The four-inch-wide tires that transform a mountain bike into a "fat bike," provide traction and increase surface area, making previously unbikable terrain accessible. Invented a decade ago by racers pedaling Alaska's Iditarod dog sled course, fat bike tires allow cyclists to take on snowy singletrack, which is exactly as terrifying and entertaining as it sounds. The sport is also the perfect complement to skiing because fat bikes flounder in powder and overachieve on hard-packed snow. In Colorado, the rule is simple: Hit the slopes when snowfall exceeds four inches and grab the bikes for anything less.

We gave the nascent sport a try in Telluride, Colorado. The Centennial State, along with Minnesota, has been at the forefront of popularizing fatbiking (called snow biking when done in snow) in the lower 48. Max Cooper, the bike whisperer at Paragon Outdoors and Bootdoctors, which rents chubby cycles out of a main street storefront, took us out for the day. He maintains a fleet of 10 fat bikes, mostly Salsa Mukluks and a few Surly Moonlanders – the Minnesota-based manufacturer’s latest and fattest – that each sport 5-inch-wide tires. We put on our ski helmets and goggles, the preferred equipment for cycling done on a ski mountain, and climbed onto the Telluride gondola.

Telluride Resort Ski Patrol will kick fat bikes off the slopes for safety reasons during normal hours of operation (Cooper says locals wait until dark and do it wearing headlamps), so we stuck to the Meadows Area hiking and biking trails adjacent to the base.

And that's where the real fun began. The Jurassic Trail, an advanced mountain biking route in the summer, was covered in snow, that had been tamped down into perfect fatbiking terrain by local dogwalkers. We followed the ridgeline west before bombing down 300 feet to pick up the Meadows Trail. The hard-packed snow evens out the trail's baby heads and death cookies into a comfortable pillow ride. Turns become exhilarating power slides.

We drifted, floated, and slid all the way down to the Telluride Valley Floor, with some short climbs and a few flats in between – a five-mile trip all told. Cooper ensured that we ended at the Telluride Brewing Company, located on the west side of town. After refueling with a Slick Eddy, half Face Down Brown and half Tempter IPA, we pedaled a pleasant three miles back to the shop on snowed-over bike paths following the San Miguel River. Our bikes elicited envious stares from the skiers clomping around in their boots.

More information: Bootdoctor's half-day guided tour costs $99. A full-day tour goes for $139. Both include the rental fee.