Demystifying 2X10 Drivetrains
A few year back, mountain biking’s two dominant drivetrain manufacturers, SRAM and Shimano, decided that the traditional nine-cog cassette simply wasn’t good enough anymore. It was time for 10-speed.
The winds of change began to blow in 2008 when bike magazines and on-line blogs first reported SRAM’s intention to switch things up. Sure enough in late 2009, the Chicago-based component manufacturer unveiled its new, top-shelf XX 2x10 drivetrain. Soon after, SRAM expanded its offering, releasing X0, X9 and X7 2x10 groupsets.
Sensing the inevitable sea change, Shimano followed suit, unveiling it’s own 10-speed group in 2010. The Dyna-Sys drivetrain was added to company’s top-line XTR and XT cross country groups, and to their SLX all mountain group.
Reviews of both manufacturer’s new component groups were almost universally positive, but questions of compatibility were raised. Here’s a basic breakdown of each group, plus what you need to know about compatibility:
As you’ve surely guessed, SRAM dubbed its new group 2x10 because it pairs a double chainring crankset with a 10-speed cassette. What is surprising about the drivetrains is that they have essentially the same range of easy and hard gears as traditional 3x9 systems.
How is that possible? First off the 10-speed cassette has an extra cog and a wider range (11-36 vs. 11-34 on the old 9 speed). Secondly, the double cranks have a wider jump between the small and large chainrings. SRAM’s double chainring is available in either 28-42 or 26-39 teeth combinations. Traditional triple chainrings are 22-32-44.
SRAM says that 2x10 provides the same number of useable gears as 3x9, but with reduced weight, faster front shifting, and less overall complexity. This is possible, according to SRAM, because of their new X-Glide chainrings. These rings are specially sized so that every tooth on the small ring aligns perfectly with a tooth on the big ring. The teeth are also specifically shaped to facilitate each shift, up or down. Indeed, SRAM 2x10 is lighter, simpler and more precise, but there are some compatibility issues.
SRAM’s 10-speed drivetrain components are all cross compatible with just a few exceptions. The 2x10 drivetrains require a double left hand shifter, double crank with the X-Glide rings, 10-speed chain and double front derailleur. But their 3x10 drivetrains need a triple left hand shifter, 10-speed triple crank, 10-speed chain and triple front derailleur.
SRAM’s 10-speed mountain bike derailleurs (XX, X.0, X.9 and X.7) are also now compatible with their 10-speed road shifters (Red, Force, Rival and Apex). That means you can run Rival shifters with an XX rear derailleur and wide range X.7 10-speed cassette for mountain centuries. Unfortunately, their 10-speed mountain bike derailleurs are not compatible with their 9-speed mountain bike drivetrains.
Shimano revamped all the key parts of their 10-speed Dyna-Sys drivetrain. The cassette, front and rear derailleurs, shifters, chains and cranks are all unique and essential to the operation of the new system. Like SRAM’s new system, the Dyna-Sys rear derailleur has more direct cable routing, tighter shifter actuation ratio, redesigned chainrings, and wider range cassettes. The D-S cranks are available in both 2x10 (D-S XTR only) and 3x10.
Shimano also redesigned the Dyna-Sys specific asymmetrical chain. The D-S chain has four distinctly different outer plates to speed shifting. Their triple cranks now have tighter ratios (24-32-42 vs. 22-32-44) and their D-S XTR double chainring is available in three gear ranges (28-40, 30-42 and 30-44).
Shimano’s Dyna-Sys products are compatible with components in the Dyna-Sys line from SLX to XTR. But there are limitations when you go outside the line. For instance you cannot use a Dyna-Sys derailleur with 9-speed shifters. The only part that did not change in this new group is the front/left shifter.
Shimano’s Dyna-Sys XTR 2x10 drivetrain requires a Shimano D-S XTR left hand shifter that is convertible for double or triple, a Dyna-Sys XTR double front derailleur, a D-S speed chain, and Shimano XTR double crank.
Shimano’s 3x10 drivetrains require a triple left hand shifter, 10-speed D-S triple crank, 10 D-S speed chain and Shimano D-S triple front derailleur. Shimano’s D-S 10-speed rear derailleurs (XTR, XT and SLX) are NOT compatible with Shimano road shifters nor with other non-D-S ATB shifters.