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Summer was ending. Biking on dry singletrack was quickly coming to end. The Mountain Trails Foundation of Park City, Utah planned on adding more groomed snow trails in the winter. This is how I found myself on the saddle of a 2018 Diamondback Oso Dos fat bike.
After miles of riding snow-covered single track and quickly learning that winter riding is not at all the same as riding on dirt, I gathered my thoughts on Diamondback’s mid-tier fat bike offering. Full disclosure: Diamondback worked with Outdoor Gear Reviews to help source this bike for review purposes. Here are the five major takeaways.
Frame Geometry and Specs:
The Oso Dos is a big bike with a big aluminum frame at the center of it all. I personally ride a large frame size, and with that comes some large geometry specs. The chainstay length, for example, is a massive 460mm needed to clear the huge Kenda Juggernaut tires while the wheelbase tops out at 1142mm on the large frame. So it’s a long rig, made even longer by the extra inches a fat tire brings to the front and rear of the bike. The head tube angle leans towards the steeper side at 68.5°, which helps keep a rigid aluminum fork very upright while riding. Diamondback also added rack and accessory mounting holes pretty much everywhere, allowing for some serious customization for bikepackers or endurance riders.
The Oso Dos is Diamondback’s mid-tier bike in their three-product Oso fat bike line. Components are right inline with what a buyer would expect. A Shimano Deore 10-speed drivetrain is paired with an FSA Comet 2x crankset. The Deore build works very well for a base-level performance MTB drivetrain, with short snappy shifts and Shimano’s own clever two-way release upshifting trigger system. The 2x crankset is the only disappointing element as the second higher chainring is hardly utilized at all while riding on snowy single track. A 1x crankset, even if limited to just 10 speeds, would be a far more viable choice.
The Oso Dos fits TRP Spyke mechanical disc brakes to it’s wheels. Using a powerful dual piston design, they are surprisingly good in the stopping power department and even better for modulation. That’s important as consistent modulation on descents is far more valuable during winter riding than blunt stopping power that is largely lost on the slick surface.
To keep the price down, Diamondback also fits the Oso Dos with a variety of in-house parts. Handlebars, stems, wheels, seats, pedals, seatposts (sorry, no dropper) and grips wear the Diamondback name, all of which do just fine for the job they’re designed to do with the exception of the foam grips. That’s the one item I immediately updated after one ride on the Oso Dos, and I’ll bet most other riders will follow suit.
Finally, the HUGE 4.5-inch-wide Kenda Juggernaut tires are fantastic. Lots of grip in most scenarios and can easily handle minimal pressures in the low teens. The Juggernauts really come alive during surface transitions, moving from hard pack snow to loose snow to ice without any noticeable difference in grip.
It’s a big boy to be certain, tipping the scales at 35 pounds. Most of that weight comes down to the big Kenda tires and heavy stock wheels.
Despite the length of the bike and the huge Kenda tires, the Oso Dos feels relatively agile considering what the rider is piloting. The bike’s steep rigid fork helps keep steering precise and accurate, which is largely opposite of what initial impressions suggest you’ll get from the bike. That said, tight hairpins do tend to have a feeling of being just a bit tighter with so much bike having to move through the turn.
The rider sits over enough of the rear tires to really maximize grip on climbs but remains aggressively positioned for solid attacks on descents. In fact, I quickly found my hands got ‘rider’s numb’ if I wasn’t careful to balance my weight on the downhill.
For choppy sections of ungroomed trails, the Oso Dos definitely lets you feel what’s beneath the wheels by way of the rigid fork. Even with so much tire rubber taking the hits below me, I was surprised just how much the bike transferred bumps up to the cockpit. For that reason alone, some riders may find the top tier Oso with a 100mm RockShox Bluto fork is a better choice…for $500 more.
Bump sensitivity aside, the Oso Dos really does a good job of bringing as much responsiveness and agile feel to snow riding as one could reasonably hope for from a fat bike.
Diamondback sells the Oso Dos for $1,499, which sits pretty much in the middle of the price spectrum for mid-level fat bikes. Most equipment a rider is going to want for a fat bike is checked off the list with the Oso Dos out of the box. Things like front forks and dropper posts aren’t absolute necessities and always items that can be added after a season of riding the stock parts. My only complaint is the lack of a 1x front crankset for a $1.5k price tag. Hopefully future versions of the bike will drop the higher chainring and opt for a more simple drivetrain.
For those who haven’t actually fat biked on snow, prepare for an experience that won’t feel similar to biking on hard packed dirt single track. It requires a lot more low gear pedaling on climbs, different line selections through corners and a constant awareness of speed vs ability to stop on slick ground.
Diamondback clearly kept that in mind when designing the Oso Dos. The bike straddles the line of being able to introduce beginners to winter riding but also act as a bike that can grow with skill set. On top of nice aesthetics and good components, that “dual-application” is worth the price of the bike alone.