Originally Posted by
Brocephus
While digging through a couple bins of spare parts, I found I have several Shimano 9 sp chains left over from years ago, and a new 10 sp cassette, that I got for a future service my current road bike (I installed a new KMC 10-sp chain last year, soon after snagging this bike on Criagslist, but will be looking to replace both the cassette and chain at the end of this year.)
I tried Googling the question, and though i found info saying Shimano's 9, 10 and 11 sp stuff are interchangeable, I didn't find a direct answer to my question, and I suspect the wider 9sp chain will be somewhere between "less than ideal", to "completely incompatible".
Any good info is much appreciated.....
*Some* Shimano 9 and 10 speed drivetrain components are interchangeable within limits (e.g. rear derailleurs). Unfortunately chains are not on that list, at least not reliably. A 9sp chain is almost a full millimeter wider than 10sp (6.6-6.8 mm vs 5.9 mm). So it can be too wide for the spacing of the 10sp sprockets and can start to rub against the adjacent sprockets, causing noise and shifting issues. Supposedly you can go in the other direction (10sp chain on 9sp cassette) with more success, but most people don't bother since the narrower chains are more expensive and often don't last as long.
The gap between 10 and 11 speed chains is less (< 0.4mm I think) so there's a bit of flexibility there, however in general there is very little compatibility between 11 speed groupsets and anything else. Road 11 and mountain 11 aren't even cross-compatible (except some cassettes, I think). The one exception is the newer Tiagra 10sp groups which use 11sp road actuation ratios on the rear derailleur, so you could use a Tiagra 4700 RD with 11 road speed shifters (e.g. Ultegra R8000) and an 11 speed cassette and it should work (and vice versa)