Last spring SRAM unveiled their new 12-speed, 1x mountain bike drivetrain amidst the rolling hills and vineyards of Massa Marittima, Italy. It was a picturesque setting to begin getting acquainted with the new gruppo, dubbed 'Eagle', but it's the miles that took place on home turf after that initial introduction that really matter.
A massive range courtesy of a 10-50 tooth cassette, and a host of other improvements over SRAM's previous offerings all look good on paper, but how did the Eagle components fare after four months of riding in conditions that ranged from sunny to sloppy and everything in between? We'll get to that soon enough, but first, a brief recap for those who missed the initial First Look article.
The biggest talking point about Eagle has to be the 12-speed cassette. With a 10-50 tooth spread it offers a 500% gear range, a number that's in the realm of what you'd get with a 2x drivetrain, except that there's no front derailleur required with Eagle. The tooth count of the first 11 cogs on the Eagle cassette are the same as they are on SRAM's 11-speed 10-42 cassettes (10-12-14-16-18-21-24-28-32-36-42), with the 10-tooth cog sitting in exactly the same position.
The spacing between each cog is ever-so-slightly tighter, and the final 50-tooth cog sits two millimeters closer to the spokes than the 42-tooth cog would on an 11-speed cassette. Despite the extra cog, the cassette still works with a standard XD driver body, which is welcome news for riders calculating all the parts they'll need to purchase in order to upgrade their drivetrains. Weighing in at 360 grams, the $360 USD cassette is approximately 100 grams heavier than an XX1 11-speed cassette.
XO1 Eagle Derailleur
The XO1 Eagle derailleur ($220) isn't radically different from SRAM's 11-speed options, but the lower pulley wheel does have two extra teeth to allow it to work with the expanded cassette range. The cage itself is also longer, causing a slight reduction in ground clearance – when positioned in the 42-tooth cog the bottom of the Eagle derailleur's cages sits approximately three centimeters lower than that of an XO 11-speed derailleur.
Other updates include version 3.0 of SRAM's roller bearing clutch mechanism, a revision that's designed to create a smoother feeling as the cage moves forward while still providing enough retention to keep chains from bouncing off. The Cage Lock button, which is used to take the tension off the derailleur in order to make it easier to remove the rear wheel, has also been relocated away from the front of the derailleur to better protect it from impacts. The B-knuckle (the portion of the derailleur that's threaded onto the hanger) has been tweaked to help keep the mounting bolt from unthreading itself, and there's now a bushing around the mounting bolt that lets the derailleur pivot forwards and back without bringing the bolt with it.
The shifter keeps the same familiar SRAM ergonomics, but of course, there are now 11 clicks. The smaller trigger drops the chain down one cog at a time, and the larger thumb paddle can be used to move the chain up to five cogs at a time depending on how far it's pushed.
Eagle 12-Speed Chain
SRAM says the Eagle chain is “the quietest, strongest, and most wear resistant chain in the world.” We'll see about that, but in any case, the overall dimension are narrower than an 11-speed chain, and the pins are flush with the body in order to keep them from hanging up on the cassette cogs.
Eagle Chainring / Crankset
That big cassette may be the star of the show, but the Eagle chainring is also worth a look, especially since it's compatible with 11-speed chains as well. The teeth have a much more aggressive profile and a revised shape, changes that are intended to increase chain retention along with reducing the amount of noise created by the chain rubbing on the teeth, especially at the far ranges of the cassette.
The XO1 carbon cranks use SRAM's familiar direct mount interface to secure the chainring, and are available in 170 and 175mm lengths. They're not just for XC riding either - SRAM tested them to the same standard as their DH cranks in order to ensure they could handle aggressive trail riding and enduro racing.
Installation of the Eagle drivetrain is relatively straightforward, although there is one important part of the setup that needs extra attention: adjusting the B-gap, or the distance from the upper derailleur pulley to the cassette.
A plastic tool is included with the drivetrain to facilitate the process, and SRAM have also created a video that outlines the process. With the bike in the sagged position, the tips of the largest cog's teeth are supposed to line up with the outline on the tool. A 3mm hex is used to adjusted the derailleur's position, and after that it's just a matter of making any fine adjustments necessary by using the shifter's barrel adjuster.
On the Trail
The first couple of miles on the Eagle drivetrain were, well, a little noisier than I'd expected. The cassette emitted a sort of creaking / groaning sound, almost like a door hinge in need of some oil. And then, suddenly, the noise stopped, and silence took its place. It seems as if there's a bit of a bed in period with the cassette, and the sounds I heard was everything getting settled in. I've experienced this on more than one test bike, and in all instances the sound goes away after a few miles and doesn't return.
When talking about drivetrains, there inevitability seems to be two different camps of riders that crop up – those who feel that anyone who needs more range than what's provided by an 11-32 cassette are somehow inferior, and those who want to spin their way up vertical walls, and want the absolute easiest gear possible. Me? I'd put myself somewhere in the middle. I live in an area surrounded with ridiculously steep logging roads, and I don't feel any shame in using my granny gear to get to the top of a climb, especially if the alternative is getting off and pushing. I took full advantage of the Eagle cassette's 50-tooth cog, especially towards the end of long days where my legs felt like they were filled with concrete. For my chainring, I went with one that was two teeth larger than what I normally run (a 34 rather than a 32-tooth) in order to gain range on both ends of the cassette. With this setup I found myself spending more time closer to the middle of the cassette rather than in the larger, easier gears, which meant that I always had a bailout gear or two for when things got extra steep.
Shifting is crisp and quick, without any hesitation between gears. Not surprisingly, it feels almost exactly like an 11-speed XX1 drivetrain, except that there's now one more click. There's a silky smoothness to the way the chain interacts with the cassette and chainring that makes it all feel like one cohesive system, rather than an amalgamation of components. In other words, it feels really, really nice. The eight-tooth jump from the 42- to the 50-tooth cogs did sometimes sound a little louder than the other shifts, but the chain always ended up exactly where it was supposed to be, even when shifting on a steep uphill. That jump between those final two gears didn't bother me out on the trail, although it may take time for riders that are more particular about their cadence to get used to it. As I mentioned, I typically used that cog as a bailout, a last ditch effort to keep my momentum on tricky climbs.
What about backpedaling? It's no secret that on certain 11-speed drivetrains, and depending on the chainline, riders have reported issues with the chain dropping down the cassette when they backpedal. I made a conscious effort to backpedal more than usual when I was riding an Eagle-equipped bike, and in all instances the chain stayed in place. This was the case on multiple bikes with various chainlines and rear axle spacings.
As far as completely dropping the chain, I've only had that happen twice, and that's over the course of a test period that included hundreds of miles on extremely rough trails. Of course, a chain guide still isn't a bad idea, especially for racers, but I've was impressed with how well that chain stayed in place no matter what type of nastiness I was pinballing through.
Last month was one of the wettest on record here in the Pacific Northwest, which gave me plenty of chances to cap off the test period by dunking the derailleur in puddles and coating the entire drivetrain in a mixture of loam and mud. Throughout all of the inclement conditions the sensation while pedaling remained impressively smooth. I'm not sure whether to attribute that to the new tooth shape, the redesigned chain, or the revised upper pulley wheel, but in any case the grinding / gritty feeling that can occur in the mud on SRAM's 11-speed drivetrains was absent.
I also didn't need to re-tighten the derailleur on to the hanger – once it was installed it stayed in place, right where it belonged. The clutch tension has also remained consistent, and feels the same throughout the full range of the pulley arm.
The wide range of the Eagle drivetrain's cassette is going to be the most appealing trait for many riders, but it's the little things like the improved B-knuckle, the elimination of the narrow wide teeth on the derailleur's upper pulley wheel, and the revised chainring profile that help make this SRAM's best mountain bike drivetrain yet. The price is fairly high at the moment, but don't forget, this is SRAM's top-of-the-line gruppo; it's not a stretch to imagine that more attainable options are in the works.- Mike Kazimer