A funny thing is happening in the mountain bike world. More and more folks are realizing that, for some applications at least, a ‘traditional’ 3 x 9 gear set-up may be overkill. After years of having 3 gears up front (this has pretty much been the standard since the earliest days of mountain biking, and at first was one of the main features to distinguish the mountain bike from its 2 chainring’d on-road cousins) some riders are moving to just 2 chainrings.
It’s worth pointing out that in the early days we only had 5 or 6 cogs in the rear, so by adding a 3’rd chainring up front we had 15 or 18 gears instead of 10 or 12. That’s a huge difference in range. Now that drivetrain design has advanced to the point that we can have a 10 speed cassette in the rear we can eliminate 1 of the 3 chainrings up front and still have 20 gears!
What’s more, the 20 gears have a much more ‘usable’ range with less gear ratio overlap. For those who have never stopped to think about it, some of the gear combinations in a 3 x 9 set-up are virtually wasted because more than 1 combination provides nearly the same ratio, meaning that some combinations are almost redundant. In other words, you don’t really have 27 gearing choices. Confused? Read bike tech legend Sheldon Brown’s explanation here, or calculate the ratios on your own bike’s set up by going here to see which combinations are redundant.
Many riders have recognized this inefficiency for years and as rear cassettes expanded more folks have ditched one of their chainrings up front, but the new 2 x 9 home made set up wasn’t optimal. If you changed the circumference of the two remaining chainrings to provide a more optimal range you would likely alter the alignment of shifting ramps, creating less than perfect up and down shifting. Moving to a 2 chainring setup may also detrimentally affect the chain line in your most commonly used gears, and trying to address chain line issues by adjusting the bottom bracket width (and in turn the driveside crank position) can have a negative impact on your q-factor. Don’t know what we’re talking about? Don’t worry, because the folks at Sram do, and they’ve created a new product line that addresses these issues and works well right out of the box.
Introduced last year on the super high end XX group, 2 x 10 speed shifting is now available on X0, X9, and X7 groups as well, making the set-up much more attainable for most riders. In the process of addressing gearing inefficiencies the folks at Sram have also developed a range of drivetrains that are lighter and simpler than their predecessors. Not bad. They’ve put together a website specific to their 2 x 10 line here.
While we won’t write the obit for the 3 x 9 drivetrain just yet (and while we don’t think there’s a necessity to ditch what you’ve got if it’s working well for you) we do wonder if 2 x 10 is the beginning of a new standard that will eventually trickle down to most mountain bikes. If you’re an early adopter come into the shop and check out the 2 x 10 stuff we’ve got in and/or can order in. Maybe it’s for you.