At the last count there were 12,682 different types of bottom bracket available within the cycling industry. Okay, that might be a ‘slight’ exaggeration but choosing the correct bottom bracket for your bike can be a nightmare.
As a frame builder the first thing you will have to consider is how you want the bottom bracket to interface with your frame – at this point you can choose between threading the bottom bracket shell (in a metal frame), bonding in a threaded metal insert (for a carbon frame) or leaving it as a smooth tube. Threading the tube/fitting an insert does at least create some standardisation in terms of the bottom bracket (to a point) but then the frame builder can choose between an English (BSA) style measuring 33mm in diameter and 68mm in width or Italian style (34mm diameter and 73mm width) or the more modern T47 (46mm diameter) to add a little spice into the mix.
And then we come onto the bottom brackets that fit into a smooth shell. Not threading the shell is obviously a more cost effective way of constructing a frame but it does allow for an even wider range of choice. BB30, PF30, BBright, BB86, BB90, Specialized OSBB, Colnago Threadfit, BB386 Evo, Praxis M30 – these are just some of the shared or proprietary bottom bracket systems that rely on bearings being pushed into the shell.
Oh and don’t get us started on bottom bracket axles….