Derailleur is a French word, spelled dérailleur in French, derived from the derailment of a train from its tracks. Its first recorded use was 1930. Various derailleur systems were designed and built in the late 19th century. One example is the Protean two-speed derailleur available on the Whippet safety bicycle. In 1937, the derailleur system was introduced to the Tour de France, allowing riders to change gears without having to remove wheels. Previously, riders would have to dismount in order to change their wheel from downhill to uphill mode. In 1949 Campagnolo introduced the Gran Sport, a more refined version of the then already existing, yet less commercially successful, cable-operated parallelogram rear derailleurs. 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.
Before the 1990s many manufacturers made derailleurs, including Simplex, Huret, Galli, Mavic, Gipiemme, Zeus, Suntour, and Shimano. Campagnolo only makes equipment for road and cyclocross. 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, a lever directly controls the continuously variable position of the derailleur. To shift gears, 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 on that sprocket. The rear derailleur serves double duty: moving the chain between rear sprockets and taking up chain slack caused by moving to a smaller sprocket at the rear or a smaller chainring by the front derailleur.
Rotate the barrel adjuster clockwise to help the chain shift up, there is likely a larger issue with the bike. If it won’t shift when you click it, how to Adjust a Rear Derailleur, removed a lot of mystery on adjustments. This article indicated the distinction between barrel nut and limit screws distinct roles in the shifting operation; keep pedalling the bike and rotate the barrel. Once you’ve adjusted one gear to shift smoothly, ” not a “déraillement. Used by SRAM; or closest to the frame fork.
In order to accomplish this second task, it is positioned in the path of the bottom, slack portion of chain. Although variations exist, as noted below, most rear derailleurs have several components in common. They have a cage that holds two pulleys that guide the chain in an S-shaped pattern. The components may be constructed of aluminium alloy, steel, plastic, or carbon fibre composite. High normal or top normal rear derailleurs return the chain to the smallest sprocket on the cassette when no cable tension is applied. This is the regular pattern used on most Shimano mountain, all Shimano road, and all SRAM and Campagnolo derailleurs. In this condition, spring pressure takes care of the easier change to smaller sprockets. Low normal or rapid rise rear derailleurs return the chain to the largest sprocket on the cassette when no cable tension is applied.
While this was once a common design for rear derailleurs, it is relatively uncommon today. The distance between the upper and lower pulleys of a rear derailleur is known as the cage length. Cage length, when combined with the pulley size, determines the capacity of a derailleur to take up chain slack. There are at least two methods employed by rear derailleurs to maintain the appropriate gap between the upper jockey wheel and the rear sprockets as the derailleur moves between the large sprockets and the small sprockets. One method, used by Shimano, is to use chain tension to pivot the cage. This has the advantage of working with most sets of sprockets, if the chain has the proper length. A disadvantage is that rapid shifts from small sprockets to large over multiple sprockets at once can cause the cage to strike the sprockets before the chain moves onto the larger sprockets and pivots the cage as necessary.