First Look: Rocky Mountain’s 27.5-inch prototype Sherpa fatbike

Rocky’s new adventure model can flip-flop between 27.5 fatbike and standard 29er

27.5 29er Fat Bike Sea Otter Classic

“Practical” isn’t a word that’s generally associated with fatbikes. Yes, they’ve come a long way since their introduction as more-or-less a novelty—and the recent unveiling of a legitimate new suspension fork, and subsequent production full-sus frame designs surely broadens their usability horizons. But one new model that’s pragmatic by design is Rocky Mountain’s prototype Sherpa fatbike. By taking a more subtle approach to the genre—if subtle is a word that can be assigned to the cycling equivalent of a monster truck—the Canadian company may have cracked the code on making the fatbike feasible for mass consumption.

Rather than going whole hog with the bodacious five-inch-wide tires of most fatbikes, Rocky Mountain exercised some restraint where the rubber-hits-the-trail. Working in partnership with WTB, the Sherpa rolls on custom 27.5-inch hoops and accompanying 2.8-inch-wide Trailblazer prototype tires—a combo designed to give you most of the go-anywhere float of larger fatbike treads with less rotating mass to lug uphill. It also gives the Sherpa some unexpected extra versatility.

Because it sports only modestly-fat tires and a sidewall height that puts the diameter equal with a standard 29-inch setup, the Sherpa’s custom 27.5-inch wheel/tire combo fits on a standard Fox 34 29er fork with room to spare—no extra-wide shock or geometry tweaks required. The Sherpa’s fork and carbon front triangle are actually from an off-the-shelf Rocky Mountain Element 970.

In the rear, Rocky did have to widen the yolk a bit to get adequate tire clearance. But even so, it accommodates a 29-inch wheel as well, making the bike convertible between a 29er and a 27.5-inch fatbike with only a wheel change.

Proposed as a bikepacking rig, Rocky Mountain laced the Sherpa’s front rim to a German SON (Schmidt’s Original Nabendynamo) dynamo hub that connects to Supernova’s Plug III stem cap USB charging port to keep your GPS device topped-off.

For gearing the bike uses a Race Face narrow/wide 32-tooth single chainring up front and a Shimano 10-speed cassette in the rear with OneUp Components’ 42-tooth low gear conversion. Rocky finished the bike with a Painthouse Customs sherpa-themed paint job.

Rocky Mountain says they are just testing the concept to see if there’s interest in the design at this point. But judging from the response at Sea Otter, we wouldn’t be surprised to see some version of it in the company’s 2015 line.

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About the author: Don Palermini

Chicago-born Don Palermini became a cycling-based life-form in the sixth grade after completing a family road bike tour of his home state. Three years later he bought his first mountain bike to help mitigate the city's pothole-strewn streets, and began exploring the region's unpaved roads and trails. Those rides sparked a much larger journey which includes all manner of bike racing, commuting, on- and off-road bike advocacy, and a 20-plus-year marketing career in the cycling industry that landed him at his current gig with Santa Cruz bicycles. Now residing in the San Francisco Bay Area, his four favorite words in the English language are "breakfast served all day," together in that order.

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