“Man, I don’t want my bike deciding for me when it’s time to shift!” That was our very first line of thought when we heard about Shimano XTR Di2’s Synchro Shift system. But like so many of the ranters out there in Internet land, we totally misunderstood what Di2 Synchro Shift was about and how it worked.
In a nutshell, Syncro Shift is a function/mode found on Shimano’s new XTR Di2 groupset which allows you to have a drivetrain with multiple chain rings (i.e. 2×11 or 3×11), but only use one shifter. This has the advantage of allowing you to maintain the wider gear range of a mutli-ring drivetrain, but makes for a simpler, cleaner and lighter cockpit, or allows you to run a dropper post lever in place of the second shift lever.
To be 100% clear, Syncro Shift is not an automatic shifting mode. It only shifts when you tell it to – it won’t go all Skynet on your arse and start deciding when it’s time to change gears autonomously!
As you probably know, in a multiple chain ring drivetrain, there is significant overlap/duplication of gear ratios. Even in a 3×11 drivetrain, there are really only 15 or so unique gears (in a 2×11 drivetrain it’s even less, only 12 0r 13). What Syncro Shift allows you to do, is use every single one of these unique gears sequentially, without having to think about the front derailleur at all. This is because Syncro Shift mode handles the front shifting in order to maintain that sequential order of gear changes.
As you move up or down the gear range, the front and rear derailleurs are shifted in tandem in order to maintain the logical progression of gear ratios. Because you don’t have to think about the front shifting, from a rider’s perspective, it’s like you’ve got a single chain ring, but with a 15 gears out back (or 13 if you’re using a 2×11 setup).
Confused? Watch the video below. It explains all the shift modes in detail – please note, this was shot months ago, early on in our testing.
Even once we understood what the system was all about, some reservations remained, mainly that we’d somehow be ‘surprised’ by the front shift occurring. Needless to say, that hasn’t been an issue. The system gives you a loud double beep to alert you that a front shift is about to occur, and even if it did not, the front shifts occur with such precision and so quickly that they’re really just as smooth and seamless as a rear shift.
Di2 actually has two Synchro Shift modes, designated by S1 and S2 on the display. Using Shimano’s E-Tube software (which is PC only!) you can customise the shift patterns for each Synchro mode, in order to best serve different situations. For example, we configured S1 as our ‘trail’ mode, adjusting the shift mapping so that the chain dropped to the smaller chain ring earlier, weighting the gearing range towards the lower end, and maintaining a straighter chain line overall. S2 we configured as our ‘race’ setup, so the chain would remain in the large chain ring until we’d downshifted to the very lowest gear on the cassette, and only then would it drop the chain to the smaller ring. When shifting back up the range in S2, we configured the shift patterns to be more aggressive, with a larger jump in ratios between gears 3 and 4. Either way, as long as you know which of the two modes you’re in, the behaviour of the system is completely predictable.
Front shifting normally demands a fair bit of attention, even if it’s largely subconscious in more experienced riders – shifting under heavy pedalling load can lead to all kinds of dramas, like snapped chains, bent chain-ring teeth, dropped chains or ruined derailleurs. Then there’s the consideration of cross-chaining, running gear combos that cause premature wear of your drivetrain or sub-optimal performance.
Synchro Shift removes these issues from the ride experience entirely. You can shift under load whenever you want with total confidence that there’ll be no dramas, the chain slots into the next gear perfectly and won’t over-shift or drop off the chain ring. And because the front derailleur and rear derailleur work in tandem, you’ll never find yourself running really extreme chain lines inadvertently either.
In this regard, Synchro Shift really does deliver some of the aspects we like about 1×11 drivetrains, but with the benefit of multiple rings.
Undeniably, Synchro Shift is better than using two separate shifters – we can’t imagine there will be many riders out there who’ll opt to run separate front/rear shifters once they’ve experimented with Synchro mode. But the million dollar question is: Is Synchro Shift better than a 1×11 drivetrain?
And that IS a very good question. Do multiple chain rings combined with Synchro Shift offer sufficient benefits over a 1×11 system to justify the complexity? Or are you better off saving the weight, expense and battery life and just going for a 1×11?
The answer, of course, is that it depends on your priorities. We’ve configured our Di2 system with both all the possible variants: 1) 2×11 with two shifters 2) 2×11 with one shifter and Synchro Shift 3) 1×11. We straight up can’t see any benefit of option 1, but when it comes to options 2 and 3, there are pros and cons.
A significant factor is gear range. If you want a larger gear range, then a multiple ring system is better, hands down.
We raced our XTR Di2 equipped bike at the Convict 100 Marathon race, and we relished having a full gear range of a 2×11 drivetrain – it made a long, hard day in the saddle easier, both on the climbs and on the flat, fast road sections. We could have done it on a single-ring, but it would have been a tougher ask.
The chart below serves as good comparison of the relative gear range offered by Shimano 3×11, 2×11, 1×11 and, for comparison, SRAM 1×11.
If the single chain ring option is your preference, then it’s possibly worth looking into other cassette options which offer a broader range of gearing than the standard XTR 11-40. The heavier (but much more afforadable) XT cassette is available in an 11-42 spread, or you could theoretically run a SRAM 10-42 as well (though Shimano would obviously say this was a no-no). The standard 11-40 XTR cassette offers a good spread, and the gear ratios are well spaced, but it is a bit constraining overall.
On the plus side of a single-ring set up is that there are decent weight savings to be had in ditching a front derailleur, chain ring and shifter – with XTR, those savings amount to approximately 290g. Going to a single ring is also quieter, and looks bad ass.
We have dropped the chain on our XTR drivetrain in both 2×11 and 1×11 configurations. This is no huge surprise – it’s not a Shimano issue, and we’ve thrown the chain on SRAM 1×11 setups many times too. The saving grace of a having a front derailleur, is that if the chain does come off, you’re more likely to be able to pedal it back on, whereas if it comes off a single-ring your only option to stop and put it back on. (Or, of course, you could run a chain guide if you’re using 1×11).
Synchro Shift is much more demanding of your battery life than either manual shifting or 1×11 modes. The front derailleur uses the lion’s share of the battery juice, because it requires a lot more force to execute each shift, and Synchro Shift puts it to work more often. We also seemed to experience accelerated chain wear in Synchro Shift mode, though we’re reluctant to 100% attribute this to Synchro Shift, nor can we explain it other than to say that perhaps we didn’t have our Synchro Shift configured to deliver nice, straight chain lines.
If we had to make a choice between running a single-ring or running 2×11 Syncro Shift, what would we bolt to our bike? Once again, it would depend on what we wanted to do. We’re happy to admit that we’re suckers for the simplicity, ease of use/maintenance and clean lines of a single-ring drivetrain, and 90% of the time the gearing range it provides is fine. We’d be happy to live with the small compromises in gear range on our home trails, where the speeds are never that high, and the climbs aren’t that long.
But if we did more racing (of any sort; marathons, Enduro, cross country), or if we regularly rode in steeper, bigger terrain then we’d go for a 2×11 with Synchro Shift all the way. We’d also most likely pair it up with an 11-42 cassette as well, just to extend the gear range even further.
Interestingly, if the choice was to run 1×11 or 2×11 in a mechanical groupset (i.e. no option to have Synchro Shift), then we’d most likely opt for a single-ring. For us, being able to position a dropper seat post lever in place of the left-hand shifter is a really big deal – it makes using a dropper much, much easier, and when we’re able to use the dropper post quickly and easily, we enjoy the ride a lot more.
As we’ve outlined above, Synchro Shift makes the front derailleur desirable again. It allows you to have your cake and eat it – a bigger gear range, but with far fewer of the downsides you’d normally associate with a front derailleur and a left-hand shifter. Is it a revolution? No. Does it make us pause in our headlong rush towards single-rings on ever bike? Yes.
For more reviews and our experiences with XTR Di2 read on: