The HollowTech II 12-speed Dura-Ace chainset offers the optimum balance of light weight and rigidity, making it the global choice for road racing's elite riders Hollow outer chainring, giving vast improvements in rigidity and increased weight savings The hollow outer chainring has essentially removed outer chainring flex, hugely improving shift performance making it precise even under high load These industry leading HollowTech II 4 arm cold forged hollow crank arms have been evolved to increase rigidity, reduce weight, and improve strength The teeth have been developed to work only in conjunction with the 12-speed chains for improved contact providing more efficiency and improved power transfer There is a wide range of chainring ratios and crank arm lengths available enabling customisation for all riders and racing disciplines HollowTech II integrated bottom bracket design uses a wider bearing placement and larger axle diameter for increased stiffness and efficiency Bottom bracket seal design has a minimal bearing interface gives superbly smooth rolling and increased durability.