Derailleur
When derailleur on the bicycle is called the front shifting device with derailleurs . The derailleur controls the movement of the chain on the front two or three chainrings .
technology
Until the 1960s , it was common to change the chain using a so-called transfer mechanism . This switched axially (parallel to the crank axis). In addition, no Bowden cables were used, but the circuit was operated directly with the hand or foot.
In the meantime, the derailleurs, like the rear derailleurs , are built with a parallelogram guide and operated with a shift cable and a spring : when the cable is tensioned , the chain is pushed onto the next larger chainring, this process being made easier by climbing aids on the chainrings; When the cable is released, a spring pulls the chain onto the next smaller chainring. With electronically controlled derailleurs , a digitally controlled servo or linear motor carries out the movement.
Derailleurs are classified according to their capacity; good models can shift differences of more than 15 teeth. Mountain bikes (3x9) have a capacity of 22 teeth (gradation 22-32-44).
Since around the middle of the 2010s, a derailleur has been partly dispensed with, especially on higher-quality mountain bikes (often called a single drive). In order to continue to guarantee the highest possible bandwidth, pinions with up to 12 gears and around 10–50 teeth are available. A tidier cockpit / handlebars, less technology and often a lower weight are mentioned as advantages. A disadvantage is usually a not quite as large under- / translation as mentioned with 2/3-way drives.
Classification
Front derailleurs are usually divided by the type of assembly and cable routing.
Train routing
Top pull - down pull
There are models with shift cable routing from above ( top pull - mostly on mountain bikes ) and from below ( down pull - racing bikes ). Many models are also available as a dual-pull version. Cable routing from below or above is possible (depending on the frame).
Assembly
Top swing - down swing
Furthermore, depending on the position of the fastening clamp, a distinction is made between the (classic) downswing models, in which the parallelogram cage hangs below the clamp, and the so-called topswing models, whose axis of movement for the cage is above the clamp. The main reason for the introduction of the top swing derailleur are newer forms of bicycle frames , in which the classic downswing derailleurs can no longer be attached, for example by a non-continuous seat tube.
E-type
This type of derailleur is mounted between the bottom bracket and the frame. There is no clamp that has to be attached to the frame. This allows a further increase in the variety of frame designs. Some full suspension frames have a "derailleur stub" to which the derailleur can be attached. This is not necessary when using E-Type derailleurs. The selection of E-type derailleurs is usually limited.
Direct mount
The front derailleur is fixed directly to the frame at a specified position using screws.
literature
- Michael Gressmann, Franz Beck, Rüdiger Bellersheim: specialist knowledge of bicycle technology. 1st edition, Verlag Europa-Lehrmittel, Haan-Gruiten, 2006, ISBN 978-3-8085-2291-2