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Shimano Dura-Ace 7970 Di2 Internal Wire Kit

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Item # SHI0633

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Once you have your Di2 switches, be it road or time trial dual control and satellite switches, you'll need to finish the job with two Shimano Dura-Ace 7970 Di2 Internal Wire Kits -- the Shimano EW-7970 for the rear (lower) harness and SM-EW79A for the front (upper) harness. The Di2 Rear Wire Kit, EW-7970, has long enough wires to reach the derailleurs and the battery pack. It plugs into the five-pin connector below 'Junction A' on the front harness, which plugs into the shifters.

For the rear harness, there are three different harness lengths. The smallest will fit on bikes from 36cm and larger. And the largest will fit bikes up to 66cm. Shimano tells us that the Medium kit will fit most bikes -- being that there's a cable wind on 'Junction B' that is positioned below the bottom bracket where you can wrap up to 120mm of cable slack. The Medium seems to fit bikes up to 58cm in size, though that should only be taken as a rough guide.

To determine the best sized external harness for your bike, Shimano recommends measuring from the bottom of the bottom bracket shell to the back of the bottom of the head tube. Call this measurement 'B.' Then measure from that same point on the bottom of the head tube to the bottom of the handlebar next to the stem. Call this measurement 'A.' Add A and B, and subtract 30 to get X -- the size needed. The Small is 770mm long and handles measurements from 650-770mm. The Medium is 830mm long and can handle measurements from 710-830mm. The Large measures 890mm in length and can take care of measurements from 770-890mm. If you have a bike that's designed to have an internal wire through the down tube, and have the battery mounted under the bottom bracket, select the Short Cradle version. Likewise, if you're bike frame is Di2 specific and built for the wires to run completely inside the frame, select the Internal version. Both the Short Cradle and Internal harnesses will accommodate the largest frame sizes.

When you look at each kit, it seems like there are four wires. That's due to Junction B. Essentially, there's a wire from the front harness to Junction B, wires from Junction B to the front and rear derailleurs, and a wire from Junction B to the battery. In addition to the wiring harness, the kit comes with the battery bracket, six segments of Black cable cover to secure the cables to the frame, two different length screws for securing Junction B to the bottom bracket cable guide on the frame, and a cable tie which can be used to further secure the battery bracket to the frame.

The Shimano Dura-Ace 7970 Di2 Internal Wire Kit is available in the color Black and in the options for EW-7975-A2 Internal, EW-7975 Internal, and EW-7975-A1 Internal.

Tech Specs

Compatible Components:
Dura-Ace 7970 Di2
Recommended Use:
road cycling
Manufacturer Warranty:
3 years

Size chart


Di2 Reference Guide


Note: This reference is meant to be used as a guide for creating a Shimano Di2 drivetrain package. For further assistance please feel free to give us a call.


Battery and Wires:

Our Shimano Di2 packages are built for three standard configurations based on battery location and wire routing. First, you'll need to determine if your frame uses an internal or external battery mount, and whether the routing is either internal or external. Below is a guide for which battery, charger, mount, and junction boxes are required for your configuration.

Battery and Wire Configurations
 BatteryBattery ChargerBattery MountJunction AJunction B

External Battery

w/ External Routing

SM-BTR1 SM-BCR1 SM-BMR2 SM-EW90 A/B 3/5 port SM-JC40

External Battery

w/ Internal Routing

SM-BTR1 SM-BCR1 SM-BMR2 SM-EW90 A/B 3/5 port SM-JC41

Internal Battery

w/ Internal Routing

SM-BTR2 SM-BCR2   SM-EW90 A/B 3/5 port SM-JC41

Battery Mounts:

The SM-BMR2 battery mount is available in three configurations -- Long External, Short External, and Long Internal. Both Long versions are to be mounted using the bottle cage mounts, while the Short version is designed for Di2-specific frames with either a chainstay or down tube mounting location.



There are two junctions needed for completing your Di2 build -- A and B.  Junction A, SM-EW90, is located at the handlebars and available in both three- and five-port options. The three-port option is intended for standard shifting with a left and right hand shifter. If you have the intention of using Shimano's satellite sprint shifters, or a combination of time trial shifters and shifter/brake levers, the five-port junction box will be the necessary selection.

Depending on your frame specification, Junction B (SM-JC40 or SM-JC41) is located either internally or externally at the bottom bracket area. Accordingly, SM-JC41 is designed for frames with internal wire routing, while SM-JC40 is intended for external wiring options.


E-Tube Wires:

For your convenience, we've created wire packages for your Di2 build kit in the sizes Small, Medium, and Large. Below, you'll find which wire lengths are included in each kit. Additionally, we've recommended a kit size based on your frame size.

 E-Tube Wire Length Chart
Down Tube Wire 700mm 750mm 950mm
Front Derailleur Wire 300mm 350mm 400mm
Rear Derailleur Wire 500mm 550mm 600mm
Battery Wire 300mm 350mm 400mm


 E-Tube Wire Frame Size Guide
Frame Size  47-52cm 53-56cm   57+cm

Please Note:

E-Tube Wire length suggestions are an approximation. 

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Unanswered Question

I have a Ridley Excalibur size Medium,...

I have a Ridley Excalibur size Medium, what length of cables do I need?