SRAM quietly introduced the XDR freehub body some time ago, but really hadn’t pushed a lot of knowledge about it out into the interwebz. XDR, which stands for “XD Road”, is simply a modified version of their mountain-bike XD Driver Body that was introduced with XX1. That system was designed to allow for a wider range cassette by making room for a smaller cog than would fit on a regular freehub body.

So, why a road specific version?

If you remember back to when 11-speed road bikes became a thing, there were ample warnings (guidelines, really) that if you were going to put an 11-speed freehub body on your 10-speed wheelset, you’d probably need to re-dish the wheels. Why? Because the 11-speed body was slightly longer, which meant the wheel’s centerline was pushed slightly toward the non-drive side. Which meant your tire could sit too close to the seat- and chainstays on that side, too. There’s a full tech breakdown on this right here with diagrams to illustrate exactly what changed.

SRAM XDR 12 speed road bike freehub body

Now that all road wheels come with an 11-speed body, SRAM needed a way to make their 11-speed XD-style cassettes fit those wheels without requiring yet another re-dish. Which is quite forward looking, really, since SRAM doesn’t even make a road-specific XD cassette yet. But 3T is for their new Strada aero road bike, and that one’s designed around the XDR standard.

But, mountain bikes never really changed their freehub spacing to accommodate 11-speeds. The 10-speed versions worked because they could dish the larger cogs to follow the contour of the spokes. Because XD was designed around that 10-speed spacing, SRAM needed to make it wider to fit on 11-speed road bike wheels.

So, XDR is 1.8mm wider than XD. To use an XD cassette on XDR, you need a 1.8mm spacer on the back of the cassette. And it doesn’t take much to imagine that space being better used for a 12th cog in the near future.

Zipp.com

43 COMMENTS

  1. As 1.8 mm is less than half the pitch of 11-speed cassettes, we can expect 12-speed cassette spacing to be narrower as well? Cantilevering over the spokes only goes so far…

    • There was that article earlier about both SRAM and Shimano having submitted patents for chainring left/right shifting. To 1x with more complexity than 2x.

  2. Can someone explain to me what I’m missing here? XD allows for 11 and 12 speed cassettes on MTB’s because the largest cogs cantilever over the spokes. If the XDR body takes up essentially the same space as a current 11 speed road freehub, how is it allowing additional space for a 12th cog? I.e. current 11 speed Shimano / SRAM / Campy cassettes, all of which use essentially the same spacing, take up the same amount of space on an 11 speed road freehub that XDR will, no? So, if a 12th cog is added, it too will need to cantilever over to some degree which could prove problematic based on how big that cog is correct? I might be missing something here about the spacing though, can someone explain.

    • What you’re missing is that it’s SRAM and they’re addicted to complexity. They seem very good at coming up with good ideas and then tying it down to some odd interface standard that the rest of the industry will either ignore (Torque Cap forks) or subvert.(narrow wide chainrings). They’re so addicted to new standards it wouldn’t surprise me if their design building had toilets that were only compatible with specific staff member’s backsides.

    • SRAM did not specifically cite the XDR as made for fitting 12 speeds; they said it is, essentially, an (road) 11-speed wider version of XD (which is, inherently, the same width as 10-speed). This would allow wheels to be built such that they can be more easily switched between regular 11-speed and XD cassettes (plus a 1.8mm spacer).

      -Ed

    • jbt – i don’t know a huge amount about MTB standards, but the article is saying that for 11 speed, rather than lengthen the cassette and alter the dishing of rear wheels, the inner cog was designed to overhang the spokes. Conversely, road freehub bodies were lengthened so that’s where the small amount of extra space comes from, according to what’s written.

      Again, that’s just my understanding of the above – and I’ll add a caveat emptor that I’m pre morning coffee…

  3. The road hub doesn’t have the need for BOOST spacing so the flanges of the hub can be closer together to allow for the longer cassette body

  4. worst explanation I have heard, “it allows you to change the freehub body with out needed shims or spacers, you can use the normal XD cassette with a 1.8mm spacer” Yes but what is the point, the current XD body already has an 12 spd cassette that works with it, so will XDR go to 13?

  5. Has anyone heard word on expected DT Swiss XDR freehub availability?

    I’d love to give that 3T cassette a go (42×9 ~ 51×11; 42×32 ~ 35×28) when those land and might as well get the road driver if it’s close.

    It’s kind of surprising that SRAM didn’t do an XD 10-36 a year or so ago- could have been good for both tourers (with a double) and cadence-sensitive XC racers.

    • it seems weird that 3T’s cassette is only 11 speed but needs the XDR and not just an XD? I’m in the same spot as you. I have the DT XD freehub and use the 10-42 with a 50t chainring. With the new 3T cassette I could drop the larger cassette, drop the chainring size and use a lot less chain links while still getting a good range saving a little back end weight.

      • I suspect that the 3T will work just fine on an XD body- but as the XD body is a little narrower than the 11s road (which is on my wheels now) I’d just as soon go that route and be ready for 12s if & when it arrives rather than re-dishing my current (inaccessible nipple) build. That’s my thought anyhow.

        My gravel bike has an XD 10-44 (XX1 w/Wolf Tooth GCX) and 42t oval ‘ring, which has been a lot of fun- but the steps and range are more than I’ve wanted on the road.

        • The inaccessible nipples on my otherwise fantastic Syncros wheels mean that eventually I will switch to another wheelset. What a lame ‘feature’.

  6. Bottom line is the 130mm road hub width is simply too narrow, using 135/142 MTB standards is the way forward but Shimano/SRAM etc want you to have to invest in a new standard, take 12mm front thru axles and flat mount brakes as prime examples of this.

    Same goes for the road BB 68mm width, by simply changing to the 73mm MTB width we have much more space for larger tires but the big players want more of your money than they deserve.

    • 12×142 is the new standard road hub. BB386 on gravelbikes to make place for short chainstays and wide tires. Cannondale uses 73mm on their BB30a standard already.

      12 speed with 9 or 10 as smallest and 32 or 36 as biggest would be awesome for a single chainring setup. I think 42 is way too big.

    • Indeed. I have never understood why road bikes didn’t scale up to 135-mm hubs around the time that 8-speed drivetrains became popular. I guess there’s an argument to be made for keeping the Q-factor narrow, but it entails serious compromises.

    • Isn’t XDR a moot point if road bikes adopt 12×142 rear-end spacing en mass? My 12×142 CX bike is already running 1x using a 10-42 XO cassette on MTB wheels/hubs, with SRAM Force1 mech and shifters.

      Chain line is right down the middle of the cassette and Q-factor is unaffected. Now just waiting on a 12-speed road shifter so I can drop in an eagle cassette. XDR just seems like a distraction and an excuse to sell more product. No sale.

  7. @blah blah blah: I personally do not – I loathe it actually. I cant help but feel like all of these “solutions” are half-step, band aid measures. The clown needs to be blown up. More and more, I am gravitating toward the notion that boost spacing is the solution for gravel bikes

  8. The road bike spacing is going away from 130 (non-disc) and going to 135/142 spacing like road disc. SRAM is “most likely” doing the same. Shimano is developing the new groups right now. Additionally XTR will have two cassette body options. One for industry to use and the new one which will be proprietary for Shimano use only (12 speed w/ largest 51t rear cassette). SRAM most likely will be doing similar moves mirroring Shimano. This is the behind the scene talk at Eurobike w/ PD mgrs. NDA’s are signed but so no one openly gave all the details at once. Gathered from mulitple sources it “sounds” like this is the general direction for drivelines. 130OLD is starting to die for MY19’… not sure how far down the 135/142OLD road will go (non-disc). Wheel manufactures everywhere are getting ready for wider non-disc road.

  9. 1x on the road is an answer looking for a problem. A problem we don’t have. It brings no value whatsoever (except more profitability for SRAM).

    • Ed,
      Have you tried it? Lighter, less expensive, similar range to a mid-compact (esp. with 12s), and lower maintenance. Accute chain angles can be a little noisy, but assuming an entry-to-mid-range target customer it’s better than cross-chaining or persistent front derailleur rub. Feels like a win for a good chunk of the recreational market.

  10. all this new stuff makes my head hurt. Keep tweaking standards so that we can fit 12 cogs w/ a 9 or 10 tooth small cog so we can ride 1x. Or we could just keep riding 2x, using the wheels and cassettes we already have, and keep the same range of gears with smaller steps between.

  11. While this will enable the use of 12 speed XD cassettes on road bikes, I think the real game change will be when sram, shimano or campag produce the close ratio cassettes required for road riding/racing an then market them at a price that is not so high as at present (Sram XG 1275 cassette €200, Dura Ace 9000 11-28 €140.00). Obviously the 12 speed rear mech and shifters will need to come to market.
    As several of the above posts have mentioned, I think cassette ratios somewhere around 10-36 would be ideal. A 10-36 paired with a 48t chainring will give you a spread of ratios that is a near to if not identical to a 53/39 11-28 conventional road drivetrain. I’ve ridden a 1 x drivetrain (52t chairing 11-36 cassette) for 18 months and its very very good, the only downside is the big ration jumps further up the cassette. I think the increase of 2 cogs on the 12spd cassette will sort this issue.

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