The second generation Shimano 11-speed Dura-Ace design, the 9100 series, maintains the 24mm Hollowtech II crank spindle size. As such, the 68mm BSC, and 70mm Italian threaded, external bottom bracket cups remain essentially the same as the 9000 series.

Dura-Ace 9000 moved to a smaller cup and bearing size, with massive improvements in seals, overall drag, and a reduction in weight from the 7900. The new bearings and seals offered a 50% reduction in friction so your cranks will spin with less system drag. Shimano precisely engineers their highest quality steel ball bearings for this unit and with the seal effectiveness improved, infiltration and corrosion is incredibly unlikely, even with regular bike cleanings during the rainy seasons or during cyclocross. This combination of reduced friction and and essentially service-free long life span is a great counter to much more expensive ceramic bearing systems that may have slightly lower drag numbers, but are more susceptible to infiltration and must be clean and greased with special grease regularly.

The smaller external diameter of the shell won't fit older 44mm external diameter, 16 notch tools outboard bearing cup tools. This design has a 39mm OD, with a 16 notch spline receiver. Park Tool offers the BBT-49 for this set-up, and other options are widely available. You receive drive and non-drive specific threaded external cups, plus the internal (and mandatory) dust sleeve, which integrates the two cups to seal out any issues from inside the frame, such as water that gets in through the seat tube/seatpost junction. While we carry many options, we do highly endorse the BB-9100 threaded bottom bracket. Performance and longevity are excellent, and it is trouble-free at a great price. Not only is it Dura-Ace worthy, but it works with all 24mm spindle Hollowtech II road cranksets from Shimano.