Under the proposed rule, tire manufacturers would be required to submit data to NHTSA on the fuel efficiency, safety, and durability of each covered tire model. (For the proposed testing metrics and procedures, see “Testing Requirements” in the Rule Map.)

NHTSA is seeking comments on its procedure for what constitutes noncompliance with the reporting and rating requirement it intends to establish. It wants to determine a range of tolerance within which a manufacturer’s reported ratings may deviate, without penalty, from the ratings produced by NHTSA’s own testing.  Generally, NHTSA proposes to require that the manufacturer’s rating be either less than or equal to the agency’s rating as determined by the specified testing procedures, or within a specified tolerance range.

Fuel Efficiency
NHTSA proposes a fuel efficiency tolerance of plus or minus 5.5 % of the rolling resistance force (RRF) determined through the specified test procedure.  The agency discovered through its test data that the RRF of a tire varies according to the tire’s load rating.  Although  smaller tires with a smaller load-range index displayed smaller variations than tires with larger load-range indexes, the RRF remained within 5.5% of the respective means.  So, a tolerance of plus or minus 5.5% seems appropriate to account for this source of variance.

NHTSA recognizes that other variables (e.g., different batches of material; different manufacturing dates; variations in testing machines and labs) may cause a variations in measured RRF.  The agency seeks comments and proposals on these various factors.  Proposals should be supported with data.

Safety
With respect to the reported safety (i.e., traction) rating, NHTSA proposes that the adjusted peak coefficients of friction for asphalt and for concrete must each be within 0.06 of the respective peak coefficients determined by the agency.  (See Rating Formula; Safety Testing).   The 0.06 number is based on test data in which peak coefficients of friction for asphalt and concrete were recorded for many tire models, and the average and standard deviations were calculated for each.

As with the fuel efficiency tolerance, NHTSA recognizes that other factors may affect the variation of the peak coefficients.  The agency is seeking comments and proposals on these various factors, and requests that they be supported with data.

Durability
NHTSA proposes a tolerance in the durability (i.e., treadwear) rating of 2.5 mils per 1,000 miles of the Uniform Tire Quality Grading Standards (UTQGS) wear rate.  (See Durability testing).  The agency arrived at the 2.5 number through testing on the ASTM E1136 Course Monitoring Tire, using the UTQGS specifications found in 49 CFR 575.104(e).

As with the fuel efficiency and safety tolerances, there are other factors that may affect the variation of this rating.  The agency is seeking comments and proposals on these various factors, and requests that they be supported with data.