Interpretation ID: nht75-2.9

DATE: 11/19/75

FROM: AUTHOR UNAVAILABLE; William T. Coleman, Jr.; NHTSA

TO: Hon. J. L. Whitten - H.O.R.

TITLE: FMVSS INTERPRETATION

TEXT: This is in further reply to your letter of October 3, 1975, for Mr. Charles Russell of WJLJ, regarding tire failures on ambulances in Tupelo, Mississippi.

Pursuant to the National Traffic and Motor Vehicle Safety Act of 1966, the Department's National Highway Traffic Safety Administration (NHTSA) has issued Federal Motor Vehicle Safety Standard No. 109, 49 CFR 571.109, which specifies performance and labeling requirements for new tires for use on passenger cars. Among the labeling requirements is that such tires must have their load ratings molded into or onto both sidewalls. Standard No. 119, 49 CFR 571.119, establishes similar requirements for new tires for use on trucks, buses, trailers, motorcycles, and multipurpose passenger vehicles (MPV's). The choice of standard applicable to a given tire depends on that tire's primary intended use. These standards apply to tires, and not to vehicles.

To ensure that new vehicles are equipped with proper tires, the NHTSA has also issued Standard No. 110 for passenger cars and a proposed new Standard No. 120 that would apply to vehicles other than passenger cars. Briefly, Standard No. 110 requires each new passenger car to be equipped with tires which meet Standard No. 109 and which are of sufficient load carrying capacity, as evidenced by the load ratings found on the sidewalls. As proposed, Standard No. 120 would require MPV's (including ambulances) to be equipped with tires which meet either Standard No. 109 or No. 119, and which are of sufficient load carrying capacity. In the case of Standard 119 tires, sufficiency of load carrying capacity would be calculated directly from the tires' load ratings. In the case of Standard 109 (passenger car) tires mounted on an MPV, sufficiency would be determined by dividing the tire load ratings by a 110 percent correction factor before comparing these ratings with the vehicle's weight ratings. The use of passenger car tires on new ambulances would thus not be prohibited by the new standard, provided this load rating correction factor is applied. This provision would recognize an established practice which has not been found to preserve a safety hazard. Passenger car tires generally provide a softer, more comfortable ride than truck tires, because the latter operate at higher inflation pressures, and thus may even be more desirable on ambulances, provided they are of adequate load carrying capacity. The NHTSA expects to issue Standard No. 120 in the near future.

For your convenience, I am enclosing copies of Standards Nos. 109, 110, 119, and the proposed Standard No. 120.