Indexing a rear derailleur is the single most useful drivetrain skill you can learn: it makes every gear shift crisp, quiet, and instant. If your chain hesitates, rattles, or skips between cogs, the indexing is out. This guide walks you through exactly how to index a rear derailleur at home in about 15 minutes, what each adjustment does, and how to fix the problems that crop up along the way.
What “indexing” a rear derailleur actually means
Modern shifters move the derailleur a fixed, pre-set amount with every click. Indexing is the process of aligning those clicks so that one click of the shifter moves the chain exactly one cog up or down the cassette. When indexing is correct, the upper guide pulley sits directly beneath the cog you have selected. When it drifts out of alignment, the pulley sits slightly to one side, the chain runs against the next cog’s teeth, and you get the familiar clicking, ghost-shifting, or refusal to climb into a gear.
Indexing is a tuning job, not a repair. It corrects the cable tension that controls lateral derailleur position. It does not fix bent parts or worn cables — so a quick inspection comes first. If you are newer to wrenching, it helps to read our overview of essential DIY bike maintenance repairs before you start, so you recognise the parts referenced below.
Tools you’ll need
- A bike stand, or a way to lift the rear wheel so you can pedal by hand (a friend holding the saddle, or hanging the bike).
- A 5mm hex/Allen key for the cable pinch bolt.
- A Phillips screwdriver for the limit screws (some derailleurs use a hex).
- Clean rag and a little chain lube.
- Optional: cable cutters and a new inner cable if the old one is frayed.
Before you start: three pre-indexing checks
Indexing will never hold if something underneath it is wrong. Spend two minutes on these checks first — they are the reason most home tuning attempts fail.
1. Check the cable and housing
Shift into the smallest cog (highest gear) and look at the inner cable. Fraying, kinks, or sticky, gritty housing add friction that makes precise tension impossible. If the cable is worn, replace it first — here is our step-by-step guide to replacing a shift cable on a bike. A fresh cable also stretches slightly in its first few rides, which is the most common reason indexing drifts after a tune.
2. Check the derailleur hanger alignment
The hanger is the small bracket that attaches the derailleur to the frame, and it bends easily in a crash or a tip-over. A bent hanger angles the whole derailleur and makes clean indexing impossible no matter how carefully you set tension. Sight down the cogs from behind: the two pulleys and the cassette should line up vertically. If they look twisted, address the hanger first — our guide on how to fix or replace a bent derailleur hanger covers it.
3. Set the high and low limit screws
Limit screws (marked H and L) cap how far the derailleur can travel at each end — they stop the chain throwing into the spokes or off the smallest cog. They are not part of indexing, but they must be set first. With the chain on the smallest cog, turn the H screw until the upper pulley lines up directly under that cog. Then, with the chain on the largest cog, set the L screw so the pulley sits under it without the chain trying to climb over. Once the limits are right, leave them alone — indexing happens entirely with cable tension.
Step-by-step: how to index your rear derailleur
Step 1 — Start in the smallest cog with zero tension
Click the shifter all the way to the highest gear (smallest cog) so there is no cable tension pulling the derailleur. Turn the barrel adjuster — the knurled dial where the cable enters the derailleur or shifter — fully clockwise, then back it out two full turns. This gives you room to add or remove tension in both directions later.
Step 2 — Set the baseline cable tension
If you have just fitted a new cable, loosen the 5mm pinch bolt, pull the cable taut by hand (no pliers needed — finger-tight is enough), and re-tighten the bolt while holding it. The goal is to remove slack without adding load. The derailleur should still sit cleanly under the smallest cog.
Step 3 — Shift up one cog and watch the chain
Pedalling by hand, click the shifter once to move toward a larger cog. The chain should climb smoothly and sit quietly on the next cog. This single shift tells you everything: if it works cleanly, your tension is close. If it hesitates or won’t climb, the cable needs more tension; if it overshoots or rattles past the cog, it has too much.
Step 4 — Dial tension with the barrel adjuster
This is the heart of indexing. Turn the barrel adjuster counter-clockwise (out) to add tension when the chain is slow or unwilling to climb to a larger cog. Turn it clockwise (in) to remove tension when the chain is noisy on a cog or shifts past it. Make changes a quarter- to half-turn at a time, pedalling and shifting after each adjustment until that one shift is silent.
Step 5 — Work through the whole cassette
Once the first shift is clean, run up through every cog one click at a time, then back down. Each shift should be immediate and quiet in both directions. Pay attention to the middle cogs — a setup that is perfect at the extremes but rattles in the middle usually needs a small tension tweak. Re-check from the smallest cog when you are done, because adjustments interact.
Fine-tuning with the barrel adjuster: a simple rule
If you only remember one thing, remember this: noise tells you which way to turn. When the chain is slow to climb onto a bigger cog (toward the wheel), add tension. When it is slow to drop onto a smaller cog or rattles against the larger one, remove tension. Always adjust in small increments and test after each one. The barrel adjuster is also your trailside fix: a half-turn out usually restores crisp shifting when a new cable settles in mid-ride.
Common indexing problems and how to fix them
Chain skips or ghost-shifts under load
If shifting is fine on the stand but the chain jumps when you pedal hard, the cause is often tension settling rather than indexing itself. Add a quarter-turn of tension at the barrel adjuster. If skipping persists across several gears, a worn chain or cassette may be the real culprit — see our breakdown of why bike gears slip for the wear-related causes.
It won’t shift into the largest or smallest cog
That is a limit-screw issue, not indexing. Revisit the H and L screws from the pre-checks above. Too tight on the L screw blocks the climb into your easiest gear; too tight on H stops the chain reaching the fastest cog.
Shifting was perfect, then drifted after a ride
New cables stretch. This is normal. A single half-turn of the barrel adjuster outward almost always brings the indexing back. Build a quick drivetrain check into your routine using our complete bike maintenance checklist so small drifts never become annoying rides.
How often should you re-index?
For most riders, a quick indexing check every month or two keeps shifting sharp. Re-index whenever you fit a new cable, swap a cassette or chain, travel with the bike, or notice shifting going vague. Because the adjustment lives entirely at the barrel adjuster once the setup is dialled, maintenance is usually a 30-second tweak rather than a full re-tune.
When to hand it to a mechanic
If you have set the limits, fitted a fresh cable, confirmed the hanger is straight, and the derailleur still won’t index cleanly, stop adjusting. A persistently poor index after all that usually points to a worn drivetrain, a tired derailleur clutch or spring, or a hanger that is subtly bent beyond eyeball tolerance. A shop has a hanger alignment gauge that removes the guesswork. Otherwise, indexing is one of the most satisfying skills to own — five minutes with a barrel adjuster transforms how your bike rides.
