In respect to any motor vehicle designed, used or maintained primarily for the transportation of property which is not equipped with a plate or marker showing the manufacturer’s gross vehicle weight rating, for purposes of stopping distance requirements, the weight of a vehicle shall be determined as follows:
(a) Any motor vehicle having less than six wheels is the equivalent of a vehicle having a manufacturer’s gross vehicle weight rating of less than 10,000 pounds.
(b) Any motor vehicle having six wheels or more is the equivalent of a vehicle having a manufacturer’s gross vehicle weight rating of 10,000 pounds or more.