Originally Posted by
cranky old road
Well. I'm not a machinist. In any event, even if I or my calipers are measuring incorrectly, I put more like 52/1000ths of an inch of wear on each six links before changing the chain (assuming there is an error of measurement and it is linear). I've gotten around 6K miles each on two chains and I anticipate I'll get 18k on the cassette, measuring as I do and following Campagnolo's instructions.
I recommend a spacing increase of only .035-.040 inch before tossing the chain, which is about TWICE what Campy suggests. I can only do that by alternating the use of three chains - changing them when they are half worn. If you're using a chain until the spacing increases by .052, that's far more than twice what Campy recommends.
The one time that I left a Campy 10 chain on a new cassette for 6,000 miles, it wore the 19T enough that it skipped with a new chain, even though the chain had little elongation. Whether you get chain skip after that much wear will vary depending on how well the wear is distributed among the cogs. I did a lot of climbing in the 28/19 and the 28/21, when I had a 53/39/28 triple, used in the mountains.
I never recommend that anyone leave a single chain in use until the spacing increases by .040. It runs a great risk of chain skip.