How Aging Tires Can Cause Unexpected Blowouts
Gone are the days of just measuring your tire tread with a penny to see if you need to replace them. Now you need to know your tires’ birthday too! Because research indicates that tires more than six years old should be retired, regardless of their tread depth or their miles on the road.
As tires age and are exposed to heat, the rubber deteriorates. That’s because rubber absorbs oxygen, which causes what is called thermo-oxidative aging. Sean Kane, president of Safety Research & Strategies, Inc., an organization that researches and analyzes motor vehicle issues, gives us an everyday point of comparison:
“If you take a rubber band that’s been sitting around a long time and stretch it,
you will start to see cracks in the rubber.”
Research over the past 40 years, and even earlier, raised questions about the safety risks of aging tires, but the rubber industry and automakers were slow to share this information with lawmakers or consumers.
- In 1985, tire manufacturer Uniroyal first publicly shared its concerns about the tire safety of newly introduced radial tires, which were advertised to last much longer than old style tire models.
- The national uproar over Ford Explorer rollovers in the early 1990s focused on SUV stability standards, but failed to note that tires older than six years experienced tread separation that, at highway speeds, contributed to lethal accidents.
- In 2002, the National Highway Traffic Safety Administration (NHTSA) proposed an aging test for tires, but opposition from the rubber and auto industries was so powerful that the proposal went nowhere.
- Five years later, in 2007, NHTSA delivered a Research Report to Congress on Tire Aging, with the results of a study of tire-related auto insurance claims between 2002 and 2006. This research indicated that 77% of tire-related claims came from five hot-climate states, and 84% were based on tires more than six years old.
- Finally, in 2008, NHTSA issued a consumer advisory urging motor vehicle owners to check with manufacturers about tire aging to see what they recommended. Car safety advocates continue to call for actual regulations about tire age, but to date none have surfaced.
The most visible symptoms of dangerously aging tires are tiny cracks in the sidewalls, but deterioration is not always visible. Rubber breakdown can be caused not only by actual age, but by climate, conditions of use, and history on the road and on the shelf.
- Hazardous cracks may appear in a tire’s sidewall, tread, or any other component. The sidewall brings structure and stability to the tire and meets the tread at the shoulder. The tread itself includes tread blocks, tread voids, and tread grooves. Another element, the tire bead, is not visible, but it holds the tire on the rim.
- Research demonstrates that climate and weather conditions hasten a tire’s aging process and therefore, tendency to develop cracks. Tires driven in warm-weather states with year-round exposure to sunlight are especially susceptible, as are tires driven in coastal states.
- Because they have not been used on the road, most consumers don’t realize that tires that have been stored for several years are vulnerable to age-related deterioration. A spare tire in the trunk has been described as “baking in a miniature oven,” even though it never has been used.
- Automobile dealers, tire stores and repair shops often keep “new” tires on the shelf for years, which actually have become “old” tires by the time they are sold and installed. Unsuspecting consumers pay for new tires, but when they drive out the door, they are immediately vulnerable to tread separation that could result in a blowout.
- Your tires’ on-the-road experience is also a factor in their aging process. Tires that have not been properly inflated, have hit the curb too many times, or have been repaired for punctures will wear out faster than those that have been well maintained.
The good news about tire safety is that now you can easily determine the age of a tire, whether you are purchasing it new or used. DOT (Department of Transportation) and NHTSA regulations mandate that the date of manufacture be stamped on all tires.
Here’s how you can find out the age of your tire and make sure your family’s safety is not threatened by “elderly” tires:
- Your tire contains a lot of information, such as service description (“P” for passenger car, for example), tire width, aspect ratio, internal construction (“R” for radial), rim diameter, load index, and speed rating (“H” for can be safely run at speed up to 130 mph for extended periods). All of this is important, but most important is the manufacture date.
- Federal law requires that tire makers provide standardized information that is permanently stamped on the sidewalls of tires sold in the U.S. The entire DOT number with the date is branded on the outside; only the letters “DOT” with the first digits of the tire identification number are stamped on the inside. The date is the number following the DOT code, which was originally required to track tire production in case of recall.
- Tires made after 2000 have a four-digit number after the DOT code. The first two digits stand for the week, the other two for the year that the tire was made. For example, if your tire reads, “1411,” that means it was manufactured in the 14th week of 2011.
- Tires manufactured before 2000 have a three-digit number after the DOT code to indicate the date. So the number “146” could mean your tire’s birth date was the 14th week of 1996 . . . or maybe 1986. In any case, tires manufactured before 2000 are by definition more than six years old and should be discarded.
- Some tires not originally intended to be sold in the U.S. are manufactured without being tested to conform to U.S. Federal Motor Vehicle Safety standards. These untested, uncertified tires are not permitted to use the DOT stamp and are not legal to drive in the United States.
After checking your tires’ birthday, you should provide regular maintenance and follow safe-tire guidelines that will keep them healthy during their six-year life span. Then, at the end of six years, put them out to pasture.
- ConsumerReports advocates that drivers check their car’s tire pressure each month to prevent uneven wear and unexpected problems. The NHTSA reports that tires underinflated by more than 25% are three times more likely to cause a crash related to tire problems than tires with proper inflation. So it is critical to know the level of inflation appropriate for your tires (measured in psi, or pounds per square inch), which is stamped on your sidewall. Tires tend to lose their inflation at the rate of one to three psi’s each month.
- Monitoring your tire’s tread is important too. Research proves what we all know: Tire-related crashes are more likely as tire tread wears. A NHTSA study found average tire-related accident rates of 2.4% when tires had near full tread depth, and 16% when tires were worn out. ConsumerReports recommends shopping for new tires when the old tires have about 4/32 inches tread; at that tread level crash risk is estimated at about 8%.
- Get rid of existing tires that are past their six-year expiration date, regardless of their tread, driving history, or what the manufacturer recommends (some tire makers say their brands can last 10 years or more). Have your tires inspected regularly along with your regular tire rotations.
- Be wary of buying “new” tires from small tire shops or auto repair shops that do not have much business and likely have tires that have been stored in their inventory for years. This also can be a problem with huge big-box retail stores that buy tires in huge volume and may have “leftovers” that are beyond their safe six-year life span.
- The cost savings of used tires are outweighed by the risks they pose to your family’s safety. Even if you check used tires’ manufacture date and they are less than six years old, you must take into account the driving conditions to which they have been subjected. Were these tires kept properly inflated? Were they owned by a teenager who regularly bounced off the curb or had an accident or two? You have no way of knowing . . . so it’s either “buyer beware” or, the better choice, “don’t buy ‘em.”