Shimano Deore XT 2x10 Speed Dyna-Sys Drivetrain M785
The brand new 2012 Shimano XT groupset has been redesigned from the ground-up, drawing heavily on the M980 XTR components line with features such as the double chainring crankset, integrated I-Spec mounts and the Vivid Index shifting technology. Although the previous XT groupset adapted the 10 speed technology to the M770 platform, the new M780 is designed specifically around the Dyna-Sys technology, which shows in the provision of the 2-ring crankset and the matching 2x10 front derailleurs that take front shifting speed to a whole new level. Combined with the wide-range 11-36t cassette, crisp Deore XT rear derailleur and shifter pods, you've got yourself a lighter, more efficient and more usable drivetrain than ever before. While XTR is Shimano's premier XC line, Deore XT will always be the original mountain bike groupset designed to appeal to trail & All Mountain riders across the globe. 

From Shimano:

"Shimano has been making mountain bike drivetrains for more than three decades, including eight generations of Shimano Deore XT (the original MTB drivetrain) and six generations of its flagship XTR group. Each generation is a reflection of the riding that defined the sport and the technology that defined the era. True to this legacy, our next-generation Dyna-Sys drivetrain brings with it the legendary quality, durability and performance riders expect from Shimano, all packaged to meet the ever-evolving demands of today’s riders".

So what exactly have they improved on?
Well aside from the obvious inclusion of a 10 speed cassette, Shimano have made several key changes to imrpove shifting on your bike. The XT Chain itself is now an asymmetric number, with one side that is made to work optimally with the shifting pins and ramps on the front cranks as you move into a bigger chainring, and the other side is made to work with the shifting ramps as it climbs up the cassette. This is particularly noticeable when shifting under load, as the 10 speed drivetrain is so much quicker and more accurate than previous generations.
The XT Cassette has a larger spread of gears than the old M770 version, with an 11-36t option giving you a super low gear for technical climbing and being particularly popular with bigger-wheeled 29er bikes. They still have an 11-34t option which will be better for XC riders, and both cassettes feature ratios that are tighter due to the extra cog.
With the change in ratios at the back, the XT Crankset is now available in a slick 2-ring version for riders wanting to go the full 2x10. There are 2 ratios available for the M785 crankset; 38-26t and 40/28t. For 29er riders, trail riders and those that experience a decent amount of climbing, go for the smaller ring setup. If you're racing or tend to spend most of your time in the big chainring on your current 9 speed setup, the 40-28t XT crank will be the one for you. And no need to stress about locking yourself into a specific gearing option, you can always swap out the chainrings to the smaller or bigger models as your riding requires.

And what does this mean out on the trail?
Well the main benefit is that you'll reduce the amount of shifting up front, which most people will agree is a very good thing. With a bigger spread of gears at the back, you can spend more time using a single chainring with less need to shift around up front, leaving you to spend more time focussing on the trail ahead. The double crankset not only reduces front shifting, it also provides more ground clearance under the bottom bracket and drops weight over triple chainring versions. You can access all of the cassette sprockets with each chainring, so not having to worry about crossing the chain excessively is a nice change for riders who hate having to look down at the gears to see what's going on. With the asymmetric chain and Shimano's Dyna-Sys gearing, shifts are smoother and faster than ever before, though the increased feedback through the shift levers provides a more positive feel than previous Shimano drivetrains that could have been considered a little too stealthy and silent.

The Shimano Deore XT M785 Groupset includes:

• Shimano XT Crankset: M785 with 38/26t or 40/28t ratio
• Includes XT Bottom Bracket
• Shimano XT Shifters; Choice of standard bar clamps or integrated I-Spec Mount (for use with M780 brake levers)
• Front XT Derailleur (Hi Clamp, Low Clamp, E-Type or Direct Mount - check your bikes specifications) 
• Rear XT Derailleur; Medium cage for 2x10 setups
• Shimano XT 10 speed Chain
• Shimano XT 10 speed Cassette (11-34t or 11-36t ratios available)

The 2012 Shimano Deore XT Groupset provides XTR level technology at a trail-ready pricepoint