Drivers, especially in the hot and dry climate of Arizona, need to remember that a vehicle tire is made of rubber. Over time, all rubber degrades to the point where it is no longer usable. To illustrate, imagine a rubber band that gets left in a drawer for a few years. It becomes brittle and when you try to use it, it may likely snap in half. Unlike rubber bands, however, the degradation of rubber in tires may all be internal and NOT visible to the naked eye. As tires age, the adhesion of the steel belts may be compromised by as much as 75%, likely resulting in a tread separation, often at highway speeds. When this occurs, drivers often lose control of the vehicle with devastating results. Not surprisingly, this degradation process (known as thermo-oxidative degradation) is accelerated in hotter climates.
As of 2013, all major vehicle manufacturers in the United States, as well as Europe and Japan, warn about the risks of tire aging in their vehicle owner’s manuals. The word choice varies, but essentially all the manuals recommend replacing your tires once they reach 6 years old. But how do you tell a tire’s age? These answers are simple, but you have to know where to look.
Since 2000, all tires sold in the United States have been required to include a full 12-digit DOT code on the sidewall of the tire. The last 4 digits of this code represent the manufacturing date of that tire -- the 2-digit week and the 2-digit year. For example, if your tire was manufactured in the 5th week of 2011, the 4-digit code would read “0511”
– and if you had a tire that’s already that old, the vehicle manufacturers would all recommend that you replace it, regardless of remaining tread depth. This warning applies to spare tires, as well.
Only one side of the tire necessarily has all 12 digits of the DOT code. If that DOT code is mounted inboard, you may have to crawl under your vehicle with a flashlight. If neither side has a 12-digit DOT, your tire may have been manufactured before 2000 … don’t risk it – replace it.
Only buy new tires from a licensed retailer. Do not buy used tires, no matter how inexpensive they are. Even if they are less than 6 years old, used tires could already have serious internal damage that you won’t be able to see.
We always advocate replacing all four tires at once with tires that were manufactured within the last year or so. If for some reason you cannot replace all four tires, put the two new tires on the rear axle and put the two best remaining tires on the front axle. While this may seem counter intuitive, most experts agree that it is easier to maintain control of a vehicle during a front tire failure than a rear tire failure. Tires are also assigned a Uniform Tire Quality Grade (UTQG) rating.
Generally this consists of a three digit tread wear rating, a letter grade traction rating – “AA”, “A”, “B” and “C”, and a letter grade temperature rating – “A”, “B” and “C”. The temperature rating represents that tire’s ability to dissipate heat. This consideration becomes more important if you drive in hot climates; especially at highway speeds and in a vehicle with a high center of gravity, such as a truck or SUV, the heat build-up in a tire is often a cause of tire failure. Many tire dealers have websites where you can input your vehicle year, make, and model to see the available tires for your vehicle. The best websites show the UTQG rating next to the tires.
You still need to pay attention to tread wear. Everyone in the industry agrees that if you have 2/32 of an inch or less of tread depth at any location, it is time to replace the tire. But many tires experience failures before the tread gets that low; accordingly, even if your tread gets down to 4/32 of an inch, it’s best to replace the tire. The “penny test,” as most of you know it, still works reasonably well to measure this depth. Stick Abe’s head upside down into the tread; if you can see his whole head, there’s not enough tread. Maybe because pennies are tough to find nowadays, most modern tires also have wear bars (circled at upper right) in the grooves of the tread; when the tread is worn to near the same level as the wear bars, it’s time to replace the tire. Some tires wear unevenly (lower right), so it’s important to look at the whole thing to make sure you don’t have any low spots. When a tire tread separates, it almost always begins where the tread is lowest.
Even if the tire is less than 6 years old and has enough tread, you still need to be on the lookout for cracking, chipping, or weathering (left) on the sidewall of a tire. This is most often seen when a car is parked in the sunlight, so that the sidewalls of the tires bake in the hot sun. A tire can fail because of sidewall damage as well, so be careful.
It is well publicized that tires can fail due to under inflation and over inflation; therefore, tire maintenance is critical to minimizing this risk. Industry experts recommend that you check tire pressure each month and, in addition, before you embark on a long road trip. To ensure proper tire inflation, refer to your vehicle manufacturer’s recommended tire pressure and not the range of tire pressure indicated on the sidewall of your tires. The manufacturer’s recommended tire pressure can be located in your owner’s manual, as well as your door placard (right 2 courtesy of the National Highway Traffic Safety Administration) usually located in the door jam of the driver’s door (right 1).
Especially if you are planning to drive at freeway speeds in Arizona, high quality tires are just as important to the safety of your passengers as wearing seat belts. As we approach summer long-distance driving season, now is the time to have a tire professional inspect your tires for age, tread depth, and other potential problems. The sign at your neighborhood tire shop which boasts a “Free Tire Inspection” is not just some trick to get you to buy new tires. If they recommend replacing your tires, use that money you are saving by not flying to your destination to get new tires and ensure your passengers’ safety.
Have a pleasant and safe summer driving season!
Contributing Attorney: Charles Williamson practices in the area of product liability at Stark Williamson & Clausen LLP.