Chains wear - fact! The rate of wear (or more specifically 'stretch') depends on how clean you keep your chain and drive-train together with the type of riding you do.
From experience I can say that most people think their chain is ok and isn't unduly worn but the reality is somewhat different. I've lost count of the number of times I've had to replace chain rings and cassettes due to premature wear. A chain is getting ready for replacement at 0.75% stretch!
There are various ways to check if your chain is stretched.
- A rough check is to to lift the chain off the front chainring. If it lifts and you see daylight coming through under the chain, it could be ready for replacement.
- Buy and regularly use a chain checker. A simple one is two sided: one side checks 0.75% wear ('replace chain soon'), the other checks 1% wear ('replace chain immediately').
- Another way is to use a ruler. The normal technique is to measure a one-foot length, placing an inch mark of the ruler exactly in the middle of one rivet, then looking at the corresponding rivet 12 complete links away. On a new, unworn chain, this rivet will also line up exactly with an inch mark. With a worn chain, the rivet will be past the inch mark. This gives a direct measurement of the wear to the chain, and an indirect measurement of the wear to the sprockets:
- If the rivet is less than 1/16" past the mark, all is well.
- If the rivet is 1/16" past the mark, you should replace the chain, but the sprockets are probably undamaged.
- If the rivet is 1/8" past the mark, you have left it too long, and the sprockets (at least the favourite ones) will be too badly worn.
Pictured below is a digital chain checker.