Choosing a Road Bike Frame for Shimano Di2

Posted at: Nov 2, 2021

Shimano's Di2 electric shifter is attractive for its lightweight parts and reliable shifting.In order to convert to Di2, not only do you need to purchase Di2 parts, but also your road bike frame needs to be Di2 compatible.

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It is best to buy a Di2 compatible frame

The best way to be sure is to buy a frame that is Di2 compatible; Di2 compatible frames will say “Di2 compatible” in the specs of the bike.

Di2-compatible frames are designed with Di2-compatible wire routing, such as a special hole for the electric wire to go to the front derailleur.

When you buy a used frame with the complete car disassembled, it may be difficult to confirm whether it is Di2 compatible or not (e.g., there is no manufacturer’s spec list), but in that case, it is best to choose a frame that was equipped with Di2 as a complete car.

How to check if your current frame is compatible with Di2 (interior type frame)

Is there a hole from the handlebar into the frame?

When installing Di2 on an interior frame, the junction B unit will be installed inside the down tube, so the electric wire from junction A under the handlebars must be routed inside the frame.

In the case of internal frames, the outer wire is usually designed to pass through the downtube even if it is mechanical, so there is no problem.

Is the BB area penetrated?

In order to connect the battery, derailleur, and junction unit with electric wires inside the frame, the down tube, BB, and chainstay must be penetrated. In many cases, the BB area is penetrated in internal frames, but just to be sure, remove the BB once and check how it is structured.

It is important to note that this is the case for road bikes with aluminum or chromoly frames. If the BB shell is tubular and there is no route to the down tube and chain stays, you will have to either modify the frame to force the electric wire through, or give up on the interior and use the exterior type.

Is there a routing for the wires from the battery?

Di2 is an electric shifter, so it needs a power source (battery).

There are two types of batteries for Di2.

  1. interior type that is installed in the seat post
  2. exterior type installed on the down tube

If you have an interior type frame, you will most likely use a battery that fits into the seat post.

Exterior Di2 battery (top) and interior SiDi2 top post battery (bottom)

If you are using an internal battery, check the length and thickness beforehand, as there are some cases where the battery cannot be inserted depending on the diameter of the seat post and the length and shape of the seat tube. In some frames, the bottle cage hole in the seat tube may interfere with the battery and prevent it from fitting.

If you want to use an exterior battery with an interior frame, find a way to connect the electric wire from the exterior battery to the interior junction B.

In order to use an external battery, either of the following conditions is required

  1. the pitch of the dowel holes in the bottle cage is too narrow
  2. there is a hole for the electric wire to pass through the frame

For Di2 compatible frames, special holes and mounting bolts may be available under the chainstays.

Is there a hole to connect the front derailleur?

In most of the interior type frames, the outer wire that comes through the down tube goes directly under the BB to the rear derailleur, so the routing for the rear derailleur is usually not a problem even if you have Di2.

On the other hand, the routing for the front derailleur of an interior frame is the same as that of a mechanical one, where the wire is passed up from the wire guide under the BB, but only the inner wire, not the outer wire, passes through here in most cases. This route does not allow the electric wire of Di2 to pass through.

Therefore, with the interior Di2, the electric wire needs to go outside the frame to connect the junction B inside the down tube to the front derailleur outside.

If your frame is Di2 compatible, there is a special hole in the seat tube. (If the mechanical type is standard, it is filled with rubber gaskets.

Hole for front derailleur of Di2 compatible interior type frame (blocked by rubber gasket)

If there is no hole to connect to the outside, you will need to modify the frame to get the electric wire out.

How to check if your current frame is compatible with Di2 (exterior type)

Di2 is available for exterior type frames, so even full exterior type frames can be converted to Di2.

Di2 compatible with both interior and exterior systems

In the case of full exterior Di2 conversion, Junction B is the key.

External junction B uses the wire guide mounting hole under the BB, but if the hole is just a hole or the mounting position is special depending on the frame, junction B cannot be mounted and Di2 conversion is not possible.

Di2 exterior type junction B unit

Other than that, there are no special restrictions for the exterior type, as the electric wire runs outside, but the BB area tends to get cluttered with wires, so it is necessary to route the wires well or use bands to bundle them up.

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