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 3×9 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 substantially quieter than before and shift far more smoothly than anything we’ve yet seen from sram: the new x-glide tooth profiles are substantially quieter than before and shift far more smoothly than anything we’ve yet seen from sram James Huang
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.
The bb30 version of the truvativ xx crank is the lightest in the line at just 694g: the bb30 version of the truvativ xx crank is the lightest in the line at just 694g James Huang
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 2×10 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.
The truvativ xx crank shifts the chainline inboard for two-ring use so that all gear combinations are quiet and smooth: the truvativ xx crank shifts the chainline inboard for two-ring use so that all gear combinations are quiet and smooth James Huang
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 2×10 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.
The pull lever is still adjustable for angle but now 3mm shorter than x.0 and made of carbon fibre: the pull lever is still adjustable for angle but now 3mm shorter than x.0 and made of carbon fibre James Huang
Shifter internals are specific to XX’s 2×10 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 2×10), 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.