The maximum weight on any single axle, two consecutive axles spaced within eight feet or less, three consecutive axles spaced within nine feet or less, or four consecutive axles spaced within 14 feet or less shall not exceed 18,000 pounds, 34,000 pounds, 43,000 pounds, or 51,500 pounds respectively multiplied by a factor of the axle weight in tons allowed on the restricted route divided by nine.