When to replace a cassette and chainrings

A cassette typically lasts two to three chains if you replace each chain at the wear limit, and chainrings often last four or more. Let a chain wear past its limit and the cassette usually has to go with it. The clearest sign is a new chain that skips under load on your most-used cogs.

Calculator

Rule of thumb: a cassette lasts 2 to 3 chains, chainrings 4 or more, if you replace each chain on time.

Check the signs

New chain skips on your most-used cogs (replace now)
Teeth look like shark fins or hooks
Chain sucks or drops on the chainring
Worn cogs shine with sharp edges

Your estimate

Chains used on this cassette

I replaced every chain at the wear limit

Conditions

Cassette life

about 2.6 chains

Chainrings: about 4.3 chains

78 % used

Fine for now

About 3 chains per cassette when chains are replaced on time (1.5 when worn too long), fewer in wet conditions; chainrings last about 1.7 times as long.

The rule

A cassette typically lasts two to three chains if you replace each chain at its wear limit, and chainrings often last four chains or more. If your chains last about 3,000 km, two to three chains is roughly 6,000 to 9,000 km, or about 3,700 to 5,600 miles. Let a chain run well past its limit and the cassette often has to go with it.

These are LeCoach rules of thumb, not manufacturer data. Real life varies a lot with weather, cleaning, lube, cog material and how much you use one or two favourite gears. That is why this page counts in chains rather than kilometres: chain wear is what wears your cogs. This calculator is one of the free LeCoach cycling calculators.

Chains replaced on time?	Conditions	Cassette lasts	Chainrings last
Yes	Mostly dry	about 3 chains	about 5 chains
Yes	Mixed	about 2.6 chains	about 4.3 chains
Yes	Often wet or muddy	about 2.1 chains	about 3.6 chains
No	Mostly dry	about 1.5 chains	about 2.6 chains
No	Mixed	about 1.3 chains	about 2.2 chains
No	Often wet or muddy	about 1.1 chains	about 1.8 chains

Chainrings last longer because they have more teeth to share the load. Each tooth on a big chainring engages the chain far less often than a tooth on a small cog.

The signs: how to check

You cannot measure a cassette as easily as a chain, so you check it by behaviour and by eye.

New chain skips on your most-used cogs. This is the hard sign. Fit a new chain, then ride hard in your favourite gears, standing up on a short climb. If the chain jumps under load, the cassette is worn.
Teeth look like shark fins or hooks. Compare a cog you use a lot with one you rarely use. Worn teeth lean forward and lose their symmetrical shape.
Chain sucks or drops on the chainring. A worn chainring can hold on to the chain at the bottom and pull it up into the frame, or let it drop on 1x setups.
Worn cogs shine with sharp edges. Polished tooth flanks with a thin, sharp tip are a sign of heavy wear.

Look at chainrings the same way. On a 1x drivetrain the narrow-wide teeth hold the chain, so worn teeth often show up as chain drops on rough ground.

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Estimate yours

The estimate is based on how many chains have run on this cassette and whether you replaced them on time.

Chains used on this cassette. Count the chains, including the one on the bike now.
"I replaced every chain at the wear limit". On, the calculator assumes about 3 chains per cassette. Off, it assumes about 1.5, because each overdue chain wears the cogs much faster.
Conditions. Mixed weather cuts the estimate by 15 %, often wet or muddy riding by 30 %.

The chainring estimate is 1.7 times the cassette estimate. The progress bar shows how much of the cassette life you have used.

Worked example. You are on your second chain, you replaced the first at the wear limit and you ride in mixed conditions. Your cassette lasts about 2.6 chains; chainrings about 4.3. You have used about 78 % of the cassette, so the verdict is "Fine for now". The third chain is likely to be this cassette's last, so check for skipping when you fit it.

Common mistakes

Fitting a new chain on a worn cassette and blaming the chain. If a new chain skips, the cogs are the problem.
Replacing the cassette but keeping a worn chain. The worn chain starts wearing the new cogs straight away.
Forgetting the chainrings. After two or three cassettes, inspect the chainrings closely.
Only checking the smallest cogs. Wear concentrates on the gears you use most, often in the middle of the cassette.
Ignoring chain wear. The cheapest way to save a cassette is to measure your chain every month.

When the estimate changes

Wet winters and muddy rides wear cogs and rings much faster.
Lighter cogs, such as alloy or titanium, usually wear faster than steel ones.
Riding one gear a lot, on a flat commute or a turbo trainer, concentrates wear on one or two cogs.
Good chain care extends everything. Clean, well-lubed chains carry less grit, so see how often to lube a bike chain.
Single chainring setups put all the wear on one ring.

If you are replacing the cassette anyway, the bike gear ratio calculator shows what a different range would do to your gears, and the bike maintenance schedule keeps the rest of the bike on track. Ask LeCoach anything about your riding and your next event, and it answers from your own data.

Sources

Park Tool. Chain wear and replacement. Repair help: why chains are replaced at 0.5 % or 0.75 % wear to protect cogs and chainrings.
LeCoach wear estimates: rules of thumb used by this calculator, not manufacturer data.

Frequently asked questions

How long does a bike cassette last?

A cassette typically lasts two to three chains when you replace each chain at its wear limit. If your chains last about 3,000 km, that is roughly 6,000 to 9,000 km. If you let chains run well past their limit, a cassette may last only one or two chains.

How do I know if my cassette is worn?

Fit a new chain and ride hard in your most-used gears. If the chain skips under load, the cassette is worn. You can also compare teeth on a cog you use a lot with one you rarely use: worn teeth look hooked, like shark fins, with sharp, shiny edges.

Do I need a new cassette with a new chain?

Not if you replace the chain on time. A cassette typically outlasts two to three chains. You only need both together when the new chain skips on your most-used cogs, which usually happens after a chain has been left well past its wear limit.

How long do chainrings last?

Chainrings last longer than cassettes because their teeth engage the chain less often. This calculator estimates about 1.7 times the cassette life, or about 4.3 chains in mixed conditions when chains are replaced on time. Check them for hooked teeth, chain suck or chain drops.

Why does my new chain skip?

Almost always because the cassette, or sometimes a chainring, is worn to the shape of the old chain. The new chain no longer sits properly on the hooked teeth and jumps under load. Check that the gears are indexed correctly, but if they are, replace the worn cogs.

Can I replace just one cog?

On most modern cassettes the cogs are joined in blocks or machined as one piece, so you replace the whole cassette. On some older or simpler designs individual cogs can be swapped. In practice, if your most-used cogs are worn, the rest are usually close behind.