Tires are manufactured by bonding rubber to fabric plies and steel cords. And despite the anti-aging ingredients mixed into the rubber compounds, there is a realization that tires are perishable, as well as a growing awareness that some tires will actually age out before their treads will wear out.
For the most part today's tires deliver more miles and years of service than ever before. In the 1970s, typical bias ply tires lasted less than 20,000 miles and were only expected to be in service for about two years. In the 1980s, early radial ply tires offered a treadwear expectancy of about 40,000 miles during four years of service. And by the turn of the century, many long-life radial tires extended treadwear to about 60,000 miles during four or more years of service. While passenger car and light truck tire technology and American driving conditions in the past resulted in tire treads wearing out before the rest of the tire aged, it may not always be true of today's even longer lasting tires that are approaching 80,000 miles of treadwear.
How many years will tires last before aging out? Unfortunately it's impossible to predict when tires should be replaced based on their calendar age alone.
The U.S. National Highway Traffic Safety Administration (NHTSA) and tire manufacturers are currently studying the many variables. Exposure to the elements (sun and atmospheric), regularity of use (frequent or only occasional) and the quality of care (maintaining proper inflation pressure, wheel alignment, etc.) will all influence the answer. So while tire life depends on the service conditions and the environment in which they operate, the difficult task remains how to identify all of the variables that influence a tire's calendar age and attempt to quantify their influence.
The British Rubber Manufacturers Association (BRMA) recommended practice issued June, 2001, states "BRMA members strongly recommend that unused tyres should not be put into service if they are over six years old and that all tyres should be replaced ten years from the date of their manufacture."
"Environmental conditions like exposure to sunlight and coastal climates, as well as poor storage and infrequent use, accelerate the aging process. In ideal conditions, a tyre may have a life expectancy that exceeds ten years from its date of manufacture. However, such conditions are rare. Aging may not exhibit any external indications and, since there is no non-destructive test to assess the serviceability of a tyre, even an inspection carried out by a tyre expert may not reveal the extent of any deterioration."
More recently, The Japan Automobile Tire Manufacturers Association (JATMA) recommended practice issued May, 2005, states "customers are encouraged to have their vehicle tires promptly inspected after five years of use to determine if the tires can continue to be used (recommends spare tires be inspected as well). Furthermore, even when the tires look usable, it is recommended that all tires (including spare tires) that were made more than ten years ago be replaced with new tires. Additionally, because in some cases automobile makers--based on the characteristics of the relevant vehicle--stipulate in the owner's manual the timing of tire inspection and replacement. Please read and confirm the content of the owner's manual."
Several European vehicle manufacturers of high performance sports cars, coupes and sedans identify that "under no circumstances should tires older than 6 years be used" in their vehicle owner's manual. However, it should be noted that European recommendations must include driving conditions that include roads like the German Autobahn, which allows vehicles to be legally driven at their top speeds for extended periods of time.
While American driving conditions don't include the high-speed challenges of the German Autobahn, Chrysler and Ford Motor Company joined their European colleagues in 2005 by recommending that tires installed as Original Equipment be replaced after six years of service. (General Motors declined to offer a recommendation until a more scientific analysis of driving conditions and tire aging could be completed).
It is important to take into account Original Equipment tires are mounted on wheels and put into service right after being received by vehicle manufacturers, so their calendar age begins immediately. However the same cannot be said of tires properly stored in a tire manufacturers' warehouse or in wholesale distribution centers before they go into service. Properly stored tires that are protected from the elements and not mounted on a wheel age very slowly before they are mounted and put into service.
Experience has been that when properly stored and cared for, most street tires have a useful life in service of between six to ten years. And while part of that time is spent as the tire travels from the manufacturing plant to the manufacturer's distribution center, to the retailer and to you, the remainder is the time it spends on your vehicle.
Check this statement from the RMA:
http://www.rma.org/RMA%20Tire%20Service%20Life%20Statement.pdf
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