The new Shimano Dura-Ace SM-BB9000 Bottom Bracket continues the Shimano tradition of the outboard bearing, and like the whole 9000 group set, it's lighter, stronger, and faster than previous iterations. If this is your first endeavor with Dura-Ace, you should know that Shimano has long been the pioneer of external bottom brackets. In fact, its outside bearing positioning has proved to be so beneficial that Shimano adapted the same principles to its wheels. The efficiency of the system can be credited to its wide bearing stance. This distributes weight more evenly, and thus enhances stability and power transfer. With the new Dura-Ace generation, you'll find that Shimano decreased the SM-BB9000 bearing size for a stellar weight reduction over 7900. This alone enabled the bottom bracket to decrease bearing friction, but the most notable benefit comes from BB9000's new seals. The new sealing system results in a 50% reduction in drag without compromising bearing protection. Less weight, smoother bearings, and increased longevity -- purely Dura-Ace.