Best Bike Derailleurs

Best Bike Derailleurs

Derailleur is the French word for a bicycle gear mechanism that moves the bike chain from one cog or sprocket to another. The derailleur also has a mechanism for taking up the slack in the chain as it moves to smaller cogs.

Many of these problems can be fixed by adjusting the derailleur. Eventually, though, there comes a point when further adjustments won’t be enough to keep things moving smoothly, and you need to install a new derailleur.

In this article, we’ve put together a collection of the best Rear Derailleurs that are currently available on the market. To help you find the perfect Rear Derailleur among a wide variety of options, we constantly update our collection with new and trending models. When you make any purchase from our independently chosen collection, we may earn some commission.

5 Best Bike Derailleurs of 2021:

1. Shimano RD-M8100 / RD-M8120

Shimano RD-M8100 / RD-M8120

When purchasing this derailleur you have to choose from two versions. Both the RD-M8100 and the RD-M8120 are part of Shimano’s Deore XT M8100 series. The former is for a bike with a single front chainring, while the latter is compatible with double front chainrings. You get different gear combinations and slightly different specs with each version. However, that’s where the differences stop. In terms of performance and feel, they are almost identical.

These rear derailleurs are packed full of technologies that make it better than the rest of Shimano’s line-up. After testing we have verified that a bumper added to the cage, a chain stabilizer, large pulley wheels, and other features do fulfill their purpose as claimed. The improvements include high chain tension, low wear and noise, and most importantly, quick and seamless shifting. Additionally, not only do they have a sturdy build, but they also have a compact design that greatly decreases the chance of damaging impacts on the trail.

  • Fast and Smooth Shifting
  • Double Front Chainring Option
  • Great Chain Tension
  • Wide Speed Range
  • Clutch can get stuck sometimes but can be easily fixed
  • Chain stabilizer will rust if even slight moisture gets in

2. RD-R9150 Dura-Ace Di2

RD-R9150 Dura-Ace Di2

We were excited to try out the electronic shifting on the rear derailleur RD-R9150 Dura-Ace Di2. While we could easily rely on the smooth shifting, the braking force was adequate enough for rasy modulation . We also found that the shift levers were extended so that the “click” during gear shift is more profound.

Using the E-Tube app from Shimano, we could shift over multiple sprockets. As the app can be run on Windows, Android, and iOS – customizations were much simpler and quick than before. Thanks to Synchro-shift, we were able to choose from 3 modes for shifting. Junction A featured the button which we double clicked to shift between the modes even when we were riding. Installing the RD-R9150 rear derailleur was a real challenge. However, once set up properly, there were hardly any issues as we bounced between the gears on the road.

  • Synchro-Shift Technology
  • Single button design
  • One Cage Size
  • Shadow Design
  • All firmware would need to be updated for proper functioning

3. Shimano Deore 9

Shimano Deore 9

When you are looking for a good MTB derailleur, you want to make sure that you are buying an affordable yet durable piece of equipment. This excellent derailleur provides quick and precise shifting. It is also very durable and reliable thus offering outstanding performance in all conditions.

This rear derailleur weighs less than 300 grams yet can help you shift gears in all terrains. It is compatible with various 9-speed MTBs and is very easy to install. You can also use it with your 7-speed bike with no problems whatsoever. You don’t have to be an expert because it is very easy to install. The pin bushings are fluorine-coated. This guarantees that your rear derailleur will last for long. This coating protects the derailleur from humidity that can cause rust thus affecting the shifting of the gears. It is easy to adjust for flawless and silent operation.

  • Affordable rear derailleur
  • Fluorine-coated
  • Easy to install and adjust
  • Precise and quiet shifting
  • Compatible with various MTBs regardless of their speed
  • Might get a little bent but you can easily bend it back for a flawless performance

4. SRAM X-Horizon Rear Derailleur

SRAM X-Horizon Rear Derailleur

Are you worried about noise and stiff chain movements? Here is a solution! With this SRAM X-Horizon Rear Derailleur being integrated with the pulleys, chain tensions are taken care of by directing the movement to the horizontal axis. What makes this product unique is its pulley offsets and 12-tooth X-sync wheels. These pulleys tend to manage the cage length with the chain movement better than the traditional pulleys.

It is also equipped with the roller-bearing clutch to avoid derailleur failures and cage-lock system, making installation, adjustment, and removal of derailleur convenient. The X-actuation ensures the right gear ratio, particularly for SRAM 1x, to ensure effortless shifting throughout the cassette. With all these above features, this 11-speed bike derailleur stands out as one of the best.

  • Comes in dimensions of 17.9 x 13.4 x 10.4 inches and is black
  • Minimum cog size of 11 teeth and a maximum of 34 teeth
  • Light in weight making it suitable for smaller bikes with a total of 4.2 ounces
  • Can be fitted to most bike models with minimal effort
  • Cannot be shipped outside the United States
  • No fitting instructions included

5. SRAM GX Eagle


The SRAM GX Eagle Rear Derailleur is part of SRAM’s popular GX Eagle groupset. The installation is surprisingly easy. It should take about an hour if you include installation of the XD driver. As in all SRAM mechs, the cable management is great. You can also use this mech with Eagle XX1 and Eagle XO1 components without a problem. Moreover, you have flexibility with the cassette size as well. This derailleur has the best combination of overall quality and price among all of SRAM’s rear derailleurs.

The performance you get while riding is simply incredible. The shifting is probably one of the smoothest that we have experienced. There is also no bounce or chain slap even during intense jumps and drops. This is made possible by many technologies that are usually found only in the most premium derailleurs. Other than that, we found the cage lock to be the most convenient feature of this unit. You can push it forward and lock it in place to add extra chain slack. This makes the removal of wheels and the chain a very simple process.

  • Good Compatibility
  • Sharp and Smooth Shifting
  • Almost Zero Chain Slap
  • Cage Lock Technology
  • A bit on the heavier side, considering the price

How To Choose The Right Bike Derailleurs

A few factors that you need to consider before buying the right derailleur for your bike are as follows:

  • Longevity: Whether you’re looking for a new rear/front derailleur or a replacement, longevity is one of the first factors that you need to be particular about. Aluminum or steel may be more long-lasting than plastic ones (although, it also depends on the brand and quality).
  • Gear ratio: Before purchasing a new bike derailleur, assess the number of gears that your setup can manage. If you are just replacing a broken/old one, you need to count the cogs in your cassette and ensure that the speed of the bike derailleur matches the speed of the shifter.
  • Cage length: The cage length is the distance between the upper and lower pulleys of a rear/front derailleur. Deciding on the best derailleur according to the cage length determines the speed, range, and shifting of your bike.
  • Mode of gear shift: Several products offer mechanical and electronic shifting. If you opt for electronic shifting, you need to choose a front derailleur with compatible gears and brake.
  • Tooth capacity: Tooth capacity refers to the difference between the smallest and largest cogs, which is then subtracted from the difference between the smallest and largest chainrings at the front.
  • Weight: The derailleur that you opt for must weigh in a way that is compatible with your bike/bicycle’s weight. Usually, mountain bike riders can go for a lower weighted derailleur for better control and command on rough terrain. In contrast, road bikers can have a slightly increased weighted derailleur.

Which brand of derailleur should I buy?

Which rear derailleur do I need? Shimano, SRAM and Campagnolo are the three main players in the drivetrain market.
Microshift, Box, Rotor, FSA and others all also make groupset components, but it would be beyond the scope of this article to cover all of these.

As a general rule of thumb, it’s best not to mix and match drivetrain components from different brands. While things such as cranks, chains and cassettes are mostly inter-compatible between brands, generally speaking, shifters and derailleurs aren’t.

In brief, Shimano, SRAM and Campagnolo all use different cable pull ratios (the amount that a derailleur moves for every millimetre of cable pulled through by the shifter), and mixing parts will result in very poor shifting.


  • All the major manufacturers agree that cross-chaining — running the chain at extreme angles from front to rear — puts excess friction on the chain and moving parts. Translation: cross-chaining is bad.
  • The low-limit screw on the derailleur adjusts how far it can move toward the lowest gear. If the chain is falling off the largest cog (the lowest gear) and getting tangled in the spokes, you can often adjust it to solve the problem with the low-limit screw.
  • The high-limit screw does the same thing as the low-limit screw but at the other end of the scale. It adjusts how far the derailleur can move toward the highest gear. It the chain is falling off the smallest cog (the highest gear) and getting caught between the frame and the cassette, use the high-limit screw to adjust the derailleur.
  • Slow shifting up and down the cassette can be due to a build-up of debris. Slow shifting can also be caused by the derailleur, hanger, or cassette becoming loose. To troubleshoot, clean the derailleur and chain, then check to ensure that everything is tight and properly aligned.

Final Words

So, these are all of the Best Rear Derailleurs available on the market. We hope this collection was helpful to find the right Rear Derailleur for the money. However, we recommend checking out the features, benefits, and problems of each of these Rear Derailleurs before taking your decision.

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