Originally Posted by
lortman
the Di2 road shifters won't shift a MTB rear derailleur. In summary, this solution would be very expensive. So I'm not sure this is the way to go. Now I just read some articles about Sram's 1x drivetrains with an 11 speed 10x42 and a wide range of front rings. Would this work? Has anyone tried this solution? Would it be less expensive? Thanks for any help.
The Sram 1x11 drivetrain is for MTB (and now cyclocross) and won't give you enough range on a road tandem. I use the 1x11 on my full-suspension MTB and have to choose between a 26T or 28T ring depending on the terrain. This is a minor issue because spinning out is not common.
A better option is to upgrade to a Ultegra 2x11 mechanical shifting with 50-34 compact cranks. You should be able to use a long cage RD for the 34T cassette. The front shifting will be better and the 34 x 34 ratio will allow you to do very steep climbs.
If your budget allows, the Ultegra 11sp Di2 is fantastic. The front shifting is extremely precise and reliable. It's much better than the mechanical Ultegra, especially with the long cable run and higher torque on a tandem.