News Article about Tire Age Limits

pnichols wrote:
Well ..... most/all of the tire experts'/engineers' explanations above do not seem to account for cases such as that of our current (GMC) pickup:.....

Well, let's see if we can.

pnichols wrote:
......

The former set of Cooper tires on it were AT LEAST 12 YEARS OLD before I replaced them recently ... due only to not much tread depth left. Their sidewalls showed no cracking whatsoever and the truck set most of it's life out in the California sun. This situation closely duplicated that of an old Ford pickup we had for years before the GMC.

However, of course both pickups were rarely loaded with any weight to speak of in their beds. So .... I'm very close to coming to the conclusion that it's WEIGHT ON THE TIRES WHEN THEY'RE ROLLING that's the most damaging to their internal structure - especially the sidewalls. It's weight that distorts the sidewalls (bulging them). Think of doing this distortion hundreds (thousands?) of times per minute when going down the highway. This ultra-high flexing and the heat that it creates has got to be hard on the mechanical and chemical structures of any tire. Of course this amount of flexing and heating is way reduced in a lightly loaded pickup - hence, IMHO, the reason for RV tire sidewall cracking is ultimately due to the weight that they're carrying when in motion.

There is no question that load on a tire increases the operating temperature of the tire. A fully loaded (but not excessively loaded) tire will operate at temperatures that age the rubber up to 4 times faster than a lightly loaded one.

Second, is that some tire manufacturers use sidewall rubbers that don't show cracking very readily. Unfortunately, those types of rubber are unsuitable for use INSIDE a tire. So even a heavy used tire might not show sidewall cracking and still be on the verge of failing inside.

And lastly, the types of failures we are discussing here are fairly rare. Even the infamous Firestone ATX has been described as having a failure rate of a fraction of a percent. That means that many, many people will have no problems with their tires - but that doesn't mean their particular experience (or in this case, non-experience) proves that the explanations are incorrect. It means that we are looking at things under a microscope and discerning very small differences.

So you are right, load on a tire ages a tire faster. That's one of the things that Tireman9 was trying to point out - that there are other things involved in tire aging, not just ambient temperature.

j-d wrote:
....But I have a question about Tire Age. Limited Service Spares, so common in cars, minivans and so on. They may not leave the trunk for a decade. I can imagine they're formulated for Shelf Life not Tread Wear, but is that true? If I keep one inflated, can I count on it after a dozen years or so?

2 thoughts:

1) No, I don't think any special consideration is made for temporary spares. They are made out of essentially the same materials that regular tires are made out of.

2) Temporary spares are supposed to be used for at most 50 miles (at 50 mph max!). That's a whole lot different than 50,000 miles (with occasional bursts to 75 mph!). From an engineering perspective, that difference is HUGE - and means that even an older spare will likely survive that small bit of use - just as it was intended to do.