What is Di2 synchro shift?

Of the many different things Shimano's Di2 system can do, Synchro Shift might be the smartest but also one of the most misunderstood. Lots of riders don’t try Synchro Shift out because they just don’t really understand what it is and what it isn’t. So here’s an explanation of what Synchro Shift does do, doesn’t do, and why you might fancy giving it a go.

In semi-Synchro Shift, when you shift the front derailleur the rear derailleur will shift automatically. So, if you shift from the small ring to the big ring, the rear derailleur will jump up a couple of cogs in order to smooth out the transition and keep your cadence more consistent, and if you shift down from the large to the small ring, the rear derailleur will shift the opposite way. This is the default, but you can customise it to move up to four cogs at a time if you want to.

With full Synchro Shift the system will automatically choose your gear for you, and all you need to do is press the button for ‘up’ or ‘down’. Essentially the system finds the next gear in the sequence cutting out some of those jumps that can happen because of tooth size differences at the upper end of the cassette. It’s the sort of thing that can prove quite useful if you’re out riding and trying to keep in a certain heart rate or wattage zone, because your cadence wont be changing massively when you shift gears. That’s not to say that the system will be double shifting (i.e. front and rear shifts at the same time), there are only a few points on the cassette where that will happen, but the goal is to make changes in gear as small as possible for a better riding experience.

The even smarter part is that Synchro Shift is fully customisable. In the E-Tube app you can either choose from a couple of pre-set gear maps or make one of your very own, tailored to how you like to ride. Even if you don’t want to try Synchro Shift, E-Tube makes a huge amount of your Di2 system customisable, so it’s worth checking out if you fancy trying something a little different.

How to change between shift modes

If you’re using either the older (stem mounted) junction box – SM-EW90 – or the newer, integration junction box – EW-RS910 – changing shift mode is done the same way. All you need to do is double click the button on the junction box and lights will flash to tell you what shift mode the system is in.

• If the red and green lights both stay solid for 2 seconds, you’re in manual shift mode.
• If the red and green lights blink twice, you’re in semi-Synchro Shift mode.
• If the red and green lights blink three times, you’re in full Synchro Shift mode.

So that's Synchro Shift. If you fancy something different, why not try it out on your next ride?