At the core of a high-performance mountain bicycle lies the rear derailleur, which serves as the pivotal component enabling a superior riding experience across diverse terrain.
When installed, fitted, and tuned with precision, a high-quality rear derailleur provides precise, responsive gear changes and seamless shifts, allowing cyclists to seamlessly navigate variable path conditions.
Fundamentally, the rear derailleur serves to accurately shift through a wide gear range and maintain optimal chain tension through advanced precision pulley systems and progressive spring designs.
As technologies progress, leading mountain bike rear derailleurs have incorporated lighter yet durable materials, enhanced chain management mechanisms, and faster-acting mechanical or electronic actuation.
Furthermore, preeminent derailleur models now feature bi-directional or low-profile configurations, better-shielding components from impacts during demanding riding.
This review explores the premier options in mountain bicycle rear derailleurs, considering innovative features, wide compatibility, and high performance.
Through an analysis of the latest designs and technologies, this guide aims to assist mountain cyclists in selecting a rear derailleur Optimizing performance, durability, and the riding experience across all terrain conditions.
With an apt rear derailleur, riders can confidently tackle any path with expertise, confidence, and enjoyment.
Best Mountain Bike Derailleurs (9 Picks Reviewed)
We have curated a selection of the premier mountain bicycle rear derailleurs currently available. We evaluated factors including reliability, durability, minimal weight, and simplicity of use, as well as real-world testing and user reviews, to determine the optimal choices.
Selecting a highly capable rear derailleur directly impacts your riding experience and joy. Thus, peruse our top recommendations for the finest mountain bike rear derailleurs present today and discover the ideal component elevating your cycling.
1. SHIMANO RD-M640 Zee
- Weight: 275g
- Speeds: 10
- Total Capacity: 25T
- Max Low Sprocket: 36T (Freeride spec)
- Price: $42.97 – $87.99
The SHIMANO RD-M640 rear derailleur accommodates gravity mountain bikers pursuing an optimal component at an accessible price point.
As part of the ZEE M640 series engineered for downhill and freeride cycling, the RD-M640 incorporates SHIMANO SHADOW RD+ technology to reduce chain slap and stabilize the chain line across demanding terrain.
It also features a low-profile design minimizing risks of damage from impacts or other obstacles. The RD-M640 presents two specification options optimized for versatile freeride riding (11-36T) or swift downhill performance (11-28T).
The 11-36T configuration enables a wider gear range permitting the most aggressive riding styles while the 11-28T configuration facilitates faster, more responsive gear changes crucial to downhill riding.
The RD-M640 may mount directly to the frame or using a standard attachment, with a shortened cage length and single front chainring compatibility. Weighing 275 grams with a total 25-tooth capacity, it provides a lightweight yet durable solution.
Compatibility with Shimano 10-speed chains and shifters such as the ZEE M640 shifter ensures the RD-M640 delivers precise, reliable gear changes even across rough, technical terrain.
Constituting an advanced clutch rear derailleur, the RD-M640 suits riders requiring Shimano 10-speed performance in a compact form factor.
Appropriate for downhill and freeride cyclists seeking high-performance, hard-wearing, and budget-friendly components, the RD-M640 helps optimize the riding experience.
Through design, technologies, specifications, and quality, the SHIMANO RD-M640 rear derailleur fuels the passion of gravity mountain bikers.
2. microSHIFT M26 Speed Long Cage
- Weight: 330g
- Speeds: 11
- Total Capacity: 41T
- Max Low Sprocket: 46T
- Price: $16
The microSHIFT M26 Rear Derailleur constitutes an affordable component enabling mountain cyclists to upgrade their drivetrain with extensive versatility and capability at an accessible price point.
Engineered for 7/8-speed systems, it supports a range of 11 to 36 tooth cogs and proves compatible with Shimano 8-speed components, facilitating use of mixed or matching parts.
The M26 Rear Derailleur features steel and composite construction, delivering durability and reliability across diverse terrain conditions. Its extended cage maintains up to 45 teeth of capacity, allowing flexibility in selecting chainrings and cassettes optimal for specific riding styles.
The M26 Rear Derailleur also demonstrates smooth, precise shifting through spring-loaded tension adjustment and direct cable routing.
The M26 Rear Derailleur provides functionality and performance comparable to a Shimano XTR 11-speed medium-cage derailleur including wide range, rapid gear changes, and minimal weight at under half the cost.
The M26 Rear Derailleur furnishes similar capabilities and benefits for less than half the price of the Shimano XTR model, representing an economical upgrade enhancing the mountain biking experience.
Through specifications, technologies, quality, and value, the microSHIFT M26 Rear Derailleur facilitates progression in the passion of gravity and enduro mountain bikers on a budget.
3. Shimano Deore XT RD-M786 SGS
- Weight: 284g
- Speeds: 12
- Total Capacity: 41T
- Max Low Sprocket: 51T
- Price: $89
The Shimano Deore XT RD-M786 rear derailleur accommodates mountain bicycles with 10-speed drivetrains.
As part of the Shimano Deore XT M780 series engineered for high performance, the RD-M786 incorporates several innovative designs optimized for those desiring a Shimano 12-speed derailleur.
The RD-M786 features SHIMANO SHADOW RD+ technology, reducing chain slap and improving stability by maintaining proximity of the derailleur to the cassette.
It includes an adjustable clutch mechanism preventing chain drop and enabling optimal performance across variable conditions.
The RD-M786 presents medium (GS) and long (SGS) cage length options. The GS configuration reaches 35 teeth total capacity, suiting a maximum 36T low sprocket and 18T front difference.
The SGS configuration attains 43 teeth capacity, supporting a maximum 36T low sprocket and 22T front difference, with sealed bearings, fluoric coated bushings and hollow axles reducing mass and advancing efficiency.
The RD-M786 proves compatible with HG-X 10-speed chains, purpose-built for mountain bicycles with Dyna-Sys technology. Directional plates optimize shifting and minimize wear.
The RD-M786 may also mount directly to the frame via Direct Mount, eliminating the B-link and improving precision of shifting. The RD-M786 includes silver or black finishes, averaging 262g (GS) or 266g (SGS) weight.
It represents one of the optimum composites of performance, durability and value for those desiring a Shimano 12-speed derailleur, delivering smooth, precise and reliable shifting across challenging terrain.
Through innovative technologies, durability and quality, the Shimano Deore XT RD-M786 rear derailleur enhances the riding experience of enduro and trail mountain bikers.
4. SRAM Eagle GX X-Actuation
- Weight: 290g
- Speeds: 12
- Total Capacity: 40T
- Max Low Sprocket: 52T
- Price: $120
The SRAM Eagle GX X-Actuation trigger shifter enables precise, dependable gear changes requisite to the 11-speed mountain bicycling experience.
As part of the GX Eagle platform optimizing ride potential through expansive gear selection, color choices, and compatibility, it proves suitable for new 10-52 tooth cassettes furnishing a 520% range and improved mud clearance or 10-50 tooth versions.
The GX Eagle X-Actuation shifter features a redesigned cage architecture advancing chain management and an aluminum pull lever.
Permitting versatile mounting in multiple positions and integration with additional controls through the MatchMaker X clamp facilitates customization meeting any riding style.
Available in black or red finishing weighing 122 grams, the GX Eagle X-Actuation shifter delivers technological capabilities and quality previously reserved for the championship caliber.
Seamlessly compatible with Eagle cassettes for the gear range and durability fueling progressive challenging terrain, an overhauled cage architecture and premium components ensure exceptionally precise, dependable, and optimized performance across conditions.
Through advanced, rider-inspired engineering and nuanced details enhancing both the range and joy of each ride, the SRAM Eagle GX X-Actuation trigger shifter optimizes the mountain biking experience.
Via innovative design, premium materials, and engineered details maximizing capability while preserving lightness and ease of use, the SRAM Eagle GX X-Actuation shifter enables riders to conquer terrain previously unimagined.
5. Sram Rear Derailleur XX1 Eagle AXS
- Weight: 350g
- Speeds: 12
- Total Capacity: 40T
- Max Low Sprocket: 52T
- Price: $605
The Sram Rear Derailleur XX1 Eagle AXS constitutes an electronic derailleur facilitating precise, rapid and dependable gear changes requisite to the mountain bicycling experience.
As part of the XX1 Eagle AXS groupset optimized for XC and trail riding, it incorporates a carbon cage, titanium hardware, rainbow colorway and overload clutch protection.
Possessing a shortened cage relative to mechanical Eagle derailleurs, it secures superior ground clearance and optimized chain wrap.
Supplying a 520-percent gear range comparable to 2×11 drivetrains, compatibility with the SRAM AXS app permits customization of settings and firmware updates.
Satisfying IPX7 water and dust proof standards, the derailleur proves capable of handling conditions of any race day.
Lightest, stiffest and strongest in class, the derailleur instantaneously shifts from a single touch even under maximal chain loads.
The Sram Rear Derailleur XX1 Eagle AXS constitutes the pinnacle of lightweight, high-performance 12-speed electronic shifting.
Through premium yet lightweight carbon and titanium materials, optimized stiffness, strength and clearance, innovative design and connectivity enabling full customization, the Sram Rear Derailleur XX1 Eagle AXS electronic derailleur maximizes potential for progression across terrain.
A shortened cage, weather resistance, rainbow aesthetic and expansive, precision-tuned gear range combine in this component, enabling conquest of routes previously unimagined.
6. Box One Prime 9 X-Wide Rear Derailleur
- Weight: 290g/10.2oz
- Speeds: 9
- Material: Aluminum
- Color: Black
- Price: $183
The Box One Prime 9 X-Wide Rear Derailleur facilitates precise gear changes requisite to versatile, progressive mountain bicycling.
Accommodating a wide-range 9-speed cassette with the increased difference between the smallest and largest sprockets for navigating diverse terrains and gradients, it incorporates optimized designs for durability, reliability, and simplified use.
Engineered to suit cassettes reaching 11 to 50 or 11 to 52 teeth, it integrates a clutch mechanism preventing excess chain movement and noise with a tri-pack clutch reducing friction.
An adjustable chain gap optimizes shifting performance and chain retention across conditions.
Compatible with any 9-speed shifter and chain, for installation on most mountain bike frames, the derailleur presents 290 grams of mass in a black or silver finish.
As part of the Box One Prime 9 drivetrain system, it aims to furnish simplicity, longevity, and dependability for the dedicated mountain cyclist.
The Box One Prime 9 X-Wide Rear Derailleur delivers a versatile yet durable gearing solution for progression to increasingly advanced trails.
An expansive, optimized cassette range combined with low-maintenance, high-quality design ensures the ease and enjoyment of each ride with this component.
Via specifications enabling ambitious riding, comprehensive compatibility, and durability fortifying every journey, this rear derailleur maximizes the potential for development in the passion of each mountain biker.
Though versatile, durable, and reliable, enabling any route, the Box One Prime 9 X-Wide Rear Derailleur maintains a simplified approach, facilitating focus on the trail ahead rather than technology translating power to progression.
7. Shimano XTR RD-M9120 XTR
- Weight: 8.5oz (241g)
- Speeds: 12-speed
- Material: Aluminum
- Color: Black
- Price: $277
The Shimano XTR RD-M9120 rear derailleur facilitates precise, optimized gear changes requisite to mountain bicycling with 2×12-speed drivetrains.
As Shimano’s premier range of components for off-road cycling, the XTR M9100 series aims to maximize potential across terrain through innovative technology, enhanced longevity, and exceptional performance.
The RD-M9120 incorporates SHIMANO SHADOW RD+ technology, reducing chain tension, excess movement, noise in the lower gear position, and risk of drop/slap across rugged conditions.
A low-profile design minimizes susceptibility to damage from rocks and obstacles. Larger 13T pulley wheels improve chain management, and shifting smoothness, especially under high pedaling loads.
A sealed bearing pulley system decreasing friction and wear, a hollow axle and sunken type pulley bolt reducing mass and improving rigidity with a fluoric coated link bushing enhancing durability and movement fluidity together advance this rear derailleur.
Compatible with new Shimano 12-speed cassettes providing a wide range of ratios for diverse terrains and progressive riding styles, the RD-M9120 suits a maximum 45T low sprocket and 10T front difference.
Weighing 241 grams with a sleek series finish, the RD-M9120 delivers superior performance, dependability, and quality for dedicated off-road cyclists.
The Shimano XTR RD-M9120 rear derailleur maximizes potential across challenging terrain through innovative, high-performance engineering.
Components of the XTR M9100 platform as SHADOW RD+ technology reduce excess movement and noise while optimized, durable designs and premium materials improve both the operational lifespan and responsiveness of each progressive ride.
8. Shimano Alivio Rd-m3100 Rear derailleur
- Weight: 100g
- Speeds: 9
- Material: Plastic
- Color: Black
- Price: $32
The Shimano Alivio Rd-m3100 Rear derailleur facilitates gear changes requisite to mountain bicycling, providing a 9-speed rear derailleur and low-profile design for aggression encountering fewer interruptions.
As part of the Shimano Alivio M3100 series, a budget-friendly groupset delivering reliable performance and durability, it incorporates a SHIMANO SHADOW RD design reducing damage susceptibility and retaining chain proximity to the frame for stability.
Possessing a total 45T capacity, it supports a wide range of gear combinations.
Compatible with HG 9-speed chains and fluoric-coated link bushings for smooth shifting, the rear derailleur mounts directly or via a conventional hanger with an adjustment barrel enabling precise fine-tuning.
Available in silver hue and weighing approximately 320 grams, the Shimano Alivio Rd-m3100 Rear derailleur satisfies the quality versus price balance sought by those desiring a simple, affordable mountain bike built to navigate diverse terrain and conditions.
Difficult to surpass budget components from Shimano, it facilitates progression in the passion of riding.
The Shimano Alivio Rd-m3100 Rear derailleur delivers a durable, dependable, and economically feasible gearing solution for the mountain biker on a budget.
Features such as a low-profile design and SHADOW RD technology reduce susceptibility to damage across rough, aggressive riding combined with an expansive cassette range and premium details enhancing every ride in this component.
Though designed and priced for simplicity, the Rear derailleur maximizes potential and optimization of enjoyment in each progressive journey.
9. microSHIFT | Acolyte Rear Derailleur
- Cassette Range: 12 – 46t
- Cage Length: Medium
- Speeds: 8
- Material: alloy
- Color: Black
- Price: $33
The Acolyte 8-Speed Rear Derailleur presents a product from microSHIFT, a company specializing in drivetrain components, designed for mountain bicycles with a single chainring and wide-range cassette used.
Compatible with 12-42T and 12-46T 8-speed cassettes, it can accommodate a maximum 46T cog size. Possessing a medium cage length and 41T capacity, it lacks a clutch mechanism, reducing excess movement, weight, and friction at the cost of chain slap/drop prevention.
Only compatible with microSHIFT Acolyte shifters, this rear derailleur facilitates simple, intuitive shifting for beginners, youth, or those on a budget. Direct-path cable routing ensures smooth, responsive operation with durable metal construction.
Suitable for commutes, touring, or kid’s mountain bikes demanding reliability and affordability, this rear derailleur balances performance and cost.
Available in black or silver, weighing 280 grams, and costing approximately $33, it comprises an economical 8-speed rear derailleur option.
For budget-oriented riders desiring 1x drivetrain simplicity and versatility without financial constraint, the Acolyte 8-Speed Rear Derailleur delivers durability, ease of use, and value.
Though lacking a clutch, sacrificing minimal excess movement for lightweight, low-friction design and cost-effectiveness, this rear derailleur maximizes the enjoyment of any journey.
Compatibility with microSHIFT and wide-range cassettes supports progressive riding across diverse terrain at an accessible price point.
Guide to Buying the Best Mountain Bike Derailleur
A mountain bike derailleur facilitates gear changes by moving the chain between different cogs on the rear cassette and chainrings on the front crankset. It is a critical component for adapting to various riding conditions on mountain bikes.
When selecting a mountain bike derailleur, consider the following factors:
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Know your drivetrain type
There are two predominate drivetrain configurations for mountain bicycles: single-speed with wide-range cassette (1x) and multiple front chainrings with narrow-range cassette (2x/3x).
A 1x drivetrain employs a rear derailleur with clutch mechanism to prevent excessive chain slack and dropped chains across the cassette range.
A 2x or 3x drivetrain necessitates a front derailleur to shift the chain between chainrings in addition to a rear derailleur managing smaller jumps in cogs. Select a derailleur compatible with your specific drivetrain architecture.
Know your speed and compatibility
Derailleur, cassette and shifter components are produced in various speed classes, such as 8, 9, 10, 11 and 12 speeds.
For optimal performance, compatibility and durability, match the speed rating of your derailleur to the speed of the cassette and shifter.
Combining incompatible components can lead to poor shifting, premature wear and mechanical failure. Ensure a seamless and confident transition between gears for all riding conditions.
Know your cage length and capacity.
The cage length of a rear derailleur refers to the distance between the upper and lower pulleys that guide the chain.
Longer cage lengths provide a greater maximum capacity, the largest differences in teeth between the smallest front and largest rear sprockets the derailleur can accommodate.
Select a rear derailleur with a cage length and capacity rating that suits the sprocket ranges of your cassette and chainrings. An improperly capacity-rated derailleur will not shift effectively across the full range of gears.
Know your budget and preference.
Pricing for mountain bicycle derailleurs spans from budget-oriented basic designs to high-performance, precision engineered components for elite and professional use.
Consider available finances and the attributes most valuable to your riding needs such as weight savings, durability, aesthetics or advanced features.
While more expensive options may realize marginal improvements, a derailleur at any price point from a reputable brand can suit most recreational uses.
Personal preferences also come into play, some preferring mechanical simplicity while others appreciate electronic convenience. Make selections that maximize enjoyment of the ride.
In summary, several factors must align for a derailleur to adeptly and reliably manage the gearing system of a mountain bicycle.
From drivetrain type to speed and capacity specifications, ensuring compatibility at each level leads to optimal performance, reduced frustration and an engaging riding experience.
Though budget will ultimately determine options, knowledge and consideration of available choices will yield a derailleur that suits both mechanical requirements and personal preferences.
Care in selection and installation will provide countless miles of confident and carefree riding on trails near and far. Please contact for guidance or recommendations to find the derailleur ideal for your machine.