Bike Chain Wear and Service Interval Checker
Read a chain wear measurement against the right threshold for your drivetrain, and see which service jobs are due or overdue by mileage.
No chain checker? Measure twelve links with a steel rule — pin centre to pin centre. A new chain is exactly 12 inches. One sixteenth over is 0.5%, one eighth over is 1%. Done carefully this is at least as accurate as a cheap checker, several of which read high because they rest on the roller, and rollers wear too.
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Why the measurement is worth ten seconds
- Chains do not stretch. The plates do not lengthen — the pins and rollers wear, so the pitch grows. Everyone calls it stretch and the mechanism matters, because it is what reshapes the sprockets.
- A worn chain reshapes the cassette to match itself. Fit a new chain to that cassette and it skips under load, in exactly the gears you use most. Now you are buying both.
- Which is the whole economic case. A chain is cheap, a cassette is not, and the difference between replacing one part and three is a measurement that takes ten seconds.
- Grit wears chains, not kilometres. A neglected chain in wet conditions can be finished in under a thousand kilometres, while a clean one in the dry goes five times as far.
How to use
- Measure with a chain checker, or twelve links with a steel rule.
- Enter the reading and your drivetrain speed.
- Add kilometres since your last service and the conditions you ride in.
- Do the overdue jobs before the ones that merely look interesting.
Frequently asked questions
Do chains really stretch?
No, and the mechanism matters. The side plates do not lengthen — the pins and rollers wear, so the pitch between links grows. It gets called stretch universally, but knowing it is wear explains why a worn chain reshapes the sprocket teeth rather than simply sitting loose.
Why does the threshold depend on drivetrain speed?
Because narrower chains have less material and reshape a cassette sooner. Eleven and twelve-speed chains are generally replaced at 0.5 per cent elongation, while older and wider chains tolerate 0.75 before doing real damage. Using the wider figure on a modern drivetrain is a common and expensive mistake.
What happens if I leave it past 1 per cent?
The chain has by then reshaped the sprocket teeth to match its own pitch. Fit a new chain to that cassette and it skips under load, in exactly the gears you use most, so you end up buying both. That is the entire economic case for measuring: a chain is cheap, a cassette is not.
How do I measure without a chain checker?
A steel rule against twelve links, pin centre to pin centre. A new chain is exactly 12 inches over that span. One sixteenth of an inch over is 0.5 per cent and one eighth is 1 per cent. Done carefully it is at least as accurate as a cheap checker, several of which read high because they rest on the roller — and rollers wear too.
How long should a chain last?
Anywhere from under a thousand kilometres to five thousand, and the difference is grit rather than mileage. A neglected chain ridden in wet, gritty conditions is finished quickly; a clean one in the dry goes several times as far. Which is why the answer is to measure rather than to count kilometres.
Do I need to replace the cassette every time?
No — roughly every third chain, if each chain was replaced on time. That is the payoff for measuring. Skip the measurements and you replace them together, more often, and buy chainrings sooner as well.
How reliable are the service intervals?
They are planning figures, not rules. Brake pads should be checked against their wear line rather than a mileage, tyres wear at very different rates front and rear, and everything shortens in the wet. Use the list to notice what you have forgotten, not to defer something that looks or sounds wrong.
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