Synchronized Shifting - the complete guide
When Shimano introduced the Dura-Ace R9150 series in 2016 they also released Synchro Shift. Then, a few months later, they made Synchronized Shifting available for Ultegra 6800 and Dura-Ace 9000 users as well.
At the time of writing Synchronized Shift is available on all 11 speed Di2 series. That includes MTB and GRX groupsets.
If you want to skip ahead, use these links:
- What is Synchronized Shift
- Synchronized Shifting requirements
- Change shift mode
- Set up Synchronized Shift using E-Tube Project for Windows
- Using the E-Tube mobile app to set up Synchronized Shift
- What to do when your cassette / chainrings are not listed
- Synchro Shift with FD-6870 / FD-9070
What is Synchronized Shift
Di2 Synchronized Shift is Shimano’s name for their automatic shift modes. Yep.. modes. There isn’t just one Synchro Shift, but actually two distinct modes, Full Synchronized Shift and Semi Synchronized Shift.
According to Shimano; “(full) Synchronized Shift is a function that automatically shifts the front derailleur when the rear derailleur is shifted, allowing the derailleurs to work together efficiently.”
When the other mode - Semi Synchro Shift - is selected, the bike will shift the rear derailleur automatically when you shift the front derailleur. In this mode the bike compensates for the front shift by moving the rear derailleur one or two gears.
Of course you can also decide not to use the Synchro modes at all. That is referred to as Manual mode - because, as you might have guessed, you’ll be shifting everything manually.
Let’s briefly run through each Synchro mode.
Synchro Shift (S2)
So, knowing that (full) Synchronized Shift automatically shifts the front derailleur, how does that work exactly?
Some people think the bike keeps track of your speed and cadence and automatically shifts for you. Others think there is some other kind of intelligence at play.
This would be amazing, but Synchro Shift is not that clever. It just automatically shifts the front derailleur when the rear derailleur reaches certain predefined gears. These shift points can be set and fully customized by the user as we’ll discuss below.
When shifting from 11T towards 28T the system will automatically shift from the big ring to the small ring between 25T and 21T
You can still shift the front derailleur manually any time you like, of course. Note that when you shift the front derailleur yourself it will not shift the rear derailleur to compensate.
Semi Synchro Shift (S1)
When your bike is set to Semi Synchro that means it’ll automatically shift the rear derailleur to compensate for any front derailleur shift. This will reduce or even eliminate big jumps in gear ratios when shifting the front derailleur.
It won’t shift the front derailleur automatically, but some people actually prefer Semi Synchro. Personally I went back and forth between full and semi synchro, then used semi exclusively for about six months and then finally settled on Full Synchro Shift.
Switching modes is easy though, so just experiment and see what’s right for you.
(more on switching modes right here)
Manual Mode (M)
I know I said there are two synchro modes,but technically this is not a synchro mode at all. In manual mode the bike doesn’t shift for you at all. It is all about full manual control, just like you’re used to.
Synchronized Shifting requirements
Sounds interesting? It’s very likely that your bike supports Synchronized Shifting - all 11 and 12 speed Di2 groupsets do. All you need is the BT-DN110 internal battery or the BM-DN100 external battery mount.
Synchro shift will work on these Di2 series:
- GRX RX815
Mountain bikes have been able to run synchronized shifting for a while now. The requirements are slightly different.
Change Shift Mode
Reading all of the above, chances are pretty good that your bike can do synchro shifts. On Ultegra R8050, Dura-Ace R9150, GRX and newer this will be set up for you out of the box. The older series Di2 may require a firmware update first.
So how do you actually perform synchro shifts?
Simple - you switch your bike to the shift mode you like and then just shift. That’s it.
How? By double pressing the button on your Junction A. Doing so will cycle through the three shift modes. The default mode configuration is as follows:
- Mode M - Full manual shifting
- Mode S1 - Semi Synchro shift
- Mode S2 - Full Synchro shift
I say default configuration because these S1 and S2 modes are fully customisable. You can set them up any way you see fit.
You could for example set both shift modes to full synchro, but have the automatic shift points differ for each mode. Or set both modes to semi synchro, or mix things up a bit.
What shift mode are you in?
Let’s go back to that button. Knowing that double pressing the Junction A button will change selected shift mode, how can you tell what mode you’re in?
The LEDs on your A Junction will tell you. They light up different depending on the selected mode.
- Solid red/green lights: manual shift mode
- Twice blinking red/green lights: shift mode 1 (default: semi-synchronized shift)
- Three-times blinking red/green lights: shift mode 2 (default: synchronized shift)
Set up Synchro Shift using E-Tube Project for Windows
Once connected click the Synchronized Shift button under Gear Shifting on the Customize tab.
You’ll now see the basic setup screen where you can change:
- FC: The installed Front Chain rings
- CS: The installed cassette
- Synchronized Shift Interval: How quickly synchro shifts happen
- Gear Position Control: whether or not Gear Position Control is enabled.
Click Next and you’ll be shown the shift mode setup screen.
On this page you can set up both Shift mode 1 and Shift mode 2.
Directly behind the S1 and S2 labels you’ll see the current setting for that mode. In the image below S1 is set to Semi-synchronized shift and S2 is set to Synchronized shift. You can change these simply by selecting the preferred mode from the list.
I’ll leave these to the defaults to avoid confusing new users, but feel free to play around with it to see what happens.
Customise Semi-synchronized shift
Configuring Semi Synchronized shift isn’t hard, you just need to know what it is you’re changing. You can change two values: Rear up on front down and Rear down on front up.
These do exactly what they say they do.. they change the amount of gears the rear derailleur shifts up/down when you shift the front derailleur up/down.
Shifting up means shifting to a harder gear, while shifting down refers to an easier gear.
You can use this to compensate for front derailleur shifts, basically making the jump in gear ratio smaller.
Set up (full) Synchronized shift
The (full) Synchronized Shift settings may look a bit more intimidating, but they’re fairly straightforward as well.All you do is drag the white boxes to your desired position.
If this seems a bit cryptic, don’t worry. Let’s walk through changing the upshift. On my bike that means shifting from the 39T to the 53T.
Starting at the 28T at the top left, follow the green line all the way to the right, to the white box (gear ratio 3.0.0 or 39Tx13T). When you shift the rear derailleur one more time it’ll move to the 19T and also shift the front derailleur. The resulting gear is 53Tx19T, with a gear ratio of 2.79.
If you follow the gear ratios closely you can see that, as you shift up, you move through the following gear ratios:
2.29 (17T), 2.60 (15T), 2.79 (14T), 3.00 (13T) and then back to 2.79T (19T). This last step means that the bike shifts to an easier gear, even though you have been shifting to harder gears for a while.
Let’s change that now.
Doing so isn’t hard, you simply drag the lower white box to the preferred gear / gear ratio. In this example I’m setting it up to shift from gear ratios 2.79 to 3.00 and then to 3.12.
Of course you could also select gear ratio 3.53, that’s up to you. Personally I like the jump in gear ratio to be relatively small when shifting up, but this is highly personal.
When setting up the downshifts you basically repeat the above process, but this time follow the blue line from the lower right to the top left.
This bike is set to a bit of an extreme downshift. When in the big ring it’ll shift all the way to the last gear, the 28T. It’ll then shift the front derailleur to the little ring and the rear derailleur to 25T. This is pretty severe cross-chaining, so let’s fix that.
I’ll set it up to shift the front derailleur when the rear derailleur reaches the 21T, or the fourth gear from the bottom. The most sensible gear to shift to seems to be the 17T, resulting in a shift from gear ratio 2.52 to 2.29.
In this scenario you’re shifting to an easier gear and you’re most likely climbing - or having a hard time at least. You could therefore also decide to jump to the next gear instead, from 2.52 to 2.05. Take the time to experiment and settle on what works for you.
When you’re happy with the settings just click the Apply button at the bottom left of the window. And don’t forget to disconnect E-Tube Project when you’re done with the app.
Set up Synchro Shift using the mobile app (Android/iOS)
If you have a D-Fly, Wireless Unit or Display installed on your bike then you can also use the mobile app to set up Synchronized Shifting. The process is very similar to the one described above, with subtle differences.
For example, the mobile app features some pretty cool animations displaying how the bike moves through gears. It also allows you to set multiple presets and select the ones you like.
This is pretty cool, but it also means the mobile app can be a bit intimidating and confusing. I have written a separate page on setting up synchronized shifting using E-Tube Project for mobile, so read up all on configuring synchro shift there.
What to do when your cassette / chainrings are not listed
If you’ve installed a 105 series or non-shimano cassette or chainring you will have noticed that you cannot select that cassette in the E-Tube app. You cannot tell your bike the exact gearing that is installed and you cannot insert custom cassettes / chainrings.
The only cassettes and chainrings you can select in E-Tube Project are the ones that match the Di2 series currently installed on the bike. Have you built a bike with different series components? The rear derailleur determines what cassettes you’ll be able to select.
Seeing as setting up (full) Synchro Shift is done by telling the system to shift from certain gears to other gears you can imagine that not being able to actually select your gears can be a problem.
So what can you do when you cannot select your installed cassette or rings?
Select the closest match.
Why? Well, there are a couple of reasons. First of all, the selected cassette / chainrings influence the displayed gears and gear ratios on the Synchro setup screen.Also, Gear Position Control is automatically enabled or disabled depending on the selected gearing.
Selecting the closest match will result in a displayed gear ratio that is pretty close to your actual gear ratios. In fact, in most cases it will not be off at all.
Even if a gear’s number of teeth or gear ratio are wrong, you can still set up synchronized shift. The trick is to look at the gear’s index.
Basically, if you set it up to synchro shift when the rear derailleur reaches the 3rd gear from the top, it’ll always do that - no matter what cassette is installed.
Synchro Shift with FD-6870 and FD-9070
Synchronized shift works on the older 6870 and 9070 series too - after you install the required firmware updates. It makes sense for this Synchro Shift to be just like that on the newer series. All it really does it shift one derailleur instead of the other at certain points on the cassette, right?
Specifically: the point at which the bike shifts from the big to small ring can only be set to the last two sprockets or cogs on the cassette.
Those white boxes under the 50T/Top column are the gears you can move the light blue coloured box to - this is the gear at which the bike will shift from the big to small ring. As you can tell from the image, this limitation is only there when using FD-6870 (or FD-9070).
This actually put me off using Synchro Shift on my 6870 bike for a while and I switched to semi-synchro. After a while I switched back to (full) Synchro and learned to live with its limitations. Whether or not this works for you is ultimately up you, but it's good to know.
Did you manage to set up your synchronized shifting? Do you have any questions? Let me know or post a comment below.
If you're looking for roughly the same content in video form, have a look at GPLama's Di2 playlist.