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Tested: Atomik Chubby 43 27.5+ Carbon Wheelset

A unique approach to carbon rims with a terrible, terrible name

One complaint you'll often hear about carbon wheels is that they ride harsher than aluminum ones. That may be a distant third behind also having a shorter lifespan and a higher price tag, but we'll talk about that later. Carbon rims are harsh for a few reasons. One is the nature of carbon itself. It's naturally more rigid and, in its own way, stronger than aluminum. It simply doesn't want to bend. But the other reason carbon rims are stiffer has to do with the way tubular carbon structures have to be made. The expanding air bladder inside of a carbon mold works best when it can expand in all directions equally. A cross-section shaped like a circle is ideal, but a long, thin crescent moon is definitely not. And with rims getting wider, it would follow that, if they're carbon, they have to get taller too. The taller the rim, the less it will flex, and the harsher the ride will be.

The semi-single-wall design on the Chubby 43 combines low weight, low profile, and remarkable comfort.

And with really wide rims like, say, plus-size rims, that's especially problematic where widths often exceed 40 millimeters. One bold approach a few brands take is to build single-wall rims. You probably haven't owned a single-wall rim since you were on training wheels, and there are plenty of good reasons. Double-wall rims are laterally stiffer and make for an overall stronger wheel, but there's little point in seeking maximum lateral wheel stiffness on a relatively squishy plus-size bike. And anyway, though I try and slash my plus bike as hard as I do my normal bike, the death I predict for its wheels will come in the form of a small crack under a big rock strike, not total destruction from a too-short or too-sideways landing.

On either side of the spokes, there are strips of high-density foam instead of hollow cavities.

To be fair, the Atomik Chubby 43 rim is technically not a single-wall. There are cavities that run on either side of the spokes, but they're not hollow. A high-density foam strip that is only a few millimeters thick runs inside each cavity. They add some strength without the limitations of constructing a truly hollow cavity. Atomik went with this thin profile to achieve that compliance we talked about, but also to lessen the rim's exposure to direct rock strikes. Debris kicked up from the tire is more likely to glance off the low-profile rim or miss it entirely. And their unique shape makes the Chubby 43s light. At 470 grams, the rim is lighter than many non-plus carbon trail rims out there. And it's not because they ignored impact strength. The hookless sidewalls are 3.5 millimeters thick. Not record-breaking, but above average, which also describes the rim's 36-millimeter inner width.

It’s what’s inside that counts. This cross-section shows what makes the Atomik Chubby 43 rim so unique.

Single-wall construction presents a unique problem in the world of tubeless tires. Traditional double-wall rims do have spoke holes to deal with, but at least they're on a level surface. Run tape over exposed spoke nipples, and it becomes a crumpled mess. On rims like the Atomik Chubby 43, taping requires specific technique and special care. Atomik recommends a strip of traditional tubeless tape covering the spokes and another wide strip of Gorilla Tape on top, but one not wide enough to extend up onto the bead seats. With multiple steps and fewer smooth surfaces, avoiding wrinkles while taping the Chubby 43s is both more difficult and more important than on traditional rims. But once I managed it after much trial and error, it finally was time to ride.

My test pair were laced to DT Swiss 350 hubs. The set weighs a hair under 1,800 grams, and I rode them part-time with 2.85-inch Onza Canis tires and part time with 2.8-inch Maxxis Rekons. I rolled them under my 2017 dream build, the Devinci Marshall. It's a bike that's purpose-built to get itself in over its head, which is precisely the torture-testing I wanted to put these single-wall carbon fiber rims through. And they succeeded. My goal was to pinch-flat hard enough to ruin a tire, or at least have to plug it. I succeeded. Twice. Turns out the rim succeeded as well. Your results may vary, but so far mine have no dents and no cracks.

The thin profile rim isn’t just for trail feel. It makes for a thinner target for trail debris, often fatal to carbon rims.

Just as importantly, they succeeded in delivering a more compliant ride than I'm used to from a carbon rim. I'll admit that it's hard for me to notice subtle differences in rim feel when I've got the squish of a plus tire between me and the ground. But the extra compliance on the Chubby 43 is not subtle. When I was running my PSI in the mid-teens, any high-speed round-edge impacts that weren't sharp enough for the tire to swallow were significantly less harsh on these wheels. Square-edge hits were more difficult to notice because the soft tire already handled the initial impact, but then I experimented with adding a PSI or two. I found that these rims allowed me to run slightly higher pressure on my plus tires without getting bounced around. It's the perfect configuration for reluctant fans of big tires who choose to run them slightly firmer to minimize squirm and pinch flats.

And regardless of tire pressure, I never felt any affect the Chubby 43's design had to lateral stiffness. That alone says a lot. For having such an unorthodox design, they ride like normal carbon wheels, just ones that are much more trail-sensitive. And they're priced like normal carbon wheels. They're not over-the-top expensive like Enve or Knight, nor are they dirt cheap like some of the direct-from-asia imports. The DT 350-equipped $1,700 set I tested is pretty middle-of-the-road, but you can upgrade to Industry 9 or Profile Elite hubs for an extra $400. No matter what Atomik wheelset you buy, they're all hand-laced in the U.S. You'll even get a card with the tension meter readings for each spoke, signed off by your wheel's builder. You can pick your axle and freewheel configuration, as well as one of 13 sticker colors.

There's an impressive attention to detail from construction to assembly to presentation. It seems the only thing that wasn't well thought-out was the name Atomik Chubby.

 

atomikcarbon.com/chubby-275-plus/

 

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