It wasn’t all that long ago, that there weren’t many options at all when it came to fat bike wheels. It was aluminum and black – that was about it. Thanks to the rapid expansion of fat biking, that has quickly changed. Now, you can find just about everything, including carbon fiber in 80 or even 100mm rim widths.
At this point, carbon fiber is already pretty widely accepted as a material for road and mountain bike wheels, but fat bikers seem to still be on the fence. Carbon holds the potential for weight savings, but its durability, especially while running low pressures, seems to be the stumbling point for most. Because of that, Atomik says they designed their Phatty 85 rim to be strong enough for year ’round use – something it seems to live up to…
Differing from many of the carbon fat bike rims on the market, the Phatty 85 is a cross between a single wall and dual wall rim. Using their HDP (High Density Performance) Foam Core technology, instead of hollow sections inside of the rim the Atomik is filled with ‘aerospace’ foam. That foam core is then sandwiched in carbon fiber which allows Atomik to make an extremely low profile, yet strong rim – something they claim results in drastically improved impact strength while also having a positive effect on the ride quality.
Measuring 85mm externally, and 77mm internally, the rim is just 16.2mm deep. One of the added bonuses to the design that doesn’t really get talked about, is that the inner side of the rim is smooth, and convex. This makes it so snow, mud, sand, whatever, just slides off rather than packing up on the surface and getting trapped in grooves and holes. Available in 32h only, the rims carry a claimed weight of 590g and run $625 each.
When considering the weight of any fat bike rim, it’s important to also factor in the necessary rim strips and/or tape. Aluminum rims have gotten quite light thanks to the vast cut outs, but those usually require a heavy rim strip, plus tape on top. Something like these Phatty 85s will only require a layer of tape (or none at all for brands like HED), so there is some weight savings there. As I noted in the first post on these wheels, initially they were shipped with standard tubeless rim tape which worked to some degree. The original tape had to be replaced with a single layer of Orange Seal 75mm tape, which eventually sealed and is the way I’m running them today. Atomik’s Wayne Lee actually recommended a single layer of Gorilla tape, which will weigh a little more but it should seal a lot better since the rim profile is so concave.
Once set up though, the tubeless system was flawless. Regardless of tire pressure, there were zero burps, and the 3.5mm bead hook seemed to do a great job of holding the tire in place.
In addition to the rims, you can also buy complete wheelsets from Atomik with your choice of hubs (starting at $2000). In this case, Atomik laced up a set of Onyx hubs to match our 150 x 15/197 x 12 fat bike. You definitely pay a weight premium with the Onyx hubs, but the trade off seems to be impressive all weather durability and… silence. We’ve had these wheels mounted up for a full season with dirt, mud, snow, slush, sand, road salt, and sea salt all putting the Onyx seals to the test. The only thing out of the ordinary, was recently it was a little more difficult to remove the axle to change the free hub and required a little tap with a dead blow mallet. Winter conditions, and particularly ocean conditions can wreak havoc on bike parts, but the Atomik wheels are still going strong.
The wheels could be built a bit lighter with different hubs, the wheels are still fairly light at 1088g for the front and 1348g for the rear (weighed with tubeless tape and valves).
During the course of testing, the Phatty 85s split their time between my Borealis Echo, and the 9:ZERO:7 Tundra Michael had in for review. Between the two of us, the wheels experienced a wide range of riding conditions and varied experience with fat bike riding. I’m positive there were at least a few rim strikes on rocks and large roots, but the rims remain unscathed. In a similar time span I have dented or flat spotted aluminum rims (and broken other carbon rims) thanks to low tire pressures and high speeds. Neither Michael or I are particularly heavy (150 and 185lb), but we both ride pretty aggressively on fat bikes – read: do stupid things, ride fast, and crash lots.
I guess that’s the biggest takeaway from our time on the Atomik 85s. You get the weight closer to the lighter end of the spectrum, but the durability (at least in our experience) seems better than many aluminum fat bike rims. Combine that with a great ride quality and stiff wheel build to quality hubs, and the Phatty 85s are a stellar option for year ’round fat.
