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Technical FAQ: Installing electronic shifting on a bike without internal cable routing

Editor’s Note: Lennard Zinn’s regular column is devoted to addressing readers’ technical questions about bikes, their care and how we as riders can use them as comfortably and efficiently as possible. Readers can send brief technical questions directly to Zinn.

Dear Lennard,
With the hype of electronic shifting dying down and the reality of great performance being proven, I’ve a couple questions, which I think many others have.

1) Are framesets designated Di2 framesets also compatible for EPS?

2) For those of us who want to upgrade to electronic shifting but don’t have a frameset with internal cable routing (and can’t afford to buy a new frameset because of the purchase of Di2 or EPS) can you give a bit more insight than that offered in the blogosphere of how to adapt for the upgrade? Perhaps examples of externally routed cables as well details on how to drill holes (what tools are necessary and the such) into carbon fiber framesets to internally run cables?
— Van

Dear Van,
The answer to question No. 1 is yes. Campagnolo followed the published Shimano frame specifications for Di2 wire holes, which is 8mm by 7mm on the frame holes. The hole between the water-bottle bosses for the battery wire is 14mm by 7.7mm.

Original Dura-Ace 7970 Di2 has four-conductor wires with large, waterproof connectors at the derailleurs, shifters and Junction A (the junction box at the front with the two indicator LEDs on it). Ultegra 6770 Di2, on the other hand, has two-conductor wires with small connectors on both ends. The size of EPS connectors is halfway between the two Shimano connector sizes.

The fat end of a Dura-Ace 7970 Di2 wire is 9mm and won’t go through the 8mm by 7mm specified holes, but the thin end is 6.5mm, and it will. The fat end doesn’t need to go through the frame holes, as the fat connections are only for derailleurs, shifters and Junction A. The thin end slides in through the frame holes and goes to Junction B at the bottom bracket.

On Dura-Ace 7970 Di2, these thin connections are not waterproof and require heat-shrink tubing to seal them. The fat, waterproof connections require a tool (the Shimano TL-EW01) to plug and unplug them, but the thin, non-waterproof connections can be pushed together and pulled apart by hand.

Ultegra 6770 Di2 wires are universal and can plug into anything — derailleurs, shifters or junction boxes. They come in a vast array of lengths, as they can be used anywhere in the system. Their connections are only 5mm in diameter and are waterproof without heat-shrink tubing required. All of these connections require a different tool from the Dura-Ace one (the Shimano TL-EW02) to plug and unplug them.

EPS wires have 6mm-diameter waterproof connections. They also require a special tool (the Campagnolo UT-CG020EPS) to plug and unplug them. The wires are hard-wired into the Power Unit housing the battery as well as the system’s “brain,” which converts analog signals into digital ones. For huge frames or other special applications, Campagnolo offers extension cords with connectors on both ends.

EPS grommet kits are designed to fit in the same holes as Di2. Frame manufacturers using non-standard holes generally supply their own grommets for electric wires with the frame.

The water-bottle battery mounts for Di2 and EPS both work on frames designed for a Di2 battery. The same goes if a frame has a secondary pair of threaded holes atop the down tube below the bottle bosses or under the down tube by the bottom bracket.

The only time you might run into problems with compatibility with EPS is if you have a frame made for internal wiring with a seatpost battery.

An aftermarket seatpost battery (or a standard battery housed in a seat bag under the saddle with a wire running down through the seatpost clamp) is only possible with Di2, not with EPS. That’s because the Shimano battery is just a battery, whereas the EPS Power Unit houses a battery with a complex circuit board, as well as an LED diagnostic indicator and ports for computer wires and for a shutoff magnet.

Shimano can separate its battery, because its “brains” are in each derailleur, and the thing inside the battery case is a power supply only. With the EPS system, the “brain” translating on-off analog commands into digital ones to be sent to various parts of the system is in the circuit board inside the Power Unit, and those parts are inseparable.

So a frame built for a seatpost battery will not have a hole for wires coming from the EPS Power Unit — be it in the standard down tube location(s) or in the seat tube or somewhere else down near the bottom bracket where you could mount the Power Unit.

In answer to question No. 2, you have to get Di2 if your frame does not have internal routing; there is as yet no Campagnolo EPS external-wire kit.

Furthermore, I cannot imagine a frame manufacturer’s warranty that you would not be voiding by drilling holes in your frame. If you choose to do it anyway, Shimano does make round 7mm grommets, so you could use a standard 7mm drill bit for metal; it would drill through carbon without problems. I hope you know what you’re doing if you attempt this, because drilling in some spots would certainly compromise frame longevity.

For Shimano external wiring, you simply run the Di2 wires along the outside of the frame and lightly tape them in place initially. You mount Junction B with a screw into the threaded hole under the bottom bracket shell for the shift cable guide.

Junction B for external wiring has pins sticking up that allow you to wrap extra wire; it will take up 120mm of wire slack from the various wires. You secure the wires with adhesive wire cover strips; clean the frame with rubbing alcohol where the adhesive will go.

Semi-external routing is just as I have described with the long wire running inside the down tube. There is a hole drilled up near the head tube and one down near the bottom bracket shell for it, and you seal them with grommets.

If you were to drill enough holes in your frame for fully internal routing (on the down tube near the head tube, on the down tube near the battery, on the seat tube near the front derailleur, and on the right chainstay near the rear derailleur), you need to make sure that your holes from the bottom bracket shell into the down tube and right chainstay are large enough — and, in the case of the chainstay hole, are located properly — or you still wouldn’t be able to do the internal wire routing.

The wires from the battery, derailleurs and Junction A all come out of the bottom bracket, where you plug them into Junction B. You then shove the entire rat’s nest (Junction B and all of the wires emanating from it) up into the down tube. So that hole must be at least 16mm in diameter, and even a 16mm hole requires a lot of tight bending of the wires to jam them and Junction B up through it; I think it should be a lot bigger yet.

The hole into the chainstay must be at least 12mm in diameter, and its inboard edge must be at least 16.5mm from the right end of the bottom bracket shell, so that when you screw in the bottom bracket cup (or press in the bearing into the shell), you don’t impinge upon (and cut) the wire.

The hole up into the seat tube must be large as well for easy access and for allowing the wire from Junction B to the front derailleur to go from the down tube hole into the seat tube hole without being cut by the hole edges when the plastic sleeve for the bottom bracket is pressing up against it.

So, while it is certainly more aesthetic to use internal wires, your frame warranty will not be void and you will endure a lot less hassle if you simply buy a Di2 kit for external wiring and route the wires externally. If you later buy another frame with holes for internal wiring, you can get a new wiring harness at that time and transfer your Di2 system over to the new frame.