Bike rear derailleur: definition, types, how to choose and adjust

What is a bike rear derailleur?

A bike rear derailleur is a spring-loaded mechanical or electronic device mounted near the rear dropout that shifts the chain across the cassette to change gears, enabling riders to adapt to varying terrain and cadence demands efficiently. First developed in the early 1900s in France and later refined by Tullio Campagnolo in Italy with the Gran Sport (1949), rear derailleurs have evolved from rudimentary levers and cables to today’s precise, lightweight systems featuring clutch mechanisms, wide-range compatibility, and wireless electronic shifting used across road, mountain, gravel, and touring bikes.

How does a rear derailleur work on a bike?

A rear derailleur works by moving the bike chain laterally across the cassette’s sprockets using a spring-loaded arm and two jockey wheels (pulley wheels), allowing the rider to change gears for varying terrain and speed. In mechanical systems, the derailleur is actuated by cable tension from the shifter, while in electronic systems (wired or wireless), small servo motors receive signals from the shifter to move the derailleur with precision; in both cases, the cage, parallelogram linkage, limit screws, and B-screw interact with parts like the cassette, chain, derailleur hanger, and shifters to maintain correct gear alignment and chain tension.

How does an electric bike rear derailleur work？

A rear electric derailleur works by using a small servo motor inside the derailleur body that receives signals from an electronic shifter (via wired systems like Shimano Di2 or wireless like SRAM AXS) to precisely move the derailleur and guide the chain across the cassette. The system includes components like the electronic shifter, battery, derailleur motor, jockey wheels, limit screws, and derailleur hanger, eliminating the need for shift cables and offering quicker, more accurate shifts, auto-trim functions, and improved reliability in all conditions.

Are rear derailleurs interchangeable?

No, rear derailleurs are not universally interchangeable because they vary by brand, drivetrain speed (e.g., 9-speed, 11-speed), cable pull ratio, and mounting standard. But, many derailleurs within the same brand and groupset family (e.g., Shimano 11-speed road) can be swapped, provided the cassette, shifters, and chain are compatible.

Are rear derailleur hangers universal?

No, rear derailleur hangers are not universal because they are frame-specific, designed to fit unique dropout shapes and bolt placements across different bike brands and models. But universal replacement options like the SRAM UDH (Universal Derailleur Hanger) are becoming more common and supported on newer frames.

Are all rear derailleur bolts the same size?

No, all rear derailleur mounting bolts are not exactly the same size. Though most use a standard M10x1 thread, the bolt head design and tool interface (5mm, 6mm, Torx) can vary between brands and models. But nearly all modern derailleurs are designed to fit into standard derailleur hangers, making general compatibility common across most mainstream bikes.

Who invented the rear derailleur?

Paul de Vivie, also known by his pen name Vélocio, invented the concept of the rear derailleur in France in the late 1800s, developing early multi-gear systems to help riders tackle mountainous terrain more efficiently. Tullio Campagnolo, an Italian inventor, later refined the design in 1949 with the introduction of the Gran Sport, the first modern parallelogram-style rear derailleur, which set the standard for how rear derailleurs function today—combining precision, durability, and on-the-fly gear changes for competitive and recreational cycling.

What parts are in a bike’s rear derailleur?

In a bike’s rear derailleur, the main parts include the mounting bolt, B-tension screw, limit screws (high and low), parallelogram linkage, jockey wheels (upper and lower pulleys), cage (outer and inner plates), spring mechanism, and cable anchor bolt, each playing a critical role in shifting performance and chain tension management.

1. Mounting Bolt: Connects the derailleur to the derailleur hanger on the bike frame and provides the main pivot point.
2. B-Tension Screw: Adjusts the vertical distance between the top jockey wheel and the cassette to optimize shifting across different cog sizes.
3. Limit Screws (H and L): Control the derailleur’s range of motion to prevent the chain from overshifting off the cassette.
4. Parallelogram Linkage: Allows the derailleur body to move laterally in a straight path, guiding the chain accurately between gears.
5. Jockey Wheels (Pulleys): The upper pulley guides the chain onto the correct cog while the lower pulley maintains chain tension.
6. Cage (Outer and Inner Plates): Holds the jockey wheels in place and determines the derailleur’s capacity and chain wrap.
7. Spring Mechanism: Provides tension to return the derailleur to its resting position and maintain chain tension during shifting.
8. Cable Anchor Bolt: Secures the shift cable, allowing it to control derailleur movement based on rider input from the shifter.

What is a direct-mount rear derailleur?

A direct-mount rear derailleur is a derailleur that attaches to a specially designed direct-mount derailleur hanger, bypassing the traditional B-link and providing a more rigid connection, better clearance for large cassettes, and easier wheel removal, commonly used in modern MTB and some road frames.

What is rear derailleur capacity?

A rear derailleur’s capacity is the total number of chain teeth it can take up, calculated by adding the difference in chainring teeth (front) and the difference in cassette cog teeth (rear); for example, a derailleur with a 40T capacity can handle a drivetrain where the chain must accommodate up to 40 teeth difference.

What is a rear derailleur hanger?

A rear derailleur hanger is a small, replaceable metal tab that connects the rear derailleur to the bike frame, designed to bend or break in a crash to protect the frame and derailleur; it’s frame-specific and critical for alignment, shifting accuracy, and safe derailleur function.

Can a road rear derailleur on a mountain bike?

Yes, a road rear derailleur can be used on a mountain bike if the drivetrain components (shifter, cassette, chain) match in brand and speed, such as using a 10-speed Shimano road derailleur with a 10-speed Shimano MTB shifter. But, compatibility is limited because road and MTB derailleurs often use different cable pull ratios, cage lengths, and max cog capacities, so mixing components without verifying an exact match can lead to poor shifting or limited gear range.

What are the materials of bike rear derailleurs?

The materials of bike rear derailleurs commonly include aluminum, steel, carbon fiber, titanium, and composite/plastic, each chosen for their specific properties like strength, weight, corrosion resistance, and cost-efficiency, depending on the performance level and intended use of the derailleur. These materials are strategically used across derailleur parts such as the main body, cage plates, bolts, pulleys, and linkage arms, with high-end models prioritizing lightweight and precision, while entry-level derailleurs focus on durability and affordability.

What are the types of bike rear derailleur?

The types of bike rear derailleur include classifications based on brand (e.g., Shimano, SRAM, Campagnolo), bike type (road, mountain, gravel, touring), mounting style (standard hanger or direct-mount), and shifting type (mechanical or electronic: wired or wireless), as these distinctions help match derailleurs to the correct drivetrain system, frame design, and rider preference for optimal shifting performance.

Bike rear derailleur types sorted by brand

Bike rear derailleurs sorted by brand include major manufacturers like Shimano, SRAM, Campagnolo, and microSHIFT, each offering distinct technologies, design philosophies, and compatibility standards that affect shifting performance, drivetrain integration, and user experience across road, gravel, MTB, and commuter bikes.

Which brand of rear derailleur should I buy?

You should choose a rear derailleur based on your drivetrain brand, bike type, and riding goals—for example, go with Shimano for broad compatibility and smooth shifting, SRAM for advanced features like wireless AXS and 1x MTB setups, Campagnolo for high-end road performance, or microSHIFT for reliable, budget-friendly options that often work with Shimano systems.

Bike rear derailleur types sorted by bike type

Bike rear derailleur types sorted by bike type include road, mountain (MTB), gravel, and touring, each designed with specific gear ranges, shifting precision, and durability to suit the terrain and riding style of that category.

1. Bike rear derailleur for road bikes: Optimized for close gear ratios and fast, precise shifting, these derailleurs typically support shorter cage lengths, lighterweight and are used with narrow-range cassettes for high-speed cadence control on smooth pavement.
2. Bike rear derailleur for mountain bikes (MTB): Built for durability and wide gear range, MTB derailleurs feature clutch mechanisms, longer cages, and high-tooth capacity to handle rough terrain and steep climbs.
3. Bike rear derailleur for gravel bikes: Designed as a hybrid between road and MTB, gravel derailleurs usually feature medium cage lengths, wide cassette compatibility and are often available in clutched or 1x setups for reliable performance over mixed surfaces.
4. Bike rear derailleur for touring bikes: Focused on durability and load-carrying capacity, touring derailleurs support triple cranksets, wide-range cassettes and use long cage designs to maintain smooth shifting under heavy gear loads.

Bike rear derailleur types sorted by mounting style

Bike rear derailleur types sorted by mounting style include standard mount and direct mount, categorized based on how the derailleur connects to the derailleur hanger and frame, which affects clearance, ease of wheel removal, and frame compatibility.

1. Bike standard mount rear derailleurs attach directly to the derailleur hanger using a B-link, and are the most common style across road, MTB, and gravel bikes, offering wide compatibility with traditional frame designs.
2. Bike direct mount rear derailleurs eliminate the B-link and bolt directly to a specific direct-mount hanger, providing increased stiffness, better cassette clearance, and simplified wheel removal, which is especially beneficial for modern mountain bikes with wide-range cassettes.

Bike rear derailleur types sorted by shifting type

Bike rear derailleur types sorted by shifting type include mechanical shifting and electronic shifting (both wired and wireless), as these categories define how the derailleur receives shifting input—either by cable tension or digital signal, affecting precision, weight, and maintenance.

1. Bike mechanical rear derailleur: A traditional system that uses cables and housing to pull the derailleur via shifter input; it’s known for being affordable, easy to service, and widely compatible, though it may require more frequent adjustment.
2. Bike electronic rear derailleur (wired): Uses battery-powered motors and wired connections to receive shift commands from the shifters, delivering fast, precise, and consistent shifting with less need for tuning—common in Shimano Di2 and Campagnolo EPS systems.
3. Bike electronic rear derailleur (wireless): Operates via wireless protocols like Bluetooth or ANT+, powered by onboard batteries (e.g., SRAM AXS), offering clean cable-free setups, customizable shifting, and high performance, but at a higher cost and requiring battery monitoring.

Mechanical vs electronic rear derailleur

Cyclists compare mechanical and electronic rear derailleurs because they represent two fundamentally different shifting technologies that affect performance, maintenance, cost, and rider experience. Choosing between them depends on your budget, riding discipline, precision needs, and comfort with technology—making the comparison crucial for informed drivetrain decisions.

How do you choose a bike rear derailleur?

You can choose a bike rear derailleur by considering key factors such as drivetrain compatibility, number of speeds, cage length, total capacity, shifting type (mechanical/electronic), bike type, weight, and longevity, all of which impact how well the derailleur will perform with your setup.

1. Drivetrain Compatibility: You can choose a derailleur that matches your shifters, chain, and cassette brand and model, ensuring the actuation ratio and shifting logic work together smoothly.
2. Number of Speeds: You can select a derailleur designed for the same number of gears on your cassette (e.g., 9-speed, 11-speed) to maintain precise indexing and shift accuracy.
3. Cage Length: You can pick a short, medium, or long cage depending on your front chainring setup and chain wrap needs—long cages are best for wide-range or 2x/3x drivetrains.
4. Total Capacity: You can ensure the derailleur’s total capacity (tooth difference it can handle) matches your front and rear gear spread to prevent chain slack or tension issues.
5. Shifting Type: You can choose between mechanical or electronic shifting, depending on your preference for simplicity or high-tech precision and customization.
6. Bike Type: You can select a derailleur built specifically for road, MTB, gravel, or touring, as each is designed with unique features like clutch systems or gear ratios.
7. Weight: You can consider derailleur weight if you’re looking to reduce bike mass for performance, with carbon or titanium components used in higher-end models.
8. Longevity and Durability: You can look for a derailleur made with robust materials like alloy or steel and with sealed pivots or clutch systems to ensure long service life under your riding

How do you install a rear derailleur?

You should install a rear derailleur by following these steps: attach it to the derailleur hanger, check derailleur alignment, set the B-tension screw, route and secure the shift cable, adjust the limit screws, fine-tune cable tension, and test shifting to ensure proper performance.

1. Attach to the Derailleur Hanger: You should thread the rear derailleur’s mounting bolt into the derailleur hanger using a 5mm Allen key, tightening it snugly without cross-threading.
2. Check Derailleur Alignment: You should inspect that the derailleur is vertically straight and aligned with the cassette cogs, using a derailleur alignment tool if necessary.
3. Set the B-Tension Screw: You should turn the B-tension screw to adjust the gap between the upper jockey wheel and the largest cassette cog, usually keeping a 5–6 mm gap for smooth shifts.
4. Route and Secure the Cable: You should pull the shift cable through the derailleur’s anchor bolt, remove slack, and tighten the bolt to ensure responsive shifting control.
5. Adjust the Limit Screws: You should use a Phillips screwdriver to set the high (H) and low (L) limit screws, which prevent the chain from shifting off the smallest or largest cogs.
6. Fine-Tune Cable Tension: You should use the barrel adjuster on the derailleur or shifter to dial in cable tension, ensuring the chain lands cleanly on each cog during shifting.
7. Test Shifting: You should shift through all gears while turning the pedals to confirm smooth, accurate movement across the cassette, making any final tweaks to tension or limit screws if needed.

How does the chain go through the rear derailleur?

The chain passes through the rear derailleur by entering the derailleur cage from the top, wrapping over the upper jockey wheel (guide pulley) that aligns it with the selected cassette cog, then looping down and around the lower jockey wheel (tension pulley), which maintains chain tension before exiting toward the chainring and front derailleur. This routing keeps the chain properly tensioned and guided as it shifts between gears on the cassette, with the cage, pulleys, and derailleur hanger working together to ensure smooth, efficient drivetrain movement.

Do I put the derailleur on before the rear wheel?

Yes, you should install the rear derailleur before the rear wheel because it allows easier access to the derailleur hanger and mounting bolt, ensures proper alignment, and helps when routing the chain correctly once the wheel is in place.

How do I know what size rear derailleur I have?

You can know what size rear derailleur you have by checking the cage length (short, medium, or long)—usually printed or stamped on the derailleur itself—or by measuring the distance between the two jockey wheels and referencing the manufacturer’s specs. You can also identify it by looking up the model number (typically engraved or printed on the derailleur body) and comparing it with the brand’s published derailleur capacity and cage length charts.

Do I need a long cage for 10-speed?

Yes, you need a long cage derailleur for 10-speed if you’re using a wide-range cassette or a 2x/3x front chainring setup because a long cage provides the necessary chain wrap capacity to handle large differences in gear sizes.

But, if you’re running a 1×10 setup with a narrow gear range, a medium or short cage may be sufficient.

Can SRAM derailleur use a direct mount hanger?

No, most SRAM rear derailleurs are not designed for direct mount hangers because they are built for standard derailleur hangers using a B-link-style attachment. But, SRAM has supported the UDH (Universal Derailleur Hanger) standard on some newer MTB derailleurs, which offers similar benefits and compatibility with certain frame designs.

How do you adjust the rear derailleur?

You can adjust the rear derailleur by setting the high and low limit screws to restrict over-shifting, adjusting cable tension using the barrel adjuster, and fine-tuning the B-tension screw to control jockey wheel-to-cassette clearance. Make sure the derailleur is properly aligned and the chain shifts smoothly across all gears.

How do you adjust the Campagnolo rear derailleur?

You can adjust the Campagnolo rear derailleur by using a 2.5mm or 3mm Allen key or screwdriver to fine-tune the H and L limit screws, and rotating the inline cable tension adjuster (usually near the shifter) to achieve crisp, indexed shifts through the cassette.

How do you adjust the SRAM rear derailleur?

You can adjust the SRAM rear derailleur by turning the limit screws (marked H and L) for cog range, setting the B-screw to align the upper pulley with the largest cog, and adjusting cable tension via the barrel adjuster for smooth shifting. For SRAM MTB models, ensure clutch (if present) is engaged.

How do you adjust the ETap rear derailleur?

You can adjust the SRAM eTap rear derailleur using the micro-adjust feature on the shift buttons, which allows for small shifts in derailleur position electronically. Also ensure the B-gap is correctly set using SRAM’s supplied spacing gauge and that the derailleur is properly paired and indexed.

How do you adjust Shimano rear derailleur?

You can adjust the Shimano rear derailleur by turning the high and low limit screws to restrict derailleur travel, then adjusting cable tension with the barrel adjuster until the chain shifts smoothly across the cassette. Use the B-tension screw to fine-tune the guide pulley’s gap from the cassette.

How do you adjust the Di2 rear derailleur?

You can adjust the Shimano Di2 rear derailleur by entering micro-adjust mode via the junction box (hold button until LED flashes), then use the shifter buttons to incrementally fine-tune derailleur position for perfect indexing. Ensure the limit screws and B-screw are pre-set manually before electronic tuning.

How do you adjust the microShift rear derailleur?

You can adjust the microSHIFT rear derailleur by turning the limit screws to prevent chain overshoot, using the barrel adjuster to set proper cable tension, and adjusting the B-screw to maintain optimal pulley-to-cog distance. Cable routing and tension setup are nearly identical to Shimano systems.

Are SRAM and Shimano rear derailleurs compatible?

No, SRAM and Shimano rear derailleurs are not compatible because they use different cable pull ratios and actuation systems—Shimano uses 2:1 or RAPIDFIRE/SLR, while SRAM uses 1:1 or Exact Actuation/X-Actuation. Even if the number of speeds matches, the indexing will not align properly, leading to imprecise or unreliable shifting.

How do you check rear derailleur alignment?

You can check rear derailleur alignment by using a derailleur hanger alignment gauge to compare the position of the hanger (and thus the derailleur) relative to the cassette cogs. A properly aligned derailleur hanger ensures the jockey wheels are vertically in line with each gear; if bent, it must be straightened to prevent shifting issues.

How do you adjust cable tension on a rear derailleur?

You can adjust cable tension on a rear derailleur by turning the barrel adjuster, usually located on the derailleur or shifter—turn counterclockwise to increase tension (for sluggish upshifts), or clockwise to decrease it (for slow downshifts). Proper tension ensures precise indexing and accurate gear changes.

How do you adjust limit screws on rear derailleur?

You can adjust limit screws on a rear derailleur using a Phillips screwdriver to turn the high (H) and low (L) screws, which physically restrict how far the derailleur can travel. The H-screw sets the limit for the smallest cog (high gear), and the L-screw for the largest cog (low gear), preventing the chain from overshifting off the cassette.

Can you change the cage on a rear derailleur?

Yes, you can change the cage on some rear derailleurs if the manufacturer designed it to be serviceable, allowing you to swap between short, medium, or long cage lengths to match gear capacity needs. But, not all derailleurs are built to allow cage replacement, and compatibility must be checked with the exact model and generation.

Why is my rear derailleur not shifting?

Your rear derailleur is not shifting because of improper cable tension, a bent derailleur hanger, worn-out cables or housing, or incorrect limit screw settings. These issues can cause incomplete movement of the derailleur, preventing the chain from aligning with cassette cogs.

Why is my rear derailleur not shifting to the lowest gear?

Your rear derailleur is not shifting to the lowest gear because the low limit screw (L-screw) is set too tight, or the B-tension screw is too long, preventing the derailleur from moving far enough toward the largest cassette cog. It may also be due to a bent hanger or insufficient cable tension, especially in mechanical systems.

Why is my rear derailleur not shifting to the highest gear?

Your rear derailleur is not shifting to the highest gear because the high limit screw (H-screw) is overly restricted, or the cable tension is too high, stopping the derailleur from reaching the smallest cassette cog. This is often the case after new cable installation or derailleur misalignment.

How long does a rear derailleur last?

A rear derailleur typically lasts between 15,000 to 30,000 km (9,000 to 18,000 miles) depending on factors such as riding conditions, maintenance, shifting frequency, and the quality of the components. A rear derailleur’s lifespan is mainly affected by wear on the jockey wheels, spring tension, pivot bushings, and exposure to dirt or impact, with regular cleaning and derailleur hanger alignment helping extend its usable life.

Do rear derailleurs wear out?

Yes, rear derailleurs wear out because pivot points, jockey wheels, springs, and linkages experience constant tension, dirt exposure, and mechanical wear over time. Signs of wear include sloppy shifting, increased noise, or difficulty maintaining gear alignment, especially after thousands of kilometers of riding.

How much does it cost to replace a rear derailleur?

It costs approximately USD $50–$250 / EUR €45–€230 / GBP £40–£200 to replace a rear derailleur, depending on the derailleur type (mechanical or electronic), brand, drivetrain speed, and labor cost at a bike shop.

• Basic mechanical derailleurs (e.g., Shimano Tourney or SRAM X3) start around USD $30–$50.
• Mid-range models (e.g., Shimano Deore, SRAM GX) range from USD $60–$120.
• High-end or electronic derailleurs (e.g., SRAM AXS, Shimano Di2) can cost USD $200–$600+.

Labor costs for installation and adjustment typically add USD $20–$40 / EUR €18–€35 / GBP £15–£30, covering removal, installation, chain routing, and limit/tension tuning.

Final pricing also depends on whether a new derailleur hanger or derailleur alignment is needed during service.

How do you fix a rear derailleur?

You can fix a rear derailleur by first identifying the issue—such as misalignment, poor cable tension, worn jockey wheels, or a bent hanger—and then correcting it by adjusting the limit screws, realigning the hanger, replacing worn parts, or tuning the cable tension using the barrel adjuster. Regular maintenance like cleaning, lubrication, and inspecting pivot points also restores smooth shifting and extends component life.

How do you fix a bent rear derailleur?

You can fix a bent rear derailleur by first confirming if the derailleur or the hanger is bent, and using a derailleur hanger alignment tool to straighten the hanger if it’s misaligned; if the derailleur body itself is bent or damaged, replacement is usually required since structural bends can affect shifting accuracy and safety.

What causes a rear derailleur hanger to break?

A rear derailleur hanger breaks primarily due to impacts, crashes, or derailleur overextension, where the hanger absorbs force to protect the bike frame and derailleur. It can also break from chain jamming between the cassette and spokes, misaligned shifting that forces the derailleur beyond its range, or fatigue from repeated stress—especially if the hanger is made from softer materials like aluminum alloy.

How do you clean a rear derailleur?

You can clean a rear derailleur by using a degreaser and a brush to remove dirt and old lubricant from the jockey wheels, cage, and pivots, then rinsing with water and drying thoroughly before applying light lubricant to the moving parts and springs for smooth performance.

How do you protect the rear derailleur when traveling?

You can protect the rear derailleur when traveling by either removing it entirely and padding it separately, or covering it with a derailleur guard or foam wrapping while keeping it attached, especially when packing the bike into a bike bag or hard case, to prevent bending or breakage during transit.

Bike rear derailleur brands and manufacturers

Bike rear derailleur brands and manufacturers play a crucial role in drivetrain performance, offering a range of shifting systems tailored for road, MTB, gravel, and touring bikes. From premium wireless tech to budget-friendly mechanical models, each brand brings unique features and innovation to the market.