Your rear derailleur is a technological marvel. First invented in 1906, it was clunky, unpopular and had two speeds. They’ve come a long way since. The best mountain bike derailleurs today are durable, easy to tune and can shift smoothly even under load.

You should buy a new derailleur for the same reason the first one was invented: Because you want to climb better. Inventor Paul de Vivie, a writer known as Vélocio, designed it for Alpine bike riding. He became a cyclomaniac, quit trading silk and moved to Saint-Étienne to open a bike shop. He advocated for his now-ubiquitous device for 30 years before it became popular.

Like Vélocio, one of our goals at The Adventure Junkies is help you pick your gear. This guide will help you find the perfect derailleur, whether you want to conquer the Alps, win Strava segments or just get climb a little quicker.

For more of out top mountain bike gear recommendations, check out these popular articles: 

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QUICK ANSWER – THE BEST MOUNTAIN BIKE DERAILLEURS

  1. Shimano Deore XT RD-M772
  2. Shimano Deore XT RD-M786 SGS
  3. SRAM X.9
  4. SRAM Red eTap
  5. Shimano XTR Di2 RD-M9050
  6. Box One
  7. SRAM XX
  8. SRAM XX1 Eagle
  9. Shimano M640 Zee
  10. SRAM GX Type 2.1

 

 

 

MTB DERAILLEURS REVIEWS

SHIMANO DEORE XT RD-M772

Check out the latest price on:
AmazonJenson USA

BEST FOR: Trail riding on a quiet 9-speed derailleur designed to avoid hitting rocks and stumps

SUPPORTS SINGLE FRONT: Yes

WEIGHT: 227 g

PROS: Versatile front chainring options, durable, smooth

CONS: Limited lowest gear options

 

 

 

SHIMANO DEORE XT RD-M786 SGS

Check out the latest price on:
AmazonJenson USA

BEST FOR: 10-speed derailleur featuring Shimano clutch technology, designed to avoid hitting obstacles

SUPPORTS SINGLE FRONT: Yes

WEIGHT: 258 g

PROS: Versatile front chainring options, durable, smooth

CONS: None we could find

 

 

 

SRAM X.9

Check out the latest price on:
AmazonJenson USA

BEST FOR: Great 9-speed rear derailleur that can work with double or triple front derailleurs

SUPPORTS SINGLE FRONT: No

WEIGHT: 215 g

PROS: Supports 7, 8, or 9 speeds, accurate, precise, price

CONS: Loud, no clutch

 

 

 

SRAM RED ETAP

Check out the latest price on:
Amazon

BEST FOR: State-of-the-art shifting without wires

SUPPORTS SINGLE FRONT: No

WEIGHT: 239 g

PROS: Wireless, precise, smooth, accurate

CONS: Price

 

 

SHIMANO DI2 XTR M9050 REAR DERAILLEUR

Check out the latest price on:
AmazonJenson USA

BEST FOR: State-of-the-art shifting from the company that started it

SUPPORTS SINGLE FRONT: Yes

WEIGHT: 289 g

PROS: Precise, smooth, accurate, range of front chainrings

CONS: Price, wires, weight

 

 

 

 

BOX ONE

Check out the latest price on:
Jenson USA

BEST FOR: An easy to install and tune single front ring 11-speed derailleur from an independent company

SUPPORTS SINGLE FRONT: Yes

WEIGHT: 265 g

PROS: Easy to maintain, unique, Shimano compatible

CONS: Only for single front rings, price

 

 

 

 

SRAM XX

Check out the latest price on:
Amazon

BEST FOR: Racing on the lightest 10-speed derailleur

SUPPORTS SINGLE FRONT: Yes

WEIGHT: 181 g

PROS: Weight, quality, precise

CONS: Price

 

 

 

SRAM XX1 EAGLE

Check out the latest price on:
AmazonJenson USA

BEST FOR: Anyone riding a single front ring setup who wants a wide range of useful gears

SUPPORTS SINGLE FRONT: Yes

WEIGHT: 265 g

PROS: Better range than 2×10 setups, quality, precise

CONS: Price

 

 

 

SHIMANO M640 ZEE

Check out the latest price on:
AmazonJenson USA

BEST FOR: Budget users who want to run 1×10 or 2×10 setups with latest clutch technology

SUPPORTS SINGLE FRONT: Yes

WEIGHT: 268 g

PROS: Clutch technology, durable, precise

CONS: No triple support

 

 

 

SRAM GX TYPE 2.1

Check out the latest price on:
Amazon

BEST FOR: Budget users who want single, double, or triple front rings

SUPPORTS SINGLE FRONT: Yes

WEIGHT: 302 g

PROS: Clutch technology, compatibility, precise, accurate

CONS: Less durable, weight

 

 

 

COMPARISON TABLE – THE BEST MOUNTAIN BIKE DERAILLEURS

PICTURE
MOUNTAIN BIKE DERAILLEUR
BEST USE
SUPPORTS SINGLE FRONT?
WEIGHT
PRICE
RATING
PICTURE
MOUNTAIN BIKE DERAILLEUR
BEST USE
SUPPORTS SINGLE FRONT?
WEIGHT
PRICE
RATING
Shimano Deore XT RD-M772
Overall
Yes
227g
$$
4.4
Shimano Deore XT RD-M786 SGS
Overall
Yes
258g
$$
4.9
SRAM X.9
Overall
No
215g
$$
4.4
SRAM Red eTap
Electronic
No
239g
$$$$$
N/A
Shimano XTR Di2 RD-M9050
Electronic
Yes
289g
$$$$$
4.6
Box One
Maintenance
Yes
265g
$$$
5.0
SRAM XX
Low-weight
Yes
181g
$$$$
4.2
SRAM XX1 Eagle
12-speed
Yes
265g
$$$$
5.0
Shimano M640 Zee
Budget
Yes
268g
$
4.4
SRAM GX Type 2.1
Budget
Yes
302g
$
4.2

 

 

 

HOW TO CHOOSE THE BEST MOUNTAIN BIKE DERAILLEURS

NUMBER OF GEARS

If you want a new derailleur, you’re probably looking to change things up or just replace a broken part. Either way, it’s time to consider how many sprockets you need, and what your current setup can handle

Unless you’re buying new shifters, you’re likely limited to what you had before. Most shifters work with a specific rear cassette size — usually 9, 10, 11 or 12. If you buy a 9-speed derailleur and mate it to your 12-speed shifter, you’ll probably end up breaking it or a spoke by over-shifting.

If you’re looking for a new shifter, too, your options are open, and you probably want to go with an 11 or 12-speed derailleur. This is the modern standard, and it’s ubiquitous in bike shops and easy to buy cassettes, chains and cables for.

This 2013 blog from Performance Bike is slightly dated, but worth reading. They accurately predicted the transition from 9- and 10-speed to 11. The biggest change since then?

Virtually every wheel comes designed for 11- and 12-speed cassettes. You’ll need to use a usually included adapter if you want to stick with a 9-speed derailleur.

 

ELECTRIC OR MECHANICAL?

Both Shimano and SRAM have released electronic derailleurs that work with electronic shifting. If you’re upgrading to this, it’s a whole re-build as you’ll need compatible brakes, shifters and a front derailleur.

The innovation of faster, more precise shifting came to road bikes first and now appears on mountain bikes as well. Cycling Weekly breaks down the benefits and makes an argument that all riders can appreciate the upgrade, but I’d note that price is a big barrier to entry.

If you’re happy with mechanical shifting, then don’t make the switch yet. This equipment starts at around $1,200.

 

SHIFTER AND FRONT DERAILLEUR COMPATIBILITY

The compatibility issue will limit your options unless you’re doing a full rebuild of the drive train. Front derailleur, shifters and cassette all must match. Some rear derailleurs can be thrown on with a wider range, but most are very specific.

Shifting uses fairly old technology, but it’s incredibly precise. Make sure that you’re buying a rear derailleur from the same company, and usually even the same line of that brand. Each of the derailleurs we chose has its compatible partner listed on the shop pages we’ve linked to.

If considering a full overhaul, see our guide on mountain bike shifters to help get the best shifter for your new setup.

 

CAGE LENGTH

Most derailleurs come in your choice of three cage lengths: short, medium, or long. Short cage lengths are great for single front chainrings, medium for doubles, and long for triples. UK retailer Wiggle has a detailed breakdown on cage lengths and clutch technology, something I’ll explain in the next section.

If you’re looking to buy a new front derailleur and crankset, we have a guide to cranksets to help you make your selection.

 

SHIMANO OR SRAM

SRAM devotees describe their shifting as slightly snappier to explain their preference, but it’s very subjective. Go with your favorite, or just stick with what’s already on the bike.

Remember that you can’t mix and match, so if you go from one to the other, you’ll need to replace the shifters and front derailleur, too. Campagnolo is a third option for roadies, but they don’t make many components suitable for mountain bikers.

The closest they come is in their cyclocross offerings. We’ve included a derailleur from a small company, Box, which is compatible with Shimano.

 

INDEX SHIFTING VS FRICTION

Derailleurs can be used with index or friction shifters, so this choice won’t limit you. It’s all in how you set it up.

 

GEAR RATIOS

If you’re buying a new derailleur, it’s probably time for a new rear cassette, too. Check out this helpful calculator to plan the perfect ratio. It considers wheel size, cranks, front chainring, and rear cassette, to show you how many useful options you have.

 

WEIGHT

How much does weight matter? It depends on the rider. Some people will think nothing of paying hundreds to shave off a few grams; others never even look at the weight.

If you’re racing, we’ve highlighted the lightest of the bunch. For general riders, all of the rear derailleurs we’ve picked should be good as well.

 

TUNING AND ADJUSTING

Different companies have different reputations for tuning and adjustment difficulty. Shimano is said to be slightly easier to tune and adjust. Box is even easier. This shouldn’t have a lot of practical implications for your ride, but it’s part of why some people prefer Shimano.

 

VIDEO – TUNING YOUR REAR DERAILLEUR

Whichever you get, make sure to include it in your routine maintenance, covered in our mountain bike maintenance article.

 

CLUTCHES

Clutches are an innovation in mountain bike derailleurs which keep the chain on the gears even over bumps and jumps. Typically, quick changes in weighting and force can cause the chain to go slack, which makes noise and may result in a dropped chain. The clutch aims to solve this problem by keeping appropriate tension on the chain at all times.

Every manufacturer has their own system. SRAM has Type-2 and Type-3, and Shimano has Shadow Plus. When the technology debuted, they were somewhat unreliable and could make wheel changes difficult; they’ve since gotten easier to adjust and come with locking features for easy wheel removal. They are quickly becoming mainstream for all mountain bikes.

Best Mountain Bike Derailleur - Best Mountain Bike Gear Articles – MTB Equipment and Accessories for Men, Women and Kids – Mountain Biking Products Articles and Reviews
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