Interpretation ID: 12625.wkm

Mr. Pedro Matos
Quality Manager
CNB/CAMAC
Portugal

Dear Mr. Matos:

This responds to your telefax of October 23, 1996, to this office in which you asked two questions about Federal motor vehicle safety standard (FMVSS) No. 109, New Pneumatic Tires. You first asked why, in Table II of Appendix A, tires with a specified maximum load of 300 kiloPascals (kPa) are tested at a lower inflation pressure than tires for which the specified maximum load is 36 pounds per square inch (psi). You then asked why, in the kPa section of Table II, the test inflation pressures increase then decrease as the maximum kPa inflation pressures increase.

I have enclosed several notices that explain the reasons for these differing test inflation pressures. In 1977 Goodyear Tire & Rubber Company (Goodyear) and the Rubber Manufacturers Association (RMA) petitioned this agency to amend FMVSS No. 109 to permit production of a new P-type tire that was designed to use a higher maximum inflation pressure than the standard 240 kPa then permitted by the standard, but with no increase in load levels. In response to those petitions, this agency amended the standard to include a maximum permissible inflation pressure of 300 kPa because tires with higher inflation pressures have less rolling resistance which may result in increased fuel economy. However, since there would be no increase in load levels, the agency specified that the inflation pressures at which those tires would be tested would remain the same, that is, 180 and 220 kPa respectively (Enclosures 1 and 2).

Then in 1988, the European Tyre and Rim Technical Organisation (ETRTO) petitioned this agency to further increase the maximum inflation pressure, citing requests from member manufacturers. ETRTO petitioned this agency to amend FMVSS No. 109 to permit an inflation pressure of 340 kPa so that the standard maximum inflation pressure then in effect for reinforced tires, 280 kPa, could be increased for special performance requirements, but again, with no increase in tire load capacity. The agency granted the ETRTO petition citing the Goodyear/RMA petition as precedent. Again, because the requested higher inflation pressure carried no increase in load levels, the agency specified that the test pressures for the 340 kPa tires would remain at 220 and 260 respectively (Enclosures 3 and 4).

The latest maximum inflation pressure, 350 kPa, was added to the standard effective August 31, 1994. The test inflation pressures remain the same as the 240 and 300 kPa maximum pressures, namely 180 and 220 kPa respectively, for the same reasons as explained above (Enclosure 5).

I hope this explanation is helpful to you. For your information, I am also enclosing a copy of the latest version of FMVSS No. 109 (as of October 1, 1995) (Enclosure 6). If you have any further questions or need additional information with respect to our tire standards, please feel free to contact Walter Myers of my staff at this address or at (202) 366-2992.

Sincerely,

John Womack

Acting Chief Counsel

Enclosures

ref:109

d:12/5/96