By Tom Jow
Every spring, my life in the shop is one of bike envy. If one of my friends or co-workers is not getting a new bike or component to drool over (and they usually are), one of the clients is. This year the SRAM XX1 and X01 single ring drivetrains for mountain bikes are on my hot list. Of course I didn't always feel this way. When I first heard rumors about XX1 in 2012 I was skeptical as usual. With the introduction of XO1 year I have become more familiar with them and therefore, have begun to see their benefits.. For those that are unfamiliar with them, the SRAM XX1 and XO1 drivetrains use a single chainring drive with the first ever 10t-42t, 11-speed mountain bike cassette.
What makes it so cool
There are two things that make the XX1 and XO1 so cool. The first is the chain guide-less single chainring. Single ring drive has been used before on both mountain and cyclocross bikes but always required a chain guide to keep the chain from derailing in rough terrain. SRAM was able to overcome the need for a chainguide in two ways. First, the rear derailleur uses the Type 2 clutch spring introduced in the earlier XO group. This virtually eliminates chain slack caused by rough terrain. Second, they redesigned the chainrings with alternating wide and narrow teeth to provide more contact area for the chain which also helps keep it from derailing.
The next outstanding feature of the SRAM XX1 and XO1 groups is the 11-speed, 10t-42t cassette. These eleven gears provide a range nearly as wide as the popular two-ring setups. Used with a 30t chainring, the high gear is approximately 79 gear inches with a 26 inch wheel. At a cadence of 80 rpm a rider can travel at 28 mph in top gear, just 3 mph slower than a 32t-11t combination on a two-ring drive. More importantly though, the 30t-42t combination provides a low gear of 19 inches, just 3 inches more than a 22t-36t.
In addition, these single ring drivetrains are much lighter than their two-ring counterpart. Being the weight weenie that I am, I compared the specifications of the new XO1 to the existing XO two-ring setup. By removing the front derailleur and shifter, coupled with other design improvements there is a weight savings of nearly 300 grams. Also, not requiring a chain guide saves another 100 grams or more. That's almost a whole pound!
Nothing is perfect
When I was young adult, someone once warned me, “All that glitters ain't gold”. And gold is what you need to purchase one of the new SRAM drivetrains. At a cost between $1400 and $1500 you receive six of the necessary components: cranks, chainring, chain, rear derailleur, cassette and shifter. On top of this, neither group includes a required freehub body upgrade ($100-150 if you're lucky, a complete wheel if you're not). Also, that wide range gearing may sound great, but type of cranks or size of the wheels matters. The smallest chainring size on the XO1 crank is 30t due to its 104mm bolt circle diameter (bcd). The smallest ring available for XX1 is 28t. So keep in mind your gearing needs. Often times, a 19 inch low gear is barely enough. That's with a 26 inch wheel. And in these modern times, fewer riders are using a 26 inch wheel. What this means, is that with a larger 27.5 or 29 inch wheel, the gearing is going to be a little taller. Combined with the taller, wider tires that are common now, a low gear that was barely adequate before may become impossible with a single ring drive. However, if you are deterred by the price, not the gearing, there is another way.
The Do-it Yourself 1×10
For those that have do-it yourself skills, a single ring drivetrain can be built for a fraction of the cost of a complete SRAM kit. There are no less than seven companies making X-Sync chainrings, not to mention that In SRAM also makes available for sale their X-Sync chainrings for 104mm bcd cranks. As for cassettes, there are two companies (probably more by the time this goes to print), Wolftooth Components and Absolute Black Components that manufacture an add on 42 tooth cog. The other required components required are: a medium cage Type 2 (SRAM) or Shadow Plus (Shimano) rear derailleur, a 10 speed, 11-36 cassette and a brand compatible shifter and chain. The total approximate cost is as follows:
11-36 Cassette $100
42t Cog $100
Rear Derailleur $120
* to get a chainring smaller than 30t requires a crank with a bcd less than 104mm negating much of the savings.
If you already have a 10 speed drivetrain, some the components you have will work. This makes it even more affordable. For example, although a medium cage rear derailleur is recommended, a long cage will work until you can purchase a new one. Same goes for the shifter. I do, however, recommend replacing the chainring, cassette and chain at the same time to eliminate compatibility issues between chain and cogs. You will need to check to make sure your freehub body will work too.
The general process for converting your bike is to remove the front shifter and derailleur first. Then install the new components. In order to convert the cassette, the manufacturers typically recommend removing the 17 tooth cog in order to make room for the 42 tooth cog. If you are in doubt of any of your skills as a mechanic, bring your bike into your local bike shop and have them do the work.
The SRAM XX1 and XO1 groups are a major improvement in mountain bike drivetrain components. They really make the bike a lot more simple. The bike frame is easier to design without the need of a front derailleur. The is lighter with two or three less components. Riding is a lot less complicated by only having to shift one set of gears. I just wish I could afford one. But I can afford DIY option. Even with only 10 gears, my bike will be just as simple, light and easy to ride as others with a SRAM group. This may let me a little less envious of them. When they find out how much money I didn't spend, they may be a little envious of me.
Got a bike question? Email Tom at [email protected]