A comprehensive study of more than 14,000 scrap tires shows that chronological age alone cannot determine when a tire is removed from service.
The Rubber Manufacturers Association (RMA) initiated the study late last year. It inspected tires at seven large scrap tire processors in seven states and recorded the following tire information:
* date code.
* tread depth.
* whether they had been repaired or had any visible damage.
"We believe that a good starting point for a discussion about chronological age and tires was to examine tires that had been removed from service," says Laurie Baulig, RMA's general counsel.
The scrap tire survey examined more than 14,000 tires that had been removed from service. The date codes on the tires showed that the survey sample contained tires from one to 16 years old.
The RMA worked from the premise that 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. "Our data showed no magic date when tires are removed from service," says Baulig.
Here are some other study results.
* 42% of tires in the study were removed due to wear-out (had tread at or below tread wear indicators). After the first year of service, 59% of tires in the study were removed due to wear-out.
* 25% of the tires had road hazard damage.
* 17% of the tires had been repaired.
* 87.5% of the observed tire repairs were improper (not performed with a plug and internal patch as specified by RMA tire repair guidelines).
The RMA scrap tire study encompassed 14,271 randomly selected tires observed at seven scrap processing facilities in five geographic regions of the country as part of its methodology. The seven sites were located in Arizona, California, Florida, Illinois, Massachusetts, Oregon and Pennsylvania.
Trained tire technicians from RMA-member companies looked at approximately 2,000 tires at each site.
The study data has been shared with the National Highway Traffic Safety Administration (NHTSA). In June 2005, RMA wrote to NHTSA urging the agency to examine whether a relationship existed between a tire's safety performance and its chronological age. In the letter, RMA also agreed to work with the agency to provide information about chronological tire age.
(At the time, an RMA spokesman said neither the RMA or its member companies were aware of "any factual or scientific data that define a relationship between tire service life and tire safety performance.")
Another industry organization, the Tire Industry Association (TIA), has publicly pledged to fight efforts to add 'born on' or expiration dates to the sidewall of a tire.
"Adding 'born on' dates to the sidewall of tires could cause major inventory problems for independent tire dealers as consumers could request newer tires, leaving older ones to age further in a warehouse," says the association.
In addition, TIA believes that while consumers "should be aware of how old their tires are, (they) have much greater safety concerns to worry about than aging, such as proper inflation levels, safe tread depth and overloading of tires (and) vehicles."
For more information on tire aging, check out Modern Tire Dealer's May issue ("When should tires be replaced? Ford says after six years; tiremakers say after 10," page six).
