No person shall change the height of, or alter a bumper of, a private passenger vehicle so that the height of any horizontal bumper falls below the minimum distance of 16 inches or above the maximum distance of 20 inches. No person shall change the height of, or alter a bumper of, any vehicle other than a private passenger vehicle so that the height of any horizontal bumper falls below the minimum distance of 16 inches or above the maximum distance of 30 inches. Measurement shall be made from the level ground to the bottom of the bumper with tires inflated to manufacturer’s maximum air pressure. If a vehicle is not commonly manufactured with a rear bumper, measurement shall be made to the bottom edge of the chassis frame siderails. No motor vehicle that has been changed or altered so as to exceed the limitations of this section shall be driven on any way without the prior approval of the director. For the purpose of this section, in addition to the definition contained in N.H. Rev. Stat. § 259:81, the term “private passenger vehicle” shall mean a vehicle that has no provision for carrying a load other than a conventional trunk or the cargo area of a station wagon or similar type of vehicle.