Interpretation ID: nht92-1.37

DATE: 12/07/92

FROM: PAUL JACKSON RICE -- CHIEF COUNSEL, NHTSA

TO: KENNETH W. WEBSTER II -- PROJECT ENGINEER, TRANSPORTATION RESEARCH CENTER INC.

ATTACHMT: ATTACHED TO LETTER DATED 10-15-92 FROM KENNETH W. WEBSTER, II TO PAUL J. RICE (OCC 7872)

TEXT: This responds to your letter to me dated October 15, 1992, seeking an interpretation of Standard No. 110, Tire Selection and Rims - Passenger Cars (49 CFR @ 571.110). More specifically, you were interested in a clarification of the test conditions for determining compliance with the requirement in S4.4.1(b) of Standard No. 110, which provides that each rim on a new passenger car shall "[in] the event of a rapid loss of inflation pressure with the vehicle traveling in a straight line at a speed of 60 miles per hour, retain the deflated tire until the vehicle can be stopped with a controlled braking application."

In your letter, supplemented by your November 2, 1992 telephone conversation with Mr. Walter Myers of my staff, you explained that your company, Transportation Research Center Inc., has conducted tests on a passenger car that is to be marketed in the United States. Two tire and rim configurations are available with the car: a steel rim mounted with a Goodyear tire, and a decorative aluminum rim mounted with a Michelin tire. I understand these tires and rims to be the same size and to have the same nominal dimensions. In addition, I understand the tires to be of the same type and construction. You stated that you tested both tires on both rims in accordance with this agency's test procedure for determining compliance with Standard No. 110 (TP-110-02). The tire/rim combinations being tested were mounted on the left front and right rear positions, but in some cases tires made by a different manufacturer, but of the same size, type, and composition as the tires at the test positions, were mounted at the other wheel positions. You asked whether all tire and rim configurations on the vehicle for testing under S4.4.1(b) of Standard No. 110 must be made by the same manufacturer and otherwise be exactly alike. The short answer to your question is no.

Before discussing your specific question, however, I would like to explain how the National Highway Traffic Safety Administration (NHTSA) determines compliance in cases where a standard does not specify a particular adjustment position or test condition. In issuing Federal motor vehicle safety standards, NHTSA endeavors to specify all relevant adjustment positions or test conditions to ensure that our standards are objective and practicable. As a practical matter, however, it is not always possible to anticipate every conceivable adjustment position or test condition.

In those cases where a standard does not specify a particular adjustment or test condition, we consider several factors in interpreting the standard. We begin with the presumption that the requirements of the standard must be met regardless of such adjustment position or test condition, because the language of the standard does not limit the applicability of its requirements to any such adjustment position or test condition. NHTSA then examines the language of the standard as a whole and its purposes, to see if the language of the standard or its purposes indicate an implicit intent to limit such adjustment positions or test conditions and what limitation was intended.

Applying this approach in response to your inquiry, we believe that the language and the purpose of S4.4.1(b) of Standard 110 are clear, namely that the rim must retain the deflated tire until the vehicle can be stopped with a controlled braking application. The focus of the test is the ability of the rim to retain the deflated tire without unduly affecting the vehicle dynamics. Hence, the only limitation on the tire/rim combinations at the other wheel positions would be that those other tire/rim combinations that are not being tested must not unduly affect the dynamics of the vehicle (and, hence, the test result) when combined with the tire/rim combination being tested. Thus, unless testing the compact spare tire provided by the vehicle manufacturer, NHTSA would conduct its compliance testing for S4.4.1(b) of Standard 110 using tires of the same size, type (all-season, mud/snow, etc.), and construction (radial, bias-belted, etc.) as the tire being tested on the other three wheel positions. NHTSA would not, however, limit its testing to using only tires made by the same manufacturer as the tire being tested at the other three wheel positions.

I hope this information is helpful. If you have any further questions, please feel free to contact Mr. Myers at this address or at (202) 366-2992.