Spoke Magazine

SRAM release XO1 DH-specific drivetrain

Posted by Leif Roy on Thursday March 6 2014

A couple of weeks ago, Caleb and I flew down to Queenstown and spent the week hanging out with a contingent of SRAM Product Development, PR, and Marketing crew who were in town to introduce us (and a handful of other globetrotting media peeps) to two new Downhill specific products. We’ve had to keep things hush hush until today but we can now give you the low down on the new XO1 DH specific drivetrain. Unfortunately, you’ll have to wait a wee while longer to learn the details of the second product to be launched, but I will say that it’s pretty impressive and in some respects represents a bit of a shift in thinking from SRAM/RockShox. So stay tuned. Also, if you’re interested in learning more about the week itself we’ll be relaying the whys, hows, whos, and associated shenanigans in the next issue of Spoke.

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But first things first: XO1 DH. If there is one thing that SRAM seem to do well, other than media junkets, it’s innovation. Yes, they’ve had their misses over the years, but they certainly seem to get it right more often than not. The XX1 drivetrain is probably the stand-out example in recent years. According to Chris Hilton (external drivetrain product manager) the success of XX1 surpassed even his expectations. If you’re not familiar with XX1 and how it differs from more traditional two-by and three-by systems I’ll attempt to sum it up in a sentence or two. By going to a single front chainring as standard and a wide ratio 11 speed rear cassette, XX1 eliminates issues associated with front shifting and allows SRAM to improve chain management and chain retention while still providing a comprehensive range of gearing sufficient for most trail and enduro riding. In practice, this means that riders can run a simpler setup on their bikes without the need for a front derailleur or chainguide, without compromising pedalling efficiency, and without fear of suffering from dropped chains or phantom shifting. All of the key technologies that make XX1 possible, and one additional innovation, have now been translated into a downhill orientated drivetrain. Let’s take a look at what makes the XO1 DH special.

X01 DH Mini Block 7-Speed Cassette

The technology, or component, that distinguishes X01 DH from its trail orientated XX1 brethren is the DH specific 7 speed cassette. The Mini Block wasn’t spawned from the fertile minds of a marketing manager or an overzealous engineer but from observations of the behaviour of SRAM’s professional ‘Blackbox’ riders (like Stevie Smith) and their mechanics. It’s standard practice for DH riders to run close ratio road cassettes on their bikes as they simply don’t need the range of gears offered in a standard mountain bike cassette. However as cassettes have evolved to 9 and 10 speeds, DH racers have by default ended up with more gears than they need or want and so find themselves either; double and triple shifting in rapid succession during race runs, or alternatively creating custom rear cassettes with a reduced number of gears.

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The Mini Block 7-Speed cassette legitimises this practice and provides all DH racers with an optimised set of gears (10 -24) that can be quickly traversed without having to repeatedly mash away at the shifter. The compact one-piece machined cassette has additional advantages in that it is very light (“lightest cassette ever” apparently) and leaves plenty of space between the larger gear and your precious spokes. Space enough for a neat little aluminium guide ring to further reduce the chance of the chain going astray. Mating the Mini Block to the XX1 XD driver body allows the use of a compact 10 tooth littlest gear which effectively means you can run a smaller front chainring, improving ground clearance, while still maintaining the desired gear ratios. The very tidy one piece cassette is finished off in an apparently super durable ‘JET’ black finish (black is the new black!). If you’re not sure if 7 speed is for you there is a 10 speed version of XO1 DH available that uses a more traditional DH cassette and fits a standard freehub.

XO1 DH X-Horizon Rear Derailleur

There are two other key XX1 technologies that have been translated to XO1 DH and that are worth mentioning. The first is the X-Horizon rear derailleur. Unlike rear derailleurs on all two-by and three-by drivetrains, the X-Horizon parallelogram moves horizontally when shifting between gears (hence the name). Other derailleurs by comparison travel at an angle somewhere between vertical and horizontal. This means that the traditional systems are more likely to be affected by the downward forces resulting from the bumps and impacts that are a normal part of any off road riding. So in theory the X-Horizon should greatly reduce, if not eliminate, the likelihood of ghost shifting over rough terrain.

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The X-Horizon also sports the X-Sync narrow/wide jockey wheels (more on narrow/wide below) and the clutch mechanism, both of which help manage noise and chain retention.

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X-Sync Chainrings

Probably the most talked about, and now replicated, technology of XX1 is the narrow/wide chainrings (X-Sync in SRAM lingo). Because XX1 did away with the front derailleur it meant the chainrings could be engineered with chain retention and durability in mind as opposed to shifting. The alternate narrow/wide teeth on the X-Sync chainrings are designed to sync with the corresponding narrow/wide spacing in the chain. This reduces side to side play and results in fewer dropped chains and supposedly quieter running.

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Coupled with the features of the X-Horizon derailleur these are the key components that make it possible to get away with not running a chainguide on trail and enduro bikes. SRAM recommend that you still use a chain guide for DH racing as although the chances of dropping a chain are greatly reduced they are not eliminated. It was interesting to see that a few of the SRAM staff were riding DH bikes without chainguides and reported not having any issues. Some of you will have also noticed some high profile athletes like Cameron Zink also running DH bikes without chainguides. It’s also worth mentioning that power transfer up front is handled by the “lightest in class”, and uber desirable, sub 800 gram carbon cranks.

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Enough of the regurgitated marketing guff and techno lingo (sorry about all the X’s in this post by the way); what was XO1 DH like to ride? We had three days in total of riding on DH worthy trails up at Skyline, the Remarkables, and Coronet/Skippers. We rode a couple of different bikes from Devinci and Intense (both equipped with XO1 DH) and had plenty of time to put them through their paces. Having heard the thinking behind XO1 DH my initial observation was of just how instinctively I jump on a bike and start double and triple shifting through the gears. I’ve always been somewhat aware of it, but until it was pointed out to me I didn’t realise just how much I was doing it. It took me a while to break this behaviour as the 7 speed Mini Block cassette certainly reduced (but admittedly didn’t eliminate) the times when it was necessary. Once I’d readjusted my behaviour and shifting became second nature again I quickly forgot to think any further about it. Gear changes proved to be problem-free, smooth, and impressively quiet for the rest of our time on the bikes.

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In truth neither Caleb nor I are riders capable of pushing DH bikes to anywhere near their full capability, so we can hardly claim to have definitively tested XO1 DH over the course of our week in Queenstown. But from what we experienced and with confidence in the knowledge that it has been tested and proven under the hands and feet of the some of the world’s best DH racers, I’m fairly confident that XO1 DH will continue to cement the reputation established by XX1.  

  • Timjim

    Who’s the Yeti on the Devinci? :)

    • Mark

      It looks like a stoormtrooper mountain biking on his day off. Forests of Endor maybe?

  • Peter

    I have purchased a one up 42t cog for my 10 speed cassette. Do you think this new 10 speed x-horizon mech will be better suited to this system?

    • Leif Roy

      Peter I’m assuming you’re running one ring up front? If you’re not don’t even consider the X-Horizon you’ll likely destroy the derailluer.

      • peter

        of course i am. does anyone run more than one ring up front? i’ve never seen it . so will it work on the 42T or is it still a max 36T???

        • Leif Roy

          Sorry Peter I can’t give you a definitive answer as I’ve not tried it and I’m pretty sure SRAM wouldn’t recommend it. X01 is DH oriented and not intended for use with cassettes that have larger gears.

          • Leif Roy

            ‘X01 DH’ that is

  • Roberto

    That 7 speed system is great. No more locking out the top cog. No more jammed chains. And my bike will be so much lighter. Good work SRAM. Can’t wait to pimp my ride.

  • alex

    When can you tell us about the fork?