I am trying to understand bottom brackets and their compatibility. Is the bottom bracket determined by the frame, or is the bottom bracket hole the same on all frames and therefore you can use any bottom bracket on any frame?

If the BB is determined by the frame, what happens if you want to upgrade your crank this year, but a year or two then want to upgrade your frame? Are your options to getting a frame with the same BB as your old frame so that your crank will fit, or will you need to get a new crank if the BB is different, or are adapters made?

You've pretty much asked for a primer on bottom brackets and the answer to all of your questions is pretty much "it depends".

Try this article out.

https://www.bikerumor.com/2010/02/17/...ech-breakdown/

Hope this helps ^ dang.. great minds, I guess !

https://www.bikerumor.com/2010/02/17/...ech-breakdown/

The cliff notes - BB is determined by frame. Cranks tend to have either 24mm axles or 30mm axles and within reason, you can use just about any 24mm crank in any BB (with adaptors) but a 30mm crank may not fit in a BB that wasn't designed for it.

It used to be nice and easy - do you have english or italian threads? But now it's complex.

There's a pretty lively crank market on fleabay - somebody has a BB30 and needs a standard crank, that sort of thing. Don't get too worked up about it.