A rear derailleur is an essential part of a bicycle gear system that is responsible for switching the chain between different pinions on the rear sprocket set. It allows the rider to change the gear ratio and thus adjust the resistance and speed of the drive. Rear derailleurs are available in different designs and are selected depending on the type of bicycle and gear type.
Derailleur Mechanism: A derailleur consists of a movable arm fitted with a pulley (often called a "pulley" or "pinion"). This pulley is set in vertical motion by a combination of springs and joints.
Shifting: The rear derailleur is controlled by the pull of a shift cable operated by the shift lever on the handlebar. When the rider operates the shift lever, the shift cable pulls on the rear derailleur, moves the derailleur pulley and causes the chain to switch to the desired sprocket.
Spring systems: Derailleurs use springs to keep the chain at the correct tension and to make shifting between sprockets smooth. There are several types of spring systems, including parallel springs and derailleurs with a single spring element.
Wide gear range: A rear derailleur allows the rider to adjust the gear ratio depending on the terrain and riding situation.
Precise shifting: Modern derailleurs offer precise shifting with minimal friction loss, allowing the rider to switch between gears quickly and seamlessly.
Weight: Rear derailleurs are often lighter than other gear systems such as hub gears.
Wide range of options: There is a wide range of derailleurs for different bike types and gear types.
Sensitivity: Derailleurs can be sensitive to damage or alignment problems, which can lead to misshifting.
Maintenance: Derailleurs require regular maintenance to ensure optimum performance. Settings will need to be checked and possibly adjusted occasionally.
Vulnerable to dirt: Derailleurs can be exposed to dirt, dust and moisture, which can affect their function.
There are different types of derailleurs on bicycles, which can vary depending on the type of bicycle, gear system and intended use:
1. Derailleur: Derailleurs are the most commonly used derailleur and are found on most types of bicycles. They are used with derailleur systems where the chain is switched between different sprockets on the rear sprocket pack. Derailleurs are available in a range of models and qualities, from entry-level to high-end options.
2. Hub derailleur: Hub derailleurs are integrated into hub gears that are housed in the rear wheel hub. These gears use an internal mechanism to change gears. The choice of hub derailleurs may be more limited than with derailleurs.
3. E-bike-specific derailleur: E-bikes sometimes use special derailleurs designed to handle the higher torques and speeds of electric drives. These derailleurs are often more robust and can handle larger loads.
4. Road bike specific derailleur: Road bike specific derailleurs are optimized for the requirements of road bikes. They often offer a lower profile to allow for easier shifting with tight sprocket spacing. These derailleurs are also designed to be more aerodynamic to reduce drag.
5. Mountain bike specific derailleur: Mountain bike specific derailleurs are often more robust and resilient to the harsh conditions found on trails. They can have greater capacity for larger sprocket differences and are often equipped with clutch systems to prevent chain rattle.
6. Road and trekking bike derailleurs: There are special derailleurs for road bikes and trekking bikes that are tailored to the requirements of touring and commuting. These derailleurs often offer a wide gear ratio and reliable function.
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