On Jun 6, 9:04 am, Bertie the Bunyip wrote:
Yeah, that's right. I have a vague memory of an article in Popular
Mechanics about someone building one. I think they might have published
plans for it, even, as they did back then. Quite a challenge to make
something like that! I suspect it must have had a single castering wheel
hidden underneath fore or aft.

Nope. Those things had two smaller wheels that ride inside
each tire. The main tires have no inner sidewalls, and the actual
suspension is a bar that reaches into the inside of the main and has
two small wheels on each end of it that ride on the inside of the
mains' treads. They have a wheelbase of 10" or so, enough to keep the
machine upright. Fools lots of people. The flattish-looking main tires
give the game away to anyone with any mechanical knowhow.
A guy here in our area built one and drives it in the local
parades. Has hydrostatic drive, too. Runs the smaller wheels.

Dan