The weight of a truck is distributed over the part of the tires that make contact with the road. Weight/surface area = pressure, so the greater the surface area, or equivalently, the greater the Number of tires, the greater the weight of the truck can be for a given pressure. What pressure? The Pressure exerted by the tires on the road, which is determined by (but is somewhat greater than) the Air pressure in its tires. Can you see how this relates to Home Project 1?