A derailleur is a mechanism that is used to move the chain from one gear to another on a bike. It is typically located at the rear of the bike and is responsible for moving the chain between the different cogs on the rear wheel cassette. The derailleur is controlled by the bike's shifters, which allow the rider to change gears while riding.

The derailleur has two main parts: the derailleur itself, which is the mechanism that moves the chain, and the derailleur cable, which is the cable that runs from the shifters to the derailleur, allowing the rider to control the movement of the chain.

The rear derailleur is an important component of a bike's drivetrain and is responsible for precise and efficient gear shifting. It works by using a spring-loaded jockey wheel that moves the chain from one cog to another, thus changing the gear.

When it comes to the cost of replacing a rear derailleur, it can vary depending on several factors. The quality of the derailleur, the type of derailleur, and the brand of the derailleur all play a role in determining the cost. Generally speaking, a basic, lower quality rear derailleur can cost anywhere from £20 to £50, while a higher quality rear derailleur can cost anywhere from £50 to £150 or more.

It's also important to note that replacing a rear derailleur is not a simple task and it is best to have it done by a professional bike mechanic. The cost for labor can vary, but it's usually around £20-£40. The cost of the labor and the cost of the new rear derailleur must be taken into account.

Another thing to consider is that if the rear derailleur gets damaged, it may be a sign of other issues with the bike's drivetrain. It is important to check the other components such as the gears, the cassette, the chain, and the shifters to make sure everything is in good working condition.

In conclusion, a derailleur is a mechanism that is used to move the chain from one gear to another on a bike, it is typically located at the rear of the bike and is responsible for moving the chain between the different cogs on the rear wheel cassette. The cost of replacing a rear derailleur can vary depending on several factors such as quality, type, and brand. It's also important to note that replacing a rear derailleur is not a simple task and it is best to have it done by a professional bike mechanic. The cost for labor can vary, but it's usually around £20-£40. The cost of the labor and the cost of the new rear derailleur must be taken into account.

Additionally, if the rear derailleur gets damaged, it may be a sign of other issues with the bike's drivetrain, so it is important to check the other components such as the gears, the cassette, the chain, and the shifters to make sure everything is in good working condition. Regular maintenance and proper adjustment of the rear derailleur can help to prolong its lifespan and ensure smooth and efficient gear shifting.

Bike drivetrainDerailleurDrivetrain maintenanceGear shiftingJockey wheelRear derailleur