Back in the day, tires typically would wear out before they got too old. Thinning treads is the consumer indicator that a tire needed to be replaced and, 30 to 40 years ago, that was probably around the 20 to 30,000-mile usage marker.
Nowadays, tires are more durable and can last upwards of 60 to 100,000 miles. The downside, however, is consumers are unaware that steel-belted radial ply tires, despite their toughness, face aging challenges because they are made of rubber, a product that oxidizes and hardens over time.
Older tires are vulnerable to catastrophic failures since excessive brittleness from oxidation can trigger tread and belt separations. Should those tires be attached to vehicles that travel roads in hot, dry climates, then those tires will deteriorate even faster.
The challenge with aging tires is they can hide their decrepitude, unlike a mature actor relying on injectables and plastic surgery for youthfulness. Unused new tires may be stored for years before installation and look pristine, but climate, handling, and storage can exact a toll indiscernible to visual examination.
William J. Woehrle, tire group leader at Peter R. Thom and Associates Inc. and a 45-year tire industry veteran, describes the impact of current tire use and purchase habits on the problem of aging tires:
“The used tire market in online venues like eBay is thriving in part because of a resale trade in full-sized spare tires that have been salvaged and sold as new or nearly new,” he explains. “Unfortunately, these ‘forgotten’ tires probably have been mounted, inflated, and stowed in vehicles and almost certainly never rotated into service. Instead, the spare tire’s inflation pressure has been slowly oxidizing the internal rubber between the belts and increasing the tire’s susceptibility to tread and belt separations—diffusing air through the tire at a monthly rate of one to two PSI.”
Currently, there is no U.S. industry standard for when tires should be removed from service. To compound matters, manufacturers do not plan to stamp expiration dates on their wares. European countries recommend 6 years of usage. In contrast, U.S. tire manufacturers either do not offer guidance as to tire shelf life or simply suggest removal or regular inspections of 6 to 10-year-old tires. As long as a tire does not show signs of checking or cracking (the only visual traces of tire aging) and was kept in climate-controlled storage, then it may be okay to use despite its age.
Enterprising policyholders can, however, decipher a date code marked on the tire’s sidewall to determine a tire’s age. That date code is contained within the tire’s serial number and is commonly imprinted on the inward-facing side of the tire, but chances are the figures noted will be somewhat cryptic. Unfortunately, as many retail tire shop employees do not know how to read date codes, consumer ignorance is not altogether unexpected as well.
Gregory J. Quan is a Managing Engineer at Peter R. Thom and Associates Inc., a national firm of consulting automotive engineers. He can be reached at (800) 874-1664; www.prtassoc.com.