Road/MTB 10sp Shimano Incompatibility Issues
Over the past month I’ve been experimenting with different wide-range 10sp cassettes and rear derailleurs with SRAM and Shimano road shifters. I’m still not done with all the combinations, but as a preliminary warning to those riders and shops looking to use wide-range (ie 11-32, 11-34, 11-36, and 12-36 ten-speed cassettes) with Shimano road STI, you CANNOT use the new 10sp Shimano MTB rear derailleurs with road STI. Shimano 10sp road shifters will work fine on those new 10sp wide-range cassettes if you use 9sp Shimano MTB derailleurs, however.
The new 10sp Shimano mtb derailleurs need more cable per derailleur movement than previous designs and require the matching 10sp MTB shifters.