How to Index Bike Gears

The clicking, skipping and refusing-to-shift that almost every boxed bike arrives with. Fixed with one barrel adjuster, no tools, and about ten minutes.

By Stephen V.Last updated August 13, 2026How we pick

Nine times out of ten this is one hand-turned barrel adjuster and ten minutes. No tools, no parts, nothing to buy. Skip to the symptom table below if the bike is in front of you and you just want it fixed.

It is also the most common complaint about a new bike, and worth saying why: gear cables stretch. A new cable settles into its housing over the first hundred miles, tension drops, and the shifting that was fine in the shop goes vague. That is not a fault, it is a bedding-in process, and every boxed bike needs this adjustment within its first few rides.

The parts, in plain English

Four things are involved, and you only need to touch one of them.

The cassette — the stack of toothed cogs on the rear wheel. Bigger cog, easier gear.
The derailleur — the mechanism that moves the chain across them.
The cable — runs from your shifter to the derailleur. Pulling it moves the derailleur toward the bigger cogs; releasing lets a spring pull it back toward the smaller ones.
The barrel adjuster — a knurled cylinder where the cable enters the derailleur, and often a second one at the shifter. Turning it effectively lengthens or shortens the cable housing, which changes cable tension without touching the cable itself. This is the part you turn.

Indexing is simply lining up each click of the shifter with a cog on the cassette. Park Tool put it well: the job is to line up the guide pulley with the cogs so each incremental shift lands on each cog.

The symptom table

Find your symptom, make the change, ride a few meters and test. Work in quarter turns— a full turn is a large adjustment and it is very easy to overshoot and end up chasing the problem in both directions.

What it is doing	Why	What to do
Chain is slow or refuses to move to a LARGER cog (an easier gear)	Not enough cable tension	Barrel adjuster COUNTER-CLOCKWISE, one quarter turn at a time
Chain is slow to move to a SMALLER cog (a harder gear)	Too much cable tension	Barrel adjuster CLOCKWISE, one quarter turn at a time
Constant clicking or rattling, but the gear does not change	Derailleur sitting between two cogs	Quarter turn either way until it goes quiet — note which way improves it
Chain jumps two cogs on one click	Far too much cable tension	Barrel adjuster CLOCKWISE a full turn, then re-index
Chain will not reach the largest cog at all	L-limit screw too tight	L screw out a quarter turn at a time — this is a screwdriver job, not the barrel
Chain fell into the spokes	L-limit screw too loose	Stop riding. L screw IN until the derailleur cannot reach past the largest cog
Chain fell off the outside, past the smallest cog	H-limit screw too loose	H screw IN until the derailleur stops level with the smallest cog
Shifts fine in some gears, never in others, no adjustment helps	Bent derailleur hanger	Take it to a shop — this needs an alignment gauge

The rule underneath all of it, if you would rather remember one thing than a table:

Counter-clockwise adds tension and moves the chain toward the easier gears. Clockwise releases tension and moves it toward the harder gears. If a shift in one direction is sluggish, turn the barrel the way that helps that direction.

The full procedure, from scratch

Use this if the bike is new, if the cable has been replaced, or if fiddling with the barrel adjuster has stopped making things better. It follows Park Tool’s published order, which exists for a reason: each step depends on the one before it.

You need the bike with the rear wheel off the ground — a stand, or a friend holding the saddle — because you have to turn the pedals while shifting. Never do this with the bike on the ground and the wheel loaded.

Step 1 — Set the H-limit screw

Shift to the smallest rear cog. The two small screws on the back of the derailleur are marked H and L; H controls how far it can travel outward.

Looking from behind, the upper jockey wheel — the small toothed wheel the chain runs over — should sit directly in line with the smallest cog. Turn H in or out until it does. As Park Tool put it, the main purpose of the limit screw is to stop the chain going where it should not — off the outside, in this case.

Step 2 — Set the cable tension baseline

With the chain still on the smallest cog, the cable should be snug but not pulling. If someone has been turning the barrel adjuster at random, wind it fully clockwise and then back out two full turns — that gives you adjustment room in both directions rather than running out at one end.

Step 3 — Index across the cassette

This is the actual job. Turn the pedals and click one gear at a time toward the larger cogs.

If the chain is slow to climb to the next larger cog, turn the barrel adjuster counter-clockwise a quarter turn and try again.
If it jumps past a cog or rattles against the next one in, turn clockwise a quarter turn.
Keep going up and back down through every gear. Ignore the largest cog for now — Park Tool are explicit that you are looking for the setting that shifts well in every gear except the largest, because that one is governed by the L screw you have not set yet.

There is usually a range of positions that work rather than one exact point. When it shifts cleanly both ways across the middle of the cassette, stop.

Step 4 — Set the L-limit screw

Now shift onto the largest cog. The L screw controls how far the derailleur can travel inward, and it is the screw that stops the chain going into your spokes — which destroys a wheel and sometimes the derailleur with it.

The jockey wheel should line up with the largest cog and the derailleur should not be able to move any further. If the chain will not reach the largest cog, back L out a quarter turn. If it feels like it wants to go past, wind L in.

Step 5 — The B-screw

The last one, and the one nobody explains. There is a third screw where the derailleur bolts to the frame, and it sets the gap between the upper jockey wheel and the cassette teeth.

In the largest cog, that gap should be small but clear — a few millimeters. Too close and shifting is noisy and hesitant; too far and shifts feel vague. Most bikes never need this touched. Adjust it only if everything else is right and the largest cog is still noisy.

When it is not the indexing

Three things that no amount of barrel-adjuster turning will fix, and it is worth recognizing them before you spend an hour.

A bent derailleur hanger

The hanger is a small aluminum bracket that bolts the derailleur to the frame, and it is designed to bend or break so that the frame does not. Any fall on the drive side can bend it, and so can leaning the bike against a wall the wrong way.

The tell: the bike shifts beautifully in some gears and refuses in others no matter what you do, and the adjustment that fixes one end makes the other end worse. Park Tool are clear that alignment is a gauge job — you cannot reliably eyeball it, and bending it back by hand usually snaps it. This is the point to take it to a shop.

A worn chain

A chain stretches as it wears and stops sitting properly on the cog teeth. The symptom is skipping under hard pedaling — particularly in the gears you use most — rather than a shift that goes to the wrong place. Indexing will not touch it. Our chain guide covers measuring wear, and the short version is that a chain replaced on time saves the cassette, and a chain replaced late costs you both.

Dirty or dying cables

If the shifter clicks but the derailleur moves late, sluggishly, or only in one direction, the cable is dragging inside its housing. Grit and corrosion do this, especially on a bike ridden in winter without fenders. New cables and housing are cheap; they are also a job with a specific tool, so this is a reasonable thing to pay a shop for.

The front derailleur, briefly

If your bike has two chainrings at the front, that derailleur has its own H and L screws and its own barrel adjuster, and the same logic applies. It is fussier to set up and much less often the problem.

One thing worth knowing: some front-shifting noise is normal and not a fault. Chain rub in extreme gear combinations — big front ring with the biggest rear cog, or small with smallest — happens because the chain is running at a severe angle. The fix is not to adjust anything, it is to avoid those combinations. It is also one of the arguments for a single chainring.

How often this needs doing

Not on a schedule. When the symptoms appear.

A new bike: expect it in the first few rides while cables settle. This is the single most common reason a new bike shifts badly.
After a crash or a fall: check it, and specifically check the hanger.
After new cables: always, for the same stretching reason.
Otherwise: a bedded-in bike can hold its indexing for a year or more.

Ten minutes with a barrel adjuster is the highest-value maintenance skill a first-time bike owner can pick up, because it converts the most common and most demoralizing new-bike complaint into something you fix in the driveway rather than something you book an appointment for.

Questions people actually ask

Why do my bike gears click but not change?

The derailleur is parked between two cogs rather than lined up under one. Turn the barrel adjuster a quarter turn and listen — if the noise gets worse, go the other way. It is almost always a cable-tension problem and almost never anything expensive.

Which way do I turn the barrel adjuster?

Counter-clockwise adds cable tension and moves the derailleur toward the larger cogs — use it when shifting to easier gears is slow. Clockwise releases tension and moves it toward the smaller cogs — use it when shifting to harder gears is slow. Work in quarter turns and test after each one.

Do I need tools to index my gears?

For the common fix, no. The barrel adjuster turns by hand and is where roughly nine out of ten indexing problems are solved. You only need a small screwdriver for the H and L limit screws, which set how far the derailleur can travel and should not need touching unless the chain has come off the ends of the cassette.

Why does my new bike shift badly out of the box?

Because new gear cables stretch. A cable seats into its housing and end caps over the first hundred miles or so, which reduces tension and makes shifts to easier gears go slow — exactly the symptom the barrel adjuster fixes. Almost every boxed bike needs this within the first few rides, and it is normal rather than a fault.

What is a derailleur hanger and how do I know if it is bent?

It is a small replaceable bracket bolting the rear derailleur to the frame, designed to bend or snap so the frame does not. Suspect it if the bike shifts cleanly in some gears and never in others no matter how you adjust, or after any crash or fall on the drive side. Straightening it needs an alignment gauge, so it is a shop job.

How often should I index my gears?

Not on a schedule — when the symptoms appear. Expect it in the first few rides on a new bike while the cables settle, then after any crash, after cable replacement, and occasionally as housing and cables age. Once a bike is bedded in, indexing can hold for a year or more.

Sources

Specifications come from the manufacturer or the retailer listing, dated. Where a figure is not published, we say so rather than estimating it.

Park Tool — Rear derailleur adjustment — The published indexing procedure: H-limit, barrel adjuster direction, indexing across the cassette, L-limit, then B-screw, with the symptom-to-fix table (accessed August 13, 2026)
Park Tool — Rear derailleur hanger alignment — Why a bent hanger makes indexing impossible to hold, and that alignment is a gauge-and-shop job rather than a roadside one (accessed August 13, 2026)
Shimano — Component product list — Shimano's own component lineup, from which the road groupset hierarchy is read (accessed July 23, 2026)