Campagnolo is already there, and we’ve heard rumors another “S” has something in the works. Somewhere between vaporware and actual product, though, is a prototype SRAM Red eTap 12-speed that’s been flying across the interwebs lately.

One big difference between the two is the small cog on the cassette. Campy’s sticks with a standard 11-tooth cog and freehub body. SRAM’s doesn’t, opting to go with the smaller 10-tooth cog similar to what’s on their Eagle mountain bike groups.

The only way to create a cog that small is to reduce its inside diameter, which means the outside diameter of the freehub body must shrink, too. And that’s what XDR Driver bodies offer.

They also make cassette installation a lot easier because individual cogs and spacer rings aren’t used. Instead, they’re clusters or one-piece units that slip on easily and then lock into place using a traditional cassette lock ring and tool. No need for different axles or other standards, and you’ll still use a chain whip to take it off. For what it’s worth, that’s how the new Shimano XTR Micro Spline design works, too.

SRAM sent us a quick note to say that adoption of their XD and XDR freehub driver bodies continues to grow. Which is obvious if you’re a mountain biker since it’s the only way you can run their Eagle groups. And Eagle groups are everywhere now. However, roadies may not know as much about it yet. They’re about to.

how does sram xd driver body differ from xdr and how does it work This patent drawing shows how the cassette’s smaller cogs fit onto the reduced diameter section at the end of the Driver Body.

So what’s the difference between XD and XDR? It’s pretty simple, the “R” basically just means it’s for “Road”. That’s because they’re different widths and designed to accommodate the different cassettes used for road and mountain. Here’s SRAM’s description:

“The XD interface is designed for mountain bike applications and maintains the same hub spacing and flange locations used for 8, 9, and 10-speed compatible HyperGlide® freehub bodies. The XDR interface is 1.85mm longer than XD and is designed for road hub applications. XDR maintains the same hub spacing and flange locations used for 11-speed road compatible HyperGlide freehub bodies. XDR driver bodies are compatible with all XD cassettes when the cassette is installed with a 1.85mm spacer behind it.”

SRAM set up this explainer page (and video above), and we shot another video (below) with them that runs through it all.

If you look at the quick progression of Eagle groups to cover all price points, we wouldn’t be surprised to see a complete suite of 12-speed road groups from SRAM by MY2022 (assuming that 12-speed eTap group is real, of course). And SRAM charges nothing to license the design, so any hub manufacturer can offer it.

So this “news” should really only serve to comfort you that if they do indeed go to 12 speeds, wheels will likely be available from all your favorite brands. Because the hub spacing and all is the same, it means you should be able to sub in an XDR unit onto your existing 11-speed compatible road hubs as soon as that brand makes one, so you won’t even need a new wheelset.


  1. You forgot to mention that there are now SRAM cassette options for Eagle that fit an HG freehub. You lose the 10t, but also the enormous gear jump.

      • and a very distinct and noticeably poorer quality of shift. Sunrace is budget gear. Even NX is leap above the Sunrace cassettes..
        Whats the issue with the ratio spacing of Eagle? For any trained cyclist this is not an issue so why complain about till the cows come home?

        • Because he noticed the big gear jump a total of one time ever, and now he’s making a grand sweeping generalization of how it’s going to perform for everyone, on every ride, for all of time, and thus this cassette is subpar and SRAM should call it a day and make something that specifically meets his needs and his needs only, and that his assessment overrules the thousands of man-hours dozens of SRAM engineers in Germany spent developing this stuff.

          This is the dreaded cycling nocebo effect, which afflicts thousands of “cyclists” who like to keep it real by dropping knowledge culled from forums they read 10 minutes before posting.

          You see this a lot with suspension. If their friend tells them that the “mid stroke performance of this Fox fork is not optimal,” then guess what? They’re going to go on the forums and write, “I rode the Fox and its mid-stroke performance is not optimal,” after pushing on their suspension for 5 minutes in their garage. “Hmm, feels like mid stroke is a little off,” they’ll whisper to themselves as they stroke their chin and doublecheck terminology on Sheldon Brown’s website.

          I used to work in a shop and did this little experiment: Guy brings bike in complaining about the performance of his rear shock. I take it in the back, wipe down the air can and body with Windex, then bring it out an hour later. He rides it and says that there is a big difference in the way it feels when he rides it off the curb outside. This happens a lot.

          • Sooo true. It’s so funny to see a crowd of people riding fixed gear even for mtb and another crowd absolutely certain 12 is certainly not enough steps for their needs. 11 was already fine for most scenario but was a bit fiddly because for optimum race performance you would need to swap chainring depending on the course. 12 is fire and forget.

          • Indeed, Campagnolo will always be the best as they make their new stuff backwards compatible as far as possible. and their kit always just works straight out of the box. I will always be a fan because their stuff is reliable. However SRAM has really taken the innovative spirit of SACHS-Huret from hose ashes they rose and turned the industry on its head. XD/R is a superb concept that even Campagnolo can’t match because their driver body can;t accommodate a 10t sprocket. SRAM reliability has also taken leaps forward. My 10year old Force 10speed groupset has close to 50,000km on it on my training bike and a lot of that is on an IDT. I’ve replaced the cassette once and a couple of chains.
            So bring on XDR and new 12speed. The Eagle groupset on my MTB has over 8000km on it and I’ve only just replaced the chain. The cassette and chainrings are still going and don;t appear to have worn much. If SRAM brings the same longevity to the Road, we;ll buy a groupset and never replace anything till its time for a new group.

            • ShimaNO has always had planned obsolescence and planed lack of interoperability. Even before STI DuraAce was not compatible with 600/Ultegra and beyond. They would change splines, pull ratios, spacing, and on and on to create a forced market of their products.

              Campagnolo – Sachs (as you mentioned) – Mavic and others were more consumer focused with interoperability. One can look at the old Mavic BB that was available in both a Shimano or a Campagnolo/Mavic crank taper – and go into the BB shell no matter what threads were in it (or destroyed in it).

              I can fault SRAM at all for not wanting to go onto a Shimano thread hub. They at least have a good reason to want to create their own ‘standard’. Shimano on the other hand…was it not them who not so long ago was also on the bandwagon that a 10t cog stole more power than it would gain (plus wear and on and on)….still not sure who really needs that 10t……

        • Sure thing there, Record11. 1998 Chorus hubs with 11s and 2000 Record with 12s. Glad to see all the Campy fans come out of the woodwork on an article that has nothing to do with it. pffft.

          • I want to say they were 1999 hubs that are Record based on a Shamal HPW 12 wheelset….but, continue on as a typical lemming with run of the mill bits on a mass produced bike. Just try to keep the rubber side down.

  2. Huh? SRAM has been selling Force1 and Rival1 for road and cross bikes with XD drivers for a while now. Been running 1x on my cross bike with an XD driver and love it. Why does this article make it sound like XD has only been for mtb’s? That said, I would look forward to upgrading to wider range of 12spd when it comes.

    • Because it was only for mountain bikes, The 11-42 11spd cassette you get with force1 or whatever is actually from the gx/x1/xo1/xx1 mountain groupsets.

    • Because until now Force1 and Rival 1 used MTB cassettes 10-42 which work on an XD driver. XDR is a wider driver to accomodate cassettes with a large sprocket of 36T and smaller

  3. Well, I am an average people with 260w output. I am running 50/34+12/28 Dura-Ace crank and cassette, with which I am very pleased. I don’t see the point of having the 10t cog on a road bike, decreased efficiency and increased wear. Also, the last the thing I want to happen is another ‘new standard’.

    • With a 1x setup, a 10-42 at the back and a 42T ring means you have the gearing range of a wide compact double: 4.2 at the tallest gear, 1.0 at the shortest. For folks doing 1x on road who want that top end, the 10 cog offers them something otherwise hard to get without giving up the climbing end. (Now whether folks really use that top gear on the downhill runs here is another matter. I know a couple strong folks who claim they do.)

    • The 10t cog isn’t going to ear any faster as you’ll hardly use it. A 50 x 10 is a big ratio of 5. 50×12 is much smaller.
      you’ll probably be able to run a 48T big chainring to get gearing equivalency.

      Innovation isn’t needed so you don’t have to buy a new SRAM 12s Road groupset. But when its launched and you see what it offers maybe you’ll consider making the leap.

  4. Just hope that SRAM can have more then just one cassette option, maybe 10-25, 10-30, 10-34, something I wish they would do with Eagle. My mountain bike ( Turner RFX)has a 32t chain ring limit so instead of going to Eagle, I chose XX1 and use a 11-46 cassette. There was no need for a 50t cog with my 32t ring, I hardly use the 46. Before anyone says I must not ride steep climbs, I live at altitude, 7000′, most of the trails go up from there and we do have some very steep long climbs, still would never need a 32-50.

    • Shimano’s got your back : 10-45 xtr available now from Germany and as smooth or smoother than stock SRAM with an eagle chain & derailleur. You’ll need a freehub body, but it’ll probably be cheaper in the long run than the DFM nightmare that is XD cassettes.

  5. I was wondering when the build up to Red eTap 12 would start, I guess this is it. So expect the hype to go on and on (remember the long drawn out Shimano XTR 12 speed launch?). Roll on January so we can just see how expensive Red eTap is!

  6. When Sram comes out with etap12 I wonder if they will also come out with 12 speed cassettes for current Sram/Shimano road freehubs starting at 11t.

    • Not for a while, since not many will build up that group with a cheap cassette. Maybe once we see Rival 12, it will happen, but don’t hold your breath. There’s a rea$on XDr was developed.

      There are already cassettes that do what you need, since road requires finer steps, and not often wide range. What group would you use that cassette with? Shimano doesn’t offer it yet, sooo…wait?

  7. Shimano can’t deliver XTR 12 till February March 2019 do you really think 12s road is going to be a priority? Maybe 2020. Dura Ace 9100 is just about half way through its life cycle so 2020 seems to be the year for an announcement with maybe 2021 for store availability.
    And i certainly won’t be adopting microspline with those ridiculously small bearings.

  8. At some point, we’ll all stop jumping on every time someone adds a new cog at a massive expense like this. I don’t know if 12 will be the number, but the more cogs you put back there, the more precise the shifting needs to be, and bicycles get beat up. They crash, get shoved in cars, on racks.. things get knocked around all the time. When setup becomes an ultra-precise, ultra-sensitive process, that’s when I think we’ll stop playing this never ending marketing game. Innovation in this field has been at a dead stand still for a long time. Re-purposing a MTB hub for road with a 10T cog no one needs isn’t innovation.

  9. So the XD driver for 12 speeds somehow cant do the job so we have yet another standard in XDR. I sure am going to make my bikes last as long as possible from now on untill this standards race ends… Ridiculous.

    • 1) As another person already commented, XDR has been out for years. It is 1.85mm wider than an XD freehub, just like a Shimano Road 11 freehub is 1.85mm wider than a Road 10 freehub.

      2) The 12sp Eagle cassettes cantilever the 50T cog to the inside, so it actually sits closer to the spokes. It can do that because its huge, and has enough room (since spokes angle toward the rim). When your big cog is only 28t, you don’t have room to push it that far inside.

      And just like with 7, 8, 9, 10 speed…. 11 speed parts will be available for a long time.

  10. “Instead, they’re clusters or one-piece units that slip on easily and then lock into place using a traditional cassette lock ring and tool. No need for different axles or other standards”

    Can someone please explain what cassette construction has to do with axle standards? Honest question, not trolling.

  11. the 12 speed Road shifters on Sram doubletap Technologies are allready available at Stock-Rennsporttechnik in Germany. 12 speed with 3,8mm Gear ( 11sp std) usable as 11 or 12 gear, and 13 speed with 3,5mm gears (12sp std) usable as 12 or 13 gear. they sell at the moment with superrecord casettes for roaduse and eagle-cassettes or XTR for cross. cheeper solutions will come soon.

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