Is It Time to Replace Your Chain? The Stretch Test Explained

Chains don't actually stretch in the way the name suggests — the metal itself doesn't get longer. What happens is that the tiny pins and rollers wear down internally, letting the links sit slightly further apart than when new. Over thousands of pedal strokes, that adds up.

A chain checker tool is the easiest way to catch this early: it's a simple gauge that drops into the chain and shows how much internal wear has accumulated. Most mechanics suggest replacing a chain once wear passes around 0.5%, and definitely before 0.75%.

The reason it matters goes beyond the chain itself. A worn chain slowly reshapes the teeth on your cassette and chainrings to match its stretched spacing. Replace the chain alone at that point, and the new chain won't sit properly on the now-worn teeth — leading to skipping, and a far more expensive cassette and chainring replacement.

The fix is simple: check chain wear every couple of months, and replace the chain alone, regularly, before it has a chance to damage anything else. A £20 chain replaced on time is far cheaper than a chain, cassette and chainrings replaced together once it's been left too long.