OPTIMAL USE OF THE ENTIRE BEARING CAPACITY
The transmission of loads in the bearing of a bottom bracket runs from the inner ring through the balls to the outer ring. The greater the number of balls supporting the transmission of force, the lower the specific contact pressure between the ball and the raceway. There is also a direct direction between the load to which a bearing is exposed and the number of balls that support that force transmission.
Figure shows a schematic diagram of how the load affects different bearings:
Fig. A: Radial ball bearing with large radial clearance. Here a few balls are supporting the load creating a relatively small load zone, easily producing friction and sliding. It is the most common configuration for the bottom bracket shafts.
Fig. B: Angular contact ball bearing with controlled clearance.
Thanks to the preload, the force is distributed among all the balls using the entire raceway to distribute the load, generating a much lower contact pressure. This load distribution reduces the torque required to roll and the greater the demand (sprints, mountain, ..) the greater the difference.