Effectively yes, internalizing the wires may not fully be possible. There is also a BB junction box that is nice to store inside the frame as well. The BB shell is one of the contentions, both allowing wires to be run, but also to push the junction box into one of them without interfering with the BB spindle, etc. That being said, it is always possible to run the wiring and junction externally. Shimano sells a kit that runs the cables externally. It may not look great, but would be functional.

thanks for the info. I think I'll just stick with my SRAM 1X instead of running cables externally.

Keep in mind that in 2010 Di2 wire end plugs were significantly larger. Many of these internal Gen 1 Di2 wires were also a one-way fit because one end of the wire used an even larger plug. Gen 2 Di2 all use E-Tube wiring which have identical ends across all wire lengths and all components connect using the same wires. The small junctions (Junction B) can fit into many tight areas such as bottom bracket shells and even some handlebars. The only challenges are locating the larger junction (Junction A) which comes in 3 and 5 port variants (there is also a road bike variant with two connection leads) and picking an internal or external battery. You need the junction box located where you can use the trim and also plug in the charger (internal battery must use 3/5 port junction for charging).

Anyway, I wouldn't write off the Ultegra Di2 option until you check the frame for routing options. You just need to be able to fit e-tube ends out the seattube for FD, out the chainstay for RD and have a means of running one wire from the bars into toptube or downtube. I believe the e-tube plugs are 5mm diameter and the wires are slightly less than 3mm diamter.

If your shift cables are already internal you should be fine with DI2 Gen2, but the issue most likely would be around the BB area holes needed to lead the fr and rear derailleur and like the other person said, room for the junction box and battery.

Why not do ETap?

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2020 National Masters Champion - M40-44 - 400m IM
Canadian Record Holder 35-39M & 40-44M - 200 m Butterfly (LCM)

With the right tools ( like drill bits or Dremel cutting bits) you can open up cable holes and run cables internally. We did that with my old stock CR901. One hole in the top tube, and opened up the hole quite a bit under the BB. Then we went external for a short run to the Battery (water bottle mount on seat tube) - but this is not really visible. Unless you are looking in that area.


I have the LED display mode button thingy attached to the top tube with a bit of velcro. The bars I benched and opened holes so it's all integrated. I have the Old (a used) Dura Ace DI2 with pretty big plugs! But works nice after repairing the trunk cable. Not a single issue since building it.


Just took a shot of the bike last night you can see the install here:
https://twitter.com/Jagersport_com/status/739262875018006528

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