SHIMANO XTR 9000 Trail Mountain Bike Crankset - 26/36 Hollowtech II design has an optimum balance of lightweight and stiffness for better power transfer and acceleration Cold-forged anodized aluminum crank arms for high strength and resilience Small-step 2X double for increased pedaling rhythm Hollowglide technology uses a high rigidity, hollow structure on the chainring to lower weight while maintaining strength for better power transfer and quicker, more precise front shifting Lightweight aluminum outer shell with reinforced carbon inner layer is highly resilient