http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=138
Nothing Lasts Forever...and Tires Are No Exception
In the 1970s, bias ply tires wore out in about 15,000 miles during two years of service. In the 1980s, early radial ply tires wore out in about 40,000 miles during four years of service. And by the turn of the century, radial tires lasting 60,000 to 80,000 miles were providing four or more years of service on vehicles averaging about 15,000 miles per year. In all of these examples, the tire treads "wore out" before the rest of the tire "aged out."
However, not all of today's vehicles average 15,000 miles per year. Multiple-vehicle families, occasionally used recreational vehicles and vehicles driven only for pleasure are driven fewer miles per year. Additionally, enthusiast vehicles trailered to events, shows, stored or put on display for extended periods of time put on far fewer miles. It's possible to encounter ten-year-old tires with significant remaining tread depth because they've been driven less than 1,000 miles a year!
Unfortunately, the growing realization that tires are perishable means that the tires on some of these vehicles will actually "age out" before they "wear out."
How long will tires last before aging out? The U.S. National Highway Traffic Safety Administration and tire manufacturers are currently studying the many variables. Heavily loaded tires only driven occasionally in scorching climates face some of the most severe conditions, while lightly loaded tires driven every day in moderate climates experience the least severe. Add to that the amount of exposure to the elements (sun and atmospheric) and the quality of tire and vehicle maintenance practices (proper inflation pressure, wheel alignment, etc) and you have an idea of the complexity of the situation. While tire life will ultimately depend on the tires' service conditions and the environment in which they operate, the difficult task remains how to confirm and quantify it.
The current industry association recommendations regarding inspecting and replacing tires due to age originate outside the United States.
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, the U.S. divisions of DaimlerChrysler and Ford Motor Company joined their European colleagues in 2005 by recommending the 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).
Because many of the tires The Tire Rack offers are manufactured in Europe or Asia, it's common for us to receive new tires direct from the manufacturers that are six to nine months old. Additionally there are some instances where the tire manufacturer's minimum run quantities will produce enough tires to meet a few years of consumer demand for lower volume types and sizes. In these cases the tires we receive directly from the manufacturer may already be several years old. Finally, when we work with a tire manufacturer to help them clear a discontinued tire line out their warehouses, this clearance frequently uncovers some new tires that are older. These tires are typically offered at a significant discount and will most likely be worn out within their useful lifespan. Since we rotate our inventory, most of the tires we ship are less than a year or two old.
It is also important to note that the more aggressive the tires' tread compound, the shorter its life. DOT-legal competition tires would have the shortest shelf live before the aging process would begin to diminish their performance. Sometimes the tires that were just right at the end of this season will be too aged to be fully effective the next year. Max Performance and Ultra High Performance tires would be next, and so on down the line.
Our experience has been that when properly cared for, most street tires have a useful life 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 warehouse, to the retailer and to you, the remainder is the time it spends on your vehicle.
Thanks!
with the old ones before switchout.