Shimano's latest XTR crankset is, undoubtedly, its best mountain crankset ever. The crankarms themselves have received a few upgrades, mainly to reduce weight, but the chainrings have been extensively. The result is that the XTR FC M9000 2 2x Race Crankset is lighter and stiffer than any XTR crankset before. The M9000's crankarms use Shimano's tried and true formula hollow armed aluminum arms with proprietary spider and ring technology. A few changes have been made, however. The left side non drive is now hollow bonded for a reduction in weight. The drive side also loses a few grams, while it carries a new four bolt spider that is compatible all of the single or doublering configurations os Shimano's new 9000 group. The chainrings have been completely redesigned for reduced weight and increased stiffness. The rings are hollow. They are stiffer than ever, however, thanks to their carbon reinforced titanium alloy construction. Shift paths have been computer optimized for smooth and virtually instant shifting. The teeth are also titanium and have been hollowed out as well to save every possible gram.