It’s now been two years since Shimano first brought their Di2 electronic shifting to the mountain bike universe, during which time we’ve all become more accustomed to the presence of battery power on our bikes – electronic suspension lockouts and dropper seat posts, plus power meters and of course GPS units, plus other gadgets, are improving the mountain bike experience.

We’ve been riding Shimano’s new XT Di2 groupset for a few weeks now, including for seven days of non-stop riding in Finale Ligure, Italy, where it got a serious work out on some of the most superb trails on the planet. You can read our initial report on our XT Di2 test bike here, including the build process, or get all the details about the different chain ring and cassette options available for XT Di2 here.

Do we need electronic shifting in mountain bikes though?

When low cost, mechanical shifting (like the new SLX groupset we reviewed here) works so well, we appreciate it is hard to justify the extra complexity of electronics. There’ll always be the ‘don’t need it, don’t want it camp’, but we’re not in it.

The instantaneousness and the precision. Every shift happens lightning fast, and because there’s no cable friction, each shift is perfectly accurate too.

Di2 has been well proven on road bikes since 2009, and while road racing is different to mountain biking, in many regards it’s in the dirt were Di2 makes even more sense. And with XT bringing the cost of Di2 down a long way, electronic shifting is now far more relevant than in the past.

Explain please. Why does Di2 make sense for mountain bikes?

Maintenance is a big one. The quality of mechanical shifting on a mountain bike tends to degrade much faster than it does on the road, and Di2 totally removes this issue, as there are no cables to get gummed up or kinked, so your shifting stays consistent and effortless.

Consistency of shifting, no mater what the circumstances, is another big plus. On a mountain bike, panic shifting under heavy load tends to happen frequently, whereas on the road things tend to be done more smoothly. With Di2 on your bike, it doesn’t matter if you hit the button desperately as you strain on the pedals mid-way up a steep pinch, the shift will still be perfect and smooth.

So what makes electronic shifting superior to mechanical shifting?

The instantaneousness and the precision. Every shift happens lightning fast, and because there’s no cable friction, each shift is perfectly accurate too.

Chain retention is improved as well, not just because the shifts are crisp, but because you can crank up the tension in the derailleur clutch without any issue, greatly reducing chain slap. (The new XT derailleurs allow you to do this very easily using a 2mm Allen key). On a mechanical system, loading up the derailleur with heaps of tension would result in a very heavy shift action, but on Di2 you don’t need to worry about this as the motors do the work for your thumbs.

The end result is more chain security and a quieter ride, and despite blindly riding down some of the roughest trails we’ve ever encountered in Finale Ligure, we didn’t ever drop a chain.

So are there any downsides?

Compared to the mechanical cable systems that most home mechanics are familiar with, installing a Di2 system takes a little more time. You’ll need to decide where you want to store the battery firstly, plus work out the lengths of the various wires required to link it all up, because they can’t be cut to length later like a cable system.

As we’ve discussed below, installing the battery in the fork steerer tube can present some dramas. We’d recommend you put it in the top tube, or in the down tube. Wrap it securely in some kind of foam or padding to wedge it safely inside the frame and prevent it rattling.

It took us a small period of adapting to the feel and location of the shifter paddles. You can adjust the paddle positions, but they never felt quite as natural to us as the mechanical shifters we’ve been using for decades.

One issue, which isn’t a problem with Di2 per se, is related to the PRO Tharsis stem we used with our Di2 test bike. The Tharsis stem is designed to work seamlessly with Di2, and it allows you to store your battery in the fork steerer tube. To do this, it does away with a regular headset star nut and uses a threaded collar system to preload the headset bearings. It’s a finicky system that is prone to coming loose on really rough trails. Until the system is improved, we’d recommend using a regular star nut and running the battery inside your frame.

Is water an issue? 

Unless you’re taking your bike to the bottom of the harbour, you’re not going to have any water related dramas. You can wash your bike as normal, and river crossings or any of the usual water you encounter in mountain biking aren’t a problem.

How about battery life?

‘What happens if I run out of batteries?’ is one of the questions we get asked the most. Basically, if you run out of batteries, you should give yourself an uppercut. Can you remember to charge your phone every day? Then you can surely remember to charge your bike every few weeks.

The display very clearly shows you how much battery life remains, and the charge lasts for ages – in a week where we rode approximately 20 hours, the battery indicator dropped by one bar. If you’re running a front derailleur, the battery will drain more quickly because a front mech uses more juice, but still a few weeks of normal riding is what you can expect from a charge.

Does it operate any differently to XTR Di2?

Riding XT and XTR Di2 back to back, you can definitely pick up some small differences – the XTR shifting action is lighter, and the motor in the rear mech a tiny bit faster too. But then XT has some benefits over XTR too, such as the Bluetooth connectivity via the new display unit, which allows you to customise the operation of the shifting via Shimano’s iOS app.

When it comes to functionality, the XT Di2 system has all the same options as XTR, including the Synchro Shift mode (learn more about it here), so you’re talking seriously marginal differences overall.

So would you recommend it? 

If you’re looking at a new bike, put Di2 down as a big positive. We’ve already started to see a number of manufacturers speccing this drivetrain  on their 2017 offerings, and the performance would be enough to sway us in the direction of Di2-equipped bike versus a mechanical bike.

If we were looking to upgrade to Di2 on an existing 11-speed bike, then you’ll need to decide if the performance improvements are worth the cash. If you’re running a Shimano 1×11 drivetrain already, upgrading to Di2 (a shifter, rear derailleur, battery, display units and wiring) will cost you about $1200, but it will improve your ride and reduce ongoing maintenance. Weigh it up! There really are no downsides, so it’s simply a matter of whether you can justify the expense.