What is meant by “tire aging”?

The structural integrity of a tire can degrade over an extended period of time. When that occurs, tires are more prone to catastrophic failure, which could, at best, cause an inconvenience, or, at worst, lead to a crash.
The degradation of a tire occurs over time, mostly the result of a chemical reaction within the rubber components. That aging process can be accelerated by heat and sunlight.

Does climate have an effect on the aging of tires?

NHTSA research suggests that tires age faster in warmer climates. Exposure to high ambient temperatures can accelerate the tire aging process, which could contribute to tire failures, including tread separations.
Environmental conditions like exposure to sunlight and coastal climates, as well as poor storage and infrequent use can hasten the aging process.

Are some vehicles more prone to tire aging problems?

Tire aging is generally not an issue with vehicles that are driven regularly. Tires will wear out and need to be replaced before aging becomes a safety concern.
But those with occasional use - like recreational vehicles or collector cars, for example - could be susceptible.

The spares on all vehicles also are prone to aging problems because they seldom get used or replaced. In those instances, the structural integrity of the tire may be weakened - and potentially hazardous - even though the tire still has a great deal of remaining tread.

How do you detect when tires have become unsafe?

The effects of aging may not be visibly detectable. Since there is no standard test to assess the serviceability of a tire, even an inspection performed by an expert may not always reveal the extent of tire deterioration.
Vehicle owners are therefore encouraged to have their tires checked after five years of use, then annually thereafter.

How do you determine the age of a tire?

The age of the tire can be determined by checking the tire identification number on the sidewall of the tire, which begins with the letters "DOT".

The last four digits represent the week and year the tire was manufactured. On newer model tires, the tire identification number is on the outside sidewall; older models will have the identification information on the inner sidewall.

When does NHTSA recommend that tires should be replaced?

While tire life will ultimately depend on the tires’ service conditions and the environment in which they operate, there are some general guidelines.
Some vehicle manufacturers recommend that tires be replaced every six years regardless of use.
In addition, a number of tire manufacturers cite 10 years as the maximum service life for tires.
Check the owner’s manual for specific recommendations for your vehicle.
Remember, it is always wise to err on the side of caution if you suspect your vehicle has tires that are over six years of age.

Are there other reasons for tire failure?

Yes. Poor maintenance is often cited as a cause of failure. While maintenance is important for good wear and safety performance of tires, many other factors contribute to their failure.

Tire failures can be caused by a number of factors such as under- or over-inflation of tires, overloading of vehicles, road hazards, improper maintenance, structural defects, and improper installation, in addition to tire aging.


Is it a significant safety problem?

Most failures result in nothing more serious than minor property damage. For more serious crashes, NHTSA estimates that about 400 fatalities annually may have been attributed to tire failures.

Treadwear grades are an indication of a tire's relative wear rate. The higher the treadwear number is, the longer it should take for the tread to wear down.

A control tire is assigned a grade of 100. Other tires are compared to the control tire. For example, a tire grade of 200 should wear twice as long as the control tire.

Of current tires:

15% are rated below 200

25% are rated 201 - 300

32% are rated 301 - 400

20% are rated 401 - 500

6% are rated 501 - 600

2% are rated above 600

Traction grades are an indication of a tire's ability to stop on wet pavement.
A higher graded tire should allow a car to stop on wet roads in a shorter distance than a tire with a lower grade. Traction is graded from highest to lowest as "AA", "A", "B", and "C".

Of current tires:

3% are rated “AA”

75% are rated “A”

22% are rated “B”

only 1 line of tires rated “C”

Rotating tires from front to back and from side to side can reduce irregular wear (for vehicles that have tires that are all the same size).
Look in your owner's manual for information on how frequently the tires on your vehicle should be rotated and the best pattern for rotation.

Understanding Tire Pressure and Load Limits

Tire inflation pressure is the level of air in the tire that provides it with load-carrying capacity and affects the overall performance of the vehicle.
The tire inflation pressure is a number that indicates the amount of air pressure– measured in pounds per square inch (psi)–a tire requires to be properly inflated.
(You will also find this number on the vehicle information placard expressed in kilopascals (kPa), which is the metric measure used internationally.)

Manufacturers of passenger vehicles and light trucks determine this number based on he vehicle's design load limit, that is, the greatest amount of weight a vehicle can safely carry and the vehicle's tire size.
The proper tire pressure for your vehicle is referred to as the "recommended cold inflation pressure."

Remember, the correct pressure for your tire is what the vehicle manufacturer has listed on the placard, NOT what is listed on the tire itself.

Because tires are designed to be used on more than one type of vehicle, tire manufacturers list the "maximum permissible inflation pressure" on the tire sidewall.
This number is the greatest amount of air pressure that should ever be put in the tire under normal driving conditions.

Temperature grades are an indication of a tire's resistance to heat.
Sustained high temperature (for example, driving long distances in hot weather), can cause a tire to deteriorate, leading to blowouts and tread separation.
From highest to lowest, a tire's resistance to heat is graded as “A”, “B”, or “C”.

Of current tires:

27% are rated “A”

59% are rated “B”

11% are rated “C”