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Thursday, September 1, 2011

“I had a Blowout”

That’s an all too often statement heard from RV owners.

According to some data a significant portion of RV owners have experienced a tire failure in the past two years. All too often the tire is blamed but my experience from examining thousands of “tire failures” is that the vast majority of these failures can be traced to the service conditions and not some so-called defective tire. Let’s look at a few examples.

Here we see an LT type tire that is now in two pieces







This picture shows the classical “Three piece Flex Failure”. I bet you see a tread ring like this almost every day in your travels.




This tire was one I did an “autopsy” on. Looking at the “broken edge of the sidewall we can see hard body ply cord.





Taking a microscopic look at just one end we easily see the fused cord.








This is much like what we have all seen when we cut Nylon or Poly rope and then melt the end with a match. Click on the picture for a better view.
It takes excessive flexing at a high rate to generate sufficient heat to melt the cord like this.
This Body Ply cord melts at approximately 495°F. I usually say the tire was operated at less than 20% of the proper inflation and at normal highway speeds to generate this level of heat.

Before you say “Ya but I have steel body ply so it’ can’t melt”, just think about how easy it is to break a paper-clip by flexing it back and forth.




Here you are looking through the hole in the sidewall of a 22.5 size tire that ran low at highway speeds but lost it’s air because of a bad valve leak.


So was this “blowout” the fault of the tire? Or was there some reason the tire lost most of its air pressure which let the tire flex excessively? I say that based on a majority of tires I have examined, "Blowouts" like these are really Sidewall Flex failures from being operated at highway speed while the tire has lost 3/4ths of it's inflation



Next time you see a tread ring by the side of the road or hear someone say “I had a blowout” you now know one of the probable causes.

Finally, You might ask if there is a way to prevent a sidewall flex failure. I believe that if you have a properly functioning TPMS it should warn you before the tire has lost 20% of it's air. If still inflated to this level it isn't considered officially "flat" and I have never seen a tire that can generate the heat necessary to fail a sidewall if it hasn't been run "flat". If you can set your TPMS to warn you if you either loose 10% of your air pressure or it sees a temperature over 170°F in most cases you will have sufficient warning to avoid this type of catistrophic failure.

1 comment:

  1. Roger, What a great post. Spending my career in the auto repair industry (Service Engineer)I saw the same things wih cars and trucks as you. With the RV industry, I would think it would be much of the same except compounded due to the weight and tire flex on the vehicles. I'm anal about tire pressure checks, but see folks pull out of our summer park without ever checking the pressures. Thanks for a great post!! Tom

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