The Hollow Tech II 10-speed Dura-Ace chainset offers the optimum balance of light weight & rigidity&44; making it the global choice for road racings elite riders Shimano has raised the bar to a new level of performance with the development of a hollow outer chainring&44; giving vast improvements in rigidity & increased weight savings The hollow outer chainring has essentially removed outer chainring flex&44; 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&44; reduce weight&44; & improve strength The teeth have been developed to work only in conjunction with the CN7900 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 725 grams