BB90s are poo. Correctly implemented BB30 all the way, IE, with bearings that press directly into the shell, crank axle that rests directly on the bb inner race.
The way bb30 has been implemented so far is to use small bearings (not much gain in stiffness and longevity), then adapter cups for the bearing into bb shell (allows machining inaccuracy in the shell, allows the bearings to shift and creak).
BB30 should allow the use of off the shelf bearings that press directly in the shell. The larger bearings allow larger, stiffer, lightweight crank axles to be used (think ethirteen). Because the shell has no internal lips, the bb shell can be reamed in a single pass after welding to ensure excellent bearing alignment and cheaper/easier manufacturing.
I don’t understand how it could be implemented so badly by the cycling industry.
Google mid or spanish bb for BMX’s BB30 should be implemented in a similar manner to these but it’s better.
Also larger bb shell, greater seattube/downtube/whatever else interface, allows for stronger/stiffer tube junctions