forks have been made from
steel Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ty ...
,
aluminum Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It has ...
,
carbon fiber Carbon fiber-reinforced polymers (American English), carbon-fibre-reinforced polymers (Commonwealth English), carbon-fiber-reinforced plastics, carbon-fiber reinforced-thermoplastic (CFRP, CRP, CFRTP), also known as carbon fiber, carbon compo ...
,
titanium Titanium is a chemical element with the symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in ...
,
magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...
, and various combinations. For example, a fork may have carbon fiber blades with an aluminum crown, steerer tube, or fork ends. In rigid forks the material, shape, weight, and design of the forks can noticeably affect the feel and handling of the bicycle. Carbon fiber forks are popular in road bicycles because they are light, and also because they can be designed to lessen and absorb vibrations from the road surface. There have also been examples of wooden forks. However, these have not been common in the modern era.


Attachment points

Forks may have attachment points for brakes, racks, and fenders. These may be located in the crown, along the blades, and near the fork ends. These are often holes, threaded or not, and may be located on tabs that protrude.


See also

*
Bicycle and motorcycle dynamics Bicycle and motorcycle dynamics is the science of the motion of bicycles and motorcycles and their components, due to the forces acting on them. Dynamics falls under a branch of physics known as classical mechanics. Bike motions of interest ...
*
Bicycle and motorcycle geometry Bicycle and motorcycle geometry is the collection of key measurements (lengths and angles) that define a particular bike configuration. Primary among these are wheelbase, steering axis angle, fork offset, and trail. These parameters have a major ...
*
Bicycle frame A bicycle frame is the main component of a bicycle, onto which wheels and other components are fitted. The modern and most common frame design for an upright bicycle is based on the safety bicycle, and consists of two triangles: a main triangl ...
*
Bicycle suspension Bicycle suspension is the system, or systems, used to ''suspend'' the rider and bicycle in order to insulate them from the roughness of the terrain. Bicycle suspension is used primarily on mountain bikes, but is also common on hybrid bicycles ...
*
Fork tube A motorcycle fork connects a motorcycle's front wheel and axle to its frame, typically via a yoke, also known as a triple clamp, which consists of an upper yoke joined to a lower yoke via a steering stem, a shaft that runs through the steering ...
*
Glossary of cycling This is a glossary of terms and jargon used in cycling, mountain biking, and cycle sport. For ''parts of a bicycle'', see List of bicycle parts. 0–9 ; 27.5 Mountain bike: A mountain bike with wheels that are approximately in diameter and ...
*
List of bicycle parts For other cycling related terms (besides parts) see Glossary of cycling. List of bicycle parts by alphabetic order: * Axle: as in the generic definition, a rod that serves to attach a wheel to a bicycle and provides support for bearings on whi ...
*
Outline of cycling :''This article is an outline about the activity of cycling. For an outline about bicycles themselves, see outline of bicycles.'' :The following ''outline'' is provided as an overview of, as well as a topical guide to cycling: Cycling, al ...
* Motorcycle fork *
Stem (bike) The stem is the component on a bicycle that connects the handlebars to the steerer tube of the bicycle fork. Sometimes called a ''goose neck'', a stem's design belongs to either a ''quill'' or ''threadless'' system, and each system is compatib ...


Gallery

File:Leading link bicycle fork on a BuzBike.jpg, Leading link fork on a BuzBike File:Leading link bicycle fork on a Birdy folding bike.jpg, Leading link fork on a Birdy
folding bicycle A folding bicycle is a bicycle designed to fold into a compact form, facilitating transport and storage. When folded, the bikes can be more easily carried into buildings, on public transportation (facilitating mixed-mode commuting and bicycl ...
File:Lauf pivotless, trailing link bicycle suspension fork.jpg, Lauf pivotless, trailing link fork File:Cannondale Lefty Fork.jpg,
Cannondale The Cannondale Bicycle Corporation is an American division of Dutch conglomerate Pon Holdings that supplies bicycles. Its headquarters are in Wilton, Connecticut with engineering offices in Freiburg, Germany. Frames are manufactured in Taiwan ...
Lefty File:Felt B2 Pro Bayonet Fork.jpg,
Felt Felt is a textile material that is produced by matting, condensing and pressing fibers together. Felt can be made of natural fibers such as wool or animal fur, or from synthetic fibers such as petroleum-based acrylic or acrylonitrile or wood ...
B2 Pro Bayonet Fork File:Scott Sub 10 fork fracture.jpg, Scott Sub 10 with a fractured bicycle fork File:M5 Carbon High Racer.jpg, M5 Carbon High Racer with a double bladed rear and front fork.


References


External links


Adapter for bicycle forks
article

{{Commons category, Bicycle forks
Fork In cutlery or kitchenware, a fork (from la, furca 'pitchfork') is a utensil, now usually made of metal, whose long handle terminates in a head that branches into several narrow and often slightly curved tine (structural), tines with which one ...