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Derailleur gears are a variable ratio transmission system commonly used on bicycles, consisting of a chain, multiple sprockets and a mechanism to move the chain from one sprocket to another. Although widely referred to as "gears", bicycle "gears" should properly be referred to as sprockets since they are driven by, or drive, a chain; and are not driven by one another. Modern front and rear derailleurs typically consist of a moveable chain-guide that is operated remotely by a Bowden cable attached to a shift lever mounted on the down tube, handlebar stem, or handlebar. When a rider operates the lever while pedaling, the change in cable tension moves the chain-guide from side to side, "derailing" the chain onto different sprockets. To both guide the chain to the selected sprocket and maintain chain tension by taking up any slack caused by changing to a smaller sprocket, the rear derailleur has two pulleys in a spring-loaded rotating cage, through which the chain rolls in an S-shaped pattern. The pulleys are known as the guide pulley (top) and the tension pulley (bottom). Together they are commonly referred to as the jockey pulleys or wheels. The front derailleur has a cage that should touch the chain only while shifting front chainrings.
History Various derailleur systems were designed and built in the late 1800s. The French bicycle tourist, writer and cycling promoter Paul de Vivie, aka Velocio, (1853-1930) invented a two speed derailleur in 1905 which he used on extensive forays into the Alps. Some early designs used a system of rods to move the chain onto various gears. Derailleurs did not become common road racing equipment until 1938 when Simplex introduced their cable shifted derailleur. In the early 1950s the cable-operated, parallelogram variety used on today's bicycles was introduced by Tullio Campagnolo, who also invented the quick release skewer for attaching the wheels. With Campagnolo's introduction of the parallelogram derailleur, Campagnolo became the standard for high quality derailleurs for several decades with its Gran Sport, Record, Super Record gears. Before the 1990s many other manufacturers also made derailleurs, including Simplex, Huret, Galli, Mavic, Gipiemme, Zeus, Suntour, and Shimano. However with introduction of indexed gears which required all parts of the drivetrain to be specifically compatible, and the increasing use of complete groupsets made by one company, today Campagnolo and Shimano are the two main manufacturers of derailleur gears, with Campagnolo only making road cycling derailleurs and Shimano both for road and mountain bikes. American manufacturer SRAM specializes in derailleur systems for mountain bikes, but as of 2006 SRAM has introduced a drivetrain system for road bicycles. In 1964, Suntour invented the slant-parallelogram rear derailleur, which allows the jockey wheels to maintain a more constant distance from the different sized sprockets, resulting in easier shifting. Once the patents expired, the other manufacturers adopted this design at least for their better derailleurs. Modern derailleur types The major innovations since then have been the switch from friction to indexed shifting and the gradual increase in the number of gears. With friction shifting, the rider first moves the lever enough for the chain to jump to the next sprocket, and then adjusts the lever a slight amount to center the chain. An indexed shifter has distinct clicks for each gear, and the rider merely moves the lever to the click they want without a second adjustment movement. However, indexed shifters can be difficult to re-calibrate when cables stretch or when pieces are swapped out. On racing bicycles, 10-gear rear cassettes are appearing as of 2000 for a total of 20 or 30 gears. Most current mountain bicycles have three front chainrings; while road bicycles may have two or three. Many road cyclists will rarely use the smallest ring and opt for two rings to reduce weight, especially if they are participating in a race. Derailleur gears are the most common type of gears used on bicycles today. Alternative gear systems An alternative type of gear system used on bicycles is hub gears, which were popular on utility bikes until the 1970s, when derailleur systems became available in lower-priced bikes. Hub gears are still very popular in Europe, as the gear can be changed when the bike is stationary, which makes them suitable for riding in city traffic with lots of stops and starts. The gears are also enclosed in the hub, and consequently require less maintenance. However, they usually have a smaller number of transmission ratios (i.e. speeds), although lately a 14 speed internal hub gearing system became available, with a gear range as wide as a mountain bike's 27-speed derailleur system, the Rohloff Speedhub Multi-speed versus single-speed Some Fixed-gear and single-speed cyclists eschew the use of derailleurs, favoring a simpler, more rugged configuration, with fewer or no cables. They enjoy quoting Henri Desgrange, the founder of the Tour de France: "I still feel that variable gears are only for people over forty-five. Isn't it better to triumph by the strength of your muscles than by the artifice of a derailer? We are getting soft...As for me, give me a fixed gear!" (L'Équipe article of 1902) See also | ||||||||
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