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Technical FAQ: Di2 Synchro Shift and Garmin connection

Lennard Zinn provides detailed instructions on pairing Di2 Synchro Shift and a Garmin cycling computer.

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Dear Lennard,
I have a cervical fusion, and, in order to keep riding, I have to sit very upright on the bike and can’t tip my head forward. I can’t look back to see what gear I am on and I’m constantly cross-chaining, since I rarely know what gear I’m in. Is there any way to get around this issue? I’d also like to be able to see what gear I’m in. I ride with a Garmin, and I understand there is a way I can see what gear I’m in on it, but I’ve never seen that on any of my data fields.

I have Ultegra Di2 (I’ve ridden two seasons on it) with a compact crank, a GS long-cage rear derailleur, and an 11-36 cassette (I used to have a Lindarets Road Link, but on your suggestion, I took it off, and it still works fine with the 36T cog).
— Neal

Dear Neal,
There sure is! With Shimano Di2 Synchro Shift, you could just shift with one shifter (your right one, unless you were to reconfigure which lever controls which derailleur), and it would perform not only rear shifts, but also front shifts, when appropriate, and it would prevent cross-chaining. And, yes, you can display on your Garmin what gear you’re in, as well as your Di2 battery level and which shift mode you’re in. You would need to get a new battery and a Shimano “D-Fly” Bluetooth transceiver for Di2. [related title=”More Tech FAQ” align=”right” tag=”Technical-FAQ”]

The following are some instructions for using Synchro Shift and connecting a Garmin that I wrote for the chapter on electronic shifting in the sixth edition of “Zinn & the Art of Mountain Bike Maintenance,” which will be out December 16 but can be pre-ordered now.

I am quite certain that this is the most complete set of instructions available anywhere for connecting Di2 with Bluetooth and enabling Synchro Shift. The instructions are for mountain bikes, but the only difference in this case is that road bikes do not have a digital display and instead only have an upper junction box, aka, Junction A. Even though you can hook up a digital display to your road Di2 (and you can eliminate the D-Fly if you get a Bluetooth-enabled digital display) your Garmin will display everything that the digital display would, and more clearly.

Note that S2 shifting mode is the one you want, once you get your Di2 system paired via Bluetooth. S2, or full Synchro, only requires shift inputs from one shift lever, as mountain-bike Di2 systems have offered since their inception. (S1 is Semi Synchro, where every front shift is accompanied by a double shift in the rear, and M, or manual, where the right lever only controls the rear derailleur, and the left lever only controls the front derailleur.)

In S2 mode for road, as Shimano has programmed it (which you can reconfigure in the E-Tube Project app), it will shift down from the big-front-chainring/smallest-rear-cog combination through each successively larger rear cog until it gets to the second-largest rear cog. Then, when you ask for yet another lower gear with the shift button on the right lever, it will shift to the inner chainring and will concurrently do a double-shift in the rear back to the fourth-largest rear cog. Continuing to ask for lower gears will then take through those biggest cogs until you end up on the small-chainring/largest-cog combination, your lowest gear.

When you go back the other direction and ask it for progressively higher gears, it will go to smaller and smaller cogs until it gets to a few from the smallest. Then it will shift the chain up from the inner chainring to the big chainring, and, concurrently, it will shift in the rear back two cogs larger.

Hardware required for wired and wireless connectivity

Until 2016, downloading Di2 firmware, reconfiguring shifting, or performing diagnostic checks of the system all required a wired connection to a Windows PC (and not to a Mac; those remain unsupported). Now, however, Shimano’s wireless E-Tube Project app (free on the App Store or on Google Play) for iPhones, Android phones, and tablet computers affords much of the same functionality. The smartphone app allows customizing shifting and updating firmware; the tablet app offers those functions and can also check for system errors and perform the system pre-set. Furthermore, the Di2 system can interact with many Garmin and other ANT/ANT+ cycling computers, displaying battery level and current gear combination, as well as offering switching between shifting modes.

Thing is, you must have all of the appropriate hardware to get wireless connectivity. Fortunately, other than the first two generations of road Di2, all Shimano Di2 systems are backward-compatible, so you can upgrade some items to get this functionality while still using your existing shifters and derailleurs. Furthermore, all XT Di2 components are interchangeable with XTR Di2 ones.

To enable Bluetooth and ANT+ compatibility, the battery must be either the BT-DN110 (cylindrical, for installation inside of a seatpost, steering tube, or Shimano battery case — or the BT-DN100 original-shape external battery; the older versions of these batteries (SM-BTR2 and SM-BTR1) have insufficient memory for Bluetooth connectivity. You also need a transceiver in the system; this can be either a digital display with a Bluetooth chip, namely the XTR SC-M9051 (not the SC-M9050) or the XT SC-MT800, or a “D-Fly” inline unit — either the EW-WU101 (both ports on the same end) or the EW-WU111 (one port on either end). With a D-Fly inline transceiver, you also need an additional short e-tube wire.

If you want to update, check, or reconfigure your Di2 system and don’t want the expense or trouble of obtaining wireless connectivity, you can download the E-Tube Project software from and plug a Windows computer into your bike’s Di2 system with Shimano’s SM-PCE1 PC interface device and accompanying USB cable. It plugs right into the charging port on Junction A or on the digital display. You can then update firmware, diagnose and correct problems in the system, and customize shifting options on your computer screen. Without the interface device, you can still do firmware updates using the E-Tube Project software by plugging into your Junction A charger port with your USB charger connected to a Windows PC.

ANT+ connection with a cycling computer

What’s possible in communication between cycling computers and Di2 is rapidly changing. As of 2017, there are two levels of compatibility with Di2: either just displaying battery level and current gear combination on the computer, or displaying Synchronized Shift setting (in addition to battery percentage and gearing).

The instructions below apply to connecting popular Garmin computers to Di2; other Di2-enabled ANT+ computers have similar features. Garmin models going back a few years and at many price points, like the Edge 510, 810, 520, 820, and 1000, the Forerunner 735, 920, and 935, and the Fenix 5, can all display Di2 shifting status and battery percentage. Garmins that also support Shimano’s Di2 Synchronized Shift capability are limited as of this writing to the more recent Edge 520, 820, and 1000 models. Note that Di2 connectivity is not supported on older Garmin models without updated Garmin firmware.

Setting up Di2 display on Garmin:
1. Select the icon of a crossed wrench and screwdriver on the home screen. The settings menu will appear. On some (older) models, you can also access settings from any training page by touching the screen; an overlay will come up with the settings icon, as well as the home, left and right scroll, navigation search, and wireless connection icons on it To select a Garmin icon, touch it on the screen.

2. Go to the ANT+ sensor list from the settings menu. Depending on computer model, either select: (a) “Bike Profiles” and select a bike stored in memory, or (b) select “Sensors.” Alternatively, on some (older) models, if you brought up the overlay on a training page instead of initially going to the home screen, get to the “Bike Sensors” list by selecting the wireless-connection icon (it looks like a dot broadcasting to the left and right). On some (newer) models, you can directly access the sensor list from any page by pulling down with your finger from the top of the screen; it pulls down a curtain with backlight and connection options; select “Connecting to Sensors.”

3. Select “Di2” on the sensors list. If “Di2” is not one of the icons displayed, then your Garmin firmware is too old. Download “Garmin Express” online and create a login; from there, update your firmware. With updated Garmin firmware, return to step 1.

4. Select “Enable” on the “Shimano Di2” screen.

5. Select “Search” or “Connect.” Once connected, it will display, “Shimano Di2 found.” In order that the Garmin can find your Di2 system, unplug and re-plug in both wires to the D-Fly transceiver or all three wires to the digital display. If it doesn’t connect, push the mode button for about a second on your digital Di2 handlebar display until a flashing “c” appears, or Junction A until the two LEDs flash red and green. If the “c” doesn’t appear on your SC-M9051 or SC-MT800 digital display (i.e., if it passes on to adjustment mode or post-crash re-coupling mode), you must first update your SC-M9051’s or SC-MT800’s firmware with a wired connection to a PC (many of these units were shipped with the Bluetooth chip but without the firmware to make it work). If it still doesn’t find Di2, restart the Garmin and try pairing it again. Once the Garmin is paired with Di2, continue with step 6 to create a screen on which to view the Di2 functions while riding.

6. Select the settings icon. It’s the wrench/screwdriver icon. Again, find it by: a) returning to the home page, or, b) pulling up the overlay on a training page.

7. Select “Activity Profiles.”

8. Select one of the profiles.

9. Select “Training Pages” or “Data Screens.”

10. Select a page that is currently shown as “Off.”

11. Select “Enable” or “Enabled.” This turns the page on.

12. Increase, decrease, or maintain the number of fields on the page. Select “+” or “-” to change the number of fields, then select the check mark in the lower right corner. To leave the number of fields unchanged, simply touch the check mark.

13. Change fields to display Di2 information. Touch any field to open the “Select a (Data Field) Category” page, scroll (using the arrows) to “Gears” and select it; this will bring up options like “Di2 Battery Level,” “Front Gear,” “Gear Ratio,” “Gears,” and “Rear Gear,” and, with newer models, “Di2 Shift Mode,” “Gear Battery,” and “Gear Combo” will also appear. Fill as many fields as you want with Di2 fields. I recommend having at least two fields, namely “Gears,” which shows graphically which front and rear gears the chain is on, and one displaying battery percentage. With newer Garmins, also create a “Di2 Shift Mode” field to show whether you are in M (Manual), S1 or S2 (pre-programmed Synchro Shift modes), or in a custom Synchro Shift mode (which you create with your smartphone or tablet in the E-Tube Project app or on a Windows PC connected via the SM-PCE1 interface device).

14. Select the check mark at the bottom of the Garmin screen. You’re done. You now have a screen you can loop to when riding that shows what’s going on with your Di2 system. If (when) your Garmin doesn’t find your Di2 system when you turn it on to head out for a ride, you will have to go through steps 1-5 to pair them.

Using the E-Tube Project wireless app

As with ANT+ cycling computers, you’ll need either a Bluetooth-enabled digital display, or a D-Fly inline unit (either an EW-WU101 or EW-WU111) wired into your system.

1. Download E-Tube Project and open it. Find it for smartphones and tablets on iTunes or Google Play.

2. Select the Bluetooth LE connection box and push the Di2 mode button on the bike’s digital display or Junction A. Push the mode button for perhaps a second — not long enough to bring up adjustment mode. A flashing “c” should appear on your digital Di2 handlebar display, or the two LEDs on Junction A will alternate flashing green and red. If the “c” doesn’t appear on your SC-M9051 or SC-MT800 digital display (i.e., if it passes on to adjustment mode — see 6-8 — or post-crash re-coupling mode — see 6-9c), you must first update your SC-M9051’s or SC-MT800’s firmware with a wired connection to a PC (many of these units were shipped with the Bluetooth chip but without the firmware to make it work). Once the connection is made, a box with the part number of your Di2 transceiver will pop up on the phone or tablet screen; select it.

3. Update the firmware of your Di2 transceiver. This will start automatically. During the process, it will ask you to change the default “000000” ID code of your Di2 transceiver; go ahead and do this. It requests “half-width alphanumeric characters,” whatever those are; just pick another 6-digit number. At some point, the firmware update will stop before it’s complete and will give you an error message. Don’t worry; it’s not you. It’s also possible that you will be able to connect this time, and you won’t get the error message until you try to connect the next time. In that case, you won’t have to do the following step until you log onto the app next time. BTW, the tutorial on the app is not a video, with the short green bar showing how far it has (not) loaded; rather scroll to the right to view it page by page.

4. Delete your Di2 transceiver on your tablet or smartphone. Yes, really. If you don’t do this, the app will try to connect to your Di2 transceiver with the old, “000000” password and will display a spinning wheel of death without connecting. So, select “Bluetooth” in your phone or tablet settings menu. Your Di2 transceiver’s part number should appear on the list of your devices; click on its information box and select “Forget This Device.”

5. Select the Bluetooth LE connection box in the app. It will display a box with the part number of your Di2 transceiver; select that for the app to connect to. Now you should be connected again, with your new password.

6. Update firmware for all components. Ones that are up to date will be grayed out and will say “latest.”

7. Play as you wish. Now you can customize which shift buttons do what and which Synchro Shift protocols you can toggle between and how and at what points the derailleurs perform double shifts.

8. Disconnect the app. This is THE MOST IMPORTANT STEP, and it’s not obvious in the app. Click on the little three bars in the upper right of the phone screen to bring up the main menu, and select “Bluetooth Disconnected.” Right? It should say, “Disconnect Bluetooth” or words to that effect, but it doesn’t. This will disconnect your phone or tablet and save whatever changes you have made during your session.  But if you don’t do this, your Di2 components will continue to either be connected or to continue trying to connect to your phone or tablet. The symptom will be that the derailleurs will not respond to the shift buttons, and the charger will flash a fault light when plugged in; meanwhile, the Di2 battery will drain rapidly (the Bluetooth LE connection draws a lot of power), while not being able to be charged.

NOTE: A similar possibility for neglecting the most important step (saving changes and disconnecting) exists with the wired PC connection to E-Tube Project. In the main menu, the last rectangular option box was always “Complete Setup” in years past. But now with the advent of the wireless connectivity, an additional “Bluetooth LE” option box has appeared in the column; this has pushed the “Complete Setup” box to the next page, and you have to know to scroll to it. Now you know.

On a system without a digital display, once the firmware is updated so that the bike’s Di2 system is fully Bluetooth-enabled, it is Synchro-Shift enabled as well. Junction A not only controls which shifting mode the bike is in (with double-clicks of the mode button), but it also now displays it.

When you hold down a shift button (or a pair of them) to display the battery charge status, the battery LED first shows the battery status (see 6-1c), and then both LEDs show the shifting mode. If the battery LED glows green and the “+-” LED glows red, with neither of them flashing, the bike is in Manual shift mode. Two blinks of these green and red LEDs means S1 shift mode is operational, and 3 green/red blinks means the bike is in S2 shifting mode.

A paired ANT+ cycling computer that is recent enough to support Synchro Shift will also display the shift mode. And, in the phone/tablet app or in the wired PC software, you can put custom shifting patterns of your design into those S1 and S2 slots.

I hope you’re able to get this all set up. You would then not only be able to see what gear you’re in while you’re riding, but, as long as you only shift with the one shifter, you would avoid cross chaining, even without the Garmin on your bike to see what gear you’re in. All you do is simply ask it for an easier gear or a harder gear by pushing the downshift or upshift button on your right lever; it will do the rest.
― Lennard

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