Shimano just announced the latest XT and SLX mountain bike drivetrain groups with 12-speed cassettes and a raft of new technology previously only available in their top-end XTR group. While it’s no surprise that Shimano is going to offer more affordable 1×12 and 2×12 options, mountain bikers should be pleased with both the timing of the release and the performance of the new components.
I spent two days testing the latest 12-speed XT drivetrain on the incredible singletrack surrounding Bellingham, WA and here’s what I learned.
Like the 12-speed XTR group announced last year, the new XT group can be configured with either a 10-51T (Wide Range) or 10-45T cassette. Of course with the first, riders are getting maximum range (510%, slightly higher than SRAM Eagle) but are limited to a single chainring up front. The only potential downside is the gear steps aren’t uniform; that is, there are bigger jumps between gears as you move up the cassette.
Shimano calls their 10-45T cassette “Rhythm Step,” and it can be paired with either a single or double chainring crankset. Uniform gear steps help avoid abrupt changes in cadence, but this limits the gear range to 450% with a single-ring crank. However, when used with a 2X crankset (36-26T) that gear range explodes to 621%.
The 10-51T XT cassette is said to weigh about 470g and will be priced at $159.99. This is about 20g heavier than a SRAM GX Eagle cassette, but $55 cheaper.
Shimano has engineered the cog profiles to produce quick, decisive shifts when paired with a Hyperglide+ chain. The two largest cogs are made from aluminum and have a black surface treatment to make them more durable while the rest of the cogs are steel. At a glance it’s easy to identify new Shimano cassettes by the number of black cogs: XTR gets three, XT has two, and SLX has just one.
The seven largest cassette rings are fused together into a single carrier, while the remaining five cogs slide onto the driver. The cassette uses a Micro Spline design to allow for the small, 10-tooth cog and also to reduce gouging. Of course the downside is buyers will also need a Micro Spline freehub body.
The new Shimano XT crankset is offered in five different configurations which seems a little confusing at first, but it’s actually pretty brilliant.
Starting at the middle of the lineup, the M8120 crankset is designed for Boost-spaced bikes and maximizes tire and frame clearance. This option has a 178mm Q-factor. Chainring options range from 28T to 36T across all of the XT single-chainring cranksets.
Moving narrower, the M8100 crankset is designed to work with Boost (148mm rear spacing) and non-Boost frames (142mm rear spacing) plus it offers the narrowest Q-factor of the bunch at 172mm. For many older model bikes, this is going to be the best option to get the right chain line.
At the other end of the spectrum, the M8130 crankset works with “Super Boost,” 157mm rear spacing. Of course this adds a bit more to the Q-factor, ringing in at 181mm.
The remaining two options are double chainring crankset versions of the M8100 and M8120 for those who want the additional gearing range of a 2X drivetrain. The XT double-ring cranks are configured with 26T and 36T chainrings. The big ring is direct-mounted and the smaller ring is mounted to that, which means it’s possible to swap between 2X and 1X gearing up front with M8100 and M8120 cranks.
The crank arms are hollow-forged with two pinch bolts on the left arm holding everything in place. Pricing for a single-chainring crankset is set at $154.99 (not including a bottom bracket or chainring) and the weight is said to be 620g with a 32T chainring. Note, that price is 64% less than an XTR crankset which definitely makes XT accessible to even more riders. A single XT-level chainring should be priced around $62.
Shifting is where drivetrain performance is most noticeable, and much of the technology for the new 12-speed XT drivetrain has spilled over from XTR which was launched last year.
Starting at the rear end of the drivetrain, Shimano adds Hyperglide+ tech to the cassette and chain for reduced pedal shock and 33% faster shifts compared to the Hyperglide technology on the previous generation XT drivetrain. In practice, this means shifting under load is not only possible, it’s preferable to easing off the power a bit to baby the chain between gears. If you’ve ever found yourself struggling to shift in time to react to unexpected terrain on the trail, you’ll no doubt appreciate this feature. The engineering and design behind Hyperglide+ is a little complicated so check this out if you’re interested in learning more.
The new XT shifter offers many of the same benefits as before, including the ability to downshift one or two gears at a time. Shimano improved the feel of the lever action, giving a single downshift a lighter feel than a double downshift, which helps avoid accidental overshifting. They also added a rubber pad on the lever for improved control, and the XT shifters still offer 2-Way Release (a push or pull of the lever activates the shift) and Instant Release (the shift fires as soon as the lever is pushed/pulled, not after you take pressure off the lever).
The I-Spec shifter mount gives the rider 14mm of side-to-side range to get controls dialed, along with 20-degrees of rotation. Priced at $60.99, the right shifter weighs 120g.
On 2X configurations, the front derailleur shifter features just a single lever that toggles between the two chainrings with a push or pull for a simplified design.
It doesn’t appear a lot has changed with the updated XT derailleurs, though the new rear derailleur moves to 13-tooth pulleys instead of 11T to accommodate the big 51T cog. The M8100 derailleur is designed to work with a 1X drivetrain and is compatible with either the 10-45T or 10-51T cassette. Another version, the M8120 derailleur, is for the 2X drivetrain, but also works with the 10-45T cassette in 1X configuration.
The M8100 rear derailleur will be priced at $114.99 and weighs 287g.
The M8100 front derailleur is a side-swing derailleur and works with 48.8mm and 51.8mm chain lines.
On the trail
Shimano positions the XT group as trail-ready compared to the more race-oriented XTR group, and it’s an apt distinction. All of the XT components are designed to be durable, yet are constructed using high-quality methods and materials. This is also a drivetrain that’s designed to get riders up the trail as easily as it gets them down.
Let’s start with the ups. Over two days I climbed more than 5,500 feet, with one wall-like ride ratcheting up 1,100 feet in just a mile and a half. (There was also a shorter section of another ride literally known as “The Wall.”) I made good use of the 51T cog in the rear on these climbs, and it must’ve been enough because I stayed on the bike pretty much the entire time. Upshifts are swift and decisive, even as the jumps get bigger toward the top of the cassette.
Since this was my first time riding the trails in Bellingham, I found myself needing to shift at awkward times as short, steep climbs seemingly appeared out of nowhere, only to top out and vanish almost as quickly as they arrived. Hyperglide+ shifts noticeably faster than I’m used to with just a few degrees of crank rotation, making up for any lack of sufficient down-trail vision.
It took a bit of practice but I soon found myself powering through shifts more and more. This is super helpful in quick transitions where I need every bit of power I can muster to move up and over obstacles in the trail. Easing off the pedals before a shift is something most of us have gotten used to over time, so it’s liberating to smash pedals at will with little regard for the state of the chain and rear derailleur.
On pedally sections, downshifts are just as quick and the power transfer feels quite seamless, with more of a click than a thunk. Being able to downshift one or two gears at a time is a nice feature which again, allows for quick transitions.
Mountain bikers don’t tend to think about their drivetrains so much when the bike is pointed downhill. After all, Aaron Gwin can win races without a chain. Fortunately, the designers at Shimano do think about drivetrains going down, and their attention to detail was evident during my tests.
For starters, chain retention with the new XT group is excellent. I didn’t drop a single chain through rough, jangly descents, and as far as I know, no one in our group of 25+ riders did either. Of course having fresh, unworn everything — chain, chainring, cassette, derailleur — helps. However, I believe credit is due to the improved Hyperglide+ interface between teeth and chain as well.
We rode some long, steep descents in Bellingham, but that’s not to say the downs were without pedaling. Many of the trails feature doubles, kickers, and hips that beg for just a little extra speed on top of whatever gravity is able to provide. Again, the quick downshift action, whether it be one or two gears, and the near-instant power transfer makes it easier to react and take full advantage, even on unfamiliar trails.
On the first day of our test the trails were dry and dusty, and in these conditions, the XT 12-speed drivetrain worked flawlessly. Day two saw rain and damp loam, which coated the underside of my frame and drivetrain in rich, dark dirt, yet resulted in zero complaints. Again, having a team of mechanics supporting the ride with daily maintenance certainly helps, but I’m confident the design should allow all of the pieces to perform well in most conditions.
With the updated 12-speed Shimano XT drivetrain, mountain bikers are getting all of the latest analog drivetrain technology in a high-quality, reliable package at a reasonable weight and price. For trail riders, this drivetrain strikes a great balance and represents a compelling alternative to other 12-speed drivetrains on the market.
Look for availability beginning in mid June, 2019, and learn more at mtb.shimano.com.