Shimano Di2 – the dark side of the metrics

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Cervelo S3 di2Shimano Adamo ASM Shimano

This is a short article highlighting some of the wonderful things you can do with Di2.

I’m describing what I can do with a 2017 Ultegra R8050 derailleurs and DuraAce R9150 shifters which ARE more capable in the breadth of functionality they support than earlier models.

Apologies in advance if you already have Di2 and I give you false hope of newly supported functionality for your existing (old) hardware 🙁 If, however, you are considering Di2 for a new bike or even a less-likely upgrade then here are some of the things you might want to check that a) you want, and b) your ‘new’ Di2 system will be able to do.

Head Unit Display Metrics for Di2

You know how to choose data fields, you’ve done it before many times. You are a data field guru.

Except now you are now faced with more to choose from.

Shimano Di2 Edge 820 GarminThese are the choices:

  • Di2 Battery Level, Gear Battery
  • Di2 Shift Mode
  • Gear Combo (Front Gear, Rear Gear), Gear Ratio, Gears

So that’s all cool enough. As you can see, you can even display a pictorial representation of the cog you are in to save you looking down and back to check (Gears data field).

Di2 Internal Configuration

A simple lever and a piece of tensioned wire used to be enough in the good old days. Who would have thought there was much that could be configured with a simple gear change?

Well, there is.

  • Shift Mode (synchronised/semi-synchronised)
  • Gear shift speed (faster speeds seem to work better)
  • Max gear shifts per press (I can’t see why this shouldn’t be unlimited)

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If you think about it, on those occasions where you are selecting a gear by moving both derailleurs it might be possible to have the exact same gear ratio in each of the front rings. However, that clearly depends on which front rings and rear cassettes that you have. So to automate changing around that point you have to tell Di2 what rings and cassettes you have.  Hence you use the app, as shown above!

One day soon, no doubt, you will be able to have a fully automatic bike that also considers your power and cadence before auto-selecting. I reckon that’s a gadget too far but who am I to stop the march of progress?

For those of you who inadvertently shorten the life of your chains by twisting it as much as you can between small-front and large-rear gears; Di2 can also be programmed to stop those gear choices.

Switch A External Configuration

Switch A is the button on top of some of the newer shifters. An action on your head set can be assigned to: a single press; a double press and/or a press-and-hold.

On all older shifters, you probably have the ability to swap the ‘change up’ or ‘change down’ functionality over from one lever to the other ie from Switch X to Switch Y – it seemed more sensible to me to have the bigger lever, Switch Y, to move to the bigger cog. No doubt I will come to regret that choice in the future when I borrow someone else’s bike :-(.

The Shimano app, sort-of, implies you can configure SWITCH A in the app. But you can’t, so don’t try to look for that option. In the Shimano app, all you are doing is assigning a communications channel to the switch – as shown below this is the D-FLY Channel 2. There are 4 channels.

Shimano Di2 Config
Shifter Buttons/Levers


The meaning of what happens when you press the top button (switch A) is handled on the head unit. Thus there will be variation between head units. Here are some of the options you get with the Garmin Edge 820, which is probably at least broadly on par with the capabilities in the Edge 1000/1030.

Just like with your mouse/tablet there is more than one kind of click that the SWITCH A will react to. Hopefully, this slideshow will give you an indication of where to find the options to configure what happens with SWITCH A and some of the MANY options you have, at least with a half-decent Garmin.

You can configure all these actions: Next Page; Previous Page; Record Lap; Start and Stop Timer; Start Timer; Stop Timer; Turn Backlight On; Show Map; Show Compass; Show Elevation Profile; Show Lap Summary; and Show Virtual Partner. I can certainly see several scenarios where I would find those useful, had I already preconfigured the right one 🙂 Still, it’s all very clever.


One Final Consideration

You will need to program in the exact chainrings you are using. I’m not entirely clear if you need to do this in one place (the app) or in two places (also the head unit). Once you have correctly done this then your FIT file will record ALL your gear changes and you can then spend hours analyzing it on Clever stuff but not that interesting for any more than 30 minutes.

Finally, keep an eye out for these boxes near to Christmas. If you see one, you’ll know that Sants is being very kind and that you have been on the ‘nice’ list all year. Well done.

Shimano Di2





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So, that’s like 3 (single, double, hold) x 2 (left, right) = 6 separate functions that can be controlled using button A on both sides?


Does anyone know if using a Garmin 1000 with Di2 components will shorten battery levels more than without the Garmin connected via bluetooth?