Interpretation ID: nht72-5.12

DATE: 02/14/72

FROM: AUTHOR UNAVAILABLE; Richard B. Dyson; NHTSA

TO: City of Lynchburg

TITLE: FMVSR INTERPRETATION

TEXT: This is in reply to your letters of December 20, 1971, and January 4, 1972, concerning dump trucks recently purchased by the city of Lynchburg. You state that the trucks have a 24,000 GVW rating (rear axle 17,500 pounds, front axle 7,000 pounds), and were delivered with 8.25-20 tires, and ask whether there is a Federal requirement that restricts GVW rating according to tire size.

Beginning January 1, 1972, Federal regulations (49 CFR Parts 567, 568) have required all motor vehicle manufacturers to affix a label to their vehicles that contains both a gross vehicle weight rating (GVWR) and a gross axle weight rating for each axle (GAWR). These ratings are to be established by the manufacturer based upon all vehicle systems including tires. The requirements apply to the manufacturer, however, and not to the purchaser, if the vehicle is completed when he receives it. Nor is the regulation designed to regulate vehicles-in-use, which are subject to State regulation, but it is possible that some States may use these figures as a basis of determining whether vehicles are overloaded.

With reference to your particular trucks, it appears that they were manufactured before January 1, 1972, and the regulations are therefore not applicable to them. However, according to the 1971 Tire and Rim Association Yearbook, which sets recommended load and inflation pressures for all vehicle tires, the 8.25-20 10-ply tire has a recommended maximum load, for dual usage, of 3,550 pounds at 75 psi. Assuming 4 tires on the rear axle, this would be equal to a load rating of 14,200 pounds, lower than the 17,500 pounds at which the axle is rated. For single usage, the tire is rated at 4,050 pounds at 85 psi. Assuming 2 tires on the front axle, the maximum load for the axle would be 8,100 pounds, which, unlike the rear axle, is greater than the load rated for the axles.

A copy of our Certification regulations, which contain the requirements for GVWR and GAWR is enclosed for your information.