Wiring

I’ve begun acquiring the Di2 parts necessary to get the system running on the bench.  I have a rim and Alfine-11 hub in hand and am waiting on a spoke order before I begin building the wheel.  I was surprised how difficult it was to find the Alfine-11 in 36 hole silver here in the states.  Jim (aka Bike Hermit) at Bike Touring News had no trouble and I had my hub within just a few days of placing the order.

Before I can complete the initial Di2 order I need to figure out the wire I’ll need.  E-Tube wire is pricey stuff so my hope is to make an accurate enough estimate of wire lengths that I can initially purchase just the four wires I need for bench testing with lengths that will work when I do the final assembly.  Note that I could (maybe) hack this together with cheaper wire but in my experience that is never a good bet.  I’ve done my share of hacking on DIY hang gliding electronics but always splurge for wire and connectors designed for the task when I can find it.  Shimano seems to have pulled out all the stops with their E-Tube connectors and wire, if that proves to be true I’m happy to pay a premium for it.

I won’t know if this is feasible until I’ve done some testing with all the pieces, but here is my current plan for the placement and wiring of the various Di2 components:

  • All wiring routed internally
  • Shifter mounted on right handlebar
  • Display mounted on front derailleur tube
  • Battery located in front boom
  • Breaks in wiring, using Di2 couplers, where the front and rear sections join the main cruciform

I used a scale cad drawing to estimate the wire lengths.  My requirements really bump up the number and length of wires required, though with the couplers I don’t come even close to exceeding the longest wire Shimano offers (1400 mm).  From what I can tell on Amazon, Shimano manufacturers E-Tube in lengths from 200 to 1400 mm, in 50 to 100 mm increments.  However Harris Cyclery seems to offer the longer lengths for quite a bit less money.

My current thinking for installing all this stuff is that the front boom will be installed first and the wires pulled through the cruciform as the boom is inserted into position.  That will keep the wiring from bunching up in the front section.  I will need to leave a little slack to allow for leg length adjustment.  Then the rear will be installed and the motor wire pulled through in similar fashion.  My biggest concern with internal routing is that the wires will rattle against the frame tubes, I’m hoping that preventing the wires from bunching up will help.

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E-Tube wires required:

  • 300 mm Battery
  • 600 mm Cruciform
  • 650 mm x3 Display, Motor, and Shifter Front
  • 950 mm x2 Motor and Shifter Rear

The shifter has it’s own pigtail integrated into it so I only need to purchase three E-Tube wires to get the system working on the bench.  However I want to test using a couple of the junction boxes inline so I’ll order the four shortest wires in the above list.

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