SRAM unveil new XX mountain bike groupset
By James Huang, technical editor | Wednesday, May 27, 2009 9.10am
The Truvativ XX crank shifts the chainline inboard for two-ring use so that all gear combinations are quiet and smooth James Huang
The SRAM Group have brought their four component arms – SRAM, RockShox, Truvativ and Avid – together to create their first complete mountain bike groupset, dubbed XX. It's packed with features and technology, exceptionally lightweight – and expensive – and ups the ante of performance for the cross-country set. BikeRadar's technical editor James Huang headed to Borgo Pian del Mucini, Italy to find out more.
XX – what is it?
Though consumers have always been able to piece together a complete package from SRAM's four brands, XX (say "ex ex") is the company's first integrated off-road package.
Targeted firmly at the cross-country and light trail set, XX shuns the usual 3x9 drivetrain configuration in favour of a two-ring crankset coupled to a wide-range 10-speed cassette.
Total claimed weight for a nine-piece group is a stellar sub-2,300g and suggested retail price is a heady US$2,430 (approx £1,525) – over 300g lighter than Shimano XTR M970 but at a cost premium of about $2 (£1.25) per gram.
According to SRAM, shaving weight wasn't the primary focus of XX though. Rather, it was conceived to be the "lightest and best fully featured and fully adjustable" package available. Based on our initial test rides, they may well have met those goals.
The undisputed star of the group is the new 10-speed 'X-Dome' cassette weighing in at just 208g – 42g lighter than XTR even with XX's extra cog.
Like SRAM's road-going Red unit, XX consists of a nickel-plated CNC-machined 4130 chromoly 'dome' – reportedly requiring nine hours each just to mill – mated to a 7075-T6 aluminium backing plate.
In this case, aggressive machining leaves a sparse lattice of material that mud and debris can easily push through – a common complaint from the cyclo-cross crowd on Red – and the similarly milled-out backing plate on XX now also doubles as the largest cog.
The new X-Glide tooth profiles are markedly more complex than before and the unique construction allows for virtually zero cog flex for smoother chain movement under power.
Gearing options include a conventional 11-32T but also an 11-36T, which can provide nearly the same low-range gearing as a triple depending on the chainring configuration used.
Those with worries about the durability of an aluminium rear cog will be relieved to hear it can be replaced individually. In theory it should last longer than a conventional middle chainring since it is likely to be used less.
The new Truvativ XX crank is similar in construction to Red and Noir with a unidirectional outer shell surrounding an aluminium spine and foam core.
Bottom bracket options will include standard GXP and BB30 but also press-fit variants for both and all will include hybrid ceramic bearings as standard equipment.
Press-fit GXP bottom brackets will be compatible with frames designed for Shimano's press-fit system such as those from Yeti and Pivot Cycles.
Claimed weights are as low as 694g for the BB30 version and 754g for GXP – about 100g and 50g lighter than XTR, respectively.
Pedal stance width is as low as 156mm, though wider 164mm and 166mm options – each with their own dedicated crankarm moulds – will also be available depending on frame dimensions. Crankarm lengths will be limited to 170mm and 175mm for now.
SRAM have focused heavily on XX's shift performance and the X-Glide concept pays its biggest dividends up front.
Chainline is optimized for a 2x10 system with the chainrings bisecting a plane 49.5mm from the bike's centre line for quieter and more efficient running plus access to the full cassette range in either ring. Chainring options will include matched 26/39T, 28/42T or 30/45T.
Chainring combinations are intentionally matched in 1:1.5 ratios as SRAM have discovered that that magic number yields the greatest number of points where the chain can be simultaneously fully engaged between the two rings – 13 for the 26/39T, 14 for the 28/42T and 15 for the 30/45T, whereas normally there are just two – for the smoothest possible shifting under load.
Add in four sets of upshift ramps and pins, and another four sets of downshift points, and the result is what SRAM claim is their best front shifting to date.
In addition, the outer ring is machined from a 6mm-thick 7075-T6 aluminium plate and is supported by a beefy carbon spider with a proprietary 120mm bolt circle diameter while the inner ring uses a similarly XX-specific 80mm dimension.
Many will undoubtedly cry foul over yet another chainring standard but at least in this case replacement rings are expected to be fairly reasonably priced.
Admittedly, XX's 2x10 gearing doesn't quite offer the total range of a conventional drivetrain but depending on which configuration you choose it can be surprisingly close depending on the particular requirements.
For example, a 26/38T and 11-36T XX combo will yield a low gear roughly equivalent to a 22x30T and a high gear nearly on par with a 44x13T; the other extreme will virtually duplicate a triple's highest gear while mimicking a 22x25T. Not bad, all things considered.
The new shifters are based on the existing X.0 triggers with borrowed features including the aluminium-and-carbon fibre clamshell design, two-position clamp, basic two-lever layout and adjustable pull lever.
However, the XX trigger shifter bodies are more compact and the 3mm-shorter pull levers are now carbon fibre, making for an impressive claimed weight of 183g per pair – about 40g lighter than XTR.
Shifter internals are specific to XX's 2x10 system and the rear cable pull actuation is shared with SRAM's road groups. Though this makes them incompatible with other SRAM off-road bits, the Exact Actuation rear shift geometry – whereby a given amount of cable pull yields the same amount of linear derailleur movement regardless of position – is more tolerant of variables such as hanger thickness. This opens up new possibilities for cross-compatibility between XX and SRAM road groups for 'cross and touring bike applications.
The rear derailleur shares the basic X.0 features but with significant updates such as a full carbon fibre pulley cage (with a 93mm cage length optimised for 2x10), forged magnesium inner parallelogram link and forged aluminium B-knuckle and outer link for a claimed weight of 181g – about 20g lighter than X.0 or XTR.
The cable fin and anchor bolt assembly have been moved from the outer link to the inner link for additional protection from trail hazards and both pulleys use hybrid ceramic cartridge bearings.
With XX comes SRAM's first truly high-end mountain bike front derailleur. The new XX changer is built from forged 6061-T6 aluminium with a steel cage specifically designed around the XX's two-ring crankset.
Claimed weight is 118g – about the same as XTR and 36g lighter than SRAM's current top-end X-9 – and SRAM will offer the XX front derailleur in a staggering 40-odd configurations including low mount, high mount, four varieties of direct mount standards plus multiple clamp sizes and cable pull options.
High mount versions will use a neat stainless steel band clamp that should conform better around – and exert less stress on – carbon fibre seat tubes.
The Avid XX hydraulic disc brakes will borrow heavily from the existing Elixir brake (Taperbore master cylinder architecture, identical pads, similar look and feel) but a streamlined master cylinder shape, a new forged two-piece magnesium caliper and a stainless steel rotor with a six-bolt aluminium carrier bring the system weight down to just 288g (front, post mount, 160mm rotor). Center Lock hubs will require a rotor adapter.
As on SRAM's top-end Elixir models, XX will include a tool-free pad contact point adjustment but a tooled lever reach adjustment and a press-fit pivot pin for a stouter feel. Lighter alloy-backed organic pads will come as standard and rotor sizes will range from 140mm (rear only) up to 185mm.
A lighter U-shaped one-piece clamp (reminiscent of the old Single Digit Ultimate levers) fosters an updated MatchMaker X accessory clamp, too, which boasts a cleaner look than the standard Matchmaker – especially with the new remote fork lockout switch – but also a wider range of angular adjustment for the shifter pods, easier lateral position changes and more accessible bolt heads.
SRAM's quoted weights and prices for XX do not include suspension forks but they're an optional part of the package as well – though only slightly altered from non-XX versions.
All XX-level forks will include the new XLoc remote hydraulic lockout switch, which trades the old steel cable and housing for 5wt suspension fluid and nets smoother and fully sealed action plus a 60g weight reduction.
In contrast to existing RockShox remotes, XLoc operates more like a retractable pen – push it in to turn the suspension 'on' and pop it out to engage the lockout.
According to SRAM, the system may seem more complex – there are bleed ports just like on hydraulic brakes – but it's not as sensitive as the brakes to air contamination, it's easier to bleed and (in theory) should require virtually zero maintenance once set up. A built-in Floodgate knob is integrated into the design for easily tunable lockout blowoff threshold.
The race-oriented 80/100mm-travel RockShox SID XX World Cup sports a claimed weight of 1,436g – with the XLoc remote – with a new one-piece hollow carbon fibre crown and steerer assembly, and similarly shortened internals to the current SID World Cup. Lowers are now all magnesium (sorry, no more carbon fibre enhancements) but total weight has dropped nonetheless.
For several hundred dollars' savings, the standard SID XX adds 110g by virtue of its standard forged aluminium crown and steerer.
There's also an 80/100/120mm-travel Reba XX in both 9mm quick-release (1,651g) or 20mm Maxle Lite through-axle (1,781g) versions plus the versatile Revelation XX in 130/140/150mm and 120-150mm Air U-turn flavours ranging in weight from 1,695-1,825g depending on spring and dropout configuration.
SRAM haven't developed an XX-specific chain, instead opting for the existing 10-speed-compatible road units such as the PC-1090 and PC-1090R.
Hardware throughout the range is almost exclusively titanium or aluminium and nearly all of it uses a standard T25 Torx head for easy servicing – no more fumbling around for multiple wrenches.
As of right now there are no XX wheels as part of the package but given SRAM's recent acquisition of Zipp we wouldn't be surprised to see some introduced in the near future.
In fact, when we pressed SRAM's global marking manager David Zimberoff about it we got this reply: "Wheels would definitely be a great addition to the XX line – at some point." Perhaps at Interbike?
So, how does it ride?
We sampled an XX-equipped Merida Ninety-Six over three days on the trails of southern Italy and came away duly impressed.
Shift performance is the most dominant feature of XX as it's by far the best we've yet seen from SRAM – on or off-road.
Out back, the new X-Glide cassette now shifts with Shimano-like precision (finally!) but is also refreshingly smooth and quiet, especially compared to the road-going Red.
Up front, the X-Glide geometry and stouter chainring deliver real-world performance to match up to the marketing hype, and even when abused we neither dropped a chain nor experienced any chainsuck or clatter.
We can only hope X-Glide's more advanced tooth profiles soon make their way down the rest of the SRAM cassette range.
Interestingly, though XX is quite possibly the best-shifting group in the SRAM family, the 2x10 gearing requires fewer gear changes since both rings now yield more usable ratios. The full spread on the extra-wide 11-36T cassette is accessible in either chainring and the straighter chainline means that the system runs both quieter and with less friction than one would expect from a crossed combination.
Even on steeper climbs we rarely dropped down to the inner ring and were able to get back on the gas quicker after cresting the top as there was no need to double-shift both ends – a notion supported by SRAM-supported athletes Mary McConneloug and Mike Broderick (Team Kenda-Seven-NoTubes).
Braking performance is largely identical to the current Elixir CR, with smooth progression and predictable modulation, quiet operation and a snappy lever feel.
Shifter feel is subtly different from the current X.0, however, with a slightly lower total effort and feel but a seemingly higher threshold to inadvertent movement – meaning the levers are easier to push but accidental upshifts are now far less frequent. Multiple upshifts now require a somewhat more deliberate motion, however, but it's a trade-off we'll accept.
As for the XLoc, we're not entirely sure just yet. The operation is ultra-smooth but is essentially opposite to how the current PopLoc and PushLoc remotes work. This way seems to make a bit more sense as the button is easier to find when the system is locked out – a good thing after you've crested a climb and are bombing down the other side and are struggling to open the system back up.
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So what now?
SRAM say production units will begin shipping to OEM and aftermarket outlets no later than 1 July and industry support for the two-ring concept has been surprisingly robust.
Whether or not the public will see the performance gains as worth the substantial price premium remains to be seen – after all, a complete XX group will buy a rather nice complete bike – but for those who demand the latest and greatest, this now seems to be it.
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Suggested retail price
SRAM XX rear derailleur
SRAM XX front derailleur
SRAM XX trigger shifters (pair)
183g (low mount)
SRAM XX cassette
208g (11-36T); 185g (11-32T)
Truvativ XX crankset
754g (GXP); 694g (BB30)
$430 (GXP); $470 (BB30)
Truvativ XX bottom bracket
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SRAM PC-1090R chain
Avid XX brake (w/ rotor)
$373-377 (per wheel)
Avid MatchMaker X (pair)
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RockShox SID XX World Cup
RockShox SID XX
RockShox Reba XX
1651g (9mm); 1781g (20mm)
RockShox Revelation XX
1695g (9mm); 1825g (20mm)
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