Really big tires.
That's the draw of so-called "fat bikes": the really big tires. In this case, the Surly Bud (front) and Lou (rear), both aggressively knobby tires with dimensions of 26" x 4.8". Though the bead seat diameter on these tires is the same as traditional 26" mountain bike tires, their huge width gives them a monster footprint. Mounted up on rims that are 100mm wide and inflated to pressures as low as 4 psi (yes, four!), the tires' huge footprint allows the bike to float over soft terrain, like snow and sand.
Such wide tires require some interesting frame features, including a 100mm bottom bracket shell, a 190mm rear axle width, and a 135mm front axle width. Custom seatstays, hand-bent from 4130 chromoly tubing, provide clearance for wide tires without sticking out so far that you brush your heels against them as you pedal. A special RaceFace Turbine crankset provides the necessary extra width and a chainline that will allow the chain to clear the ultra-wide rear tire even in the lowest gear. In this case, I am using a SRAM 1x11 drivetrain, with a 28t chainring and 10-42t cassette. The gear range provided has proven to be just right for riding the snowy trails around Brattleboro, with lots of short and steep hills.
These beautiful low-mount disc dropouts from Paragon Machine Works hold the rear wheel in place. Rack and fender mounts are included because yes, someday this bike might have a proper rack (think about carrying XC skis or snowshoes and camping gear on a custom rack to access some deep trails by bike!) and even fenders to keep water and spray from soaking the rider.
Component choices throughout were carefully considered, as riding in sub-freezing temperatures can put special demands on gear. All controls are cable-actuated, including the Avid BB7 disc brakes and the SRAM X0 twist shifter. Teflon-coated control cables are covered by full runs of stranded Jagwire Pro housing, to keep water and muck out of the cable systems and to provide positive shifter and brake lever feel. Pedals are the Fyxation Mesa MP, made of nylon with metal spikes for traction. The nylon pedals were chosen in an effort to keep as much warmth in the rider's feet as possible- no sense in running a big metal pedal that could potentially pull heat away! Cold feet are no fun.
The twist shifter was chosen for ease of shifting when wearing thick gloves (no fumbling for a tiny trigger shifter), and ESI "chunky" silicone grips offer a large grip area and thermal insulation from a potentially cold handlebar. The handlebar itself is unique: a Jones Loop H-Bar provides multiple hand positions and ample width for control in all types of riding conditions.
The fork is a purpose-built, chromoly steel rigid fork with a segmented crown and integrated fender mounts. Extra large diameter tubing in the fork legs help provide a solid front-end feel, and Salsa sealed-bearing hubs keep water and mud at bay.
The best things about fat bikes? They are super fun to ride, and they extend your riding season and riding capabilities to cover terrain that you previously wouldn't have been able to access on a bicycle. Even those trails that are hard or impossible to ride during spring and summer can turn into sweet, snowy singletrack once the snow starts to fall.
I mean, how sweet does this trail look? Man!