Originally Posted by
woodcycl
Just learned there is now Di2 3 ring component options available for tandems ... interesting.
XTR & XT Di2 has always offered a triple option. Are you saying that Ultegra 6870 or 8070 Di2 is now available for triple cranks?
If you already climb 12 or 18% grades, then a double crankset (50/34) should be adequate. The new Ultegra 8070 rear derailleur can handle 34T cassette, and you even go to a 40T cassette using Roadlink hanger extension.
My vote is for Tetra over Dragonfly because you can get similar weight savings (eg. carbon wheels, Lightning cranks) at lower cost.
Gate CDX belt is better than timing chain.
For a new build, the Ultegra Di2 is better than eTap because it's less expensive, has longer battery life, and has synchronized shifting. The MT800 display is handy too. eTap's wireless shifting is more convenient for coupled tandems and older frames with external cable routing. With either system, electronic shifting means never missing a front shift under load and minimal maintenance.