I just upgraded my Bike Friday from a square taper bb with 2x to Hollowtech II with Shimano Cues 2x. I added the two included 3mm spacers but that did not leave enough of the spindle for the crankarm to attach to securely and for the crankbolt threads to catch the spindle. So I removed the spacers and now everything is working fine.



Shell width suggested that the spacers were required.

But these threads would not catch the spindle

Removing the spacers fixed things

I'm no expert, but I'd imagine that going from square taper to Hollowtech will push the chainrings away from the frame, and thus reduce any interference between the drivetrain and the frame. But it will also affect the chainline, which is more critical in folders with shorter-than-normal chainstays.

Question about using a mountain crankset - would the external cup bb Hollowtech II + mountain crankset push the chainline out further than the original square taper setup? Would Hollowtech II + road crankset counteract that a little?