Rear Derailleur: The Ultimate Guide for Cyclists

Are you considering a new rear derailleur? It's understandable, as it's one of the most important parts of your bike, significantly impacting ride comfort and quality. Choosing the right derailleur can seem complicated, given the sheer number of models, brands, and differences in technology. It's worth taking the time to thoroughly understand its functions, how it works, and what to look for when buying one. In this article, we'll walk you step-by-step through the most important aspects of a rear derailleur—from its construction and types to practical tips on maintenance and fitting it to your bike. This will help you make an informed decision and enjoy smooth, precise gear shifting on every ride.

Contents

1. What is a rear derailleur?
2. Types of rear derailleurs
3. Rear derailleur construction
4. Rear derailleur functions
5. How to choose the right rear derailleur?
6. Calculating capacity
7. Rear derailleur maintenance
8. Prices and quality rear derailleurs
9. Summary

What is a rear derailleur?

The rear derailleur is a part of a bicycle's drivetrain. This component is responsible for precisely changing the gear you're riding. Gear ratios can be changed individually or several times, depending on the system. Typically, the derailleur is controlled using a shift lever or a single shifter. The rear derailleur is typically attached to the bicycle in two ways: it can be bolted to the derailleur hanger or directly to the frame. In addition to the rear derailleur, bicycles also feature internal derailleurs . These derailleurs are integrated into the rear wheel hub, such as those from Shimano Nexus, Sturmey Archer, or Rohloff. Other lesser-known systems are available on the market, such as the Kappstein bottom bracket system .

Types of rear derailleurs

1. Mechanical derailleurs - traditional, gear changes are performed using a cable.
2. Electronic derailleurs – increasingly popular on sports bikes, shifting gears is accomplished by motors in the derailleur. Bluetooth control is also available (e.g., SRAM eTap).

Rear derailleur construction:

1. The derailleur cage is the longest part of the derailleur, housing the two chain guide pulleys. The cage is responsible for chain tension, and its length affects the range of sprockets it can operate.
2. Derailleur Pulleys – the upper (guide) and lower (tension) pulleys that guide the chain to the appropriate sprocket and maintain its tension.
3. Derailleur body – this part is the main element that holds the rest of the components together.
4. Tension spring – maintains chain tension and ensures its stability, especially when riding over uneven surfaces.
5. Barrel – allows for precise adjustment of cable tension, which affects gear shifting accuracy.
6. Range screws - responsible for setting the derailleur operating range.
7. The clutch is a derailleur tension regulator. It's found primarily in derailleurs designed for mountain and gravel bikes.

Rear Derailleur Outer Functions

The main functions of the rear derailleur include:

• Shifting gears improves ride comfort and pedaling efficiency, allowing you to adjust your cadence accordingly, which translates into reduced effort when climbing. This translates into increased speed on descents and flat sections, as well as reduced drivetrain wear.

• Maintaining proper chain tension ensures smooth drive operation and optimal gear shifting, which improves driving efficiency and reduces the risk of the chain coming off.

How to choose the right rear derailleur?

There are several factors to consider when choosing a rear derailleur:

1. Brand compatibility - derailleurs are usually compatible with only one groupset brand (e.g. Shimano, SRAM, Campagnolo),
2. Cart length - short, medium and long sizes available depending on the cassette size,
3. Drivetrain Capacity - allows you to calculate the maximum number of teeth in the drivetrain that the derailleur can handle,
4. Bike type - derailleurs for road, mountain and gravel bikes differ in design.

Calculating capacity

A rear derailleur has a specific range of gear ratios. Therefore, these mechanisms differ in their capacity , or their ability to handle different sprocket sizes. Capacity is the difference between the largest and smallest sprockets the derailleur can handle.
The length of the derailleur cage affects its capacity:

• Short cage – used on road bikes, designed for smaller cassettes with fewer sprockets.
• Medium stroller – also used on the road but also on mountain bikes.
• Long cage – designed for mountain and gravel bikes with a wide range, as they use large cassettes, e.g. 10-51T.

To calculate the drive system capacity, use the following formula:

 [różnica między liczbą zębów na najmniejszej i największej tarczy mechanizmu korbowego] + [różnica między liczbą zębów na najmniejszej i największej zębatce kasety]

For example, for a system with a 44-22 chainring and a 32-11 cassette:

 (44-22) + (32-11) = 43

A capacity of 43 indicates the need for a long cage rear derailleur.

Rear derailleur maintenance

Regular maintenance of your rear derailleur is crucial for its long-term performance:

1. Clean your derailleur whenever you notice it needs it. Use degreaser and a brush.
2. Lubricate guide wheels and pins regularly (sparingly!)
3. Check the wear of the support wheels and replace them if necessary
4. If your derailleur has a clutch, remember that it also requires maintenance due to the additional mechanism

Prices and quality of rear derailleurs

The prices of rear derailleurs can vary significantly, from several dozen to several thousand zlotys.
Higher prices often mean:

• Lighter materials (e.g. carbon fiber, titanium)
• Better quality bearings
• Advanced features and technologies (e.g. electronic gear shifting)
• Design

The market is dominated by Shimano and Sram products, although Italian brand Campagnolo also has its die-hard fans. In recent years, competing solutions from Chinese manufacturers have also gained traction.

Summary

The rear derailleur is one of the most important components of a bicycle's drivetrain, playing a key role in maintaining smooth and precise gear shifting. It allows you to adjust pedaling resistance to suit the terrain, which translates into comfort and efficiency. Whether you're riding on asphalt, gravel, or more challenging mountain paths, choosing the right derailleur isn't just about technical aspects, such as the number of gears, but also about compatibility with other drivetrain components, such as the cassette and shifters.

It's also worth paying attention to aesthetic details, such as color, which can add a unique character to a bike. Budget is also a key factor when purchasing, as derailleurs vary in price depending on the brand, model, and build quality. Regardless of the model you choose, regular maintenance, including cleaning and lubrication, is essential to keeping your derailleur in top condition. A properly cared-for derailleur not only increases its lifespan but also ensures long-term, trouble-free operation, significantly improving comfort and safety during every cycling trip.