Derailleur
[4] The French bicycle tourist, writer and cycling promoter Paul de Vivie (1853–1930), who wrote under the name Vélocio, invented a two speed rear derailleur in 1905 which he used on forays into the Alps.
In 1937, the derailleur system was introduced to the Tour de France, allowing riders to change gears without having to remove wheels.
In 1949 Campagnolo introduced the Gran Sport, a more refined version of the already existing, yet less commercially successful, cable-operated parallelogram rear derailleurs.
[9] In 1964, Suntour invented the slant-parallelogram rear derailleur, which let the jockey pulley maintain a more constant distance from the different sized sprockets, resulting in easier shifting.
Once the patents expired, other manufacturers adopted this design, at least for their better models,[10] and the "slant parallelogram" remains the current rear derailleur pattern.
Before the 1990s many manufacturers made derailleurs, including Simplex, Huret, Galli, Mavic, Gipiemme, Zeus, Suntour, and Shimano.
[11] The major innovations since the 1990s have been the switch from friction to indexed shifting and the gradual increase in the number of gears.
An indexed shifter has a detent or ratchet mechanism which stops the gear lever, and hence the cable and the derailleur, after moving a specific distance with each press or pull.
Many modern, high-end mountain bikes have begun using entirely one chain ring drivetrains, with the industry constantly pushing the number of rear cogs up and up, as shown by SRAM's Eagle groupsets (1 by 12) and Rotor's recent 1 by 13 drive-train.
The switches are connected by wire or wirelessly to a battery pack and to a small electric motor that drives the derailleur.
The arm pivots about this point to maintain the cage at a nearly constant distance from the different sized sprockets.
[citation needed] Low normal or rapid rise rear derailleurs return the chain to the largest sprocket on the cassette when no cable tension is applied.
[16] In mountain biking and off-road cycling, the most critical gear changes occur on uphill sections, where riders must cope with obstacles and difficult turns while pedalling under heavy load.
Cage length, when combined with the pulley size, determines the capacity of a derailleur to take up chain slack.
Typical cross country mountain bikes with three front chainrings will use a long cage rear derailleur.
There are currently several standards in use, and in each the product of the derailleur's shift ratio and the length of cable pulled must equal the pitch of the rear sprockets.
Because of the possibility of the chain shifting past the smallest inner chainring, especially when the inner chainring is very small, even on bikes adjusted by professional race mechanics, and the problems such misshifts can cause, a small after-market of add-on products, called chain deflectors, exists to help prevent them from occurring.
The diagonal chain run produced by these practices is less efficient and shortens the life of all components, with no advantage from the middle of the range ratio obtained.
