Interpretation ID: nht76-4.21

DATE: 05/13/76

FROM: AUTHOR UNAVAILABLE; S. P. WOOD for F. Berndt; NHTSA

TO: Rome Engineering & Manufacturing Co.

TITLE: FMVSS INTERPRETATION

TEXT: This responds to Remco's April 26, 1976, question whether an exclusion from a safety standard based on the gross axle weight rating (GAWR) of an axle is met by using the rating of the axle beam by its manufacturer, or whether the truck or trailer manufacturer must also consider the load-bearing abilities of the wheels, rims, and hubs used with the axle beam.

Gross axle weight rating is defined in 49 CFR 571.3 to mean:

. . . the value specified by the vehicle manufacturer as the load-carrying capacity of a single axle system, as measured at the tireground interfaces.

This definition means that the determination of GAWR is made by the vehicle manufacturer and that the axle beam rating of the component supplier cannot be the only basis for GAWR calculation. The GAWR is the value established at the tire-ground interfaces at each wheel position, and this means that the wheels, rims, hubs, and tires must be included in the determination. Thus, with regard to the exclusion from Standard No. 121, Air Brake Systems, until September 1, 1977, for any vehicle with an axle that has a GAWR of 24,000 pounds or more, the vehicle manufacturer must take into consideration each component on the axle as well as its attachment to the vehicle frame.

Sincerely,

ATTACH.

ROME ENGINEERING & MANUFACTURING CO.

April 26, 1976

TAD HERLIHY -- OFFICE OF CHIEF COUNSEL -- National Highway Safety Administration

Dear Sir:

We are in need of clarification of Motor Vehicle Safety Standard No. 121 as pertains to paragraph S3 of Part 571-S121-1, quote: "or that has a gross axle weight rating for any axle of 24,000 pounds or more."

Does this mean that a certification from the axle manufacturer that his product is rated at 24,000 pounds or more would exempt the trailer manufacturer from compliance with MVSS 121 or is it necessary to have a single axle as well as the tires, wheels, hubs, and rims on that axle rated at 24,000 pounds or more capacity before the exemption is valid?

We would appreciate an advisory opinion on this matter.

Thank you.

Very truly yours,

R. A. Plummer -- Vice President & General Manager