Largest capacity carry-on that I've seen/used would be the B&R Widebody Uprights at 22x15x9, and expandable via CX compression system. The spinner wheels take away about 1.5 inches from the bottom, whereas the upright 2-wheel set up goes all the way down. I also find the 2-wheel version to roll better on a variety of surfaces vs. the spinner set up but that's personal preference.