Nowadays, most cyclists use bikes with two gear shifters. Of course, there are models without them, and some recreational bicycles are equipped with only one shifter, which often looks unusual due to its location inside the planetary hub. Nevertheless, almost every cyclist is familiar with the gear shifting system in one way or another.
Purpose of the Rear Derailleur
The rear derailleur, also known as the rear mech, is a mechanism that allows the chain to move between the sprockets of the rear cassette or freewheel. The chain passes through the pulleys and cage of the derailleur, which moves along the axis of the cassette, shifting the chain to the desired sprocket. Additionally, the derailleur can move vertically to maintain a constant distance between the pulley and the sprockets.
Usually, the rear derailleur is controlled by a cable, although there are also electric and hydraulic systems. When the cable is tensioned, the chain moves from smaller sprockets to larger ones, and the reverse movement is achieved through chain tension. To extend the life of the derailleur and ensure smooth shifting, it’s important to change gears while pedaling and under minimal load.
Features to Consider When Choosing a Rear Derailleur
To choose the right rear derailleur for your bicycle, you need to consider its design and some technical features. Let’s look at the key points to pay attention to.
Materials Used in Rear Derailleurs
The material from which the rear derailleur is made affects the cost of the bicycle, its durability, and weight. The most budget-friendly option is derailleurs made of steel alloys, which are often installed on inexpensive bicycles. However, they are more prone to deformation and have relatively low strength characteristics.
More high-quality and expensive options are derailleurs made of titanium and carbon fiber. In the latter case, the cage is made of carbon, and the spring is made of titanium. Such devices are usually used in high-end and expensive bicycles.
An intermediate option is derailleurs based on aluminum alloys. They represent a compromise between cost and quality. Some parts, such as the spring, may be made of steel.
Pulleys
The pulleys in the derailleur serve to tension and guide the chain. There are two types of pulleys: guide pulleys and tension pulleys. They are usually made of plastic and are subject to wear, so they require periodic replacement. As the pulleys wear out, the quality of gear shifting deteriorates.
It’s important to note that tension and guide pulleys are not interchangeable. Moreover, pulleys from different bicycle manufacturers are usually not compatible with each other.
Types of Rear Derailleur Designs
When replacing a worn-out rear derailleur, it’s important to choose the right new device. Derailleurs are classified according to the following parameters:
Cage Length
This parameter, also called derailleur capacity, determines the range of gear ratios with which the device can work. It is calculated as the sum of the differences between the number of teeth on the large and small chainrings of the crankset and cassette.
Spring Direction
The most common option is Top normal, where shifting with the cable moves from smaller to larger sprockets. Most manufacturers adhere to this principle.
There is also a Low normal option, or reverse shifting, where the chain is dropped onto smaller sprockets using the cable, and onto larger ones using the spring. This design is found only in the Shimano line and has not gained widespread use due to the lack of significant advantages.
Gear Ratio
This is the ratio between cable movement and derailleur movement. It can be 1:1 (as with Sram) or 2:1 (as with Shimano). Due to this difference, the derailleurs of these manufacturers are not interchangeable, although the shifting precision is approximately the same for both options.
Frame Mounting
There are two ways to mount rear derailleurs:
- Hook mount – attached to the bicycle hub. This is a reliable method, but if the derailleur breaks, the hub may also be damaged, leading to additional costs.
- Bolt mount – attached to a hole in the frame or through a special adapter called a “hanger”. The advantage of this option is that in case of a fall, usually only the adapter is damaged, which significantly reduces repair costs.
Protection Methods
Various technologies are used to protect the derailleur from damage:
- Shadow technology, patented by Shimano. The special placement of the derailleur reduces the risk of damage in case of a fall.
- Protective cages – steel devices that are attached to the frame and protect the derailleur. They also help protect the adapter in case of a fall.
Proper Use of the Rear Derailleur
To ensure stable and proper operation of the rear derailleur, it’s important not only to adjust it correctly but also to follow certain rules of use and storage.
Increasing speed occurs due to spring tension in the derailleur, and decreasing speed is due to its relaxation. Over time, the spring may lose its elasticity, especially if you leave the bicycle in storage with a high gear engaged. To avoid this, it’s recommended to set the gear with minimal spring tension before putting the bicycle into storage.
Another common problem is pulley contamination. It’s necessary to clean them regularly and monitor their wear. A sign that the pulleys need replacement is the sharpening of the teeth (new pulleys have flat tooth tips).
It’s also important to periodically clean the derailleur mechanism itself, as it constantly comes into contact with dirt. It’s recommended to change the derailleur cables about twice a year. This work requires certain skills, so it’s better to entrust it to professionals.
Following these rules will help extend the life of your bicycle and ensure its stable operation.
Which Rear Derailleur to Choose?
When choosing a rear derailleur, you should first pay attention to your bicycle’s transmission system. It’s important to consider compatibility in terms of the number of speeds, gear ratio, mounting type, and cage size. These parameters depend on the type of bicycle, its intended use, and the installed components of a particular brand.
It’s not recommended to combine parts from different manufacturers, as this can lead to problems. It’s better to stick to one brand and, if possible, one line of parts. Physical parameters are usually described in detail by the manufacturer and indicated in the product card. When replacing, it’s best to compare the characteristics with the failed product.
Don’t try to save money by choosing the cheapest options. Such products are often of unknown origin, break quickly, are not repairable, and require constant adjustment, which can be especially problematic for beginners. In this case, it’s better to pay attention to inexpensive options of entry or mid-level from well-known manufacturers.
For experienced cyclists, it’s obvious that more expensive components are usually lighter, of higher quality, more reliable, and better meet high usage requirements.
Conclusion
Gear shifters are some of the most complex, fragile, and fine-tuning elements of a bicycle. However, modern technologies allow for the production of affordable devices capable of serving for more than one year. The main difficulty lies in choosing the right option among the many standards, sizes, capacities, and additional modules from various manufacturers.
There are different types of derailleurs, but their operating principle can be described quite simply. In this article, we have considered the current standard, and it’s better to talk about planetary and other mechanisms separately. There are a number of standards for these components that are stricter than for other bicycle elements, which simplifies replacement and maintenance.
The perfect derailleur doesn’t exist yet, and the choice always remains with the cyclist. It’s important to consider individual preferences, bicycle model, financial capabilities, and physical parameters.
