It’s a ‘hole’ new design (ho ho)

We’ve already talked about Shimano’s new shifter set up, but what of the cranks that turn the gears in the first place? Shimano’s XTR cranks have held the high ground against all comers since they were introduced so the new set up would have to be something special to be worth the upgrade.

It’s certainly the most radical looking chainset we’ve seen for a while, not least because you can see clean through the hollow axle to the other side. In their hunt for the stiffest, lightest race chainset possible Shimano have adopted a previously tried concept but added some of their own technology.

It's all a bit one sided

The idea of the driveside crank arm permanently attached to the bottom bracket axle is nothing new (Bullseye, Tioga Revolver, assorted BMX / DH units) but Shimano have certainly made the most of it. The axle itself is steel with a tiny toothed spline pattern that even has a flat section on to make sure you can’t line them up wonky.

Oversize and outboard bearings mean maximum stiffness

This then slides through the protective collar in the centre of the bottom bracket shell and rotates on oversized bearings on the outside of the bottom bracket shell. This doubles the distance between the bearings compared to previous XTR, and allows much bigger bearings to be used. To cope with the spindle stiffness the left hand crank arm is secured by a torque cap and twin opposed clamp bolts on the arm. This creates a totally rock solid pedalling platform that kicks the back of the bike all over the place until you’re used to it.

Muscley arms for pumping iron?

The crankarms themselves are broad Hollowtech units apparently designed to mirror the muscles of the leg. Happily the finish is the same glossy metallic grey as the rest of the groupset rather than pale and hairy, but then they probably weren’t thinking of our legs anyway.

The chainrings are 4 bolt pattern again, but with the rather blunt arms running up the outside of the rings. Long haul tooth wearers and log hoppers will also be glad to hear that the outer ring is a separate piece rather than part of the spider.

Despite the racey nature of the groupset, Shimano have also moved to conventional 44 tooth Compact drive (with either 24 or 22 tooth inner) rather than the old 48 tooth dinner plate. In use the rings shift smoothly and accurately as we've come to expect from Shimano, though our shifter inexperience meant changes weren't as fast as Rapidfire.

The bottom bracket fits either 68 or 73mm widths and the crankarms are available in 2.5mm increments from 165 to 180mm.

There is no single ring downhill version available though, and Shimano weren't letting slip about whether one was in the pipeline or not.

Despite the increase in stiffness overall weight is down 73g (slightly more than the overall difference between old and new XTR).

Overall

It’s very noticeably stiffer, it’s lighter and it’s easier to fit or remove, the ratio’s are more relevant for mortals and the bearings and rings can be easily replaced. The only downside is yet another new standard just when we'd got used to splined BB’s but then XTR has always been about taking the next step first.

In short it sets a whole new benchmark if you’re after the ultimate performance chainset, and we’re certainly looking forward to getting one in for a long term workout. Prices are unconfirmed as yet but expect to pay for the privilege of ownership.

Coming next

How Shimano got their new disc brakes so powerful and controlled at such light weight.