Quote:
Originally Posted by r carl
……. In fact, underinflation does not cause tread belt separation in a properly constructed, properly designed tire. …….
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I hope you meant that a SMALL amount of underinflation will not cause a tread separation, because a LARGE amount of underinflation is definitely a cause.
Ya' see, undernflation causes the tire to develop more stress and more heat (hysteresis). That heat accelerates the breakdown of the rubber and over time the rubber loses strength. When the stress becomes larger than the strength of the rubber, a separation occurs.
Quote:
Originally Posted by r carl
……. However, if a tire has manufacturing or design defects and it is run underinflated, underinflation can accelerate tread belt separation. ……..
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It's a little hard to tell, but I think you just contradicted yourself. Let me talk about design first. I'll talk about defects after.
The tire design is supposed to last as long as the tread still has usable rubber left, except for tires designed to be retreaded, where the design is more robust. The most highly stressed area of a radial tire is under the top belt - at the edge. The term "strain density" was invented to describe how to quantify the way and the amount of stress in this area. Tire engineers design radial tires such that strain density is below a certain level (determined by the material being used.)
Note that I didn't say that the goal of the design is to have NO strain density. It is always there. The point of the design is to get it low enough that the tire will survive past the worn out state.
Put another way, if you were to continue to operate the tire, it would eventually fail - generally with a tread separation.
Google SN curves. Note that the X axis is a logarithmic scale and there is no end point.
Defects: I classify defects as 1) Things that are there that aren't supposed to be there, and 2) Things that are supposed to be there that aren't. I suppose you could add a third category where something is there but badly placed, but I tend to throw that into #1.
In the 100 of thousands of failed tires I have examined, I've only seen a handful of tires that have had defects. By contrast, the majority of tires were undetermined - that is, there wasn't anything visible that I could point at. I've always attributed those to "Design".
But some of the tires show signs of overdeflection (underiflation/overload - 2 sides of the same coin.) - some severely overdeflected. As an exercise, the company I worked for tested tires severely over deflected and got - you guessed it - tread separations.
Quote:
Originally Posted by r carl
……. Unfortunately, it is virtually impossible for the consumer to determine whether a steel belted radial tire is underinflated by visual inspection. ……
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Not exactly. Underinflated tires will generate more heat and that, in turn, results in higher hot operating pressures. Measuring the pressure after an hour of operation will give you an indication of whether or not a tire is underinflated or not.
Quote:
Originally Posted by r carl
……. It is often difficult, if not impossible for people who are forensic tire experts to determine upon visual examination whether a tire has incipient tread belt separation prior to the actual failure of the tire that causes the steel belt(s) and tread to separate from the carcass.
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Again, not exactly. A bulge is an indication there is a separation.
Further, we have tools that can look inside a tire without damaging it. The old way was X-rays and holography (shearography), but nowadays, they use MRI's and the like.
And we tend to use the term "incipient separation" to mean a small, barely detectible separation. It's a failure, nevertheless. but it hasn't reached the point where the tire has failed catastrophically and that catastrophic failkure is imminent.
But to get to the point in your post: There are a significant number of failed tires where underinflation is the cause. Has this been abused by tire manufacturers? Yes, it has. Does it mean that the consumer is never to blame for the failure? No, it doesn't.
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