SRAM teased upcoming their XX1 group in May, showing not only the first 11-speed cassette for mountain bikes, but also the first dedicated complete group designed around a single front chainring.

Now, they’ve let loose the specs and details. Available in October 2012, the XX1 group introduces an entirely new Type2 X-HORIZON rear derailleur that has an interesting movement range to accommodate the massive 10-42T cassette range. The crankset uses new carbon arms designed specifically for a single chainring, and the chainring and cassette pulleys are designed with narrow and wide teeth to fit inside the inner and outer chain links to keep the chain stable. The cassette rides on a new XD Driver Body freehub body that’s (for now) only available for SRAM and DT Swiss wheels.

Click on through for more!

2013 SRAM XX1 1x11 mountain bike drivetrain group

The ring uses X-SYNC tooth profiles, an alternating pattern of narrow and wide tooth profiles. This not only helps manage the chain (like a built-in guide), but SRAM says it improves durability and stability. It’ll be available in even number tooth counts only (obviously): 28-30-32-34-36-38. It’ll be offered in both BB30 and GXP formats. All chainrings use the same BCD, so you can swap them in and out, and you can do so without removing the crankset…a big bonus. There’s a chance you’d have to shorten/lengthen the chain if you went from one extreme to the other.

Claimed weight with BB is 650g, about 50g lighter than the standard double BB30 crankset.

2013 SRAM XX1 1x11 mountain bike drivetrain group 11-speed 11-42t cassette

The cassette started out as a 9-36 during initial testing, but ended up at the larger 10-42. The 10t cog does not double as the lock ring as expected, and the entire piece comes in at a claimed 260g (versus 208g for an 11-36 XX 10-speed). Tooth range is listed as 10-12-14-16-18-21-24-28-32-36-42.

UPDATE: There is a 21T cog, which we originally thought might be a typo since it’s the only odd number in the system (derailleur pulleys are 12T each) and that it might throw off the alternating chain/chainring tooth profiles. SRAM’s MTB PR guy says because cassette’s cog tooth profiles aren’t alternated like the chainring, they don’t throw off the synchronization of the chains inner and outer plates with the chainring. There’s not really a technical explanation of why it doesn’t, it just doesn’t.

2013 SRAM XX1 1x11 mountain bike drivetrain group

The cassette uses their single-piece machined X-Dome design. The new XD Driver Body steps down as it moves away from the hub, providing a smaller diameter section for the 10t cog. DT Swiss sorta let the cat out of the bag at Sea Otter when they announced 11-speed ready mountain bikes wheels, so we new something was coming, but they didn’t say anything about a proprietary freehub body. The idea isn’t new in and of itself, Hope and Kappius and shown similar systems, albeit slightly more integrated, but it’s the first from two major component manufacturers. We’re seriously hoping it becomes an open standard that other hub and wheel brands can offer.

UPDATE: It’ll work on all of DT Swiss’ Star Ratchet equipped wheels (most of their high-end stuff) and on SRAM’s Rise 60 wheels. It won’t work on the Rise 40 wheels because they use a different driver body. Lalonde says nothing changed inside the driver body compared to a freehub body, just the outer shape was changed to accommodate the 10T cog. Theoretically, it pops on and off a hub the same way a standard freehub body would (depending on hub model, of course), which means it’s not a stretch that we’ll see it offered as an option on other brands. The design is open for other wheel manufacturers to use without licensing.

SRAM says it saves a 6-8g over a traditional freehub body, but that it offers better stable connection between the cassette and hub. They’re being intentionally light on the details until the Crankworx events this summer, but we’ll be seeing them before then and press for info.

UPDATE: While it looks like the 10t cog is the lock ring, it’s not. The “tube” on the inside of the XX1 cassette is the “lock ring”. There are still splines on the Driver Body, but they’re all the same so you don’t have to line anything up. You slide the cassette on and then use a standard cassette lock ring tool, which threads the entire cassette on rather than just a lock ring on the end.

Generally, much of a chain’s plate design is to facilitate front shifting. This chain is a 1×11 specific model that SRAM says is “optimized for use without front shifting.” They’re claiming it’s stronger, with a new finish to reduce wear. At face value, this means you won’t be able to run this system with a double up front, and the alternating tooth profiles mean you can’t sub in a Shimano chain (unless, perhaps, you were to replace the pulleys on the rear derailleur…but then you’d likely need a really, really long chain to accommodate that range. Hmmm…)

2013 SRAM XX1 1x11 mountain bike drivetrain group horizon type2 rear derailleur


One of the biggest changes comes at the rear derailleur. Rather than a parallelogram that’s set at an angle to move the upper pulley diagonally along the lower half of the cassette, the X-HORIZON rear derailleur moves in a perfectly horizontal (get it, horizon?) plane. In order to keep the upper pulley moving up or down across the cassette, it’s offset far back from the cage’s upper pivot. Once you see it, it’s a pretty darn simple solution. Another benefit is that the horizontal plane is perpendicular to the up and down forces your bike will see as it goes over bumps and drops, meaning even the worst terrain won’t affect shifting performance. To minimize chainslap and noise, it uses their Type2 clutch mechanism to hold the chain tight and Cage Lock to ease wheel removal. Cable routing also looks to be drastically improved, similar to the way it’s routed on the new Red road group.

This diagram shows the difference in movement patterns for the X-HORIZON rear derailleur versus a traditional mech. Claimed weight is about 220g for the rear derailleur (compared to 181g for the lightest XX model).

2013 SRAM XX1 1x11 mountain bike drivetrain group with trigger shifters or grip shift

You’ll have the option of running it with the new Grip Shift or their trigger shifters, both 11-speed specific.

Overall, weight savings from the crankset is countered by the cassette and rear derailleur, but as a system it should come in reasonably lighter by eliminating the front shifter and derailleur.


  1. Cole33 on

    I dont think the 21 is a typo. It makes sense as a step up from 2 tooth increments to 3, then to 4. Also the rear cassette doesn’t look like it has the alternating teeth like the front chainring does, so they don’t have to worry about even or odd teeth numbers.
    I’d be curious to see if the Horizon rear derailleur movement will trickle down the line to their 2×10 if it turns out to manage the chain better.

    • Alex on

      The Horizon rear derailleur is single front ring specific. It relies on chain tension to move up and down and follow the rear cassette. Odd teeth on the cassette are okay because the total number of links in the chain is even.

  2. Dan Gerous on

    The 21t cog is not a typo. The cassette doesn’t have the wide/narrow teeth of the ring. As you shift through the cassette, there is no way to time the shifts so the chain would always be timed with a wide/narrow teeth design… so odd teeth counts are okay. The front work since you install the chain correctly then it stays in sync forever.

  3. Woody on

    Looks like the perfect setup to me. Very rarely ever change gear up the front, always in the middle ring. Interesting to know what the whole weight saving would be. Bit of a shame it will super super dollar when it comes out. I guess we will have to wait a few years for a sensible price.

  4. Cole33 on

    Besides an 11 speed chain, i’m not sure there’s anything special about it. They just took advantage of the wider sections of the links in a chain. And it wouldn’t have to be longer at all, most likely it will be shorter than a standard 2×10 setup. The range is bigger in the rear, yes; but the overall range of the 2×10 is greater. Think 10 to 34 and 42 to 34 versus an 11 to 26 and 36 to 39.

      • Cole33 on

        11 rear – 26 front.
        36 rear – 39 front
        yes its cross ring, but you have to fit your chain to those combinations. standard 2×10 setup on SRAM’s 120BCD

    • nh on

      I think the early rumours were that the chain would be the same as a standard 10 speed chain. They just squeezed another gear in the cassette using the newly designed free hub which is the special thing about it.

  5. ALAN ROXX on

    Oh man finally, this is hecka nice. I’ve been on 1×10 for a few years on all my mtn bikes with 10-36 cassette. Less clackety clack and FD on mtn bikes just suck.


  6. Ken Bognar on

    The XX1 offset upper pulley is definitely not a new idea. If you look back at Shimano mtb derailleurs of a few years ago they all had offset upper pulleys and Shimano road derailleurs still use the offset pulley. Not sure why they went away from it with the mtb stuff.

  7. Sam on

    Really nice article. It’s good to know that bike and its parts manufacturers are still developing new things to keep us bikers excited. Now what they need to develop is some sort of belt-drive system that is capable of changing gears!!

  8. Singletrackroadie on

    Question: will the gripshift version have a lock-on grip on the right hand side as well available. Don’t want to buy the rear (i.e. left shifter) and then have another brand on the right (exaple ODI)?

  9. Coach Ahmadi on

    Love it. I have been running XX 1×10 for the past two years and never missed the front chainring for racing or riding. No I did miss it on the 3rd lap at Fontana two years ago, but now I don’t need to.

  10. RodeGeek on

    Note that the published “available” date is not correct. I wouldn’t expect this group to be in stores before April (2013).

  11. srespass on

    this product looks great! i am hoping it will work on my freeride/dh rig, how stable is it on rough terrain at 30 – 40 mph? install with a Hammer Schmidt?


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