Di2 Cable theory

t_willo

Hello.
Is there a general rule of thumb for selecting a length of di2 cable to run between certain components?

I have heard various theories about adding 400mm to whatever you need?

Any experts out there?

dannbodge

Nope.
Use whatever size cable you want, just make sure there is some slack.

Generally you add more to the battery to junction box A so you can pull out the seatpost to access the battery.

BetterShifting_Terry

Shimano's general rule of thumb is to measure the length you need, then go the next size up, and then add 50mm.

That means if you measure 170mm, the next size up is 200mm, and Shimano's recommendation would be 250mm.

When in doubt, choose the longer wire. You can usually tuck excess wire away in the frame.

Shimano's rule of thumb for the seatpost battery to Junction B is different from what I posted above, but it's pretty crazy.. something like [distance from Junction B to battery + seatpost length + seat tube length]... but yeah. Like Dannbodge says, make sure you can pull out the entire seatpost with the battery still connected to the Junction B.