A study undertaken by the Rubber Manufacturers Association (RMA) claims there is no correlation between the end of a tire’s “safety performance” and its chronological age. RMA released its study data in mid-May after examining some 14,000 scrapped P- 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, aged one to 16 years in the sample. “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.

The study did not consider reasons that the examined scrap tires were taken out of service. “We wanted to focus on measurable, recordable things that we could see,” said an RMA spokesman. The study only compared the tire’s manufacture date (from DOT codes) to the date the tire was examined, and the on-site scrap tire inspections took place between Oct. 18 and Dec. 21, 2005.

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.

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 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, and they recorded data at scrap processing facilities in Arizona, California, Florida, Illinois, Massachusetts, Oregon and Pennsylvania, said RMA.