Originally Posted by
twocicle
Not sure what Right-Side-Drive (or SSD) has to do with missing gears... basically nothing. Really, it's just a matter of chainring count as dictated by the currently available road Di2 FD limitations.
Even in a triple setup, the new mtn Di2 FD won't give you more range in the chainrings because of its severe ring capacity limitations as mentioned earlier in this thread.
True it is the ring count that limits the gears but the primary reason for giving up a triple is often to allow for the right side sync. It seems that the main reasons two rings get used on tandems are either Di2 or right side sync ruling out a triple. I haven 't seen too many posts about a modern double ring, left side sync, mechanical shifting tandem.