How Safe Can An Old Tire Be?

June 13, 2010

Tire aging has surfaced as an issue in a civil trial that has two huge automotive names defending themselves in a Montana courtroom. Ford and Firestone are two of the defendants in the case. The details of the accident emerged as lawyers made opening statements and were reported in the online version of the Great Falls Tribune. Tire aging was treated by All Car Advice recently.

In 2003 a 1989 Ford Bronco II rolled over when tire tread was lost on a tire positioned in the driver’s rear. The driver was ejected from the SUV and suffered “a closed-head injury, permanent cognitive impairment and paralysis” according to the report. Lawyers representing the four parties involved revealed their respective positions to the jury.

The plaintiff’s position is that design flaws in the tire and the Bronco II contributed to the rollover as did the decision to sell the truck with four allegedly mismatched tires.

Firestone’s attorney contended that the failed tire was the result of a combination of conditions: its age, inflation level, and repair history. The tire was said to have been the original spare tire and was 14 years old. Firestone contends the tire was not properly inflated, was punctured and had a damaged bead and steel belt.

An attorney representing the local used car dealer who sold the car refuted the plaintiff’s position saying that the accident occurred two years after the sale and that it was sold with a matching set of tires. As for the spare, the opposing attorneys had differing opinions as to the culpability for its use. The car dealer contends that there was no record of what kind of spare was sold with the car and that the old tire could have been purchased by the plaintiff after the sale. The other side believes that the car dealer should have known the age of the tire at the time of the transaction.

Although there are other facets of this case, the age of the failed tire and whose decision it was to use it may prove to be pivotal. A 2003 NHTSA test conducted on tires from Phoenix area tire stores found that technical properties like “Peel Strength” and “Ultimate Elongation” decrease with increasing age and mileage. But more importantly the study found that the changes in “the physical material properties of the tire rubber compounds can be explained by chemical changes in the compounds and interfaces”

Consumers, of course, can only base their decision to put a tire in service on the date of manufacture and not laboratory testing. One conclusion that was made in the previous All Car Advice post, which was that one of the first things that you should do when purchasing a used car is to determine the age of the tires including the spare. Instructions on this procedure can be found in the June 8, 2010 post.        

[Great Falls Tribune, NHTSA]

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