The chain is the cheapest part of your drivetrain and the one that decides how long the expensive parts last. Checking it takes two minutes and is the highest-return thing you can measure on a bike.
Chains don't really stretch — the pins and rollers wear, and the chain gets functionally longer. As it lengthens, it stops meshing correctly with the cassette teeth and starts reshaping them to match.
That's the whole problem. Replace the chain in time and you replace one cheap part. Leave it and the cassette wears into the worn chain's shape, so a fresh chain skips on it and both have to go. On a modern 12-speed group that difference is substantial — and it's entirely avoidable with a two-minute measurement.
| Drivetrain | Replace at | Why |
|---|---|---|
| 11 and 12-speed | 0.5% | Narrower chains and thinner cassette teeth: less margin before damage starts |
| 8 to 10-speed | 0.75% | More material to give, so a longer usable life |
| Past 1% | too late | Assume the cassette goes with it, and check the chainrings |
The fast way. Drop the tool into the chain and read where it falls: it'll tell you 0.5%, 0.75% or 1% directly. Worth owning if you maintain your own bike — it pays for itself the first time it saves a cassette.
Works fine and costs nothing.
| Where the pin at 12" sits | What it means |
|---|---|
| Dead centre | Essentially new |
| About 1/16" past | ~0.5% — replace now on 11/12-speed |
| About 1/8" past | ~1% — the cassette is already taking damage |
Chains don't wear perfectly evenly. Checking the same section of chain gives you a trend you can trust rather than a number that bounces around.
All of these mean you're already past the ideal point — worth knowing, but they're late warnings, not early ones:
We measure chain wear in the free diagnostic and in every tune-up, and we tell you where you are before replacing anything.
Measure it. A chain checker is the quick way; a ruler works too. On a modern 11- or 12-speed drivetrain, replace the chain at 0.5% elongation. On 8- to 10-speed, you can go to 0.75%. Past that you're no longer replacing a chain, you're replacing the cassette with it.
Put the bike in the big chainring, line the ruler's zero mark up with the centre of one chain pin, and measure 12 inches along the chain. On a new chain, the pin at 12 inches sits dead centre. If it sits about 1/16 inch past, you're near 0.5% and it's time. At 1/8 inch past, the cassette is already taking damage.
A stretched chain doesn't sit properly in the cassette teeth and wears them into a matching shape. Then a new chain skips on the old cassette and you have to replace both. That's how a $30 job becomes a $150 one — and on a high-end 12-speed group, considerably more.
It depends entirely on conditions and how you lube it, not on the calendar. A well-maintained chain lasts a long time; a chain ridden wet and dry-running can be done in a few hundred miles. That's why measuring beats guessing.
You can catch the late signs: shifting that hesitates under load, a chain you can lift noticeably away from the front of the big chainring, or skipping in certain gears. Those all mean you're already past the ideal replacement point — useful, but not early warning.
Yes. Chain wear is measured in the free diagnostic and in every tune-up, and we tell you where you are before anything gets replaced.
Chain wear is measured in every free diagnostic. Two minutes, no charge, and you'll know exactly where you stand.