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How the rear derailleur works

A bicycle derailleur is a crucial component of a cycling machine. It directly impacts the speed and the covering distance of a rider. It is a guiding mechanism that allows cyclists to change chains from one sprocket to another.

Derailleur helps the chain convert the energy released by the cyclists when pedaling. It modulates this input and transfers it to an ideal output manifested through distance and speed. Both front derailleur and bicycle rear derailleur work using the same principle. Therefore, it is important to understand their functionality in order to know the overall workings of a bicycle.

The Basic Function of Bike Derailleurs

The transmission is a key component of the bicycle transmission system. They usually have chains, sprockets, and entire mechanisms that help move the chain from one sprocket to another. The derailleur is basically a sprocket, usually triggered by the energy received by the pedal. The sprocket located on the rear wheel is called the rear derailleur.

What is a rear derailleur? The bicycle rear derailleur has two basic functions-keeping the chain tensioned and shifting gears. It is deliberately positioned in areas where the chain is slack from time to time. Due to this specific task, the derailleur is often referred to as a chain tensioner.

Keep the chain tight
In order to maintain the tension of the chain, no matter what gear you use, the derailleur usually adjusts its position to maintain the tension of the chain. The derailleur will move according to the movement position of the chain. Depending on the gear used, the chain may move to the largest sprocket or the smallest sprocket.

Once the chain moves to the largest sprocket, the rear derailleur reduces the tension because the chain is wrapped around the sprocket. If the chain reaches the smallest sprocket, the derailleur will increase the tension because the chain is slack in this position. The function of the derailleur is to balance the tension on the chain.

Switch gears
Another function of the derailleur is to shift gears. The derailleur helps the rider change gears by moving the bottom of the chain from side to side. When riding a bicycle, the rear derailleur changes and brings tension to the bicycle chain. When this happens, the force from the front sprocket will be transferred to the rear sprocket. This creates excessive tension where the rear derailleur needs to be balanced. To do this, the derailleur will move the chain to another sprocket, especially when you press the pedal hard.

Components of the rear derailleur
What is a rear derailleur
Since the rear derailleur is an indispensable part of a bicycle, it is important to understand the different parts of the rear derailleur and how they work. The bicycle rear derailleur is divided into parts with specific functions, as well as:


1. Construction
Normally, the rear derailleur is located under the rear flywheel and is properly connected to the bicycle chassis using a bracket. There is a mounting bolt to fix the derailleur to the derailleur hanger of the bicycle frame.

The cassette tape has a spring-loaded linkage mechanism, usually called a parallelogram. You will notice that this linkage mechanism has a cage with two pulleys on it. They are called pinch wheels or guide wheels or “G” wheels (top) and tension wheels or “T” wheels (bottom).

These pulleys play a very important role in the chain tensioning system. The top pulley is responsible for driving the chain from one sprocket to another. On the other hand, the main function of the tensioner is to compensate for the slack in the chain and provide the correct tension in the process. It ensures that there is sufficient tension between the driving sprocket and the driven sprocket.

2. Process
The components mentioned above are triggered by cables aligned with the shift toggle. When you use the toggle, the cable will tighten, slack, or stay in place. When this happens, the parallelogram connecting rod will move along the diagonal axis and drive the cage and the pulley to move.

When the cage moves, the “G” pulley or guide pulley will be brought to the direction of the desired sprocket. Whether the pulley increases or decreases the tension, it will also adjust the tension of the chain.

Usually, when you shift to a lower gear, the chain will automatically transfer to the larger sprocket. During this process, the bicycle derailleur will move inward and upward following the instructions of the chain, and reach the selected sprocket. Once the tension in the chain increases, observe that the “T” pulley moves away from the “G” pulley.

3. Index
Indexing is another important process of the derailleur. It is the movement of the derailleur triggered by the cable switch. Indexing is a crucial process that allows your bicycle gear to shift smoothly and seamlessly.

Normally, your bicycle derailleur is connected to the gear lever using a cable that passes through the housing. The index shifter allows the cable to move with each click. The gear lever is used in conjunction with the barrel adjuster and can be found in the derailleur body or the gear lever. These regulators are used to ensure smooth operation of the gear shifting between gears.

Therefore, it is important to have a correctly indexed derailleur to prevent the chain from falling between the sprockets or driving skewed. When this happens, both the chain and the tape will be damaged.

4. Limit screw
The part that prevents extreme movement of the derailleur is the stop screw. Basically, the derailleur has a limit screw, and the rear derailleur is adjusted by preventing the rear derailleur from reaching the limbs. limit

Bicycle rear derailleur protector
The bicycle rear derailleur protector is used to protect the rear derailleur to prevent accidents from damaging the derailleur.
It can effectively protect the transmission in the event of a fall and collision while riding a bicycle, and prevent external impact from damaging the transmission.


But there are also drawbacks, that is, there is a greater possibility of safety hazards when riding a bicycle, because the rear derailleur has a certain thickness, which increases the gap between the wheel components, which is easy to cause on rugged and bumpy roads. The rear wheel is not firm and the rear wheel falls off.

The rear derailleur protector will also damage the rear wheel frame to a certain extent.

Extended information:

Steps to install rear derailleur protector

1. First of all, see if the hole position of the rear derailleur protector matches your frame.
2. Unscrew the screw on one side of the transmission, and pass the protector into the rear hub bearing.
3. Let it be tightened with M5 or M6 screws.
4. However, some are locked on the shaft. After installation, put the rear derailleur to the loosest position to see if it can be touched. If you hit it, tap it out a bit, and make sure you don’t hit it and it’s okay.

The rear derailleur protector of the bicycle is mainly to protect the transmission. If the bicycle falls, the rear derailleur protector will play a protective role and can reduce losses.
However, there are potential safety hazards when the rear derailleur is installed. The thickness of the rear derailleur is 1-2mm, which undoubtedly increases the thickness of the wheel set. If the vibration is too large on a mountain or a relatively bumpy road, the rear wheel may fall off, and the rear derailleur workmanship Almost, after it is installed, the gap between the wheels will be very large, causing the wheels to be unstable.


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