SRAM XX Groupset 2x10 Speed
Designed as a complete system, the amazing mountain bike specific SRAM XX drivetrain takes shifting to a whole new level. Including the brand new Truvativ XX Crankset, matching X-Glide front derailleur, PC-1091 chain, hollow CNC machined cassette, snappy XX trigger shifters and the carbon-fiber happy XX rear derailleur, the SRAM XX groupset packs in State of the Art technology and materials for a high performing and super light weight package. While Shimano has long held the mantle when it comes to smooth gear changing, the latest XX components have re-written the rule book and created the fastest and most accurate shifting drivetrain available. 

Being the very first 10 speed groupset on the market, SRAM XX has brought forward new technologies and innovation to an otherwise stagnant drivetrain market that had seen little change over the past 25 years. Designing the XX group around a wide-range 10 speed cassette that features an 11-36t spread, SRAM were able to downsize to a double crankset instead of the traditional 3-chainring cranksets that have been used on mountain bikes since their invention. While many riders have been experimenting with 2-ring drivetrains for a number of years prior, limitations in crankset design and available gear ratios meant it was always a bit of a bodge-job that never quite had the usability or smoothness of a regular 3x9 drivetrain. The Truvativ XX crankset uses a double-specific chainline that allows the rider to use the entire cassette range in each chainring so you can minimise front shifting. Aside from being lighter than a 3-ring crankset, you also get more ground clearance from the XX cranks and a smaller range of movement for the front derailleur that reduces the chance of dropping a chain. 
The main advantage of using a 10 speed cassette is the smoother gear changes thanks to the tighter ratios between each cog, so that the rider can maintain a smoother cadence while riding through varying terrain. With a smaller gear range up front, a shorter chain length can be used as well as a shorter cage for the rear derailleur, so shifting speed is enhanced further, with less overall chain slack. With your choice of cassette and chainring ratios, you can design the perfect XX drivetrain for your riding style and terrain.

X-Glide Technology
Designed as an integral part of the chainrings, cassette, chain and front derailleur, the X-Glide system incorporates very specific chainring ratios, shift gates, ramps and pins to create the fastest shifting drivetrain available. Traditional chainring geometry forces a compromise between up and down shift locations, none of which have ideal timing. In fact, half of the possible shift locations are skipped on each crank revolution. The more shift locations you try to incorporate, the worse the timing compromise will be: either your chain jams, causing chain suck, or the chain just fails to shift and runs across the top of the rings until it hits the next shift location. Those days are over with X-Glide.
X-Glide is the common denominator that gives XX its unmatched shifting performance. With X-Glide, all four upshift locations are identical and can be picked up by any outer link. The result? Up and down shift locations have perfect timing, for an almost instant shift—even under load!

From SRAM:

"Precision. Consistency. Victory. The very first 2X10 group in mountain biking delivers unparalleled shifting performance at an incredibly light weight. X-Glide™ technology incorporated into the chainrings equals a front shift that has never been this crisp. By maximizing the number of perfectly aligned points between the large and small chainrings, X-Glide shifts when you shift. This is XX".

The SRAM XX Groupset includes:

• Technology: X-Glide, Exact Actuation
• SRAM XX Crankset
• SRAM XX Shifters
• Front XX Derailleur 
• Rear XX Derailleur; Medium cage for 2x10 setups
• SRAM PC-1091 10 speed Chain
• SRAM XX 10 speed Cassette XG-1099 
• Optional: GXP Team/BlackBox Bottom Bracket
• Total System Weight: 1621 grams (not including BB)

Choosing your XX Drivetrain
With a number of different available options to suit different frames and different riding conditions, you will need to select the necessary components for your bike and riding style.

• Crank Length: Coming in both 170mm and 175mm lengths for different length legs, most riders will need the standard 175mm option. Riders under 5'6" should choose the shorter 170mm length.
• Q-Factor: This measurement is the horizontal distance in width between your right and left crank arms. A wider Q-Factor provides mores stability and is generally better for female riders with wider hips. Road riders will prefer the smaller Q-Factor option on the XX cranks as it mimics the narrower pedal stance of road bikes. However, the narrow option can sometimes be too tight for some frames and cause contact with the chainstays: Check with your frame manufacturer to determine which options are compatible.
• Chainring Ratio: XX Cranks are available in a smaller 39/26t ratio that will suit 29er bikes, trail riders and those who frequent steep terrain. For flatter trails or powerful XC riders, the larger 40/28t ratio will provide a higher gear, at the expense of a smaller chainring for steep climbing.
• Bottom Bracket: The majority of frames on the market are designed around a standard threaded bottom bracket shell, though many modern bikes are now coming with a press-fit bearing system. The standard GXP axle (24mm) fits regular threaded bottom brackets with the addition of the GXP Team BB. It will also fit pressfit bottom brackets that use GXP bearings or Shimano bearings with a GXP adapter. BB30 relies on a larger diameter bottom bracket axle (30mm) that requires a BB30 specific frame. Unless you have a BB30 frame, choose the standard GXP crankset.
• Front Derailleur Clamp: The XX front derailleur comes in 3 different mount options. Low (Top Swing) & High (Bottom Swing) mounts use a standard band-style clamp that wraps around the seat tube and come in both 31.8mm or 34.9mm diameters. E-Type Direct Mount (or S3 in SRAM speak) uses two mounting holes that bolt onto the frame instead of a clamp like a traditional high/low mount front derailleur. Check with your frame manufacturer to determine which model you require.
• Front Derailleur Cable Pull: Bottom or Top pull refers to the direction that the front derailleur cable is routed. If the cable comes up from under the bottom bracket shell, it is a Bottom Pull. If the cable comes down from above the seat tube, it is a Top Pull.
• Cassette Ratio: While most riders will choose the wider 11-36t cassette ratio for maximum gear range, the XX cassette is also available in a tighter 11-32t ratio for even faster and slicker shifting. However, you do lose some low end gears so this ratio would be recommended for smoother terrain with less elevation.