The Yampa from Borealis, a start-up fat bike company launched this summer by an ex-employee from 9:Zero:7 Bikes, isn’t the first carbon fatty we’ve ridden. That honor went to the Salsa Beargrease, a stunning, 24-pound race bike at the vanguard of fat development. But whereas the Beargrease was built around “small” 4.0-inch race tires, the Yampa pushes the snowball even farther up the slope by making a lightweight bike (1270-gram frame) with clearance for five-inch tires.
Our size medium Borealis XX1 measures just 27.2 pounds. That’s pretty much the same as last season’s well-loved Fatback, but the flotation and fun factor is much bigger thanks to 100mm Clown Shoe rims and 4.8-inch Bud and Lou tires. And the good times will get even sillier as soon as Borealis begins delivering their Carbondale carbon rims later this winter, which the company claims will bring the complete bike weight down to around 22 pounds.
I spent three big, cold days on the Borealis over the weekend, and it didn’t disappoint. The extra-wide, deeply lugged tires had no trouble floating through eight inches of powder, yet the bike never felt piggish, even when the grade kicked up to 18 percent. The Borealis is a true mountain goat, too, with the big tires and super stiff front end (thanks to the tapered head tube and thru-axle fork) making it simple to glide right over tricky rock passages. My only ambivalence so far is that the SRAM XX1 drivetrain spec’d with a 32-tooth ring up front, which seemed a bit stout for steep and soft conditions.