By now, you’ve hit the trail a handful of times and you’ve noticed your mountain bike’s shifting seems tired, or is ghost shifting on you. Time to replace your drivetrain. Your timing is good because component manufacturer SRAM just revolutionized mountain-bike gearing with its new 2x10 system--two gears up front, ten in the back (as opposed to the common 3x9 system).
Why is the 2x10 (sram2x10.com) revolutionary? Because it saves weight, narrows your stance for better skeletal alignment, reduces cross chaining, and just plain works better.
Fewer chain rings equal less weight, of course, but shouldn’t more gear combinations (3 x 9 = 27) be better than fewer (2 x 10 = 20)? No, because in the 3x9 there areredundant gear combinations (you actually end up with more like 22 gears), whereas every one of the 20 gear combinations in a 2x10 is distinct and functional. In my testing on the trails of Mount Ashland, Oregon, I didn’t miss the extra chain ring, either climbing or pedaling downhill. And because you only have to switch between two chain rings up front, rather than three, shifting is faster.
Furthermore, the 2x10 system reduces cross-chaining--when your chain gets bent out of line in the large rings up front and the small gears in back. Because the distance between the smallest rings on the rear cassette and the largest ring on thefront crank is narrower, the chain will run straighter. In fact, the chain in a 2x10 system is a few links shorter than one in a 3x9.
That’s not the only reason it works better. SRAM’s X-Glide technology is a system of up-ramps and gear teeth shaped to make shifting between the large and small front chain rings more efficient, with less of the “slop” often experienced while shiftinggears. Briefly, while transitioning between the large and small rings, the chain is engaged on more gear teeth than on a traditional set-up. In my experience, the chain clunked right into place every time.
A side benefit of 2x10 is that because there are only two chain rings up front, the space between your pedals is narrower, which means riders will pedal with betteralignment between the ankles, knees, and hips.
The drive train components--front and rear derailleurs, crank set, rear cassette, and shifters--come in four different price tiers, from the ultralight XX ($1,502) to the more durable but still super-light XO ($1,353) to the more budget-conscious X9 ($703) and X7 ($503). According to SRAM, the only difference between the XO, X9, and X7 should be in weight, with no drop off in durability. The XX is marketed to elite racers.
If you're shopping for a whole new rig, check out SRAM's list of mountain bikes that come standard with the 2x10 system.
--Frederick Reimers is the former editor of Canoe and Kayak magazine. He reviewed tents and sleeping bags for Outside's 2010 Summer Buyer’s Guide.