Automatic shifting probably isn't something that most mountain bikers spend much time thinking about. After all, modern 1x drivetrains aren't exactly mentally taxing to operate, and with a minimal amount of practice smooth shifting becomes second nature. But what if you didn't need to touch the shift lever at all during a ride? Or what if a bike was set to automatically shift when you were coasting, selecting the right gear by the time you start pedaling again?
Both of those scenarios are possible with Shimano's latest XT Di2 Linkglide electronic drivetrain, which is designed specifically for e-bikes. The group was announced at Eurobike last year
, but it's only now starting to show up on select bikes. I was able to spend two days trying out the system, enough time to get a grasp on how well the concept has been executed, and what aspects are the most relevant to mountain bikers. The Basics
As I mentioned, the new XT Di2 drivetrain is only compatible with e-bikes running Shimano's 600 or EP801 motor. It's powered by the same battery that provides pedaling assistance, which means there's no need to charge a separate battery... but it also means that it's not wireless.
The system can be configured in four different ways. Full manual shifting
is just what it sounds like – the system shifts only when one of the shift levers is pushed. Full manual shifting with Free Shift enabled
allows for shifting while coasting – the motor rotates the chainring forward while the cranks remain stationary, and the derailleur moves at the same time, making it possible to select the ideal gear for an upcoming terrain change without needing to pedal.
In the automatic shifting while coasting mode
, manual shifting is required when the cranks are turning, but the automatic shifting system takes over when they're stationary and the bike is moving. Fully automatic mode
puts the computer in charge, and the derailleur will move to the appropriate gear based on information gathered from sensors in the motor. Things like cadence and speed are taken into consideration, and the algorithm decides when to shift. There's a decent amount of customization available in this mode that's designed to help riders have the auto-shifting match their preferred pedaling style.
To add an additional layer of confusion, there are two versions of the drivetrain, XT Di2 Hyperglide+ and XT Di2 Linkglide. Hyperglide+ is the lighter weight option, based around a 12-speed, 10-51 tooth cassette. It doesn't have the fully automatic shifting option, although it can be configured to shift automatically while a rider is coasting, and shifting manually while coasting is also possible.
Fully automatic shifting while pedaling and coasting is only available with the Linkglide drivetrain, which uses an 11-speed, 11-50 tooth cassette. Setup
One of the biggest hurdles the system faces is the amount of experimentation required to get it personalized for each rider. I can see the setup process being daunting for a beginner, which also happens to be the type of rider who would be most likely to use the fully automatic setting.
Shimano's app allows for two different settings to be adjusted – shift timing and climb response. Shift timing adjusts when the computer will decide to make a shift. Riders choose a numbered setting between 50 to 100 (Shimano says 72 is a good starting point), and then adjust accordingly depending on how the response feels on the trail. That number doesn't directly correlate to cadence, but the higher the number the faster the cadence will end up being.
Climb response sets the torque threshold for a shift. Basically, if you push hard on the pedals, as you would during a climb, the drivetrain will shift to an easier gear. Choosing a higher number (there are 5 levels) for the climb response will create more time before the shift to an easier gear is initiated. It's worth mentioning that a sudden stomp on the pedals, like what would happen if you sprinted out of a start gate, will make it want to shift to an easier gear. That's not exactly the ideal scenario when you're trying to put down as much power as possible, so if you're racing or tend to sprint everywhere, then manual shifting while pedaling might be the better bet.
The final setting involves selecting a start gear. This is the gear that the system shifts towards when a rider is slowing down. Imagine stopping at a trail intersection. What gear would you want to be in when starting up again? More than likely, that's the best choice for a starting gear. It's also the gear that the system will likely be in after slowing down for a tight turn, or technical section of trail. Ride Impressions
So, how well does it actually work? Better than I'd expected, to be honest, although I wouldn't say it's 100% perfect - I still regularly used the shift levers to fine tune the gear selection when the system didn't behave the way I wanted it to. That said, there were several instances when it was genuinely impressive. One particular section of trail had a flat approach to a fairly steep slab of rock, and I was able to leave the shifter alone while the derailleur moved the chain to the appropriate gear as I climbed, making the shifts exactly when I would have on my own. There were also times while descending that I heard the chain move to a different cog, and was then able to pedal out of a corner with the bike already in the correct gear.
Even after a fair bit of adjusting the settings via the app there were still times when I found myself pedaling in a harder gear than necessary, or when the system shifted at an inopportune moment. More experimentation on a wider variety of terrain would be needed to tweak it even futher – I'd need to do repeated laps on the same section of trail to get it closer to matching the shifting experience I was looking for. As I mentioned in the setup section, the amount of tinkering required to really get it dialed in seems to be fairly high.
Taking a step back from the automatic part of the shifting, the actual shifting feel on the Linkglide cassette was very good, especially under load – I'd fully agree with Shimano's claim that it's smoother than Hyperglide+, which already worked well under power.
I get the sense that Shimano created the auto-shifting algorithm, realized that it worked well, and are still trying to figure out where to implement it. Realistically, I think electric commuter bikes are the ideal use case – I can see riders who haven't been on a modern bike appreciating the fact that they don't need to think about the nuances of shifting on their trip to work or the store. Shimano has done automatic shifting in that realm before, but this is by far the best iteration of it yet.
The good news with this technology is that it's not an all-or-nothing proposition. Riders that purchase an e-bike with XT Di2 will be able to decide which mode best suits their needs, rather than being locked into one setting. Personally, full manual shifting with Free Shift is the mode that I'd probably use the most, and I have a feeling that's the one many mountain bikers would immediately appreciate - there are all sorts of on-trail scenarios when being able to shift while coasting can come in handy.
It's going to be interesting to keep an eye on this system and see where the technology goes. Personally, I'm more curious about what Shimano's response to SRAM's Transmission drivetrain will be, but in the meantime I guess I'll keep myself occupied playing around with the thousands of different motor and shifting settings to see if I can unlock a combination that works well enough to convince me to let the computer take charge and do all
of the shifting.