The Hollow Tech II 10-speed Dura-Ace chainset offers the optimum balance of light weight & rigidity, making it the global choice for road racing's elite riders Shimano has raised the bar to a new level of performance with the development of a hollow outer chainring, giving vast improvements in rigidity & 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 Hollow Tech II cold forged hollow crank arms have been evolved to increase rigidity, reduce weight, & improve strength The teeth have been developed to work only in conjunction with the CN-7900 chain for enhanced contact providing more efficiency & enhanced power transfer There is a wide range of chainring ratios & crank arm lengths available enabling customisation for all riders & racing disciplines Hollow Tech II integrated bottom bracket design uses a wider bearing placement & larger axle diameter for increased stiffness & efficiency Bottom bracket seal design has a minimal bearing interface gives superbly smooth rolling & increased durability Weight including bottom bracket 725grams