Hollowtech II crank and bottom bracket combines race-proven hollow forging technology with the integrated crankset & bottom bracket. Weight is reduced while rigidity & power transfer is radically increased. In addition to Hollowtech II integrated design; the crank arms are hollow which provide amazing strength and rigidity at a light weight. Finally, SG-X chainrings enable super smooth front shifting. Special tooth profiles, pick-up spikes and ramps help make the front derailleur shifts quiet, easy and trouble free for you the rider.