rear cable is external routed, there is no path through chainstay unfortunately so I thought easiest route is just straight through BB at the base and run wire upto FD and along chainstay to rear, gonna clean it up with some metal backed tape, or even the DI2 SM-EWC1 cable tidy. hole from seat tube into the BB is 8mm so im sure i can fit 2 wires through. just keep concerning myself with removing material from bb im sure it will be absolutely fine