Interpretation ID: nht90-3.98

DATE: July 5, 1990

FROM: Roger C. Fairchild -- Esq., Shutler and Low

TO: Paul Jackson Rice -- Chief Counsel, NHTSA

TITLE: None

ATTACHMT: Attached to letter dated 9-26-90 from P.J. Rice to R.C. Fairchild (A36; Std. 109; Std. 110; Std. 119; Std. 120)

TEXT:

Our firm advises a number of motor vehicle industry clients regarding their obligations under various Federal statutes and regulations. On behalf of a client, we request your opinion regarding the proper interpretation of Federal Motor Vehicle Safety Standards 110 and 120 (49 C.F.R. 571.110 and 571.120), as they relate to certain recommendations for tire selection and pressure/load determinations contained in publications of the Tire and Rim Association ("TRA").

Background

The TRA Year Book is one of the tire industry standardization publications that are listed in section 4.4.1(b) of FMVSS 109 and in section 5.1(b) of FMVSS 119. Under section 4.2.1(c) of FMVSS 109 and section 6.6 of FMVSS 119, tires must have maximum load ratings (molded on the sidewall in accordance with section 4.3(c) of FMVSS 109 and section 6.5(d) of FMVSS 119) that are not less than the lowest of any specified values printed in the listed publications, for tires of that size designation. Under section 4.2.1 of FMVSS 110, the vehicle maximum load on a tire may not be greater than the maximum load rating on the tire sidewall. In addition, section 4.3.1(c) of FMVSS 110 provides that, if a tire pressure other than the maximum pressure is specified on a passenger car tire placard, the vehicle loading condition for that pressure must be specified, and that pressure must be one that will support the vehicle load on the applicable tire, as specified in the listed publications or in a separate submittal by the tire manufacturer. Moreover, it is our understanding that NHTSA has interpreted FMVSS 120 to require that, for vehicles other than passenger cars, the vehicle load on each tire (at the recommended inflation pressure) must not exceed the tire's load rating at that pressure, as specified in the listed publications.

Thus, NHTSA generally requires that the tire selection process and tire information labels must reflect pressure/load relationships that are determined by reference to publications such as the TRA Year Book. However, NHTSA standards do not specify the exact part of each of these publications that is to be used in determining compliance with NHTSA standards. In fact, the publications include some "advisory" requirements that do not appear to be used in determining compliance with the FMVSS.

Examples of TRA criteria that are not clearly referred to in NHTSA standards are those criteria relating to vehicle speed capability.

Although FMVSS 109 and 119 include tire high speed tests, we understand that, in general, no separate provision is made in the FMVSS to account for vehicle high speed capability.

Questions

We request that you inform us as to whether the following three TRA criteria are used in determining compliance with FMVSS:

1. Vehicle Load Adjustment for Speed (Passenger Cars)

The 1990 edition of the TRA Year Book provides that "for applications above 210 km/h (130 mph), both vehicle normal load and vehicle maximum load shall be multiplied by a factor" that is based on the vehicle's maximum speed capability (see Enclosure 1). The Year Book goes on to state that "the resultant vehicle normal load must not exceed 88 percent of the tire maximum load and the resultant vehicle maximum load must not exceed the tire maximum load. In addition, the resultant vehicle maximum load as determined above must not exceed the tire load corresponding to the inflation pressure specified by the vehicle manufacturer."

It is our understanding that the adjustment factor described above is not used in determining compliance with FMVSS 110 or 120. As with the TRA provisions, section 4.2 of FMVSS 110 requires that the vehicle normal load on a tire must not exceed 88 percent of the tire's maximum load rating and the vehicle maximum load on a tire must not exceed the maximum load rating (as marked on the tire sidewall). However, unlike the TRA provisions, the terms "vehicle normal load" and "vehicle maximum load" are defined in section 3 of FMVSS 110 without reference to the speed capability of the vehicle. No explicit reference to the above described adjustment factor appears anywhere in the Federal standards. Therefore, we conclude that the vehicle speed adjustment factor is not applicable under the Federal standards.

2. Vehicle Speed Adjustment for Inflation Pressure (Passenger Cars)

The TRA Year Book also requires that the "speed category of the tire must match or exceed the theoretical maximum speed of the vehicle." The theoretical maximum speed of the vehicle is defined by TRA as the actual maximum speed, as adjusted for tire inflation pressure using another factor specified by TRA. (See Enclosure 2.) TRA also recommends minimum inflation pressures for vehicles of high maximum speed capability. We are aware of no reference anywhere in NHTSA regulations to tire speed categories. Therefore, it is our understanding that the TRA provisions set forth in Enclosure 2 are not used in determining compliance with Federal safety standards.

3. Load Limits at Various Speeds for Diagonal and Radial Ply Truck Tires

TRA also provides for adjustments in recommended tire inflation pressure and "service load" for tires used on trucks and buses, depending on the maximum speed capability of the vehicle (see Enclosure 3).

FMVSS 120 does not explicitly define the required tire pressure/load relationships for trucks and buses. However, section 5.1.2 of that standard provides that the sum of the maximum load ratings of the tires

fitted to an axle must not be less than the applicable GAWR. The maximum load ratings of truck tires are determined under section 6.6 of FMVSS 119 without reference to the vehicle application. The only explicit reference in FMVSS 120 to vehicle maximum speed capability is an exclusion from the requirements of section 5.1.2 for vehicles whose maximum speed attainable in 2 miles is 50 mph or less. Thus, we do not see a basis for using the TRA standard set forth in Enclosure 3 to determine compliance with Federal standards.

Conclusion

In our opinion, the TRA Standards described above should not be used in determining compliance with Federal safety standards. In general, using such private standards would have the effect of delegating to several distinct organizations the power to amend Federal standards in ways that are potentially inconsistent. Moreover, TRA standards are typically made effective on publication, so no advance lead-time would be provided to vehicle manufacturers with respect to new TRA standards. (If NHTSA determines that the above mentioned "advisory" requirements of the TRA standards must be used in determining compliance with the FMVSS, please inform us how NHTSA would deal with this lead-time concern, consistent with section 103(e) of the Safety Act.)

If you have any questions regarding this letter, please contact me at 818-1320 (local number).

Enclosures

Selection of Tires for Passenger Cars and Station Wagons (Source: The Tire and Rim Association 1990 Year Book) (text omitted.)

Vehicle Speed Adjustment (for inflation pressure) (text omitted).

Load Limits at Various Speeds for Diagonal and Radial Ply Truck Tires Used on Improved Surfaces (text omitted).