Tire Age

Tire Aging – Part #1


 

Nothing Lasts Forever...and Tires Are No Exception

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 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, Chrysler, Ford Motor Company and General Motors have joined their European colleagues by recommending that tires installed as Original Equipment be replaced after six years of service.

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 Tire Rack 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.

Our 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.

Tire Aging – Part #2

 

Should Drivers Replace Old Tires Even if Their Treads Aren't Worn Out?

While most drivers' past experience might not indicate it's necessary, the growing realization that tires are perishable means tires on some vehicles will possibly age out before they wear out. Composed of steel belts, fabric plies and rubber compounds, the structural integrity of tires can degrade over an extended period of time as the result of chemical reaction within the rubber components, cyclic fatigue, abuse and road hazards.

Tire aging isn't typically an issue with vehicles driven frequently. However, the lower annual mileages put on sporadically used motor homes, enthusiast vehicles driven for pleasure and collector cars trailered to events could make tire calendar age an important consideration. Tire age is also a concern for the often unused spare tire in a car's trunk, suspended under a pickup's cargo bed or hung off the back of an SUV.

Unfortunately no one is absolutely sure of how long tires will last because of the many variables. Heavily loaded tires on vehicles stored outdoors in sunny, scorching hot climates and only driven occasionally face some of the most severe service conditions and potentially have the shortest calendar lifespan. In contrast, lightly loaded tires on vehicles parked in garages and driven daily in moderate climates experience some of the least severe service conditions and potentially have the longest lifespan.

Then there is the influence of how well drivers maintain their tires (regular cleaning and pressure checks along with periodic rotations and wheel alignments), use and/or abuse them (drive on them when overloaded or underinflated), as well as the possibility of irreversible damage from punctures, cuts and impacts with potholes, curbs and other road hazards. A tire's original durability will be permanently compromised if it is uncared for, abused or damaged.

Therefore every tire's life expectancy ultimately depends on the environment in which it operates and its individual service conditions. The difficult task remains how to attempt to quantify tire life based on calendar age. Arbitrarily replacing tires prematurely based simply on age may result in tires being discarded before their time, contributing to increased operating costs, as well as waste disposal and recycling concerns.

Since Tire Rack sells tires manufactured in North and South America, as well as Europe, Africa and Asia, it's common for us to receive new tires directly from manufacturers that are already six to nine months old. Since we rotate our inventory, most of the tires we ship are less than a year old.

However some low volume tires in sizes for limited production vehicles can only be efficiently manufactured periodically where one short production run may produce more than a year's worth of global supply. In some of these cases, Tire Rack might receive new tires directly from the manufacturer that are already several years old.

There are also some occasions where we work with a tire manufacturer to help them clear out their inventory when they discontinue a tire line. While this may uncover some new tires that are several years old, these clearance tires are typically offered at a discount and will wear out before they age out.

Tires are stocked in Tire Rack distribution centers under favorable storage conditions. Protected from exposure to direct sunlight, moisture and hot and cold temperature extremes, our inventory leads a sheltered life compared to the tires mounted on wheels, installed on vehicles and exposed to the elements, road grime and brake dust.

Tire manufacturer's replacement tire warranties begin when the tires are purchased and typically last 4 to 6 years from that date. This allows the tire manufacturers' limited warranty to accommodate the time it takes tires to be shipped from the manufacturing plant to the warehouse or distribution center, to the retailer and to the consumer, as well as the time they spend in-service on the vehicle.

Keeping tires properly inflated is probably the most significant action a driver can take to prevent tire failure. For example, driving a vehicle with a significantly underinflated tire can permanently damage the tire's internal structure in ways invisible to external visual inspections. A U.S. National Highway Traffic Safety Administration (NHTSA) tire aging field study revealed that 30 percent of spare tires observed were significantly underinflated when first checked, Putting underinflated spare tires into service before being properly inflated would greatly increase their risk of catastrophic tire failure. The inflation pressure of spare tires should be checked monthly along with the rest of the set.

Vehicles equipped with a full-size matching wheel and spare tire should use the vehicle's five-tire pattern at every tire rotation. Not only will this prevent the spare tire from sitting idle, it will keep all five tires' tread depths roughly equivalent throughout their life and extend the tire replacement intervals (if rotating four tires would result in 40,000 miles of service, including the full-size matching wheel and spare tire into the rotation pattern would result in 50,000 mile replacement intervals).

The NHTSA tire aging field study also indicated a strong correlation of the speed rating with tire durability, with higher speed-rated tires losing the least capability with increasing calendar age. Drivers living in hot climates may want to consider purchasing higher speed rated tires than those that came as Original Equipment.

Our 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.