Science Fair Project Encyclopedia
Derailleur gears are a gear system commonly used on bicycles, consisting of a chain, multiple sprockets and a mechanism to move the chain from one sprocket to another. Modern derailleurs typically consist of a parallelogram-shaped mech device which is operated by a Bowden cable attached to a shift lever mounted on the downtube, handlebar stem or handlebar. When a rider operates the lever, the changes in cable tension move the derailleur from side to side, "derailing" the chain onto different gears. The rear derailleur has two pulleys that the chain rolls on to guide the chain to the selected sprocket and maintain chain tension. These are known as the jockey pulley (top) and the tension pulley (bottom). The front derailleur has a cage that should only touch the chain while shifting front chainrings.
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 front derailleur, Campagnolo became the standard for high quality derailleurs and for several decades true racing bicycles were all Campy, meaning that drivetrain groupset — the derailleurs, shifters, hub and chain — were all manufactured by the Campagnolo company. Today, Japanese manufacturer Shimano makes derailleur systems for racing and mountain bikes.
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.
The major innovations since then have been the switch from friction to index 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 index shifter has distinct clicks for each gear, and the rider merely moves the lever to the click they want without a second adjustment movement. On racing bicycles, 11-gear rear hubs are appearing as of 2004 for a total of 22 gears. Most current mountain bicycles have three front chainrings; while road bicycles built for racing still have only two chainrings as a weight-saving measure, and because the smallest chainring is useless to an elite cyclist on roads. 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 14 speed internal hub gearing system became available, with a gear range as wide as a mountain bike's 27-speed derailleur system.
Multi speed versus fixed
Fixed gear and single speed cyclists eschew the use of derailleurs favoring a simpler, more rugged configuration with fewer, or zero, 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)
The contents of this article is licensed from www.wikipedia.org under the GNU Free Documentation License. Click here to see the transparent copy and copyright details