Yep, that’s a custom bus built for the specific purpose of pulling around a twelve-foot-tall, four-foot-wide tire. Why?
Well, why does it need a reason? If it wants to pull a twelve-foot tire around, let it pull a twelve-foot tire around. IT CAN DO WHAT IT WANTS, LEAVE IT ALONE!
Okay, but really, in 1929 Goodyear developed a new tire they called the Airwheel. The idea was that a giant balloon tire with a small rim and massive sidewall would be able to carry a massive load and eliminate the need for costly shock absorbers. A guy named Alvin J. Musselman designed it, and Goodyear referred to it as the “Musselman Type” in press releases. They were quite proud of it, so they mounted it to a tractor-trailer and paraded it around Akron, Ohio.
But they wanted everybody to know about it, so they had Flxible Co. build them two custom three-door buses on lengthened 1929 Buick chassis with a recessed panel in the back so the giant swingarm holding the Airwheel could connect to a fifth wheel.
The first bus built went on a tour of half the states in the country for a couple years, and then the second bus was built and the pair toured the country throughout the early thirties. Goodyear also developed tires like this for passenger cars, and they can be seen mounted on the giant swingarm so you can compare them to the Airwheel. As fun of a publicity stunt as it was though, neither of the new tires caught on at the time. The passenger car tires were too expensive in the depression era, and the Airwheels were not only expensive but also ginormous. Nobody wanted them. However, Goodyear would later put ten-foot-tall tires on the B-36 Peacemaker bomber in the fifties, so they still got to make the largest tires ever fitted to a plane.