:::When the tire's lowest point is 0, the intersection of circle and line is a single point, which has volume 0, so there's no volume shared by tire and road. If the tire's lowest point were some infinitesimal, which infinitesimal would it be? What's at the point in between 0 and the tire's lowest point? Would there be an infinitesimal air-filled space between the tire and the road? Would they actually touch?