Originally Posted by
cpach
Dude, I'm one of the "current crop of mechanics" and nowhere in Shimano's technical training (either the dealer manual or in any of the S-tec videos) does Shimano recommend chain replacement on a mileage or time based interval. They recommend using a chain checker (and preferably theres--although their nicer one is actually a little more accurate than most), and replacing cogs and/or chainrings when the chain skips on them. If anything, most mechanics recommend replacement a little early because they use chain tools that slightly exaggerate chain wear, and because they also because we see how terrible people are to their bikes. If we see a chain that is 70% worn in, chances are the next time anyone checks it'll have completely blown out the cassette and chainrings on some bike for which parts are nearly impossible to find.
...thank you for your correction. Indeed the official Shimano chain literature does say "depending on usage and riding circumstances".
http://bike.shimano.com/media/techdo...9830750298.pdf
I meant no disrespect to the current crop of mechanics, other than to point out that they are working in a much different repair environment than was the case 20 or 30 years ago.
I was misled by something I read on the internet, which is always a possibility in life.
I fully agree that chains are much cheaper than chainwheels, thus ought to be changed prior to wearing out the stuff that's more expensive. I have heard from the people I know who work professionally here the "new cogset every other chain replacement" mantra. I'm not certain where it's coming from, but I know it's out there.