Other than turning them once in the garage I can't comment on durability yet. In other words, they may or may not be permanent. They go easy. With my 27-inch tires, three per wheel is enough to ensure steel-to-ground contact on said wheel/tire. With 6 of these on the work piece, the distance between the rubber tracks is only 4 inches. With 3 of them it's 8 inches, but my tires' contact patch at 26psi on the ground is 10 inches; So three is enough to keep the steel in contact with the ground.