"Chain stretch" is the most misleading term in maintenance — nothing stretches. Pins and bushings wear, every joint gains a hair of clearance, and a hundred-odd joints of hair add up to a chain that's measurably longer than it was. Here are the three ways to measure it, from five seconds to precise.
Method 1: The pull test (5 seconds, no tools)
Grab the chain at the rear of the rear sprocket — the 3 o'clock position — and pull it straight back. A healthy chain lifts barely at all; a worn chain lifts off the teeth. More than half a tooth of visible daylight is the traditional replace-it line. This test works because a worn chain's pitch is longer than the sprocket's, so it rides up and out of the tooth valleys. It's the first thing to check whenever chain noise or endless adjustment shows up.
Method 2: The measurement (2 minutes, a ruler)
Your manual lists a service limit for a span of links — commonly the length across 20 or 21 pins, with a maximum figure around 1–1.5% over nominal. Pull the lower run taut (some manuals say to hang a weight), measure pin-center to pin-center across the specified span, compare. This is the objective version of the pull test and the one that settles arguments. Measure at two or three spots, because chains wear unevenly — a chain at limit in one section is done everywhere.
Method 3: The adjuster position (a glance)
The axle adjusters are a wear odometer. Every adjustment moves the axle rearward to take up worn length; when the adjusters near the end of their marks, the chain has consumed its service allowance regardless of how it measures today. Bonus signal: if you're adjusting noticeably more often lately (the chain keeps getting loose), wear is accelerating — which it does at end of life, because worn joints wear faster.
What to do with a verdict
At or past the limit: replace, and replace the sprockets with it — a worn chain has re-machined them to its stretched pitch, and new-chain-on-old-sprockets is how you buy two chains for the price of two. Approaching the limit: budget for the kit and check the other wear signs. Well within limit: your only job is slowing the wear down, and the entire recipe is grit removal plus lube — a one-minute pass with the CC360 and a proper inside-run lube after rides. Wear you can measure is wear you can postpone.
Quick answers
How do you check chain stretch?
Three ways: pull the chain rearward off the rear sprocket (more than half a tooth of lift means worn), measure a span of links against the service limit in your manual, or note the axle adjusters approaching the end of their range.
What percent stretch means replacing a chain?
Most manufacturers set the service limit around 1–1.5% elongation over nominal length. Past that, the chain's pitch no longer matches the sprockets and wear accelerates rapidly.
Why does a chain stretch?
It doesn't literally stretch — the pins and bushings wear, adding tiny clearances at every joint that sum to measurable length across the chain.