I’ll admit it: when fat bikes, once the realm of a tiny band of Alaskan crazies who raced in the snow, started popping up on desert singletrack, and even at 24-hour races, I was skeptical. Then I tried one and understood. These things are just plain fun to ride. Plus, all that extra rubber—approximately double the width of a standard mountain-bike tire—floats through sand, mud, and singletrack just as well as it plows through snow. And as fat bikes take on more terrain, bike companies are responding with trimmer frames, quicker-handling geometries, and lighter wheels. And, inevitably, bigger tires. Case in point: the Surly Moonlander, with hulking 4.7-inch tires. Run at low pressure (6-10 psi), those bulbous doughnuts soaked up bumps like suspension and blasted over sand dunes and through mud with monster-truck ease. The cost of the oversize footprint is a little more weight (34.5 pounds to be exact), but for blasting snowdrifts and surfing arroyos, the Moonlander is as fun as they come.