Interpretation ID: nht74-3.36

DATE: 05/06/74

FROM: AUTHOR UNAVAILABLE; Richard B. Dyson; NHTSA

TO: Heavy & Specialized Carriers Conference of American Trucking Associations

TITLE: FMVSR INTERPRETATION

TEXT: This responds to your April 23, 1974, request for an explanation of the meaning and use of the term "Gross axle weight rating" (GAWR) in Federal motor vehicle safety standards.

The concept of GAWR and "Gross vehicle weight rating" (GVWR) are interrelated, and the two terms are defined as follows:

"Gross axle weight rating" or "GAWR" means the value specified by the manufacturer as the load-carrying capacity of a single axle system, as measured at the tire-ground interfaces.

"Gross vehicle weight rating" or "GVWR" means the value specified by the manufacturer as the loaded weight of a single vehicle.

In both cases it is the manufacturer who specifies the values, and he is free to specify whatever values he himself decides are correct. Both the NHTSA in its compliance tests, and the Bureau of Motor Carrier Safety on the road, will judge the vehicle on the basis of the values assigned. Therefore it is in the interest of the manufacturer to assign values which accurately reflect the load-bearing ability of the vehicle and its suspension.

The sum of the GAWR's must at least equal the specified GVWR to avoid overloading the axle systems, and the GAWR sum may, of course, exceed the GVWR. Typically the manufacturer balances the commercial advantage of specifying a higher GVWR against the expense of higher GAWR's.

The GAWR is measured at the tire-ground interfaces which means that the tires, wheels, brakes and suspension components are included in the determination. Typically an axle assembly is rated by its manufacturer, who takes into account the braking ability of the axle to stop the load. Although this factor should always have been taken into consideration, the advent of Standard 121 may cause axle and brake manufacturers to reassess the values they have assigned to brake systems in the past.

YOURS TRULY,

Heavy & Specialized Carriers Conference Of American Trucking Associations

April 23, 1974

Thomas Herlihy Office of the Chief Counsel National Highway Traffic Safety Administration

Please accept our sincere thanks for the meeting held at your offices on April 9, 1974 in which we discussed the impact of MVSS No. 121 on the heavy and specialized carrier industry. To further "introduce" you and your staff to our industry, I am enclosing a copy of our current Membership Directory and a recent issue of our monthly magazine TRANSPORTATION ENGINEER.

At the meeting we discussed briefly the intended meaning of the "24,000 pound gross axle weight rating" appearing in your proposed amendment in the March 1, 1974 FEDERAL REGISTER and you indicated that the intent was to use the current axle rating system as opposed to the MVSS No. 121 axle rating system in which braking ability would play a major limiting role. As a quick review of the enclosed magazine will reveal, this technical factor is of the utmost importance to our members who are the nation's primary users of this type of equipment.

We would appreciate a reply indicating the correct usage and application of this "24,000 pound gross axle weight rating" as it appears in that FEDERAL REGISTER item. If there are any questions concerning this inquiry, please feel free to call on us.

And again, please accept our sincere appreciation for the meeting last week.

Douglas A. Hughes

Director of Transportation

Enclosures