Two Tire Makers Add Tire Aging Replacement Guidelines for U.S. Market

Continental and Michelin recently issued Technical Bulletins on tire aging, joining a growing chorus of tire manufacturers and automakers issuing tire age replacement guidelines for the U.S. market. These bulletins are nearly identical to the Bridgestone-Firestone October 2005 recommendation that specified all tires should be removed after 10 years regardless of the remaining tread depth. They also follow guidelines published in overseas markets that have been in circulation for several years (Safety Record V3, Issue 1).

Tire age degradation hit the radar of safety advocates, regulators and members of Congress after the Firestone ATX / Wilderness recalls in 2000 and 2001, when experts concluded that age degradation played a role in the catastrophic failure of these tires. While the tire industry has known about the issue for decades, the problem initially gained traction in late 1980s after the publication of several German studies noting a disproportionate rise in failures once tires reach 6 years old. The studies recommended warnings and user-friendly date of manufacturer information on tires.
In response, some German automakers and Toyota added 6-year tire life recommendations to their owner’s manuals in 1990. Over the next ten years, others added similar warnings. The issue slipped into relative obscurity, as did most of the warnings, which were placed deep into several-hundred page owner’s manuals. But the Firestone debacle and the ensuing TREAD Act forced NHTSA to examine tire aging issues. A provision in the Safe Accountable, Flexible and Efficient Transportation Equity Act of 2005 also required the agency to report to Congress by August 2007 on tire aging, including potential regulatory testing to evaluate the risk of failure after a tire has been aged.

There are several common threads among the new U.S. technical bulletins. All recommend tire replacement after 10 years regardless of tread depth. All suggest annual inspections by a qualified tire specialist once a tire reaches 5 years old, including unused spares and tires that have experienced little use. The bulletins also claim that accurately predicting service life more precisely is not possible because of the wide range of conditions to which tires are subjected. Bridgestone-Firestone and Continental’s Technical Bulletins also defer to the vehicle manufacturers recommendations, which, in many instances, are 6-year tire life limits.

Impending NHTSA regulatory actions are expected to be based, at least in part, on the data from Ford Motor Company funded and published research on the mechanisms of tire aging and methods of artificial aging. The agency will also be using its own research project on aged tires that has generated data on aged tire performance (Phoenix Tire Data) and examination of methods of aging. The tire industry is adding to this through an ASTM working group that is examining age testing.

Ford’s addition of a 6-year age limit to its owner’s manuals in 2005 gave an additional jolt to the Rubber Manufacturers Association (RMA), which continues to claim that there is no valid criteria for determining tire service life. In a recent presentation at a tire industry meeting, Ford research scientist Dr. John Baldwin claimed that the 6-year age limit was defendable and data driven, whereas Bridgestone-Firestone, Michelin, and Continental’s 10-year position were not supported by any data. Dr. Baldwin also noted that Ford was requesting a NHTSA Consumer Advisory recommending a 6-year age limit to avoid confusion among consumers. Safety Research & Strategies first requested NHTSA consider issuing a consumer advisory in November 2004. In May 2005, following Ford’s tire-aging recommendation, SRS asked the automaker to support SRS’ push for a federal Consumer Advisory.

Regardless of the age recommendation, a lingering problem consumers face is how to decode the tire’s age. The Tire Identification Number (TIN) contains a string of 10 or 11 alpha-numeric characters, of which the last three or four provide the week and year of manufacture. The TIN is molded on one side of the tire sidewall. For example, a 10 character TIN with “029” in the last three positions means the tire was made in the second week of 1999 (or 1989). After 2000 an additional digit was added. So, for example, a TIN with 11 characters ending in “0202” indicates the tire was made in the second week of 2002. To address this issue Safety Research & Strategies petitioned NHTSA in 2004 to require non-coded date of manufacture molded onto both sides of the tire. SRS argued that a simple date of manufacture would not create a conflict with any future requirement and would only enhance the information already present. The agency has yet to address this petition.

According to Sean Kane, President of Safety Research & Strategies, “the recent spate of tire aging recommendations are a good start, but what is really needed is for manufacturers to label their tires with age expirations based on the specific construction of their product lines much the same way they provide tread wear guidelines of 30,000 or 40,000 miles for example.”

SRS has been at the forefront of tire aging and its submissions to NHTSA showing industry knowledge of the problem continue to garner significant attention. Kane recently took his message directly to the industry, presenting the case for expiration dates at the Tire Expo 2006 in Stuttgart, Germany. Kane says “this issue has reached the tipping point-we now have three major tire makers who account for nearly 50% of all tires sold with tire age recommendations in the U.S., and others with recommendations in overseas markets. Most of the major automakers also provide recommendations. The next step is to find better ways of identifying a tire’s age and its useable life-all of which can be addressed by the vehicle and tire makers.”

The first tire aging case against a vehicle manufacturer, Ford Motor Company, in Nueces County, Texas resulted in a $29 million verdict. Ford’s expert Dr. John Baldwin testified that tire aging was not a safety issue.

Copyright © Safety Research & Strategies, Inc., 2006