10 speed Di2 TT drivetrain

[nickobec]

Looking to move to electronic shifting on my (main) TT bike

Want to stay 10 speed as all my other bikes and wheels are 10 speed including powertap on my racing and training wheels.

Apparently some 10 and 11 speed parts are interchangeable http://glorycycles.blogspot.com.au/2013 ... rsion.html http://weightweenies.starbike.com/forum ... 847a107714

I know I want/need
Ultegra Di2 ST-6871 STI 2x11 (Pair) or the Dura Ace model brakes + shifting
Di2 SW-R671 Additional Shifter - bar end shifters
SM-EW90-B Junction Kit
Ultegra Di2 RD-6770 Rear Derailleur 2x10
Ultegra Di2 FD-6770 Front Derailleur 2x10 does it real matter Ultegra 2x10, 2x11 or DA 2x11?
Currently tossing up internal vs external battery

I need at least one EW-SD50 Cable

Anything else I need?

[Duck!]

The rear derailleur primarily is what determines your number of gears; the shifters are a "lazy" part of the system, opposite to mechanical systems. Officially-speaking, you must match the two derailleurs in terms of 10-or 11-sp. (i.e. for 10-sp it must be 6770 at both ends, 'cos 7970 D-A is incompatible wiring, but for 11-sp you can mix-&-match 9070 & 6870) but I have tested a mix of 9070 RD & 6770 FD without apparent issue until plugged into the E-Tube software, where it says the mismatch may result in improper function.

You will need the EW90 junction kit if you want to go internal battery, because there's no facility for charging with EW67. Also check with your frame/seatpost manufacturer if they have a mounting kit available. Due to the vast array of sizes and profiles, Shimano have left it to the manufacturers to design in compatibility, rather than trying to cater for them all themselves.

An alternative for the bar-end shifters is SW-9070, which only operate on the rear derailleur (left bar shifts it one way, right bar the other). Depends on the courses you ride as to your shifting patterns whether you want that front shifting capability from the aerobars.