The old adage goes something along the lines of ‘racing betters the breed’, in terms of the humble mountain bike drivetrain that is most definitely the case. Let’s face it, grinding metal-on-metal through axle-deep slop is hardly the most glamorous of callings but the sheer amount of technology and engineering that goes into groupsets such as the latest Shimano XTR M9100 group is staggering and, as a result, they are covered with interesting (read ‘nerdy’) little details.
Enduro racing is a tough proposition for drivetrains with the need to slog out long days being exacerbated by fumbled shifts amidst redline panic between the tapes. Shifting gears is something that the vast majority of racers do subconsciously but the detail behind the process is sometimes overlooked. Here’s a few lesser-known facts and some geekery about the latest Shimano XTR M9100 groupset:
The biggest advancement with the all-new XTR group as seen on many pro’s EWS race bikes is HYPERGLIDE+. When they made the move to 12-speed Shimano were not content to simply ‘squeeze another cog on’, instead they targeted nothing less than seamless shifting.
As riders, everyone grows up learning (the hard way) how to shift properly; politely back off the pedals and chain tension before requesting a new gear. This new system does away with the niceties and allows you to grab gears no matter where in the block you are, how hard you are pedaling or what the trail conditions are doing. No hesitation, no consideration, no lift, just shift! This makes it perfect for enduro racing as it's one more thing eliminated from a racers mind allowing them to focus on the finish.
The detail sweating it took to achieve this was colossal but one of the big break throughs was when the team extended the inner link plates on the chain. This helped to both reduce the natural vibrations in the chain whilst also increasing security allowing it to maintain better contact with the teeth of both the chainring and cassette.
GT Factory Racing have been running Shimano HYPERGLIDE+ shifting since it became available. Pic: Shimano
To accomodate a HYPERGLIDE+ rear cassette, it is necessary to fit a Shimano Micro Spline rear hub driver. The company realised that specifying a whole new rear hub would deter many riders if they were already happy with their existing wheelset so instead they licensed the design out to hub manufacturers so that most rear hubs can simply have the driver installed without a wheel rebuild being necessary.
You can learn more about Micro Spline, here:
It’s got serious roots
The latest XTR (M9100) features a lot of brand-new and hard-won technical advances but amidst all of these it’s pedigree and lineage should not be overlooked. Mountain biking is still a relatively young sport and there are very few products that can lay claim to having been almost ever-present but Shimano’s first off-road group arrived as long ago as 1983. The first lightweight XTR then emerged in 1992 as a race-focused range-topper. That original Deore XT featured the then ground-breaking RD-M700 rear derailleur. The ‘deer head’ logo may have gone but Shimano hit a home run largely thanks to its tougher off-road ready build and superb simplicity which made for a previously unseen level of mud-clearance.
The XTR rear mech features an adjustable and rebuildable clutch system. Pic: Shimano
It’s not all CAD renderings and crunching the numbers when it comes to designing a mountain bike drivetrain. OK, so a lot of it is but what’s also crucial are the materials that you use. For example, the latest XTR HYPERGLIDE+ equipped rear cassette is crafted from no fewer than three kinds of metal. Steel accounts for the bottom four cogs, the middle block of five is made from (rather posh) titanium whilst the massive top three rings are manufactured from aluminium. The aim is to keep weight at the rear axle as low as possible. The biggest ring available is a towering 51T before the ratios drop incrementally down to the smallest 10T at the bottom of the block.
Rocky Mountain Race Face Enduro Team's Jesse Melamed's XTR rear mech and cassette. Pic: Shimano
The brand’s flagship XTR groupset is famed for its light weight and even in the era of the added complexity of 12-speed shifting this remains true. The HYPERGLIDE+ seamless shifting is obviously a huge moment for the mountain bike drivetrain but those little details really are everywhere. For example, there’s the option to go with Shimano’s new SM-CRM95 chainrings which do away with chainring bolts and instead attach to the rear of the driveside crank arm.
One of the Ibis Enduro Team's race bikes running the new XTR chainring with some extra cable ties stashed in the axle of the XTR Hollowtech II crankset. Pic: Shimano
Keep looking and both Race and Trail brakes feature a stud in between the clamp and grip which contacts the handlebar ensuring that the force generated when you pull the lever goes straight into slowing you down and not into wasteful flex (look out for an indepth feature on enduro-ready brakes coming soon). There’s even a handy mark on the rear of the outer pulley cage which helps you nail the crucial B-tension settings when fine tuning your shifting.
The latest XTR shifter features a huge range of adjustment thanks to a number of mounting options. Rubberised levers guarantee accurate shifting in the wet. Pic: Shimano
Check out Shimano's This Is Home video with Richie Rude, here:
You never seem to fit a new drivetrain when you have the luxury of time, do you? It’s without fail the evening before you need to be at a race or on a big ride. Shimano have done their level best in various ways to make fitting your new set-up a bit less painful however including packaging that’s there to help.
The 12-speed HYPERGLIDE+ cassette comes on a plastic shim which allows you to mount it to the new Micro Drive-equipped hub. You remove the clip and your cassette drops into place in one easy piece eliminating the need to crawl around the garage floor looking for all the bits that you’ve just dropped and have seemingly vaporised.
Youn Deniaud and his XTR-equipped Giant Fatory Off-Road machine. Pic: Shimano
So there you have it - right from the packaging it comes in up to those valuables seconds saved via HYPERGLIDE+'s seamless shifting, Shimano's latest drivetrains are the perfect fit for enduro racing. For the pro's they have become the ultimate shifting solution and for the privateer racer, the fact that they can be mixed and matched across the 12-speed range means that their advanced technology is accessible at several pricepoints.
Shimano are the official Drivetrain, Brake & E-Bike Drive Unit partner of the Enduro World Series and EWS-E. Over the next few weeks we are going to bring you more indepth tech features and how-to's to help you to get the most from your MTB drivetrain.