Originally Posted by
RubeRad
RD capacity estimates are always conservative, you can stretch them. The two limitations are chainwrap (tooth difference between big-big and small-small) and whether the upper pulley will be bumping against the big cog. You can try to correct the latter using the B-screw, or getting a longer screw with the same threading from any hardware store. I suspect you'd be able to get your current RD off of an 11-36, but whether your current RD (mid-length cage?) can handle (46-36=10) + (36-11=25) = 35 tooth chainwrap, I don't think so. You'll almost certainly need a long cage RD for that, which means mountain, and in the 10sp era, you gotta worry about whether mountain derailleurs are compatible with road shifters in terms of cable pull.
Thanks for the advice, Rube. The RD is a Shimano 105 RD-5700A which is a short cage derailleur. I had wondered if I could push it to 34T, but was not wanting to take a risk with it. I don't know. I suppose if I could get a cheapo somewhere, I would take a chance and if it did not work, then settle for a 11 - 32T cassette.
I have bought a 34T ring for the crank on eBay. It is a Stronglight ring - not Shimano - but thought it may allow me to try out the size to assess it. It was not expensive, so nothing much wasted if it does not turn out right. Other than effort, time, etc, etc, etc!
