Do you know why trucks sometimes have earth - made wheels?

Such a phenomenon is especially evident in large trucks that attract large, heavy trailers. In fact, trucks with more axes can carry larger loads, but when they circulate empty or half full, then these extra assets no longer make sense. Moreover, the more wheels are in contact with land, the greater the cost of fuel, the unnecessary tire spending, and the harder direction of the truck. As a result, trucks have a wheel - lift system so that contact with land (backside) will remain only the axis with which a truck is picked.