I was thinking of getting a different crank on my cross bike so I went to see what the higher up models were using as a basis to figure out what would fit. I noticed that my frame specs say it uses a BB386, but the next model up (carbon frame) uses a BB30.

It's my understanding that BB30 is 68mm or 73mm wide and BB386 is 86.5mm wide. This means the down tube would need to be totally different. Why would they do that? Am I missing something?

My bike in the link below:

F65x - Felt Bicycles