Key idea
The derailleur must line up with the rear cogs. If the guide pulley sits even a couple of millimetres to one side, the chain is pulled at an angle and will skip, clatter, or jump between gears. The fix is usually a quarter-turn of one adjuster.
Symptoms of a misaligned derailleur
- Gears skip or jump, especially under pedalling load
- Constant ticking or rattling from the rear
- The chain hesitates when you shift, or shifts two gears at once
- Shifts fine one way but badly the other
What you need
- Your hands — the barrel adjuster turns by hand
- A bike stand, or a friend to lift the rear wheel
- Optional: a small screwdriver or hex key for the limit screws
Step-by-step: the barrel adjuster
The barrel adjuster is the knurled dial where the gear cable enters the rear derailleur. Turning it moves the derailleur — and its guide pulley — sideways in tiny steps.
- Get the rear wheel off the ground Use a stand or hang the saddle nose on something stable so you can pedal and shift while stationary.
- Shift to a middle gear Pedal by hand into a cog near the middle of the cassette — problems show up most clearly here.
- Sight the alignment from behind Crouch behind the wheel and compare with the diagram: is the guide pulley directly under the cog, or off to one side?
- Turn the adjuster a quarter-turn at a time If the chain rattles as if it wants a larger cog (toward the wheel), turn the adjuster clockwise; if it hesitates to climb, turn it anticlockwise. Re-check after every quarter-turn.
- Test every gear Shift up and down the whole cassette — each click should give one clean change. Fine-tune with more quarter-turns.
- Test ride somewhere safe Gears behave differently under load, so confirm with a gentle ride before traffic.
Rule of thumb
Noisy and reluctant to move toward the wheel (easier gears)? Anticlockwise. Noisy and reluctant to move away from the wheel (harder gears)? Clockwise. Always quarter-turns.
Other things that cause skipping
| Cause | Fix |
|---|---|
| Limit screws set wrong | The screws marked H and L set the end stops. Adjust in quarter-turns, and only if the chain over- or under-shoots the end cogs. |
| Bent derailleur hanger | A shop can straighten or replace it cheaply. Don't bend it back by hand — it can snap. |
| Stretched or frayed cable | Fit a new gear cable — cheap and quick. |
| Worn chain or cassette | Have chain wear checked; a chain checker costs a few pounds. |
Warning
Keep fingers, clothing and tools clear of the chain and cassette while pedalling. Never shift while forcing the pedals hard.