SRAM XX PF30 4228T Crankset w Bottom Bracket. The SRAM XX PF30 crankset truly revolutionized mountain bike drivetrains as it was the first crankset specifically designed for 2x10 use. Featuring integrated carbon fiber crank arms and an aluminum spider, the XX crankset delivers amazing off road performance and durability with no penalties in weight. The oversized chainrings are CNC machined from 6mm 7075 aluminum blanks 2mm thicker than the competition. Unparalleled stiffness is delivered by an increased Bolt Circle Diameter BCD and a two piece insert molded carbon composite construction. The XX crank geometry provides a narrow 156mm Q factor, efficient chainline and beveled crank arms to maximize clearance. Quite simply it's pure science in action. This crankset features 4228T chainrings and includes a SRAM PF30 bottom bracket.