This article is from the The Monster Truck FAQ, by Jeff Hawkins with numerous contributions by others.
A. These tires are often used on fertilizer spreaders and are called
flotation tires because they spread the vehicle's weight across a wider
surface. Some Monster Trucks have floated on water with these large tires
on. There is a used market for these tires, too.
Firestone and Goodyear both manufacture 66X43X25 Flotation Tires.