When to replace a bike chain: wear thresholds and measurement
A stretched chain wears out your cassette and chainrings, so knowing when to replace it protects the rest of the drivetrain. This page covers the elongation thresholds, how to measure them and how to fit a new chain.
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The three thresholds: 0.5%, 0.75% and 1%
Chain wear is measured as a percentage of elongation of the pitch, which is 12.7 mm (1/2 inch) on a new chain. Up to 0.5%, the chain is in good condition. At 0.5%, replace it soon: the cassette is still fine. At 0.75%, replace it now, the cassette is starting to suffer. At 1%, chain and cassette both need replacing and the chainrings are likely affected too.
The seasonal checklist is stricter for modern drivetrains: beyond 0.5% on 11 and 12-speed, or 0.75% on 9 and 10-speed, the chain needs replacing.
Replacing at 0.5% means you can run 2 to 3 chains on the same cassette. Waiting until 1% means replacing everything at once.
Measuring with a checker or a ruler
A two-sided checker such as the Park Tool CC-3.2 gives a quick answer: if the 0.5% side drops between the links, wear has started; if the 0.75% side drops, replace the chain immediately.
With a ruler or callipers, measure 12 full links pin to pin. The theoretical distance is 304.8 mm. It reads 306.3 mm at 0.5%, 307.1 mm at 0.75% and 307.8 mm at 1%.
Fitting the new chain
Use a chain matched to your speed count, a chain breaker and a quick link of the correct size. Size it against the old chain, or around the largest chainring and largest cog without the derailleur, plus 2 links.
Close the quick link, pull to lock it, then shift through all gears to check for skipping or noise.
Frequently asked questions
How many kilometres does a chain last?
The guides give averages of 3,000 to 5,000 km on a road bike in dry conditions, 1,500 to 3,000 km in XC mountain biking and 500 to 1,500 km in enduro or DH with mud and rain. These figures vary enormously with cleaning, lubrication and weather, so measuring wear remains the reliable method.
Why does a new chain skip on my cassette?
If the old chain went beyond 1% elongation, the cassette teeth have deformed to match it and a new chain no longer hooks on correctly. In that case the cassette, and possibly the chainrings, must be replaced too.
Does an e-bike chain have a different replacement threshold?
No. The threshold is the same as on a regular bike (0.75% elongation), but an e-bike chain reaches it faster.
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