Surly designed the O.D. crankset to offer frame and tire clearance while maintaining a reasonable q-factor (pedal stance). Maximizing the distance between the chain and the tire is important on fat bikes such as the Pugsley and Moonlander, or if you're running really big tires and rims on some other bike (like our new Krampus, for example). With normal cranks, wide tires on wide rims can rub the chain when in the lowest, or farthest-inboard, gear combinations. Like the MWOD crank, the O.D. crank doesn't just add a longer spindle to move the rings outboard. Rather, it does away with the big ring of a standard triple and moves the middle and granny rings to the outer and middle positions. This effectively moves the rings outboard without moving the arms outboard too. The O.D. is a simple, dedicated version of this idea. Neato!
Forged of 7000 series T6 aluminum, the O.D. crank is a 2-piece, with spindle embedded inextricably in the drive side arm. It's a dedicated 2x, although its chainline is outboard a bit compared to standard mountain cranks, and it is 9 and 10 speed compatible. The 132mm, PF41 bottom bracket O.D. crank is what goes on the Ice Cream Truck bikes, so if you've got that setup, that's your crank. Surly also offers 33t and 20t rings separately. These chain rings are designed to shift best in specific combinations….change to a 39/22t, for example, and your shifting will suffer. The bearings on which they spin are also worth mentioning: Surly upgraded the bearings on these and the Mr. Whirly and MWOD cranksets to aftermarket Enduro bearings with double labyrinth seals, meaning they actively shed and stay clean of dust, muck, and grime, even in wet and muddy climates.