Originally Posted by lyledriver
Each complete link should be 1" long.
Measure out 12 complete links on the chain.
If it is longer than 12-1/8" then it probably needs replacing.
If it is longer than 12-1/4", then you may need a new sprocket and cog as well.
Oh.. and I love the KMC 510HX
Its not the quietest 1/8" chain, but its pretty effing strong.
Close, but you mean 1/16" and 1/8", not 1/8" and 1/4". 1/4" of elongation over a foot of chain would be huge!
Yeah, like lylydriver says, just hold a good ruler/measuring tape up along side the (non-slack) chain. Center the 0 mark on one rivet, and find where the 12" mark falls. If the rivet it corresponds with is more than 1/16" from being centered on the 12" mark, you should replace the chain. If it has elongated more than 1/8", your chain is way shot and it probably has worn your chainring and cog as well. Putting a new (unstretched) chain onto the worn sprockets will accelerate the wear on the new chain. If you let your chain get that far, you should replace the cog and chainring at the same time.