Fat but skinny. Specialized's S-Works Fatboy is a Fat Bike on a diet. With its light FACT carbon frame, Sram X11 groupset, and carbon wheels, the S-Works Fatboy delivers the ultimate fat biking experience with minimal weight gain. FACT 10m is Specialized's premium carbon blend reserved for the ultimate mountain bike performance. With a unique layup, the S-Works Fatboy offers stiffness in key areas to maximise efficiency and handling while shaving grams for a low frame weight. A full Sram XX1 drivetrain is the latest chapter in evolving drivetrains, offering the same wide ratios of a standard double set up without the need for a front mech. FACT 10m Carbon Fibre Frameset is Lighter and Stiffer Than the Standard Fatboy Sram XX1 11 Speed Groupset Offers a Wide Range and Smooth Shifting With a Single Chainring HED Carbon Fibre Rims Reduce Rotating Mass for Improved Handling and Acceleration Description by Mark, Rutland Cycling Web Team.