Originally Posted by
plonz
I am in the middle of doing this with one of my bikes. For "conventional" screw in bottom brackets with spindles, the things you need to consider are: 1) Shell width 2) Thread standard 3) Taper standard 4) Spindle length.
If you're keeping your current crankset it should be an easy process. Buy a bottom bracket that has the same dimensions and standards as the current.
If you're changing cranksets things get a little sketchy. This is what I am going through right now. The taper standard must be compatible and the new crankset will likely require a different spindle length. Hopefully you can find the spindle length dimension for your new cransket online. Otherwise it's a process installing the new crank and determining the required spindle length to get the correct chainline.
Probably reads more daunting than it actually is. Good luck!
Part of my problem is that I may be moving soon and am not sure what kinda hills to expect in the near future. Triples are a major convenience for serious hills, but kinda pointless on the level. I'm also still enough of a novice cyclist that my leg strength is still increasing, so hills that were granny ring for me last year and now quite manageable on the middle ring. That is why I sometimes obsess about compatibility / interchangability -- I'm still learning what works for me and trying new things. Being able to do so without spending a fortune is important to me.
Even if the ghost of Tullio Campagnolo popped out of a lamp and granted me whatever $10000 bike I wanted; I'd be unable to pick anything that I knew would be "right" for me long term.
And, as you note, it is sometimes frustrating trying to dig up the recommended axle lengths on discount cranksets. Which makes planned purchasing annoyingly challenging.