Since 2000, the week and year the tyre was produced has been provided in the Tyre Identification Number In 1973, the average tread life of a passenger car tyre was approximately 24,000 miles. Tyre tread life has quadrupled over the last 40 years and some currently sold tyres promise 100,000 miles of tread life. As tread life becomes less of a factor in the service life of a tyre, oxidation becomes a more serious concern and particularly in hotter climates.
The evidence is clear tyres should have an expiration date. Older tyres are substantially more likely to fail than newer ones. This is because tyres are made mostly of rubber, and rubber degrades with age.
Since 2000, the week and year the tyre was produced has been provided by the last four digits of the Tyre Identification Number with the 2 digits being used to identify the week immediately preceding the 2 digits used to identify the year.
As you can imagine, most consumers either do not know that this code exists or do not understand its significance. A 2006 survey in Britain showed that only 4% of consumers are aware that tyres become more dangerous as they age. A large body of scientific evidence supports that most tyres should be replaced six years from the date they are manufactured. This six-year expiration date begins from the day the tyre was manufactured at the plant and not the date it was sold to a consumer or the date that it was installed on a vehicle.
Tyre aging is a “hidden hazard” because most consumers do not know that tyres expire in six years and it is difficult for most consumers to tell how old a tyre is without deciphering a 4 digit code that is imprinted on the side of the tyre. Fortunately, you can crack the code on the side of a tyre to determine a tyre’s actual age.
For most tyres, this expiration date should be six years from the date of manufacture. Tyres age dangerously because of a chemical process commonly referred to as oxidation, which simply means that as the tyre components are exposed to oxygen, the oxygen particles cause the flexible components of a tyre to harden and become brittle. Over time, the tyre will simply fall apart under normal stress, just like an old rubber band. Because this process occurs naturally, it does not matter if a tyre is being used, stored as a spare, or simply waiting on a store shelf for an unsuspecting consumer.
How old is too old?
This is a subject of much debate within the tyre industry and no tyre expert can tell exactly how long a tyre will last. However, on the results of experience many tyre companies, including Bridgestone, warrant their tyres against manufacturing and material defects for five years from the date of manufacture. Based on their understanding a number of vehicle manufacturers are now aising against the use of tyres that are more than six years old due to the effects of ageing.
Regardless of their age tyres should be replaced if they show significant crazing or cracking in the tread grooves or sidewall and or bulging of the tread face or sidewall. All tyres, especially unused spare tyres, should be inspected periodically to determine their suitability for service. If there is any question about a tyre suitability please consult your local expert.
Source : The Independent