How to adjust a mountain bike derailleur easily and efficiently

The MTB derailleur is one of the key components of the drivetrain. It allows for smooth gear shifting by moving the MTB chain from one cog to another or from one chainring to the next. However, a poorly adjusted derailleur can quickly turn your ride into a nightmare: chain drops, gears that won’t shift properly, annoying noises… Luckily, adjusting an MTB derailleur isn’t as complicated as it seems.

Here’s a complete guide to properly adjusting your MTB derailleur, taking into account the technical specifics and components of the drivetrain.

1. Understanding how the MTB derailleur works

Before diving into adjustments, let’s go over some basic terminology related to the bike derailleur:

MTB shifter: the gear control located on the handlebar. It operates the cable.
MTB derailleur cable: connects the shifter to the derailleur. Its tension affects shifting precision.
MTB cassette: the set of cogs at the rear of the bike.
MTB chain: the central element of the drivetrain, linking the cassette to the MTB crankset.
MTB chainrings: toothed discs attached to the crankset at the front of the bike.
Limit screws: screws that restrict the derailleur’s movement to prevent the chain from falling off the cassette.

2. Steps to adjust a mountain bike rear derailleur

1. Check the derailleur alignment

First, make sure the derailleur hanger is not bent. Even a slight bend can throw off all your adjustments. The hanger should be perfectly aligned with the cassette.

2. Loosen the derailleur cable

Using an Allen key, loosen the cable fixing bolt. This allows you to start fresh with the correct cable tension.

3. Set the H and L limit screws

H screw (High): limits movement toward the smallest cog. Shift the chain onto the smallest cog. The derailleur pulley should line up precisely with it.
L screw (Low): limits movement toward the largest cog. Manually shift the chain onto the largest cog and check for alignment.

4. Adjust the cable tension

Reconnect the cable and apply proper tension. Use the MTB shifter to test gear shifts up the cassette.

If the chain struggles to move up, increase tension using the barrel adjuster on the shifter or derailleur.
If it doesn’t shift back down smoothly, reduce the tension.

5. Adjust the B-tension screw (derailleur cage stop)

This screw controls the distance between the upper derailleur pulley and the cassette. Ideally, there should be around 5 to 6 mm between the top pulley and the largest cog.

If it’s too close, it can cause noise.
If it’s too far, shifting precision will suffer.

3. Front derailleur adjustment (if your MTB has multiple chainrings)

If your mountain bike is equipped with multiple chainrings:

Adjust the high and low limit screws (H and L) to prevent the chain from dropping off to the inside or outside.
Set the cable tension so that gear changes are smooth and effortless.
Ensure the front derailleur cage is parallel to the chainrings.

4. When should you adjust an MTB derailleur ?

Several warning signs may indicate it's time for an adjustment:

Gears that click, hesitate, or have trouble shifting.
A chain that skips or falls off the cassette.
Unusual noises while pedaling.
After replacing the cassette, chain, or shifter.

You should also adjust your MTB derailleur after a shock to the drivetrain, transporting the bike, or replacing the derailleur cable.

5. Maintenance and tips for a smooth drivetrain

Always keep your MTB chain clean and well-lubricated.
Regularly check the condition of cables and housing.
Never force the gears—if shifting is difficult, it's better to readjust the settings.
Choose a drivetrain that suits your riding style: number of gears, type of MTB crankset, etc.

Conclusion

Adjusting an MTB derailleur is above all a matter of precision and patience. By following the steps outlined, you can restore a smooth and reliable drivetrain. Whether you're riding for leisure, cross-country, or enduro, a properly adjusted MTB derailleur enhances both your enjoyment and performance on the trails.