thank you for the information. much of this i know from experience. i say "stretch," but i know it is "wear." i ride road only, no VTT. i clean chain with enviro-safe cleaner, but while is on bike. i do not remove chain except to replace, or i would have it off every week!

i have a big alloy rule, from a drafting table i purchase many years ago. it marks english down one edge and metric down the other, and is easy to use on the chains. also, when i remove the chain, i line it up with the new one, to see how much longer it becomes.

i find that until 2 000km, it is minimal, but if i go too long past that, the chain has already worn the sprokets on the cassette.

so, the next question is: how many kms (or miles) should be reasonable for average life of narrow 9 speed chain? 2003, i log 23 800km, replaced chain 13 times!