Originally Posted by
cydewaze
Mine has BB90, so I don't know for sure, but I've read that BB86 and 86.5 are the same. But I suggest you get a second opinion.
Ok a bit of perspective about PF because it is extremely easy for anybody to get lost in this sea of standards.
Below is chart to clear it all up. BB86 has a 86.5mm wide shell. Late model Trek Emondas use BB90 with 90mm shell.
But, the difference doesn't stop there. These BB's are a fundamentally different execution with different design philosophy.
BB90 uses a relatively small bore ID of 37.0mm which corresponds directly with bearing OD of 37.0mm for a slip fit right into the carbon bore BB shell...love or hate this design. ID of the bearings is 24mm which corresponds with a Shimano 24mm spindle ID from 105 to DA.
By contrast, the fractionally narrower shell BB86 uses a 41mm bore ID, and because there is more room, a plastic cup capturing 37mm OD bearings is integrated into the cups and this is pressed into the 41mm ID BB bore which again offers a 24mm bore ID to mate with Shimano cranks.
So very different BB executions.
A final word or thought is...BB86 may get the nod in design integrity. This may not be Trek's position..but in theory, if the same size bearings are buried and captured into cups, and cups have a longer bearings surface compared to stand alone bearings pressed into the carbon BB90 shell, bearing security would be better with BB86. Of course if you have a Trek with solid performing BB90, this point is debatable.
For further clarity, please see the two different types of BB's below. You will see the cups with integrated bearings with BB86 and a BB90 is simply two bearings...with seals that may require spacers or not.
Below.