Interpretation ID: nht89-3.3

TYPE: INTERPRETATION-NHTSA

DATE: 09/28/89

FROM: FRANK E. TIMMONS -- DEPUTY DIRECTOR TIRE DIVISION RUBBER MANUFACTURERS ASSOCIATION

TO: STEPHEN P. WOOD -- ACTING CHIEF COUNSEL NATIONAL HIGHWAY TRAFFIC SAFETY ADMINISTRATION

TITLE: NONE

ATTACHMT: ATTACHED TO LETTER DATED 11/01/89 FROM STEPHEN P. WOOD -- NHTSA TO FRANK E. TIMMONS -- RUBBER MANUFACTURERS ASSOCIATION, REDBOOK A34, STANDARD 109, PART 575.104; LETTER DATED 08/30/89 FROM STEPHEN P. WOOD -- NHTSA TO E. H. GALLOWAY -- UNIFORM T IRE QUALITY GRADING TEST FACILITY, RE INFLATION PRESSURES FOR TRACTION GRADING PROCEDURES IN UTQGS

TEXT: Dear Sir:

On behalf of domestic manufacturers of tires, the RMA requests that you reconsider the NHTSA position taken in your August 30, 1989 letter to E. H. Galloway concerning UTQG traction test inflation pressures. Your interpretation that metric designated ti res (including P-metric tires) which are labeled for maximum pressure in both kilopascals (kPa) and common english (psi) units should be treated the same as those labeled with english values only is contrary to long standing industry interpretation and p ractice.

The following is offered in support of our request:

1. All tires designed using the metric system are required by FMVSS 109, para. S4,3,4(a) to show not only kPa pressure information, but the equivalent value in english units (psi) in parenthesis. Thus, no tires can be sold or offered for sale in the U. S. market with pressures specified only in kilopascals.

2. Load Range B alpha-numeric and numeric tires are labeled 32 psi maximum inflation pressure as required by FMVSS 109. The design test pressure for these tires is 24 psi. Standard load P-metric tires are labeled 240 kPa (35 psi) maximum inflation pre ssure as required by FMVSS 109. The design test pressure for these tires is 180 kPa (26 psi). Since P-metric tires are normally used at slightly higher pressures by consumers in accordance with vehicle manufacturers recommendations, it is logical that they be tested at slightly higher pressures.

3. Industry and private testing organizations have been testing P metric tires for UTQG traction using 180 kPa at the NHTSA test facility in San Angelo, Texas for 10 years with no prior comment from NHTSA.

4. In summary, our members sincerely believe the intent of the regulation is to test alpha-numeric tires at 24 psi and P-metric tires at 180 kPa. We ask your timely reconsideration of your August 30, 1989, interpretation to minimize confusion within th e industry.

5. NHTSA has specified variations in test pressures for UTQG treadwear and temperature tests and in FMVSS 109 bead unseating, tire strength, tire endurance and high speed tests to accommodate the differences between P- metric (240 kPa) and alpha numeric /numeric (32 psi) tires. The same philosophy should apply to traction testing.

Sincerely,