Originally Posted by
cny-bikeman
Great a new "standard" and a press fit in the most flexed and abused bearing on the entire bicycle. I'm sure they tested it with high pedal force and many use cycles, but I wonder how much they tested it for holding up to what I call the "Roy Rogers" mount/dismount method, where one tromps one's foot on the pedal at the bottom of the stroke while swinging the other leg over.
The Shimano press fit bb bearings are the same size cartridge bearings that are used in the Shimano outboard bearing bb cups, the ones that are threaded into a conventional bb shell. The press-in bearings are encased in plastic or nylon and pressed into the frame's bb shell, and end up completely inside the shell, unlike the outboard bearings. The frame's bb shell is wider and larger in diameter than a traditional threaded shell so that the entire bearing assembly will fit inside the frame and not be exposed to the elements. Like traditional bottom brackets.
The difference is that the bearings and spindles are larger in diameter now.
We sold a few cyclocross bikes last year that were raced hard in the fall and winter in the worst of conditions, no problems at all with the Shimano pressfit bearings. FSA produces compatible bearings for these systems as well, and we found them to not hold up as well as the Shimano bearings. YMMV.
In the world of industrial bearings, I believe it's very common for machinery to use press-in cartridge bearings, FWIW. The newest press-in bb bearings on bikes are not only pressed in, but sealed very well. Here's a pic of Shimano press-in bb bearings, like the OP's:
I'm not saying the world couldn't have gotten by without press-in bb bearings, or that in some ways these systems aren't problematic, I'm just posting this to let folks know what's going on with some of these new bb systems.