[bikerjulio]

since the earliest days of BB30 in around 2000, a threaded sleeve type adapter has been available. these are pressed in with loctite, and convert the BB to BSA, so any threaded BB system can be used, including GXP. I'd consider this a semi-permanent solution although the sleeve may be pressed out with care. also reliable. SRAM and FSA make this type.

a simpler answer is Wheels Man. or Problem Solvers adapter which leaves the existing BB30 bearings in place and presses delrin cups into them, which sleeve down and space out at the same time to fit a GXP crank. advantage is simplicity, and easier to remove if it doesn't work out. disadvantage is that it relies on the existing bearings being nice and tight in the frame. if they were squeaking before, this won't help.

suggest you google "BB30 adapter" and you will see what I mean.

Vendors like Wiggle sell both types.

 

[bikerjulio]

One of the "selling points" (though no advantage IMO because my heels are already close enough to the chainstays), of BB30 was lower Q factor. Whether SRAM took advantage of this with their BB30 cranks, I don't know. You'd have to research SRAM tech docs. So Q factor is possibly wider with their GXP cranks, or not.

If you are OK with your existing bearings then go the delrin route. as I said it's easy to reverse. although I would not worry too much if the frame was converted to threaded. not everyone is a fan of BB30, and to a good portion of knowledgeable people, a used BB30 frame is a liability.