Interpretation ID: nht90-1.17

TYPE: INTERPRETATION-NHTSA

DATE: JANUARY 16, 1990

FROM: SATOSHI NISHIBORI -- VICE PRESIDENT, INDUSTRY-GOVERNMENT AFFAIRS

TO: ROBERT F. HELLMUTH -- DIRECTOR, OFFICE OF VEHICLE SAFETY COMPLIANCE, NHTSA

TITLE: NEF-31 GEN/NCI 3092

ATTACHMT: ATTACHED TO LETTER DATED 3-15-90 TO SATOSHI NISHIBORI FROM STEPHEN P. WOOD; [A35 REDBOOK; STD. 120]

TEXT: This responds to your October 31, 1989, letter regarding the compliance of 1989 Nissan pickup trucks with FMVSS 120. In my December 19th letter to you, I confirmed an extension until January 16, 1990, to respond to your request.

Nissan's responses to your questions regarding the 1989 Nissan truck are set forth in the Attachment. We wish to emphasize, however, that, based on our reading of FMVSS 120, it is not clear that the vehicles in question fail to comply with that stand ard. Nissan has followed a procedure whereby tire inflation pressures specified on FMVSS 120 tire/rim information labels are determined based on the tire's ability to support their share of the vehicle's gross axle weight rating (GAWR). The load carryi ng capacity of the tires at various pressures is determined by reference to data in tire industry standarization manuals; such as the Tire and Rim Association (TRA) Yearbook. Once a minimum pressure that is adequate to carry the GAWR is determined, Nissa n considers other factors, such as vehicle ride characteristics, to select the recommended pressure. This process results in the selection of a recommended pressure that will permit the tires to carry safely GAWR loads and will provide good vehicle ride characteristics. Nissan believes that the procedure it followed resulted in the recommendation of a tire pressure that is consistent with safe vehicle operation and is permitted under FMVSS 120.

Based on our reading of the Agency contractor's test report on this matter, it appears that the contractor has interpreted FMVSS 120 in a manner different from Nissan. However, we believe that our own reading of FMVSS 120 is consistent with the langu age used in that standard. In particular, based on our reading, we conclude that:

1. the tire label need not show the tire's maximum inflation pressure; and

2. the 1.1 adjustment factor in section 5.1.2 of the standard applies for tire selection purposes only. Nothing in FMVSS 120 requires that the relationships between tire inflation pressure and load, as specified by tire manufacturers in standardizat ion manuals or otherwise, must be universally adjusted by use of this factor. We read FMVSS 120 to require, in practical terms, that when a passenger car tire is to be used on a truck, a slightly larger capacity tire must be selected than would be the c ase if the tire were to be used on a similar size passenger car. Based on Agency statements in Federal Register notices regarding FMVSS 120, the standard apparently requires this difference in tire selection due to the greater potential for off-road use and heavy load operation (perhaps above the vehicle's rated load capacity) for trucks than for passenger cars, and not due to any inherent difference in load-pressure relationships for the vehicles.

It is our understanding that the Agency's test report concludes that the 1989 Nissan truck that was inspected by the Agency's contractor does not conform to S.5.3.5 of FMVSS 120. Section 5.3.5 specifies that the vehicle's tire/rim selection label mus t show the "cold inflation pressure for [the] tires". This provision does not specify how the "cold inflation pressure" is to be determined, or for which driving conditions the pressure must be appropriate. FMVSS 120, as originally proposed, specified t hat the label must show the "maximum cold inflation pressures of the tires with which the vehicle is equipped, as marked on the tires. . ." See 36 Federal Register 14273-4, August 3, 1971, emphasis added. In a subsequent proposal, the requirement was re vised to specify that the label must show the "maximum tire inflation pressure", deleting the reference to the tires actually on the vehicle at the time of sale. See 39 Federal Register 19505, 19507, June 3, 1974. This revision was made to recognize and continue to permit the practice of dealers changing tire sizes prior to delivery of trucks to the purchaser. 39 Federal Register 19505. The final rule establishing FMVSS 120 adopts the current language of

section 5.3.5 (as paragraph 5.3(c)), i.e., "cold inflation pressure", but the preamble does not explain the deletion of the term "maximum" with regard to the inflation pressure. See 41 Federal Register 3480, January 23 1976. Nevertheless, the change in wording suggests that the tire label must reflect some pressure other than the maximum pressure.

We believe that the context of section 5.3.5 may provide some additional guidance as to which pressure must appear on the label. Section 5.3.1 specifies that the information required under section 5.3.3 through 5.3.5 must appear either "after each GA WR" in the case of a certification label or must be "appropriate for each GVWR-GAWR combination", if a combined certification/120 label format is used. Thus, the "cold inflation pressure" selected should be consistent with the GAWR of the vehicle. This conclusion is supported by a subsequent NHTSA preamble, which states that the section 5.3.5 pressure need not be the maximum pressure, "but, the pressure specified by the tire manufacturer as sufficient to carry the load specified by the vehicle manufac turer as the tire's share of the assigned GAWR". 42 Federal Register 7143, February 7, 1977.

The 1989 Nissan truck inspected by the Agency is equipped with Firestone WR-12, P 195/75R14 M+S tires. The tires have a maximum load rating of 1400 pounds. The certification label on the vehicle specifies a cold inflation pressure of 34 psi for the rear tires and a GAWR of 2544 pounds for the rear axle. The key issue raised by NHTSA is whether the 34 psi pressure on the label is a pressure "specified by the tire manufacturer as sufficient to carry" half the GAWR, or 1272 pounds.

The regulations do not specify a procedure by which the tire manufacturer must articulate whether the tire, inflated to 34 psi, will support a 1272 pound load. For example, we believe this information could be obtained from tire industry standardizat ion manuals or from direct discussions between the vehicle and tire manufacturers.

Data in the 1989 Tire and Rim Association (TRA) yearbook show that the tires in question will support a load of 1279 pounds at 29 psi, with higher loads supportable at higher pressures. Therefore, the 1989 Nissan truck would appear to comply with sec tion 5.3.5. Moreover, the manufacturer of the tires used as original equipment on the vehicle has confirmed that the tires inflated to 34 psi, will carry 1383 pounds (which is more than half the GAWR) on this vehicle (see Enclosure 1).

However, NHTSA has apparently interpreted the required calculation procedure differently. As we understand the procedure used by NHTSA's contractor in its test report, it first calculated a "tire load limit" at 34 psi by interpolating between the loa d limits at 32 psi and at 35 psi, as specified in the TRA tables. Assuming that a linear interpolation is appropriate, the 34 psi maximum load would be 1381.67 pounds. NHTSA's contractor then proceeds to divide the interpolated load by 1.1, yielding 125 6.06 pounds. Since this figure is less than the tire's share of the GAWR (1272 pounds), the contractor concludes that a violation has occurred. Assuming that linear interpolation between the table values is appropriate and the contractor's procedure is correct, a pressure of 34.956 pounds would be required to support 1272 pounds.

We believe that the procedure followed by the contractor is not specified in FMVSS 120. In particular, we object to the contractor's application of the 1.1 adjustment factor to intermediate tire loads and for purposes other than tire selection, since the standard does not specify these procedures.

The use of a 1.1 factor is specified in section 5.1.2 of the standard for tire selection purposes. That section provides that the sum of the load ratings of the tires fitted to an axle must be not less than the GAWR. Prior to calculating the sum, th e tire's load rating shall be reduced by dividing by 1.1 if the tire is listed in Appendix A of Standard 109 and is installed on a truck, bus, MPV, or trailer. However, no specific tires are listed in Appendix A of Standard 109. It is our understanding that prior to the early 1980s, that Appendix did list certain tire sizes for use on passenger cars. Therefore, section 5.1.2 may suggest that when passenger tires are used on trucks, the tire's load rating must be reduced by the 1.1 factor prior to det ermining whether the tires are adequate to support the GAWR. According to the 1977 preamble, the purpose of applying the 1.1 factor is "to account for the generally harsher treatment (impulse and surge loading in the case of MPV's off-road) to which the tires of a vehicle other than a passenger car are exposed that is not accounted for in passenger car tire rating". Supra. Thus, it appears that the purpose for the 1.1 factor is not to deal with a difference in the ability of a tire to support a given load at a particular pressure when the tire is used on a car as compared to use on a truck. Rather, the stated intent seems to be to deal with the greater off-road use (or possibly more frequent overload situations) to which vehicles other than passeng er cars are subjected. n1

n1 It is important to note that the 1989 Nissan truck meets the tire selection criteria of section 5.1.2. If the tires' maximum load rating (1400#) is divided by 1.1, and the adjusted sum (2545#) of the two tires' load ratings exceeds the GAWR (2544# ).

The use of the 1.1 factor for tire selection purposes only is also suggested by the language of section 5.3.3. That provision references section 5.1.2 (and, thereby, the 1.1 factor) in determining whether the tire size is appropriate for the GAWR. H owever, the absence of the parenthetical reference to section 5.1.2 in section 5.3.5 suggests that the application of the 1.1 factor is not required for determining whether the tire pressure on the label is appropriate for the GAWR.

To summarize, the language used in FMVSS 120 to describe the process to be used in determining the cold inflation pressure under section 5.3.5 is ambiguous at best, and contrary to the procedure used by NHTSA's contractor at worst. These deficiencies are exhibited with regard to the following determinations:

1. Whether the 1.1 adjustment factor is to be used for purposes other than tire selection;

2. Which tires are subject to the 1.1 factor (Appendix A, standard 109);

3. The source of information on the tire manufacturer's load limit for the tire, at various pressures; and

4. The procedure for interpolating information derived from the TRA tables.

Of these factors, we believe the first to be the most significant, but all contribute to the ambiguity of the standard.

It is our understanding that at least one other vehicle manufacturer has interpreted section 5.3.5 in a manner inconsistent with NHTSA's contractor. This suggests that a problem may exist with the wording of the standard and that more is involved than a single party's misreading of clear regulatory language. If the contractor's interpretation were the only acceptable interpretation, approximately 700,000 Nissan vehicles produced as far back as 1983 could be implicated (see Attachment).

Response 5 in the Attachment lists additional vehicle/tire combinations where Nissan's specified tire pressure differs from that determined under the contractor's procedure. Nissan is now conducting additional tests to verify that these tires will su pport higher test loads. We expect that the results of this testing will demonstrate that the tires used on Nissan's vehicles have

sufficient load capacity to support their share of the vehicles' GAWR at the recommended inflation pressures. The procedure being followed involves testing the tires to FMVSS 109 procedures, but increasing test loads by multiplying them by an overload f actor. The overload factor is calculated by multiplying the GAWR by 0.5 and dividing the product obtained by the tires' load rating at the pressure shown on the vehicle's tire label (calculated according to NHTSA's contractor's procedure, i.e., using th e 1.1 factor).

The results of this testing should be available by January 31st. However, one of the affected tires (7.00 x 14) is no longer in production; therefore, a special batch of those tires is being produced. The test results for this one tire size should b e available by mid-February.

Nissan wishes to work cooperatively with NHTSA to resolve this matter. However, we believe that the language of section 5.3.5 does not clearly provide a basis for finding the 1989 Nissan truck to be in noncompliance, or for conducting a notification a nd remedy campaign under the the Safety Act.

We request that NHTSA consider the issues raised above and the results of our ongoing testing, and that the Agency concur that the Nissan vehicles comply with FMVSS 120. We request the opportunity to meet with you after you have considered the matter s raised in this letter, so that we can answer any questions you may have and discuss a resolution of the matter.

If you have any questions regarding this matter, please contact Mr. Kazuo Iwasaki of my staff, at 202/466-5284.

Sincerely,

ENC.