Originally Posted by
hamster
If I'm not mistaken, Ultegra 6800 cranksets are designed to be compatible with standard (narrow) BB shells, so, you can get an adapter to put a 6800 crankset into a BB30 frame (standard shell is 33-35 mm in diameter, BB30 is 42 mm, some others are even bigger), but you can't put a BB30 crankset into a standard frame. Many cranksets come with several installation options - you just pick the right bearings and spacers and you can install the same crankset into different frames.
^ This. If you have a 6800 crank, this is pretty easy. It is the smallest standard diameter and the right bottom bracket and/or adapter will make it fit BB30, PF30, etc. by taking up more space. Standard threaded is probably still the best fit, but the others will work (the adapters are better now-a-days). If you had (say) a BB30 crank you loved, your options would be more limited.
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