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For information about the bicycle component, see Cogset. For the song by Duke Special, see Freewheel (song).
Freewheel mechanism
Ratcheting freewheel mechanism (van Anden, 1869)


The condition of a driven shaft spinning faster than its driveshaft exists in most bicycles when the rider holds his or her feet still, no longer pushing the pedals. In a fixed-gear bicycle, without a freewheel, the rear wheel would drive the pedals around.

An analogous condition exists in an automobile with a manual transmission going down hill or any situation where the driver takes his or her foot off the gas pedal, closing the throttle; the wheels want to drive the engine, possibly at a higher RPM. In a two-stroke engine this can be a catastrophic situation: as many two stroke engines depend on a fuel/oil mixture for lubrication, a shortage of fuel to the engine would result in a shortage of oil in the cylinders, and the pistons would seize after a very short time causing extensive engine damage. Saab used a freewheel system in their two-stroke models for this reason and maintained it in the Saab 96 V4 and early Saab 99 for better fuel efficiency.





Advantages and disadvantages[edit]




Agricultural equipment[edit]


Engine starters[edit]


Vehicle transmissions[edit]



Other car makers fitted a freewheel between engine and gearbox as a form of automatic clutch. Once the driver released the throttle and the vehicle was on the overrun the freewheel would disengage and a gearchange could be made without the use of the clutch pedal. This feature appeared mainly on large, luxury cars which often had heavy clutches and gearboxes without synchromesh as the freewheel permitted a smoother and quieter change. Citroën combined a freewheel and a centrifugal clutch to make the so-called 'TraffiClutch' where the car could be started, stopped and the lower gears be changed without using the clutch pedal. This was an option on Citroën 2CVs and its derivatives and, as the name implied, was marketed as a benefit for driving in congested urban areas.

A common use of freewheeling mechanisms is in automatic transmissions. For instance traditional, hydraulic General Motors transmissions such as the Turbo-Hydramatic 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 will freewheel if first gear is engaged, but not in second or third gears; if in 'drive' it will freewheel in first or second; finally, if in low, it will not freewheel in any gear. This allows the driver to select a lower range to achieve engine braking at various speeds, for instance when descending steep hills.




Freewheels are also used in rotorcraft. As a bicycle's wheels need to be able to rotate faster than the pedals, so do a rotorcraft's blades need to 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 allows the main and tail rotor systems to continue to spin independent of the drive system. This provides for continued flight control and an autorotation landing.


In 1869, William Van Anden invented the freewheel for the bicycle.[1] His design placed a ratchet device in the hub of the front wheel, which allowed the rider to propel himself forward without pedaling constantly.[2] Initially, bicycle enthusiasts rejected the idea of a freewheel because they believed it would complicate the mechanical functions of the bicycle.[3] Bicycle enthusiasts believed that the bicycle was supposed to remain as simple as possible without any additional mechanisms, such as the freewheel.[4]

Due to the lack of popularity for the freewheel, it was not continuously re-engineered to be more useful for several decades. In 1899, American manufacturers developed the “coaster brake,” which allowed riders to brake by pedaling backwards and included the freewheel mechanism.[5] 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 of a bicycle unlike Van Anden’s initial design.[6]

In 1924, the French bicycle company, Le Cyclo, introduced a gear-shifting bicycle with a two sprocket freewheel, which would allow riders to go uphill with more ease. In the late 1920s, Le Cyclo began using both front and rear derailleurs in combination with a double chainring 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.[7]

In the 1970s, Japanese manufacturers introduced their own version of the derailleurs. The Japanese bicycle company, SunTour introduced the slant parallelogram rear derailleurs which were tilted back allowing the cage to be located farther away from the freewheel than the European version. This allowed for the chain to shift more smoothly from gear to gear. The Japanese version of the derailleur became the standard and still is today.[8]

See also[edit]


  1. ^ "Improvement in Velocipedes". Retrieved 8 April 2013. 