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Old 06-15-2016, 02:07 PM   #1
Rivet Master
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Why tires fail

Tires fail from two basic causes.

Low air pressure
and/or
Long term degradation of the rubber usually from excess heat.

Low pressure (active leak from puncture or loose valve stem or valve core are most common reasons) can lead to a Sidewall Flex failure or more commonly called a "Blowout". The sidewall cord can melt (polyester) or fatigue (steel). Many TT owners fail to realize that they will never "feel" the results of a tire loosing air till it is too late and they are surprised when the sidewall lets go. The rapid air loss "bang" even when the tire only has about 10 to 20 psi in it, is a big surprise IF they even hear it. HERE is a post on how to know if you have a run low flex failure. A TPMS can provide warning of air loss so is good insurance and can easily pay for itself.

The long term degradation of the rubber at the edges of the belts can lead to a belt and/or tread separation. Even if the tire keeps its air you can have this type of failure so a TPMS will not provide a warning. This degradation comes with age as rubber is always loosing flexibility. Just think of those rubber bands you found in the back of the desk drawer. Even in cool and dark they got brittle. HOWEVER running at or near or above the load capacity of a tire will result in increased heat generation. Increased heat actually can accelerate the aging process with a doubling of the rate each increase on 18F. Running a margin of at least 15% between capacity and measured load is a good first step. Running at higher speed will also generate excess heat.

Realizing that over half of the RVs on the road have one or more tire in overload is one main contributor to the high tire failure rate. Simply thinking that a tire will fail because the tire plant building is painted blue rather than green is not logical.

Buying the lowest cost "no-name" tires is IMO a major contributor to poor results. If the main objective is the lowest cost tire why would anyone be surprised with short tire life.
Just paying more however is no guarantee of better quality. I believe the best tool available is comparing Warranty and service support.

Can you get multi year warranty on the tires? Is it possible to get Road Hazard coverage? Is there a nationwide network of dealers who stock the brand you are considering?
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Old 08-15-2018, 11:06 AM   #2
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Due to high levels of Interply Shear (Google the term to learn more) on multi-axle trailers the best approach is to inflate your tires to the tire sidewall max. ALSO confirm with actual scale readings that you have no more than 85% of the tire ststedload capacity on the tires.
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Old 07-14-2019, 07:58 AM   #3
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Traditionally, the tire industry has attempted to shift the burden for defective tires to the victim in the accident. They assert that tread separations are the result of impact damage or underinflation. In fact, underinflation does not cause tread belt separation in a properly constructed, properly designed tire. However, if a tire has manufacturing or design defects and it is run underinflated, underinflation can accelerate tread belt separation. Unfortunately, it is virtually impossible for the consumer to determine whether a steel belted radial tire is underinflated by visual inspection. 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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Old 07-14-2019, 08:29 AM   #4
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Old 07-15-2019, 08:46 AM   #5
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Quote:
Originally Posted by r carl View Post
……. In fact, underinflation does not cause tread belt separation in a properly constructed, properly designed tire. …….
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 View Post
……. However, if a tire has manufacturing or design defects and it is run underinflated, underinflation can accelerate tread belt separation. ……..
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 View Post
……. Unfortunately, it is virtually impossible for the consumer to determine whether a steel belted radial tire is underinflated by visual inspection. ……
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 View Post
……. 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.
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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Old 07-15-2019, 10:45 AM   #6
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Quote:
Originally Posted by r carl View Post
Traditionally, the tire industry has attempted to shift the burden for defective tires to the victim in the accident. They assert that tread separations are the result of impact damage or underinflation. In fact, underinflation does not cause tread belt separation in a properly constructed, properly designed tire. However, if a tire has manufacturing or design defects and it is run underinflated, underinflation can accelerate tread belt separation. Unfortunately, it is virtually impossible for the consumer to determine whether a steel belted radial tire is underinflated by visual inspection. 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.

I had a nice lengthy reply but the forum logged me off when I tried to post. Capri (the other tire engineer here) pretty much covered the important points and maybe was a bit nicer about it.


One item I will mention is the level of automation in modern tire manufacturing. The mis-placement of components or missing components is almost impossible with today's automation.
I posted a video on my tire blog (not allowed to post the link here) so I PM the link to you.
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Old 07-15-2019, 11:38 AM   #7
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Hi (Roger) Tireman9,
Nice to see you again.

For the newer folks, here is a pretty comprehensive site for all kinds of tire related issues. http://www.rvtiresafety.net/. This along with CapriRacer (great site) site barrystireteck.com I would wager they can answer almost any question you have about tires.

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Old 07-15-2019, 12:07 PM   #8
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Hi Tireman9:

Thank you for your informative posts re tires over the years. You and CapriRacer are the people on Air Forums I trust. FWIW, we went to the Goodyear Endurance tire on our Airstream last year and, when we did so, went with the TPMS you recommended on your blog.

The reason I'm writing tho, is to explain how to recover a post that goes 'poof' because you've been logged out of a bulletin board. Usually you can step backwards in a screen using the Control + Z command. So one application of Control + Z should take you back to your post before you tried submitting it. Subsequent Control + Z commands will step you backwards in the order of operations you made in that screen, like typing.

If you are successful in stepping backwards to your post, left click in the body of the post. Then use the Control + A command to select the entire document (should become highlighted). Then use the copy command Control + C to copy the post to your cache. Refresh the bulletin board screen and, after you've been logged back in, use the paste command Control + V to enter your post in the refreshed screen.

If you are unsuccessful recovering the post with the Control + Z command and the back arrow in the upper left corner of the screen is highlighted, click it to step backwards. Do this second after the Control Z gambit, as usually this takes you to the screen you were on before you started writing your post. The forward arrow in the upper left corner should become highlighted, so you can click it to return, and then try Control + Z again.

I've had many posts go 'poof' over the years. Because of this I sometimes write a post in Word, especially if I want to verify sourcing for my comments, which is a lengthy process. I then cut and paste from Word into the "reply" box.

Thanks for sharing your expertise, and I hope these comments help the next time your hard work goes 'poof'.

Burnside
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