SRAM XX revealed

Full details of SRAM's all-new XX group are now out in the wild. We had a stab in the dark about likely features back in November 2008, so how awesome were the powers of the Bikemagic Hat Of Wild Speculation?

We said: ...the single-lever DoubleTap shifting technology (one click to upshift, two clicks to downshift) could perhaps make an appearance - SRAM already makes DoubleTap shifters for flat-bar road bikes.

They said: EPIC FAIL to kick off with, with the XX shifters using the same double thumb lever design as SRAM's existing MTB shifters but in a very compact, lightweight package complete with carbon fibre pull lever and top cover. The XX shifters share X.0's lever position adjustment, and there's a new MatchMaker X bar clamp if you want to combine all your controls. The key thing about the XX shifters, though, is that the right-hand one has ten clicks in it, which brings us neatly to...

We said: ... we wouldn't bet against a 2x10 transmission setup. Many XC racers are already using double-chainring setups, after all. A Red-style one-piece cassette looks likely.

They said: DOUBLE WIN. As the name (rather blatantly) suggests, XX is a twenty-speed setup - double chainring, ten-speed cassette. The cassette's quite a piece of work, with the middle eight sprockets (a pedant notes: SRAM, they're not "cogs"...) being CNC machined out of a single big block of steel. In a weight-saving measure, the biggest sprocket is aluminium. On the face of it that sounds like a recipe for rapid wear, but given that the XX cassette will come in either 11-32 or 11-36, it should be no worse than a middle chainring and it's replaceable without having to spring for a whole new cassette. Which is good - apparently it takes nine hours to machine the thing, so it's not going to be cheap.

While the X-Dome one-piece construction is borrowed from SRAM's Red road group, the XX cassette is a considerably more elaborate bit of work. Cyclocross racers who tried Red in the dirt reported all sorts of clogging problems, so SRAM's gone for an actually quite spectacular open design for XX, with lots of holes for mud to pass through and get away from the teeth. More holes = more CNC time, though. The result is impressively light, with an 11-32 coming in at a claimed 185g and the wide-range 11-36 at 208g.

Up front is the Truvativ double-ring crankset, the first MTB crank specifically designed for a 2x10 transmission. The arms themselves are composite carbon fibre (the arms) and aluminium (the spider) construction, with a proprietary 120/80mm BCD. Available chainring combinations are 26/39 (probably of most use to 29er riders), 28/42 and 30/45. Mathematically-inclined readers will notice that all those combinations are proportionally equal - the big rings all have 1.5 times as many teeth as the small ones. This is, as you might guess, not a coincidence. For a clean front shift, you need points around the chainrings where the chain can have one roller sat on a tooth on each ring. By choosing those particular combinations, SRAM has ensured more of those alignments. Helping things along are four sets of ramps/pins on the outer ring.

While chainline is a par-for-the-course 49.5mm, because there are only two rings the whole thing is narrower - 156mm between the outer faces of the cranks (where the pedal eyes are). The theory is that having your feet closer together is more biomechanically efficient, which seems intuitively appealing although as far as we know there's no actual evidence for it. It'll be slightly moot for owners of bikes with wide chainstays, though, as the ultra-narrow XX cranks may not fit. To accommodate that, there'll be alternative cranks with an extra 10mm of width. That's not done just by whacking in a longer BB axle - chainline is the same, the crankarms sweep out more.

As well as stance width options, you'll be presented with an array of BB choices. Or rather, most people won't - the vast majority of frames currently available have standard threaded bottom brackets into which only the GXP outboard bearing setup will fit. If you happen to have a frame designed around the BB30 push-in oversized bearing standard, there's an XX crank to fit that - it'll save you 60g.

There's also a third option - SRAM's new PressFit 30. This takes BB30-sized bearings and houses them in resin cups. You'll need a frame with a 46mm internal diameter BB shell to use them. PressFit is intended to do away with the snap rings and close tolerances that regular BB30 requires, but does the world need yet another BB standard?

We said: It's notable that nearly all of SRAM's brands are mentioned in the teaser announcement, including RockShox. We're going to stick our neck out and say that there's a strong possibility of some serious integration in the pursuit of ultimate light weight - stuff like a fork with an integrated brake caliper, shifters with built-in lockout levers, that kind of thing.

They said: FAIL for the integrated brake caliper thing, which to be fair was a pretty left-field suggestion. We giving ourselves a WIN for the built-in lockout levers, though. Bit of a cheat, as the XLoc lever's only "built in" if combined with the MatchMaker X bar mount, but our underlying suggestion that there'd be some tight RockShox integration is right on the money - there'll be XX versions of RockShox's SID World Cup, Reba and (interestingly given the XCish slant of the group) Revelation forks. The XX bit includes Dual Flow rebound control with beginning and end-stroke damping adjustment and, more pertinently, the XLoc hydraulic remote lockout. That's right, no cables. You can adjust the Floodgate blow-off valve remotely too.

We said: ...given SRAM's recent acquisition of wheel company Zipp, we wouldn't be at all surprised to see XX marking the debut of an MTB wheelset.

They said: FAIL. Maybe next year, eh?

We said: Swathes of carbon fibre and ceramic bearings all over the place are pretty much certainties.

They said: A brace of WIN there, athough as there are no hubs in the XX group there's only the BB and rear mech pulleys to benefit from ceramic bearings. All the high-tech materials put in an appearance, with the rear mech alone including carbon fibre cages, magnesium and aluminium links and a titanium spring.

We said: SRAM's top-line Red road group made waves by coming in at under 2kg for shifters, brakes, chainset, BB, chain and cassette - around 200g lighter than Shimano's Dura-Ace. If we apply a similar sort of percentage margin to XTR, then we're looking at a target weight for XX of about 2.3kg, like for like.

They said: Another mighty WIN - here's a quick'n'dirty weight comparison of XX and XTR, as close to like-for-like as we can manage:

2,257g is "about 2.3kg" in anyone's book. A direct swap from XTR to XX will save 396g (13oz). If you're in a position to use the BB30 crank, knock off another 60g (2oz). That's perilously close to a full pound - impressive stuff.

A lot of the weights are pretty similar, with mostly small margins over SRAM's Shimano rival. The brakes stand out as being startlingly light compared to XTR, though. The XX brakes use a new two-piece forged magnesium caliper, a two-piece aluminium/steel rotor, a forged magnesium lever body, carbon fibre lever blade and titanium bolts throughout. They share the TaperBore technology and tool-free pad contact adjustment with Avid's Elixir brakes. Rotor options are 185 or 160mm both ends, with an extra 140mm option for the rear.

Oh, and we said: "One thing that we'd be very surprised to see is any kind of HammerSchmidt-style planetary front transmssion - given the state of play at the moment, it's hard to see them getting the kinds of ultra-low weight and high efficiency that the XC race market will demand.

We're not going to give ourselves a WIN for accurately speculating about what won't be featured, though. If that was the game then winning would be easy - we'd have predicted a complete absence of pickled herring in the shifters, crankarms bereft of windows in the sides so you can see the tiny plastic beads inside rolling from one end to the other like a pair of high-tech rainmakers as you pedal and no bar-mounted herb garden. And that'd just be silly.

So totting up, we give ourselves a six-pack of WIN and a mere triplet of FAIL, leaving the tiny helicopter blades atop the Bikemagic Hat Of Wild Speculation spinning with pride. But what of SRAM XX itself? Where will it find itself on the win/fail spectrum? Well, with that kind of weight advantage over XTR it's got to be a win. 10-speed in the dirt is likely to be controversial, but it gives you a simpler twin-ring transmission with the range of a triple and about the same number of actually usable gears since you can get the whole cassette from either chainring. Time will tell how well it holds up.

As for price, it's looking like $2,400 and upwards for a full SRAM XX setup - we'll have to wait and see for UK prices. One thing's for sure - just as SRAM's X.0 gave Shimano a lot to think about (and resulted in the current generation of XTR), so XX will have the Big S pulling out all the stops...

Find out more at www.sram.com.