Rear derailleur (bicycle)
When derailleur (Fr .: dérailleur arrière , Eng .: rear derailleur ) at a one calls derailleur on the bicycle, the rear circuit device. The rear derailleur is usually attached to a derailleur hanger , which is located on the rear right dropout of the frame a little below the axle mount. Inexpensive variants are clamped to the axis with a special plate.
term
On a bicycle, the rear outer shifting device of a derailleur is called a derailleur. Colloquially, it is also common to simply refer to this component as a circuit , but this is not entirely correct as the entire circuit comprises many more components. In isolated cases, the terms are derailleur or About launchers in use, but these refer to the front of the derailleur.
history
The development of the derailleur is often attributed to the Italian Tullio Campagnolo , but this is not true. Paul de Vivie developed a derailleur around 1906. As early as 1889 he was using different chainrings. However, a prototype of a rear derailleur is said to have been presented at the Salon du vélocipède de Paris as early as 1869 . In 1895 Jean Loubeyre is said to have presented the «Polycelere», the first real rear derailleur, offered in the catalog of the Compagnie Générale des Cycle. Campagnolo invented the quick release hub for the rear wheel of bicycles in 1930. This hub made a relatively quick gear change possible at the time. The rider had to stop and loosen the rear wheel, put the chain on another sprocket and then fix the wheel again. Until the invention of the quick release hub, this was only possible with a tool. Since it is the racers both then prohibited and today, hub gears to use, which allow easy gear changes for daily cycling since 1902, the quick release represented the first practical system, a racing trip several times to change gear while.
The first rear derailleurs appeared after 1935 and initially shifted axially (parallel to the rear wheel axle). The first useful circuits used in races came from the Nieddu brothers from Italy, who called their circuit "Vittoria Margherita". Circuits with the name Giuseppina or Super Champion were also developed in France. These circuits were already known among top athletes, but not very common. They were very prone to failure and very dirty. The first gearshift that was widely used was the Chorus gearshift unit made by Campagnolo from 1946. The Campagnolo Record groupset, with which most competitive athletes' bikes were equipped for several decades from 1962 , then achieved worldwide fame .
Technical principle
Derailleurs are used to guide the running bicycle chain back and forth between several different sized sprockets on the sprocket set on the rear wheel and in this way to implement changing drive ratios. The device for switching between sprockets on the crank , however, is called a derailleur . It is usually operated using a Bowden cable and a shift lever within easy reach of the driver.
If the cyclist switched to the largest sprocket, the distance between the rear derailleur and the sprocket was small. If, on the other hand, the smallest sprocket was used, the chain had to bridge a correspondingly larger distance between the rear derailleur and the sprocket. Because the chain skips more poorly at a large distance, only three gears were possible with this design. It was only through the development of an inclined parallelogram cage by the Japanese company Suntour and their considerable improvements from 1984 by Shimano that the upper pulley moves roughly in the incline of the pinion cassette and thus ensures that approximately the same distance between the pulley and pinion is always maintained.
The chain tensioner is attached to the rear derailleur and compensates for the change in chain length due to the shifting process. The greater the difference between the smallest and largest sprocket (and between the smallest and largest chainring at the front), the longer the chain tensioner must be. Road bike gears with a short or medium cage can handle a difference of up to 26 teeth, while mountain bike or touring bike gears with a long cage can shift up to 34 teeth. The chain is guided and tensioned by the rocker arm in the rear derailleur .
By pulling the gear lever, the cable is tensioned and the cage of the rear derailleur moves. If the cyclist presses the gearshift lever, the cable is relaxed and the cage of the rear derailleur moves in the opposite direction by spring action. Traditionally, when the Bowden cable is tensioned, the cage moves inwards towards the hub.
The chain runs over guide rollers and jumps accordingly to a larger or smaller sprocket. Thanks to specially shaped sprockets ( Shimano names for them are Hyperglide , Uniglide and Interactive Glide ), the gear changes are less jerky and can also be carried out under a certain load.
In the past, the cyclist had to make sure that the rear derailleur cage was positioned as precisely as possible over the desired sprocket when shifting gears. Modern derailleur gears, on the other hand, have locking steps in the gear lever, which is also called an indexed gearshift. This means that you shift from gear to gear in stages. Some shift levers have detachable notches. This can be useful if the Bowden cable has lengthened over time and the steps no longer match the pinion positions and an adjustment tool is not at hand.
The sprocket package contains up to twelve (typically 7 to 10) sprockets with 10 to 50 teeth, with racing bikes often only up to 21 or 25 teeth.
Inverse derailleur
There are so-called inverse switching systems from Shimano . This technology was first introduced in 1998 in the rear derailleurs of the XTR (RD-M951) and Nexave (RD-T400) series, and later also in the Deore XT (RD-M760) and Deore LX (RD-M580).
The rear derailleur spring works the other way around: When the cable is tensioned, the cage is not pulled inwards as in a normal derailleur, but outwards (tension the cable = higher gear). The main advantage of this mechanism is that it enables smoother shifting to an easier gear, as the chain can only separate from the sprocket at the HyperGlide shift gates. With conventional rear derailleurs, this depends on the pressure of the thumb or the position of the shift gate. The inversion technology is now mature, there are also no problems with leaking spring tension.
A small advantage, especially for newbies, is that with the Inver technology the shift direction (in connection with Rapidfire levers) of the left and right hand is the same: thumb lever for heavier gears, index finger lever (release lever) for easier gears.
Shimano's name is top normal for the regular and low normal for the inverted circuit.
Footnotes
- ^ Clifford Graves: Velocio, Grand Seigneur . Retrieved March 17, 2007.
- ^ History of Campagnolo
- ↑ History of the bicycle gearshift
- ↑ Christian Smolik: Online Glossary Velotechnik - Schaltschwinge .
literature
- Pryor Dodge: the fascination of bicycles. History, technology, development . [Foreword by Hans-Erhard Lessing .] (Original title: The Bicycle ). German by Renate
- Richard Hallet: Bicycle Maintenance-Care-Repair. BVA Bielefelder Verlag, Bielefeld 2003, ISBN 3-87073-308-X .
- Frank Lewerenz, Martin Kaindl, Tom Linthaler: Das Rennrad Technikbuch. Pietsch, Stuttgart 2005, ISBN 3-613-50486-3 .
- Rob van der Plas: The bicycle workshop - repair and maintenance step by step. BVA Bielefelder Verlaganstalt, Bielefeld 1995, ISBN 3-87073-147-8 .
- Jörg Urban, Jürgen Brück: Bicycle repairs, maintenance and breakdown assistance. Gondrom, Bindlach 2007, ISBN 978-3-8112-2938-9 .
- Fritz Winkler, Siegfried Rauch: Bicycle technology. Construction, manufacture, repair . 10th revised and updated edition. BVA , Bielefeld 1999, ISBN 3-87073-131-1 .