15% off Bike Lights >

Need Gift Ideas for Father's Day?

Rear Derailleurs

(80 products)

A rear derailleur is the component responsible for moving your chain across the cassette, allowing you to change gears smoothly and efficiently.

Our range includes Shimano and SRAM rear derailleurs for road, mountain and gravel bikes. Choose from different speeds, cage lengths and drivetrain systems to match your setup.

View as

Related collections

Front Derailleurs Derailleurs Rear Bike Wheels Shimano Deore MTB Components Rear Bike Lights Bike Cassettes Brake Levers Shift-Brake Levers Shimano Brakes Bike Chains

What is a Rear Derailleur?

A rear derailleur is mounted to the rear of your bike and controls gear shifting by guiding the chain across the cassette.

It works with your shifter, bike chain and bike cassette to deliver smooth, reliable gear changes across different gradients.

MTB vs Road Rear Derailleurs

Rear derailleurs are designed differently depending on riding style.

MTB Rear Derailleurs

  • Designed for rough terrain and durability
  • Compatible with wide-range cassettes (e.g. 10–51T)
  • Often include clutch systems to improve chain retention

Road Rear Derailleurs

  • Lighter and more compact
  • Designed for closer gear ratios
  • Prioritise smooth, precise shifting

Cage Length Explained

Rear derailleurs come in different cage lengths, which affect compatibility with your cassette.

Short Cage

  • Best for smaller cassettes (older road bikes).
  • Lighter and more compact.

Medium Cage

  • Balanced option for mixed riding.

Long Cage

  • Designed for wide-range cassettes (MTB and gravel).
  • Required for larger gear ranges.

Rear Derailleur Compatibility

Choosing the right rear derailleur depends on several key factors.

Drivetrain Speed

Your derailleur must match your drivetrain speed:

  • 9-speed
  • 10-speed
  • 11-speed
  • 12-speed

Using the wrong derailleur can result in poor shifting performance.

Cassette Compatibility

Rear derailleurs are designed to work within a specific cassette range.

Larger cassettes require derailleurs with longer cages and higher capacity.

When Should You Replace a Rear Derailleur?

You may need to replace your derailleur if:

  • Shifting becomes inconsistent
  • The derailleur is bent or damaged
  • Excess play develops in the mechanism

In many cases, poor shifting can also be caused by a worn bike chain or cassette.

Choosing the Right Rear Derailleur

When selecting a derailleur:

  • Match your drivetrain speed
  • Choose the correct cage length
  • Ensure compatibility with your cassette range
  • Match your drivetrain brand (Shimano or SRAM)

Choosing the right derailleur ensures smooth shifting and reliable performance.

Explore More Drivetrain Components

Upgrade your drivetrain with compatible components:

  • bike chains
  • bike cassettes

FAQs

What does a rear derailleur do?

A rear derailleur moves the chain across the cassette to change gears. It works with your shifter to control gear selection.

Are rear derailleurs universal?

No. Rear derailleurs must match your drivetrain speed, cassette range and brand compatibility.

Can I use a Shimano derailleur with SRAM?

No. Shimano and SRAM use different cable pull ratios, so mixing them will result in poor shifting performance.

What cage length do I need?

Short cage for small cassettes, long cage for wide-range cassettes. The correct choice depends on your cassette size.

Check the max. sprocket size on your cassette then check your rear derailleur's spec.

Do I need to replace my derailleur when upgrading gears?

Yes, if you change drivetrain speed (e.g. 10 to 12 speed), you’ll need a compatible derailleur.

Back to top

Compare /4