We investigate how Shimano's mechanical XT and electronic Di2 group sets stack up against each other
Words: Kath Bicknell Photos: Tim Bardsley-Smith and Kath Bicknell
When it comes to group sets, the different choices and associated ride experiences they offer are becoming more numerous than post-ride beverage options at your local café or brewery. Until recently, the biggest question riders faced was Shimano or SRAM, and the level of goodness within a given range. But add a preference for a single or double chain ring up front, and Shimano’s customisable Di2 electronic shifting into the mix, and drivetrain choices are reflecting an ability to tailor our bikes more than ever before.
Di2 isn’t new. Shimano first went electronic on the road with their Dura-Ace Di2 group set in 2009 and followed this up with their premium dirt offering, XTR Di2 in 2014. XT Di2 was released late last year.
XT has always been the more affordable offering for the discerning mountain biker; a fraction heavier, a lot less expensive, and often incorporating further innovations prompted by the initial XTR release. So, given a chance to compare mechanical and Di2 XT back-to-back on our Trek Remedy 9.8 test bike (see page 80), how did they stack up?
One of the areas where Di2 heavily outweighs mechanical XT is through the ability to combine front and rear shifting into a more automated system: Synchro shift. This requires only the right lever for control, freeing up the thumb (and your brain) for an ergo dropper lever or suspension remote. Di2 takes care of half shifts and full shifts for you on the front, based on where you are on the rear - which is really quite a genius innovation. It also means no more rubbing front mechs or crossed chain lines when you blindly move toward either of the extremes on the back.
Shimano recently released an interactive, online drivetrain personality test, which confirmed my preference for 1x on a trail bike. Given the rest of the e-conversion going on, I took the opportunity to ditch the extra componentry up the front and run a single chain ring instead.
Another major win for anyone in the Di2 functionality department, regardless of personal preference, is precise shifting with every shift. Even under load, even when you’re sloppy with the lever, and even when your bike is absolutely, drippingly bogged-up with filthy mud. These are the major limits with the mechanical system.
While mechanical shift actuation allows you to increase derailleur tension at the cost of increased resistance at the thumb, Di2 has a motor to do that for you. This means you can run superior chain tension. The main downside here is more battery usage but, given that riders can get through a long stage race or a couple of months of regular weekend use on one charge, this isn’t a massive issue.
Unlike the XTR display unit, which requires plugging your bike into a computer, Bluetooth compatibility with the XT display allows individual customisation via the E-TUBE app. Being the highly organised person I am, I was particularly grateful for this feature - and downloaded the app, set up my shifting exactly how I like it, all while sitting in the Stromlo Forest car park. The app lets you choose which lever does what, how fast, and, among other things, encourages a handy multi-shift option. This lets you push and hold the lever, allowing the derailleur to quickly move through the whole cassette. Pushing through two to three gears at a time with a long thumb stroke on a mechanical system would make the Di2 multi-shift feature the one I missed most post-test.
Mechanical advantages, by comparison, include shifters that share a clamp with the brake levers and no need to plug your bike into a power supply every now and then. Also, older frames aren’t designed for Di2 to integrate cleanly which means you might have to be a bit creative if you’re upgrading your existing rig. But, as we’re seeing already, more frames are being designed to offer compatibility with both systems going forward.
Weight will be a deciding factor for some people but, honestly, the difference is less than your pre-ride coffee, plus or minus a croissant. Our Trek Remedy, running the 2x11 mechanical setup, with pedals and some stubborn clay on the tyres weighed in at 13.57kg. With the electronic upgrade and running a single front chain ring (bye bye front derailleur and shifter), it weighed 13.01kg (with pedals and a fraction less clay). We estimate the single chain ring conversion shaved around 282gms.
The extra weight for Di2 comes from the battery (typically hidden in the frame or the steerer tube of the fork), the rear mech (which includes the motor) and the head unit. While the head unit has advantages for riders running 2x Synchro shifting, and during set up for riders running a 1x system out on the trails, its main function is to show battery life and the gear selection on the rear. As far as future innovation goes, I wonder if we’ll soon see the Bluetooth/setup and battery meter features integrated into the rear shifter, doing away with the head unit altogether. It was nice seeing what gear I was in, but given high-end mechanical systems haven’t shown this for years, it felt like a novelty more than anything else. It does provide a port for charging, but that could surely go somewhere else in the future.
To perform the above conversion to an existing bike, you’re looking at about $1,200, plus workshop labour and consumables. If you’re building the bike up from scratch, the difference between mechanical and Di2 is about $1,000.
The most costly XT item is the rear mech which will set you back about $500 if you destroy it out on the trails, while a mechanical XT rear mech is less than $200. Some comfort here is that Di2 has a protection mode that dislodges the motor from the derailleur system on impact. This requires you to check it and reset it before getting started again. This is particularly good news if, like most of us at some point, you’ve crashed your bike, thought everything was fine and then shifted your derailleur into the spokes causing a whole world of damage and financial hurt. It’s also worth noting how well the Shimano Shadow + derailleurs stay out of harms way – their design keeps them far more inboard than the competition.
In terms of ongoing issues, Di2 basically takes care of itself. It’s always going to shift perfectly unless you bend the rear hanger - assuming you don’t put it out of adjustment manually or have a crash that would destroy either system. In that way, it’s set and forget. The mechanical system, with cables that stretch, wear, that can age 1000 years in one muddy ride, requires far more frequent servicing and maintenance if you want to keep your shifting crisp, reliable and smooth. Di2 gets my vote in this regard as there’s no need to worry about cable replacements, adjusting the tension part way through a ride or cradling your thumbs at the end of endurance events.
ON THE TRAIL
So what does all this mean when out on the trails? Basically, like all well-designed, technologically enhanced systems, Di2 means less effort worrying about the small things and an increased ability to focus on other stuff. Features that stood out immediately include the ability to shift under load, to shift through multiple gears while out of the saddle and climbing and the efficient, buzzing sound the derailleur makes with the (less effortful) tap of a lever on the bars.
On one occasion, the bike became so filthy I washed it down with a hose mid-ride just because I couldn’t handle the sound of dirt ageing the chain and the brakes. The shifting remained flawless despite the goop. And I never once dropped the chain.
While these things are nice in the short term, it’s long-term benefits that will matter to riders the most: predictable, reliable shifting, every shift being the big one. And a heap less time spent adjusting or servicing the gears between rides.
While the familiar, mechanical system does have some small advantages over Di2, when choosing between the two systems the biggest decision-making factor for most people will be cost vs experience. If you like the ability to customise your shifting, have some of the work taken care of for you, and spend more time on the trails than in the workshop, Di2 offers a lot of benefits. These are especially valuable to racers of all disciplines who crave maximum reliability and like to put every ounce of energy into attacking the trails.
When it comes to your average rider, choosing between the two will come down to individual preferences regarding weight, functionality, serviceability and ride feel to determine whether this justifies the extra spend. With so many areas in which to customise your ride experience, there’s a lot more than gear ratios or charging a battery to consider if you’re in the lucky position to be making such a choice.
Di2 Hits: Precision shifting, every shift; What maintenance?; Out of the saddle multi-shift
Di2 Misses: Not always a tidy install on older frames; De-clutters the bars in some ways but adds a little in others; Initial cost