How to Adjust Your Rear Derailleur

If your gears hesitate, rattle, or refuse to climb into the biggest sprocket, your rear derailleur almost certainly needs adjusting. It sounds intimidating, but it comes down to just four adjustments — two limit screws, the cable tension, and the B-tension screw. Work through them in order and your shifting will be crisp again in about 15 minutes.

When your gears need adjusting

Any of these are signs the rear derailleur is out of tune:

• The chain is slow to climb to a bigger (easier) gear, or drops slowly to a smaller one.
• It skips or ghost-shifts under load.
• It overshoots into the spokes, or won't quite reach the largest sprocket.
• There's a persistent tick or rattle in certain gears.

Tools you will need

• A set of hex keys (usually 5 mm for the cable anchor bolt)
• A Phillips or small flat screwdriver for the limit screws
• A work stand, or a friend to hold the rear wheel off the ground

Tip: work with the bike in a stand so you can pedal by hand and shift through every gear as you adjust. Everything below is done while turning the pedals.

How rear derailleur adjustment works

There are only three things you are setting:

• The limit screws (H and L): mechanical end-stops that stop the chain falling off either end of the cassette.
• Cable tension (indexing): makes each click of the shifter move the chain exactly one sprocket.
• B-tension: sets the gap between the top jockey wheel and the cassette.

Step 1: Set the high limit (H)

Shift into the smallest rear sprocket (hardest gear). The “H” screw controls how far out the derailleur can travel. Turn it until the top jockey wheel sits directly under the smallest sprocket — the chain should run silently, without rattling inward or hanging off the edge.

Step 2: Set the low limit (L)

Shift into the largest rear sprocket (easiest gear). The “L” screw sets the inboard limit. Adjust it so the chain reaches the biggest sprocket without rubbing the spokes and without hesitating to climb. If in doubt, err toward slightly more inboard travel, then confirm the chain never touches the spokes.

Step 3: Index the gears (cable tension)

With the limits set, shift to the smallest sprocket and use the barrel adjuster (on the derailleur or shifter) to fine-tune cable tension:

• Click one gear up (toward a bigger sprocket). If the chain is slow to climb, add tension — turn the barrel adjuster anticlockwise a quarter-turn at a time.
• If it overshoots or is noisy, remove tension — turn the barrel clockwise.

Work up and down the cassette a few clicks at a time until every shift is instant and quiet.

Step 4: Set the B-tension screw

Shift to the largest sprocket. The B-tension screw sets the gap between the top jockey wheel and the cassette teeth. Too close and it grinds; too far and shifting gets vague. Aim for a small, consistent gap (roughly 5–6 mm) in the biggest sprocket, then check it does not touch in the smallest.

Step 5: Test ride and fine-tune

Pedal through every gear under a little load — press down as you shift. Make small quarter-turn barrel-adjuster tweaks for any gear that still hesitates. A fresh shift cable and clean housing make a big difference if you cannot get it perfectly crisp.

Troubleshooting

• Will not reach the biggest sprocket: add cable tension, then check the L limit.
• Throws the chain into the spokes: back the L screw out (clockwise) slightly.
• Chain drops off the smallest sprocket: tighten the H screw.
• Good at one end, bad at the other: cable tension is off — re-index in the middle of the cassette.
• Still rough everywhere: a bent derailleur hanger is the usual culprit — worth a shop check.