Hi Ray,
Here's a bit on the topic.
Mike
Tire age as a determiner of tire condition would be a delightfully
straightforward way to measure a tire's value to its owner. Unfortunately, the
opportunity to achieve this desirable situation of linked-parameters is
complicated by the political/legal factors of tire usage, the lack of uniform
tire technology, and routinely poor user maintenance.
A tire's structural integrity isB at its best just after cooling from the
vulcanization process. My experience suggests that most of today's tires have
little chance of having structural issues at this point regardless of
technology.B Tire vulcanization completes all of the mechanical and chemical
bonds that make the textile, steel, and rubber pieces hold on to each other.
Even if the tire were never used, time would eventually cause deterioration of
both external and internal bonds as retained oils migrate, oxidation occurs,
and physical distortion of storage stresses certain areas of the product.
However,B my own personal experienceB has included both radial and biasB tires
that were stillB viable after 30+ years of storage, use,B and inflation on
collector cars. At the same time, nearly 40 years as a tire engineer has shown
me a lot of physical deterioration and structural failure in tires less than
10 years old.... which had been about the "rule of thumb" tire age for
concern. Given that most tires are initially structurally sound, most of the
early-life issues I've seen in tires resulted from poor
maintenance,B undersized tireB applications, or environmental degradation.
So....what are some of the tire age issues to consider?
1. From a tire company perspective, every tire is intended to fully satisfy a
customer and it isB likely that 99% actually achieve that goal. A company also
has to consider that a fraction of its tires will be held accountable for
accidents and lawsuits. Armed with the knowledge that tires do structurally
deteriorate over time and internal damage accumulates as a result ofB poor
maintenance.....there is less product risk if all tires in service are
"newer". In an era of rampant consummerism and legislated safety issues, there
is general agreement that tire companies, government agencies, and consumer
advocates want to have low risk tires in service. To-date, this has not
resulted in illegal-aged tires, and it is not a bad line of reasoning.
2. The actual textile, steel and rubber components inside a tire are extremely
resistant to natural deterioration. The chemical bonds between them, and the
actual exterior of the tire are less resistant to degradation.
Most car folks realize that tubeless tires "lose" inflation pressure over
time....but they may not realize that the lost air is migrating through the
tire. Inflation air contains oxygen and moisture which force there way through
a tire (that's why internal adhesion failures can show up as bubbles on a
tire's surface) and they chemically react with the tire's bonded structures as
they travel. Tube-type tires seldom pressurize internally as inflation air
migrates from the tube andB finds its way out the loose-fit valve hole in the
rim.
3.B The worst degradation of a tire structure comes from overloading or
underinflation. Both of these conditions make the tire's structure work harder
and generate more heat than intended. (If you've not thought of rubber
creating heat....B repititiously stretch a small section of a thick rubber
band and then hold it to your lip to feel the hysteretic heat increase!). Heat
deteriorates the chemical bonds in a tire, leading to separation of structural
componentsB and failure can result. So....proper inflation & pressure
maintenance contributes mightily to tire life extension.
4. External damage from mechanical sources are always risk factors that
shorten a tire's life because it visually damages the structure.
Less obvious damage results from exposure to sunlight, ozone, and tire
cleaners. All of these factors can lead to cracking of the sidewall andB tread
rubber. Since all manufacturers use different rubber compounds on the sidewall
and tread, there is alot ofB variability in cracking resistance.B The sidewall
and tread rubber protects and reinforces the structure of the tire. If
cracking becomes too deep, the cracking agent (sun, ozone, or cleaner) can
reach the textile/steel reinforcements and cause failure. Deep circumferential
cracks actually can create an unexpected sidewall or tread hinge point that
helps flex-fatigue the structure beneath.B To guard against cracking causes,
tires are designed with anti-oxidants, anti-ozone chemicals, and oils that
bleed to the surface in service to protect the tire with a chemical skin. The
gray or brown film you remove with tire cleaners is the tire's protective
skin.
So.....what reasonable steps can prolong tire life.....while it is legal to do
so?
- Use the right tire size (or larger) with adequate (or more) inflation that
is checked often
- Store tires or vehicle away from sunlight and ozone-rich (electric motors
create ozone as do ion air purifiers) environmentsB
- Clean tires as seldom as needed with gentle cleaners (painting is likely
better than cleaning if the "look" is satisfactory). Armorall, gasoline, and
brake fluid clean great but are destructive in my opinion.
- Inspect tires for cracksB since they are inevitable as tires age. Minor
cracks around letters and other sidewall featuresB are normal....as are cracks
at junctions of different rubbers (often visible by color differences as
well). If cracks become deep ....perhaps 1/10"...B and/or are continuously
circumferential while deep, a structural issue may exist or may be in
creation. Cracking at this level may look so bad, you'd be embarrassed to own
them anyway!
So, in conclusion: There are technical, social, legal, and visual reasons to
promote usage of young tires. However, tires have been routinely used in
service for periods of 10+ years with good maintenance practices. It is
probably a bad practice to arbitrarily expect 10+ years of service from your
tires....so keep the aging factors and deterioration evidence in mind while
inspecting your tires often to see how they are doing!B
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