RMA released its study data earlier this week after examining some 14,000 scrapped P-metric and LT-metric tires late last year, comparing each tire’s date of manufacture to the date it was examined.

The study showed a consistent pattern of retirement for the scrapped units. Tire date codes showed that the sample included tires that were from one to 16 years of age. “If chronological age was a determining factor in tire performance, the data would have shown a spike of tires removed from service after a particular time,” RMA said in a statement.

The study, said the RMA, did not consider reasons why the examined scrap tires were taken out of service. The study only compared the examined tire’s manufacture date (from DOT codes) to the date the tire was examined. According to RMA, the on-site scrap tire inspections took place between Oct. 18 and Dec. 21, 2005.

“If age was a sole factor in determining tire service life, our data would have shown a significant number of tires being removed from service at a particular point,” Laurie Baulig, RMA’s general counsel, said. “Our data showed no magic date when tires are removed from service.”

While the RMA claims it did not trace the history of the tires it examined, it says it is “reasonably certain” that the thousands of scrap units it looked at had been taken out of service within two to three weeks prior to examination.

Examiners did record the measurable tread depth and condition of the scrap tires – including the presence of any repairs – but the study did not consider the reasons why any of the tires were taken out of service. “We wanted to focus on measurable, recordable things that we could see,” said an RMA spokesman.

The study also found that:

• 42% of tires in the study had tread at or below tread wear indicators. Among tires older than one year, 59% were removed due to wear-out.
• 25% exhibited signs of road-hazard damage.
• 17% had been repaired, and of the repairs observed, 87% were improper – not performed with a plug and internal patch as specified by RMA tire repair guidelines.

RMA said the study was not intended to “be a forensic study or about the safety performance” of the tires that were examined. “We wanted to see if there was a ‘magic removal date,’ some consistent time frame that might indicate if tire safety performance ends at a set time.”

Study examiners were “trained tire technicians” supplied by RMA tire company members. RMA declined to say which companies provided examiners. The technicians took two to three days to examine and record data on some 2,000 tires at each of seven scrap processing facilities in five geographic regions of the country. The seven sites were located in Arizona, California, Florida, Illinois, Massachusetts, Oregon and Pennsylvania, said RMA.

Only P- and LT-metric tires were considered, and all were radials.

RMA said the study data has been shared with the National Highway Traffic Safety Administration (NHTSA), which is considering the tire aging issue.