How to adjust the rear derailleur on a road bike

Adjusting a rear derailleur is a job that every rider should be able to carry out. You’ll need some simple tools, a little patience and our guide on how to adjust a rear derailleur.

How does a rear derailleur work?

When you move the gear shifter, a cable either relaxes or increases the tension. This force releases or pulls your derailleur, shifting the chain on to the next cog. It’s this seamless movement that results in you changing gear.

Bicycle derailleurs are simple, but incredibly effective, pieces of engineering. If set up and maintained correctly, they can provide many thousands of hours of trouble-free cycling, but problems do occur.

Some signs that your rear derailleur isn’t working correctly include slipping or missing gears, being unable to reach the highest or lowest rear cogs or a lack of precision when shifting gear.

There are several reasons why your rear derailleur may need adjusting, including:

  • Wear and tear over time.
  • The rear wheel was misaligned when replaced (after repairing a puncture for example).
  • The gear cable has become damaged, frayed or just losing a little of its strength over time.
  • The rear derailleur being hit.

A misaligned, damaged or bent rear hanger can also cause problems with your gear shifting, so before working on your rear derailleur, be sure to check it. Poor gear shifting may also be caused by a worn-out derailleur or other drivetrain components.

For the purposes of this guide, we’ll assume your rear derailleur and drivetrain is in good working order and just needs a tune-up!

A step-by-step guide to adjusting a road bike rear derailleur

Road bike rear derailleurs all work in the same way, so this guide works if you have a Campagnolo, Shimano or SRAM rear derailleur.

There are two parts to setting up your rear derailleur:

  1. setting the limit screws
  2. adjusting the inner wire tension

You need to perform them both to ensure your rear derailleur will function properly.

Setting the limit screws

Each bicycle derailleur has two limit screws that control the extent of the movement of the derailleur. They’re clearly marked H and L on the derailleur.

The outer limit is set by the H screw and the inner limit set by the L screw. The H screw ensures the chain doesn’t drop off the smallest cog and get stuck in the frame, while the L screw ensures your chain won’t leap off your lowest gear and get stuck on the spokes.

When you turn the screws, the derailleur will move slightly in these directions:

  • Move H clockwise and the derailleur will move to the left
  • Move H anti-clockwise and it will move to the right
  • Move L clockwise and it will move to the right
  • Move L anti-clockwise and it will move to the left

The adjustment screws enable you to make minute and precise adjustments to your gearing.

If your rear derailleur is moving out too far and the chain is catching between the smallest cog and the frame, turning the H screw clockwise will fix this problem.

To adjust the outer limit correctly, you must ensure that the upper pulley on the derailleur is directly in line with the smallest sprocket. If it isn’t, then use the H screw to adjust it.

Setting the inner limit follows the same process. You should ensure that the derailleur sprocket is directly in line with the largest sprocket. If it isn’t, then use the L screw to adjust it.

The limit screws can be quite sensitive, so avoid making significant adjustments. Instead, work in small turns and check your progress regularly.

Setting the inner wire tension

Now that you’ve set the limit screws, you’ll want to ensure that your rear derailleur can shift between gears. The key to that is in adjusting the inner tension wire, using the plastic barrel adjuster.

The inner tension wire in your rear derailleur plays a crucial role in smooth shifting. If you experience problems shifting down the gears to a lower sprocket, you will need to release the tension. If you’re struggling to change up to a larger sprocket, then you will need to increase the tension.

To increase tension, you turn the barrel adjuster clockwise. To release it, you turn it anti-clockwise.

Making small adjustments at a time, you can now get your gears indexing correctly.

Rear derailleur adjustment tips

  • Spend some time reading about how rear derailleurs work before attempting to make any adjustments.
  • Write down the issues you’re having with your gears.
  • Check for any damage to the derailleur, other drivetrain components or rear hanger before starting to work.
  • Give your rear derailleur a thorough clean before getting started as the adjustment screws can be very dirty and greasy.
  • If you can, use a bike stand – it makes all work much easier.
  • Make small adjustments at a time.
  • Before heading out on a long ride, ensure you test your gears.
  • On your next ride, carry some essential bike tools to make minor adjustments if they’re required.