WASHINGTON—The federal government is changing the way it calculates treadwear grades under the Uniform Tire Quality Grading System to keep a lid on increases in treadwear grades.
In a final rule, effective July 24, the National Highway Traffic Safety Administration is changing the computation of the base course wear rate it uses to calculate the treadwear of passenger tires in UTQG testing.
These changes, according to NHTSA, will establish for the first time a direct comparison between the wear rates of the course monitoring tire (CMT) and the tire being tested, resulting in more consistent treadwear ratings.
The agency will measure the wear rate of CMTs four times annually and use the average rate as the basis for the base course wear rate (BCWR), according to the text of the regulation. It also will require that CMTs be no more than 1 year old at the time treadwear tests begin and must be used no more than two months after removal from storage.
This marks the first time since September 1996 that NHTSA has resorted to changes in the BCWR to prevent treadwear grades from creeping up. At that time, it set the wear rate permanently at 1.34.
In the original BCWR proposal issued June 5, 1998, the agency proposed that the course monitoring tires be no more than six months old. This drew objections from both the Rubber Manufacturers Association and Uniroyal Goodrich Tire Co. Both said such a short deadline was impossible, because CMTs must be made specially in extremely small quantities.
The RMA has no objection to the final rule, which doubles the CMT deadline, said Steven Butcher, RMA vice president-technical and standards. "The agency largely accepted what we originally suggested," he said.
The final rule appeared in the May 24 Federal Register.