ZUCA PRO MODELS HAVE THE ONE WHEEL DESIGN to fit better in overhead compartments. The ZUCA Pro is functions as a carry-on, an organizer, and makes travel glide more easily. With a built-in seat (seriously) and removable packing pouches that stack like drawers, this patented new concept in travel is like nothing else. Period. Better yet, the ZUCA Pro fits conveniently into overheads and comes with a TSA-friendly toiletry bag. The wheels are easy to replace - they are regular sized scooter wheels.