When I got in touch with Kris at 44 Bikes about a fat-bike, I knew that XX1 was only a couple of months away of hitting the market. Being a long time singlespeeder who has not used a geared mountain bike in over fourteen years, I also knew that my future fat-bike was not going to be equipped with a front derailleur. First, I wanted to keep the bike as simple as possible. Second, a front derailleur that sits smack-dab in the trajectory of mud and snow coming off the rear wheel, is the first thing to fail once said mud and snow meet freezing temperatures.
When several hubs were announced with XD1 driver bodies for XX1, I decided to equip Big Boy with SRAM’s new 1x11 drivetrain knowing full well that first hand experience was nonexistent and we’d be some of the first to do it. Kris ordered a custom anodized set of Paul hubs and an Industry 9 XD1 freewheel body, got all the XX1 components together as soon as they were available and built the bike as I’ve been riding it since February.
So, how’s XX1 been working out on a fat-bike? Exceptionally well but with a few caveats. From a gear ratio point of view, I have the gear range I need to ride in the snow and climb my local mountains. It’s rare that I’d like to push a harder gear and I never feel the need for a smaller gear. Shifting up and down works flawlessly and quickly. Not being used to a trigger shifter, I had to relearn using one and at first, I occasionally I shifted down when I really wanted to shift up. It’s been more than a decade since I last used such a thing, so no huge surprise there.
And those caveats? There are two and both are due to a fair amount of cross chaining when the chain sits on the biggest cog. Pedalling in the biggest cog works well, but rotate your cranks backwards and the chain will quickly fall off the biggest cog. Next, I’ve been seeing a lot of wear on the outer surfaces of the teeth on the chainring. The cross chaining pushes the chain links against the chainring and grinds the teeth away. With a clean chain in the snow this doesn’t happen all that quickly, but come spring and mud, you can almost watch the teeth disappear from one ride to the next.
With a symmetric setup with 170mm rear end such as my Big Boy, one has to live with that and replace the chainring every winter. A titanium or steel chainring would last longer, but may also shift wear to the chain. If one were to built a custom fat-bike for a 1x11 drivetrain, the solution would be a hub wider than 170mm, which are just now starting to appear on the market, or an offset rear triangle designed for a 150 or 170mm hub. Such an offset would allow to place the cassette in a more favorable position relative to the single chainring and reduce the cross chain effect in the biggest cog.
So, if you’re planning to run an XX1 drivetrain on a fat-bike, consider the rather skewed chainline and the increased drivetrain wear it’ll create. If you’re beginning a fat-bike project with a blank sheet of paper, consider all options to minimize the issue. It may very well be the Achilles’ heel of SRAM’s 1x11 drivetrain, as I’ve seen photos of original SRAM XX1 chainrings that display the same kind of chainring wear being used on a regular mountain bike. As soon as long term reviews start popping up on the web, we’ll know more about XX1’s drivetrain longevity.