Freewheel mechanism
![Roue libre cliquet](https://upload.wikimedia.org/wikipedia/commons/8/85/Roue_libre_cliquet.svg)
In
mechanical
Mechanical may refer to:
Machine
* Machine (mechanical), a system of mechanisms that shape the actuator input to achieve a specific application of output forces and movement
* Mechanical calculator, a device used to perform the basic operations of ...
or
automotive engineering
Automotive engineering, along with aerospace engineering and naval architecture, is a branch of vehicle engineering, incorporating elements of mechanical, electrical, electronic, software, and safety engineering as applied to the design, manufactu ...
, a freewheel or overrunning clutch is a device in a
transmission
Transmission may refer to:
Medicine, science and technology
* Power transmission
** Electric power transmission
** Propulsion transmission, technology allowing controlled application of power
*** Automatic transmission
*** Manual transmission
*** ...
that disengages the
driveshaft
A drive shaft, driveshaft, driving shaft, tailshaft (Australian English), propeller shaft (prop shaft), or Cardan shaft (after Girolamo Cardano) is a component for transmitting mechanical power and torque and rotation, usually used to connect ...
from the driven shaft when the driven shaft rotates faster than the driveshaft. An
overdrive
Overdrive may refer to:
Organizations
* OverDrive, Inc., a digital distributor of entertainment media
** OverDrive Media Console, a media player developed by OverDrive, Inc.
* Overdrive PC, a subsidiary of Velocity Micro
Technology
* Overdrive ...
is sometimes mistakenly called a freewheel, but is otherwise unrelated.
The condition of a driven shaft spinning faster than its driveshaft exists in most
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 ...
s when the rider stops
pedaling
The pedal is the part of a bicycle that the rider pushes with their foot to propel the vehicle. It provides the connection between the cyclist's foot or Cycling shoe, shoe and the Crankset, crank allowing the leg to turn the bottom bracket spindl ...
. In a
fixed-gear bicycle
A fixed-gear bicycle (or fixed-wheel bicycle, commonly known in some places as a fixie) is a bicycle that has a drivetrain with no freewheel mechanism. The freewheel was developed early in the history of bicycle design but the fixed-gear bicyc ...
, without a freewheel, the rear wheel drives the pedals around.
An analogous condition exists in an
automobile
A car or automobile is a motor vehicle with Wheel, wheels. Most definitions of ''cars'' say that they run primarily on roads, Car seat, seat one to eight people, have four wheels, and mainly transport private transport#Personal transport, pe ...
with a
manual transmission
A manual transmission (MT), also known as manual gearbox, standard transmission (in Canada, the United Kingdom, and the United States), or stick shift (in the United States), is a multi-speed motor vehicle transmission (mechanics), transmission ...
going downhill, or any situation where the driver takes their foot off the
gas pedal
"Gas Pedal" is a song by American rapper Sage the Gemini with additional vocals from fellow Bay Area rapper Iamsu!. It was produced by Dominic Wynn Woods and written by Woods and Sudan Williams. It was released on March 21, 2013 as the second ...
, closing the
throttle
A throttle is the mechanism by which fluid flow is managed by constriction or obstruction.
An engine's power can be increased or decreased by the restriction of inlet gases (by the use of a throttle), but usually decreased. The term ''throttle'' ...
: the wheels drive the engine, possibly at a higher RPM. In a
two-stroke engine
A two-stroke (or two-stroke cycle) engine is a type of internal combustion engine that completes a power cycle with two strokes (up and down movements) of the piston during one power cycle, this power cycle being completed in one revolution of t ...
, this can be catastrophic—as many two stroke engines depend on a
fuel
A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy or to be used for work. The concept was originally applied solely to those materials capable of releasing chemical energy but ...
/
oil
An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) & lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturated ...
mixture for
lubrication
Lubrication is the process or technique of using a lubricant to reduce friction and wear and tear in a contact between two surfaces. The study of lubrication is a discipline in the field of tribology.
Lubrication mechanisms such as fluid-lubric ...
, a shortage of fuel to the engine starves oil from the
cylinder
A cylinder (from ) has traditionally been a three-dimensional solid, one of the most basic of curvilinear geometric shapes. In elementary geometry, it is considered a prism with a circle as its base.
A cylinder may also be defined as an infin ...
s, and the
piston
A piston is a component of reciprocating engines, reciprocating pumps, gas compressors, hydraulic cylinders and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tig ...
s can soon seize, causing extensive damage.
Saab
Saab or SAAB may refer to:
Brands and enterprises
* Saab Group, a Swedish aerospace and defence company, formerly known as SAAB, and later as Saab AB
** Datasaab, a former computer company, started as spin off from Saab AB
* Saab Automobile, a fo ...
used a freewheel system in their
two-stroke models for this reason and maintained it in the
Saab 96
The Saab 96 is an automobile manufactured and marketed by Saab from 1960 to January 1980, replacing the 93. The 96 featured aerodynamic two-door bodywork, four-passenger seating and at first a two-stroke, three-cylinder engine, later a four-strok ...
V4 and early
Saab 99
The Saab 99 is a car which was produced by Saab from 1968 to 1984; their first foray into a larger class than the 96. While considered a large family car in Scandinavia, it was marketed as a niche compact executive car in most other markets. It w ...
for better
fuel efficiency
Fuel efficiency is a form of thermal efficiency, meaning the ratio of effort to result of a process that converts chemical potential energy contained in a carrier (fuel) into kinetic energy or work. Overall fuel efficiency may vary per device, wh ...
.
Mechanics
The simplest freewheel device consists of two saw-toothed,
spring
Spring(s) may refer to:
Common uses
* Spring (season), a season of the year
* Spring (device), a mechanical device that stores energy
* Spring (hydrology), a natural source of water
* Spring (mathematics), a geometric surface in the shape of a ...
-loaded discs pressing against each other with the toothed sides together, somewhat like a
ratchet
Ratchet may refer to:
Devices
* Ratchet (device), a mechanical device that allows movement in only one direction
* Ratchet, metonomic name for a socket wrench incorporating a ratcheting device
* Ratchet (instrument), a music instrument and a ...
. Rotating in one direction, the saw teeth of the drive disc lock with the teeth of the driven disc, making it rotate at the same speed. If the drive disc slows down or stops rotating, the teeth of the driven disc slip over the drive disc teeth and continue rotating, producing a characteristic clicking sound proportionate to the speed difference of the driven gear relative to that of the (slower) driving gear.
A more sophisticated and rugged design has spring-loaded steel
rollers inside a driven cylinder. Rotating in one direction, the rollers lock with the cylinder making it rotate in unison. Rotating slower, or in the other direction, the steel rollers just slip inside the cylinder.
Most bicycle freewheels use an internally step-toothed drum with two or more spring-loaded, hardened steel
pawls to transmit the load. More pawls help spread the wear and give greater reliability although, unless the device is made to tolerances not normally found in bicycle components, simultaneous engagement of more than two pawls is rarely achieved.
Advantages and disadvantages
By its nature, a freewheel mechanism acts as an automatic
clutch
A clutch is a mechanical device that engages and disengages power transmission, especially from a drive shaft to a driven shaft. In the simplest application, clutches connect and disconnect two rotating shafts (drive shafts or line shafts). ...
, making it possible to change gears in a manual
gearbox
Propulsion transmission is the mode of transmitting and controlling propulsion power of a machine. The term ''transmission'' properly refers to the whole drivetrain, including clutch, gearbox, prop shaft (for rear-wheel drive vehicles), differe ...
, either up- or downshifting, without depressing the clutch pedal, limiting the use of the manual clutch to starting from standstill or stopping. The Saab freewheel can be engaged or disengaged by the driver by respectively pushing or pulling a lever. This locks or unlocks the main shaft with the freewheel hub.
A freewheel also produces slightly better
fuel economy on carbureted engines (without fuel turn-off on engine brake) and less wear on the manual clutch, but leads to more wear on the
brake
A brake is a mechanical device that inhibits motion by absorbing energy from a moving system. It is used for slowing or stopping a moving vehicle, wheel, axle, or to prevent its motion, most often accomplished by means of friction.
Background ...
s as there is no longer any ability to perform
engine braking
Engine braking occurs when the retarding forces within an engine are used to slow down a motor vehicle, as opposed to using additional external braking mechanisms such as friction brakes or magnetic brakes.
The term is often confused with sever ...
. This may make freewheel transmissions dangerous for use on
truck
A truck or lorry is a motor vehicle designed to transport cargo, carry specialized payloads, or perform other utilitarian work. Trucks vary greatly in size, power, and configuration, but the vast majority feature body-on-frame construction ...
s and
automobile
A car or automobile is a motor vehicle with Wheel, wheels. Most definitions of ''cars'' say that they run primarily on roads, Car seat, seat one to eight people, have four wheels, and mainly transport private transport#Personal transport, pe ...
s driven in
mountain
A mountain is an elevated portion of the Earth's crust, generally with steep sides that show significant exposed bedrock. Although definitions vary, a mountain may differ from a plateau in having a limited Summit (topography), summit area, and ...
ous regions, as prolonged and continuous application of
brake
A brake is a mechanical device that inhibits motion by absorbing energy from a moving system. It is used for slowing or stopping a moving vehicle, wheel, axle, or to prevent its motion, most often accomplished by means of friction.
Background ...
s to limit vehicle speed soon leads to brake-system overheating followed shortly by total failure.
Uses
Agricultural equipment
In agricultural equipment an overrunning clutch is typically used on
hay baler
A baler or hay baler is a piece of farm machinery used to compress a cut and raked crop (such as hay, cotton, flax straw, salt marsh hay, or silage) into compact bales that are easy to handle, transport, and store. Often, bales are configur ...
s and other equipment with a high
inertia
Inertia is the idea that an object will continue its current motion until some force causes its speed or direction to change. The term is properly understood as shorthand for "the principle of inertia" as described by Newton in his first law ...
l load, particularly when used in conjunction with a
tractor
A tractor is an engineering vehicle specifically designed to deliver a high tractive effort (or torque) at slow speeds, for the purposes of hauling a trailer or machinery such as that used in agriculture, mining or construction. Most common ...
without a live
power take-off
A power take-off or power takeoff (PTO) is one of several methods for taking power from a power source, such as a running engine, and transmitting it to an application such as an attached implement or separate machine.
Most commonly, it is a sp ...
(PTO). Without a live PTO, a high inertial load can cause the tractor to continue to move forward even when the foot clutch is depressed, creating an unsafe condition. By disconnecting the load from the PTO under these conditions, the overrunning clutch improves safety. Similarly, many unpowered 'push'
cylinder lawnmowers use a freewheel to drive the blades: these are geared or chain-driven to rotate at high speed and the freewheel prevents their
momentum
In Newtonian mechanics, momentum (more specifically linear momentum or translational momentum) is the product of the mass and velocity of an object. It is a vector quantity, possessing a magnitude and a direction. If is an object's mass an ...
being transferred in the reverse direction through the drive when the machine is halted.
Engine starters
A freewheel assembly is also widely used on engine starters as a kind of protective device.
Starter motors usually need to spin at 3,000 RPM to get the engine to turn over. When the key is held in the start position for any amount of time after the engine has started, the starter can not spin fast enough to keep up with the flywheel. Because of the extreme
gear ratio
A gear train is a mechanical system formed by mounting gears on a frame so the teeth of the gears engage.
Gear teeth are designed to ensure the pitch circles of engaging gears roll on each other without slipping, providing a smooth transmission ...
between starter gear and flywheel (about 15 or 20:1) it would spin the starter armature at dangerously high speeds, causing an explosion when the
centripetal force
A centripetal force (from Latin ''centrum'', "center" and ''petere'', "to seek") is a force that makes a body follow a curved path. Its direction is always orthogonal to the motion of the body and towards the fixed point of the instantaneous c ...
acting on the copper coils wound in the armature can no longer resist the
outward force acting on them. In starters without the freewheel or overrun clutch this would be a major problem because, with the flywheel spinning at about 1,000 RPM at idle, the starter, if engaged with the
flywheel
A flywheel is a mechanical device which uses the conservation of angular momentum to store rotational energy; a form of kinetic energy proportional to the product of its moment of inertia and the square of its rotational speed. In particular, ass ...
, would be forced to spin between 15,000 and 20,000 RPM. Once the engine has turned over and is running, the overrun clutch releases the starter from the flywheel and prevents the gears from re-meshing (as in an accidental turning of the ignition key) while the engine is running. A freewheel clutch is now used in many motorcycles with an electric starter motor. It is used as a replacement for the
Bendix drive
A Bendix drive is a type of engagement mechanism used in starter motors of internal combustion engines. The device allows the pinion gear of the starter motor to engage or disengage the ring gear (which is attached to the flywheel or flexplate ...
used on most auto starters because it reduces the electrical needs of the starting system.
Vehicle transmissions
In addition to the automotive uses listed above (i.e. in two-stroke-engine vehicles and early four-stroke Saabs), freewheels were used in some luxury or up-market conventional cars (such as
Packard
Packard or Packard Motor Car Company was an American luxury automobile company located in Detroit, Michigan. The first Packard automobiles were produced in 1899, and the last Packards were built in South Bend, Indiana in 1958.
One of the "Thr ...
,
Rover
Rover may refer to:
People
* Constance Rover (1910–2005), English historian
* Jolanda de Rover (born 1963), Dutch swimmer
* Rover Thomas (c. 1920–1998), Indigenous Australian artist
Places
* Rover, Arkansas, US
* Rover, Missouri, US
* ...
and
Cord
Cord or CORD may refer to:
People
* Alex Cord (1933–2021), American actor and writer
* Chris Cord (born 1940), American racing driver
* Errett Lobban Cord (1894–1974) American industrialist
* Ronnie Cord (1943–1986), Brazilian singer
* Cor ...
) from the 1930s into the 1960s. Some engines of the period also tended to pass oil past the
piston ring
A piston ring is a metallic split ring that is attached to the outer diameter of a piston in an internal combustion engine or steam engine.
The main functions of piston rings in engines are:
# Sealing the combustion chamber so that there is mini ...
s under conditions with a closed throttle and high engine speed, when the slight vacuum in the combustion chamber combined with high oil pressure and a high degree of
splash lubrication
Splash lubrication is a rudimentary form of lubrication found in early engines. Such engines could be external combustion engines (such as stationary steam engines), or internal combustion engines (such as petrol, diesel or paraffin engines). ...
from the fast-turning crankshaft would lead to oil getting in the combustion chamber.
The freewheel meant that the engine returned to its idle speed on the overrun, thus greatly reducing noise from both the engine and gearbox and reducing oil consumption. The mechanism could usually be locked to provide
engine braking
Engine braking occurs when the retarding forces within an engine are used to slow down a motor vehicle, as opposed to using additional external braking mechanisms such as friction brakes or magnetic brakes.
The term is often confused with sever ...
if needed. A freewheel was also used in the original
Land Rover
Land Rover is a British brand of predominantly four-wheel drive, off-road capable vehicles, owned by multinational car manufacturer Jaguar Land Rover (JLR), since 2008 a subsidiary of India's Tata Motors. JLR currently builds Land Rovers ...
vehicle from 1948 to 1951. The freewheel controlled drive from the gearbox to the front
axle
An axle or axletree is a central shaft for a rotating wheel or gear. On wheeled vehicles, the axle may be fixed to the wheels, rotating with them, or fixed to the vehicle, with the wheels rotating around the axle. In the former case, bearing ...
, which disengaged on the overrun. This allowed the vehicle to have a permanent
4 wheel drive
Four-wheel drive, also called 4×4 ("four by four") or 4WD, refers to a two-axled vehicle drivetrain capable of providing torque to all of its wheels simultaneously. It may be full-time or on-demand, and is typically linked via a transfer case ...
system by avoiding 'wind-up' forces in the transmission. This system worked, but produced unpredictable handling, especially in slippery conditions or when towing, and was replaced by a conventional selectable 4WD system.
During the Second World War, the military Volkswagen vehicles produced by
KdF (
''Kübelwagen'',
''Schwimmwagen'') were fitted with a
ZF limited-slip differential
A limited-slip differential (LSD) is a type of differential that allows its two output shafts to rotate at different speeds but limits the maximum difference between the two shafts. Limited-slip differentials are often known by the generic tr ...
system composed of two freewheels, which sent the whole of the engine power to the slowest-turning of the two wheels.
Other car makers fitted a freewheel between engine and gearbox as a form of automatic
clutch
A clutch is a mechanical device that engages and disengages power transmission, especially from a drive shaft to a driven shaft. In the simplest application, clutches connect and disconnect two rotating shafts (drive shafts or line shafts). ...
. Once the driver released the throttle and the vehicle was on the overrun, the freewheel disengaged and the driver could change gears without using the clutch pedal. This feature appeared mainly on large, luxury cars with heavy clutches and gearboxes without
synchromesh
A manual transmission (MT), also known as manual gearbox, standard transmission (in Canada, the United Kingdom, and the United States), or stick shift (in the United States), is a multi-speed motor vehicle transmission system, where gear changes ...
, as the freewheel permitted a smoother and quieter change.
Citroën
Citroën () is a French automobile brand. The "Automobiles Citroën" manufacturing company was founded in March 1919 by André Citroën. Citroën is owned by Stellantis since 2021 and previously was part of the PSA Group after Peugeot acquired ...
combined a freewheel and a
centrifugal clutch
A centrifugal clutch is an automatic clutch that uses centrifugal force to operate. The output shaft is disengaged at low rotational speed and engages more as speed increases. It is often used in mopeds, underbones, lawn mowers, go-karts, chainsaws ...
to make the so-called 'TraffiClutch', which let the driver start, stop, and change the lower gears without using the clutch. This was an option on
Citroën 2CV
The Citroën 2CV (french: link=no, deux chevaux(-vapeur), , lit. "two steam horse(power)s", meaning "two ''taxable'' horsepower") is an air-cooled front-engine, front-wheel-drive, economy family car, introduced at the 1948 Paris Mondial de l ...
s and its derivatives and, as the name implied, was marketed as a benefit for driving in congested urban areas. Similarly, the
Saab 93
The Saab 93 (pronounced ''ninety-three'') is the second production automobile that was manufactured by Saab. Styled by Sixten Sason, it was first presented on December 1, 1955. The 93 was powered by a longitudinally-mounted three-cylinder 748&nbs ...
was available with an optional
Saxomat
Saxomat was a type of automatic clutch available as an option on Fiat 1800, Lancia Flaminia, Saab 93, Borgward Isabella, Goliath/Hansa 1100, Auto Union 1000, Ford Taunus, Trabant, other than some models from BMW, Opel, Steyr-Puch, NSU, Glas ...
clutch.
A common use of freewheeling mechanisms is in automatic transmissions. For instance traditional, hydraulic General Motors transmissions such as the
Turbo-Hydramatic
Turbo-Hydramatic or Turbo Hydra-Matic is the registered tradename for a family of automatic transmissions developed and produced by General Motors. These transmissions mate a three-element turbine torque converter to a Simpson planetary geartra ...
400 provide freewheeling in all gears lower than the selected gear. E.g., if the gear selector on a three-speed transmission is labelled 'drive'(3)-'super'(2)-'low'(1) and the driver has selected 'super', the transmission freewheels if first gear is engaged, but not in second or third gears; if in 'drive' it freewheels in first or second; finally, if in low, it does not freewheel in any gear. This lets the driver select a lower range to provide engine braking at various speeds, for instance when descending a steep hill.
Overdrive units manufactured by
Laycock de Normanville
Overdrive is the operation of an automobile cruising at sustained speed with reduced engine revolutions per minute (RPM), leading to better fuel consumption, lower noise, and lower wear. The term is ambiguous. The most fundamental meaning is ...
used a freewheel to facilitate a smooth gear change between locked mode (1:1) and overdrive mode without use of the conventional
clutch pedal
Car controls are the components in automobiles and other powered road vehicles, such as trucks and buses, used for driving and parking.
While controls like steering wheels and pedals have existed since the invention of cars, other controls have ...
. The freewheel would lock the outgoing axle to the outgoing axle in the brief transition period between the
conical clutch for locked mode disengaging and the clutch for overdrive mode engaging.
Bicycles
In the older style of bicycle, where the freewheel mechanism is included in the gear assembly, the system is called a ''
freewheel
Freewheel mechanism
In mechanical or automotive engineering, a freewheel or overrunning clutch is a device in a transmission that disengages the driveshaft from the driven shaft when the driven shaft rotates faster than the driveshaft. An ov ...
'', whereas the newer style, in which the freewheel mechanism is in the hub, is called a ''
freehub
A freehub is a type of bicycle hub that incorporates a ratcheting mechanism.
A set of sprockets (called a "cassette") is mounted onto a splined shaft of the freehub to engage the chain. The ratcheting mechanism is a part of the hub, in contras ...
''.
Helicopters
Freewheels are also used in
rotorcraft
A rotorcraft or rotary-wing aircraft is a heavier-than-air aircraft with rotary wings or rotor blades, which generate lift by rotating around a vertical mast. Several rotor blades mounted on a single mast are referred to as a rotor. The Internati ...
. Just as a bicycle's wheels must be able to rotate faster than the pedals, a rotorcraft's blades must be able to spin faster than its drive engines. This is especially important in the event of an engine failure where a freewheel in the main transmission lets the main and tail rotor systems continue to spin independent of the drive system. This provides for continued flight control and an
autorotation
Autorotation is a state of flight in which the main rotor system of a helicopter or other rotary-wing aircraft turns by the action of air moving up through the rotor, as with an autogyro, rather than engine power driving the rotor. Bensen, Igor ...
landing.
History
In 1869, William Van Anden of Poughkeepsie, New York, USA invented the freewheel for the
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 ...
. His design placed a ratchet device in the
hub of the front wheel (the driven wheel on the ''
velocipede
A velocipede () is a human-powered land vehicle with one or more wheels. The most common type of velocipede today is the bicycle.
The term was probably first coined by Karl von Drais in French as ''vélocipède'' for the French translation o ...
'' designs of the time), which allowed the rider to propel himself forward without pedaling constantly. Initially, bicycle enthusiasts rejected the idea of a freewheel because they believed it would complicate the mechanical functions of the bicycle. Bicycle enthusiasts believed that the bicycle was supposed to remain as simple as possible without any additional mechanisms, such as the freewheel.
In the UK, a roller freewheel was patented by J. White and G. Davies of Coventry Machinist Co. in 1881 and fitted to the Chelseymore tricycle, but the pioneers of fitting the freewheel to the
safety bicycle
A safety bicycle (or simply a safety) is a type of bicycle that became very popular beginning in the late 1880s as an alternative to the penny-farthing ("ordinary") and is now the most common type of bicycle. Early bicycles of this style were kno ...
were Linley and Biggs Ltd (trading as the
Whippet Cycle Syndicate) who fitted a freewheel from the summer of 1894, in part to assist the operation of their 2-speed 'Protean' gear. However by 1899 there was widespread adoption in UK bicycle manufacture of the freewheel usually combined with the back-pedal brake, and conversions were offered to existing bicycles.
In 1899, the same system in the USA was known as the “
coaster brake
A bicycle brake reduces the speed of a bicycle or prevents it from moving. The three main types are: #Rim brakes, rim brakes, #Disc brakes, disc brakes, and #Drum brakes, drum brakes.
Most bicycle brake systems consist of three main components: ...
”, which let riders brake by pedaling backwards and included the freewheel mechanism. At the turn of the century, bicycle manufacturers within Europe and America included the freewheel mechanism in a majority of their bicycles but now the freewheel was incorporated in the rear
sprocket
A sprocket, sprocket-wheel or chainwheel is a profiled wheel with teeth that mesh with a chain, track or other perforated or indented material. The name 'sprocket' applies generally to any wheel upon which radial projections engage a chain passi ...
of a bicycle unlike Van Anden’s initial design.
In 1924, French firm Le Cyclo introduced a gear-shifting bicycle with a two sprocket freewheel, which let riders to go uphill with more ease. In the late 1920s, Le Cyclo began using both front and rear
derailleur
Shimano 600 front derailleur (1980)
A derailleur is a variable-ratio bicycle gearing system consisting of a chain, multiple sprockets of different sizes, and a mechanism to move the chain from one sprocket to another.
Modern front and rear d ...
s in combination with a double
chainring
The crankset (in the US) or chainset (in the UK), is the component of a bicycle drivetrain that converts the reciprocating motion of the rider's legs into rotational motion used to drive the chain or belt, which in turn drives the rear whee ...
, giving the bicycle twice as many gears. In the early 1930s, Le Cyclo invented a four sprocket freewheel, and several years later the company combined the four sprocket freewheel with a triple chainring giving the bicycle twelve gears.
In the 1960s and 1970s, Japanese manufacturers introduced their own versions of the derailleur.
SunTour notably introduced the slant parallelogram rear derailleur design in 1964, which is tilted to keep the pulley closer to each cog of the freewheel as it shifts, providing smoother and better shifting than its European equivalents. This version of the derailleur became the standard when SunTour's patent expired in the 1980s, and is still the model for today's designs.
See also
*
Slipper clutch
A slipper clutch ''(also known as a back-torque limiter)'' is a specialized clutch with an integrated freewheel mechanism, developed for performance-oriented motorcycles to mitigate the effects of engine braking when riders decelerate.
The main pu ...
*
Sprag clutch
A sprag clutch is a one-way freewheel clutch. It resembles a roller bearing but, instead of cylindrical rollers, non-revolving asymmetric figure-eight shaped sprags, or other elements allowing single direction rotation, are used. When the unit ...
*
Saab 96
The Saab 96 is an automobile manufactured and marketed by Saab from 1960 to January 1980, replacing the 93. The 96 featured aerodynamic two-door bodywork, four-passenger seating and at first a two-stroke, three-cylinder engine, later a four-strok ...
References
{{Gears
Clutches
Automotive transmission technologies
Bicycle parts