My first post this forum, but I searched to see if this has been talked about much.
I'm building a new Madone that is coming as a bare frame. The "bottom bracket" no longer exists , per se.
There are bearing sockets integral to the frame itself. The outside diameter of any bearing used must be 37mm to fit in the socket. The inside diameter will vary with the crankset used. It turns out Trek sells washer/bushing kits for the bigger group manufacturers like Shimano , Campy ,Sram and of course Bontrager. The others BB kits aren't spec'd out or available just yet. FSA is working on ther own "BB90" (90mm wide)kit that will be available in a "few weeks". There are some ceramic bearing manufacturers like Boca , Enduro, et al, who sell cartridge bearings ($60 ish) that will work ,37mm(OD) x 24 or 25(ID) x 6 or 7 deep.The install kits Trek sells must have a tube of socket primer and lock-tite to keep the bearing from spinning in the socket. It seems simple but still has to be done correctly.
I called Trek, FSA , the bearing guys, and spent waaay too much time on the internet. I think I found out what I needed to know ,so I bought a Campy Ultra Torque crank (it has to have an axle like the newer 2 piece cranks do that take outboard bearings) and some ceramic bearings.
If I'm off base about any of this, please set the record straight so we can all share accurate information.
Hopefully it will save somebody the time to research all this stuff.