I actually read an article about this in an old Popular Mechanics someplace, only the the bodywork was a little different. I think they called it a Foomobile.
There are actually two small wheels inside each large tire, if you look at the tires they appear to be half flat. The two small wheels are still only about 16 inches apart at best, so you don't want to stomp on the brakes. Steering is done like a crawler.