Aging tires have been killing people for years. A sudden tire failure at highway speeds can often have dire consequences. Yet to date, there are no federal rules or guidelines in the U.S. for when tires must be replaced. Although there are no official expiration dates on automotive tires or truck tires, there are suggested guidelines:
Various safety groups as well as tire manufacturers RECOMMEND replacing passenger car and light truck tires when they are TEN years old (from the date of manufacture) regardless of appearance or tread wear.
In Europe, the recommendation is to replace tires after SIX years (from the date of manufacture) regardless of appearance or tread wear.
The reason why tires have an age limit is because the synthetic rubber that is used in the manufacture of the tires, as well as the synthetic fibers used in the belts and reinforcements degrade over time. As the tire ages, it also weakens increasing the risk of a sudden tire failure or blowout.
As a result of this aging process, the incidence of tire failure starts to rise after six years, and gets even worse by the time a tire is 10 or more years old.
The aging process applies to tires that are in storage in a warehouse as well as those that have been sold and installed on vehicles. Because of this, a set of tires that were manufactured 6 or more years ago but have been in storage for many years may have aged out by the time somebody buys them. This would be a concern for "new old stock" tires" or older tires that have been in storage or unused for quite a few years.
The problem with old tires is that they may appear to be in good or like-new condition, but dangerously weak or rotten on the inside, making them a potential safety hazard to anybody who drives on them.
In one such incident, the owner of a classic 1964 Sunbeam Tiger was returning from an antique car show. The tires only had 4,000 miles on them and looked good as new on the outside, but the tires were more than 11 years old. On the way home, one of the tires blew out causing the car to crash. The passenger suffered permanent brain injuries as a result of the accident.
The short answer is politics, or more aptly a lack of support by the tire manufacturers or the general public for such a requirement. Although an expiration date would obviously generate more replacement sales six to 10 years after a set of tires were made, it could also cause inventory problems for unsold tires as well as consumer backlash.
Many tires sit in warehouses for up to two years before they work their way through the retail distribution pipeline and end up on somebody's car or truck. Many tire distributors and retailers do not always track and rotate their tire stock to make sure the oldest tires are sold first (as is the case with automotive batteries). Consequently, the "new" set of tires you just bought may have already aged one or two years (or even more) BEFORE they were installed on your vehicle. That means a shorter service life for installed tires, and more replacement expense for consumers.
It is important to note that a number of variables affect the aging process that tires experience. Some tire compounds resist aging better than others, but we have not seen any laboratory tests or field tests that would show accurately how one tire compares to another. So there is no way consumers can compare tire brands or the differences between specific compounds to see which tires age the slowest and retain their strength best over time.
Environmental factors also play a big role in how quickly or slowing tires age. Exposure to direct sunlight, ozone pollution and/or high ambient temperatures accelerates tire aging. Storing tires in a cool or cold warehouse or garage is better than storing them in a hot attic, garage or warehouse.
How fast the tread wears out on a set of tires is often the determining factor as to when the tires need to be replaced. But on a low mileage vehicle that may only be driven 8,000 miles a year or less, the tires will probably age out before they wear out.
How many miles a set of tires will last is hard to predict because it depends on the wear resistance of the tread compound, tire inflation pressure (underinflated increases wear), wheel alignment (misalignment due to worn or damaged steering or suspension parts increases tire wear), exposure to road conditions (potholes, bumps, nails, etc.), and the driver behind the wheel (aggressive driving and braking accelerates wear).
Tires do have a tread wear rating on the sidewall that provides a relative means of comparing one tire to another. A higher number means the tread will generally wear at a slower rate than a tire with a lower number (say 800 versus 400). But the rating does not translate directly into number of miles because of all the other variables that affect tread wear.
All tires have a date code on the sidewall that indicates the date of manufacture. By reading the date code,you can determine how old your tires are and whether or not they have aged out.
The date of manufacture is indicated by the last group of digits in the DOT manufacture code on the sidewall of the tire. The number is often stamped in a recessed rectangle. The DOT code tells who manufactured the tire, where it was made and when. The last group of digits in the code is the date code that tells when the tire was made.
Before 2000, the date code had three digits. Since 2000, it has had four. The first two digits are the week of the year (01 = the first week of January). The third digit (for tires made before 2000) is the year (1 = 1991). For most tires made after 2000, the third and fourth digits are the year (04 = 2004).
In the photo above, the date code is 8PY806. The 8PY is a manufacturing shift code, and the date the tire was actually made was 0806, which is the 8th week (08)in the year 2006 (06).
If your tires have not aged out, you should check to see if they are worn out. Tires have wear bars (flat spots)in the tread grooves to visually indicate wear. If the tread is worn down so the wear bars are flush with the surrounding tread, the tire is worn out and needs to be replaced. If you see cords showing through the rubber, the tire is unsafe to drive on and is on the verge of failure. Replace the tire without delay! The same advice goes for any tire that has bulges, deep cracks or the tread is separating from the casing.
Tread wear can be measured using a penny. Place the penny with Lincoln's head upside down in a groove between the treads. If you can't see the top of Lincoln's lead, the tire is okay and still has some wear left in it. But if the top of Lincoln's head is flush with the tread, the tread depth is 2/32-inch (1.6mm) or less, indicating the tire is worn out and needs to be replaced.
Some experts now say the same test should now be done with a quarter. If the top of Washington's head is flush with the tread when you place a quarter upside down in a groove, the tread depth is 4/32-inch (3.2mm). Though the tire still has some tread wear left, braking, traction and handling are significantly reduced compared to a tire with more tread on it. Because of this, many experts now recommend replacing tires when the tread depth is worn down to 4/32-inch or less.