Gear shift
The gears of a bicycle is composed of a switchable gear between crank - driving and driven rear wheel, and the associated switching and control elements . With it, the cadence and the torque to be applied can be brought into a comfortable range for a given performance of the cyclist, even with different driving resistances. Gear shifts are set up similarly in motor vehicles .
Gear shifts are common on all modern bicycles. A still existing exception is the so-called single wheel without gear shift, which is preferably built as a children's bike , but is also preferred by adult purists. Bicycles without gears are also occasionally found on cheap bikes. One-way bikes are also used for artificial cycling , track bikes and BMX sports.
purpose
Most cyclists want to stay within a certain torque range when cycling - pedaling shouldn't be too difficult; however, if it is “too light”, the cyclist feels under-challenged. On the other hand, the cyclist would like to achieve his performance in a very narrow speed range, usually 60–80 revolutions per minute are recommended by sports medicine specialists and are perceived as pleasant by cyclists. Physically results from the formula
the (continuous) power that a cyclist produces, usually around 40–80 watts . Depending on the external influences (road gradient, tail / head wind, weight of the bicycle and the cyclist, air resistance, etc.), the speed for which this performance is sufficient results. However, the resulting speed can be very slow or quite high. The gear shift ensures via the gear ratio that the different rear wheel speeds can be converted into the narrow pedal speed range.
technology
Types
-
Derailleur gears (since 1940), with several pinions on the rear wheel and often also several chain wheels (common term: gears) at the front. The bicycle chain can be placed on the different gears with a rear derailleur or derailleur (front).
- Instead of the chain, the sprocket set can also be shifted sideways: "Ultra-Shift".
- A special feature was the Retrodirect , built in the 1920s and 1930s , in which two gear ratios were selected by reversing the direction of pedaling. Shifting is done by two freewheels acting in opposite directions of rotation .
-
Hub gear (since 1902) in which the different gear ratios can be set with one or more epicyclic gears ("planetary gears").
- A special feature is the continuously variable NuVinci hub
Controls
The circuit is usually operated by means of a suitable lever on the handlebar or the front frame using Bowden cables. In addition to shift levers, twist handles and two-lever handles (trigger handles, one lever each for up and down) have been produced, or it is switched by moving the brake handles sideways. The word gearshift is also used in connection with changing the gear ratios of machines and automobiles. Colloquially, this means the possibility or the corresponding lever to change the gear ratio.
- electrical / electronic circuit: regular circuit with actuation of the rear derailleur using an electrical circuit instead of a Bowden cable ; in a single case a kind of gear crane switch instead of the front derailleur
- electrically operated derailleur with "switches" built into the front chainring
literature
- Michael Gressmann, Franz Beck, Rüdiger Bellersheim: specialist knowledge of bicycle technology. 1st edition, Verlag Europa-Lehrmittel, Haan-Gruiten 2006, ISBN 3-8085-2291-7 .
- Fritz Winkler, Siegfried Rauch: Bicycle technology repair, construction, production. 10th edition, BVA Bielefelder Verlagsanstalt GmbH & Co. KG, Bielefeld 1999, ISBN 3-87073-131-1 .
swell
- ↑ Shifting without gears in: test.de, July 27, 2007, accessed on February 4, 2013
- ↑ on the frame-integrated bottom bracket circuit, see Hans-Heinrich Pardey: Die Schaltbox fürs Rad , FAZ of December 28, 2012
