It's been a question on the lips of a lot of mountain bike pundits; when will Shimano make the jump to a 12-speed rear cassette? After all, arch rival SRAM has offered its top three groupsets with 12 gears for more than two years already... and it's claimed a lot of market share for the emerging long-travel trail bike segment as a result.

All things come to those who wait, and Shimano has finally pushed the button on a 12-speed set, kicking if off with the XTR M9100 groupset. It'll come under the one name. but it's now split into two distinct arms - pure XC and enduro/trail.

However, Shimano - long a defender of the front derailleur - hasn't gone straight-12; will continue to offer the new XTR with a twin front chainring and front mech option, along with a single-ring crank. It'll also offer an 11-speed version of its new 12-speed casette, if that makes sense.

What will change, though, for the first time since 1989, is Shimano's HG freehub design, replaced to accomodate the M9100's smallest 10-speed cog. Called a Micro Spline, the new cassette body is currently only offered on the new pawl-less rear XTR hub.

The hub is a clever bit of kit, doing away with traditional pawls in favour of a toothed driver that completely disengages when there's no pedalling input... and as a result, it'll become the first silent hub Shimano has ever released. 

We understand that DT Swiss are the only other partner for the new hub standard at this point, which will limit penetration of the system in the short term. Swapping drivers won't be a possibility either, given the new design.

It will, however, be offered in both straight-pull and hooked spoke patterns, the axles will be of a larger diameter thanks to the new driver deisgn, and it'll be offered in various widths including Boost and non-Boost. Here's another cool feature - the straight-pull hubs can be laced with the same length of spoke on both sides of the wheel.

Even though M9100 will be offered with two 12-speed and a single 11-speed cassette options, the system isn't backwards-compatible with current 11-speed cassettes.

The 12-speed cassettes on offer are a 10-51t (which weighs an impressive 367g), as well as a lower-range 10-45t. The 11-speed cassette, by the way, can be used with the 12-speed shifter by way of an optional 12-to-11sp converter, and is essentially the 10-51t with the big cog removed, leaving a 10-45t version. Apparently, racers didn't want to lug about the extra 57g...

This new stuff needs new shifters and derailers, and XTR delivers here, as well. The all-new rear mech gets larger 13t pulley wheels and a carbon fibre outer cage, and is available in short-, long- and extra-long (for dual ring) cage designs. The rear shifter, meanwhile, introduces (yet) another i-Spec interface for combining brake levers and shifters.

i-Spec EV, as it's called, allows for a wider range of shift lever positioning, while the shift effort has been greatly reduced, too, according to Shimano.

Another cool addition is the introduction of a i-Spec EV compatible dropper post lever that will work with any brand of cable-actuated post. Oh, and if you are one of the 13 people in the world still using two-by XTR, the new front shifter drops a paddle for easier operation.

The crankset is built with the same hollow alloy construction method as Dura-Ace, and single direct-mount rings are available from 30 to 38t... and you can guarantee the aftermarket will offer versions very soon. Another neat addition is a single-hex key crank release bolt.

Shimano will, for the first time ever, offer an XTR-spec chainguide in various fitments, too. If you'rew REALLY keen on using the proferrred 38/28t double, it'll fit onto the crank via a Shimano BB tool-shaped, ewrr, tool that will be included with aftermarket cranks.

Brakes, too, have come in for a complete overhaul. The two-piston option comes with a lighter weight carbon brake lever and magnesium master cylinder with the option to adjust the reach of the lever arm, while the all-alloy four-piston brakeset offers greater fluid volume, tool-free reach adjust function, free stroke adjust function and Servo Wave.


Aussie pricing and most weights haven't been formally announced, but Shimano claims the XC version of the group will be around 150g lighter in total, despite the extra gear.

MBA says: this is a long-awaited boots and all revamp of Shimano's premium off-road groupset, and the company freely acknowledges it missed the boat when it came to developing and marketing a single-ring version of XTR.

However, the past has been banished, and XTR - as has always happened in the past - will serve as the precursor for a wider roll-out of 12-speed components from the big S over the next 12 months or so.

Availability across a wider range of inhouse and aftermarket rear hubs is going to be paramount to a wide-ranging deployment, though... and it's interesting that Shimano didn't preview a wheelset with this XTR group.

Having said that, DT Swiss does build wheels for many of the industry's aftermarket players, and has a decent OE (original equipment) penetration in its own right. 

Expect to see a smattering of 2019 bikes ship with the new XTR group, while aftermarket bits will start to appear later this year.


This article was originally posted on  Mountain Biking Australia website...