Question about tire company building bad tires. Are China Bombs built on purpose?

This as a long post but I wanted to share the type of questions i sometimes get.

" Good Morning' Roger. First, thank you for helping to dispel the misinformation about the care & feeding of consumer tires. 

    My training & work history is in the military & general aviation world. After a 24 year Air Force career and 17 years with Cessna in Wichita KS I've learned a great deal about tires. I've also had a near miss with some tires back in the day. 

   I had a set of Light Truck tires on our '84 Ford E350 15 passenger van. Not long after a tire story broke in the news, I looked at the tires installed on our van. No defects noticed, inflation correct, continue in service. 4 days later, while on the road to KC from Wichita I felt a vibration develop. I pulled to the shoulder and discovered a blister in the sidewalk of a rear tire. I installed the spare & the trip continued without incident.

    The following Monday I presented my defective tire to my local tire dealer. He was very apologetic for the defective tire. He replaced the remaining tires with a set of Bridgestones of comparable size. The whole incident was handled well.

   At the time I couldn't get the one tire that failed. I wanted to perform an autopsy of sorts. The dealer wasn't having any of that, which I understand. At the time the problem with the tires was explained to me that the sidewall de-lamination was caused by an incomplete cure process. The process was incomplete because a manager thought the vulcanizing process would run its course even after the tire was removed from the press. It was later reported that an inferior compound was used in the process. 

    So, I guess my question is, in the Light Truck tire incident, was it improper substitution of a material or a management failure in order to increase production that lead to the failures? Do Chinese made tires exhibit similar problems? Can the NTSB outlaw them? It's all above my pay scale. Just want to see some reliability in RV tires.

   I will continue to recommend your Blog to others in an effort to combat the misinformation surrounding tires. 

   Reply when you get time. It's a cold Sunday morning here & I'm working on the second cup of coffee. In this day & age, I don't do anything in a hurry & my upper arm is getting cold as my sleeve is rolled up waiting on my vaccine, but we'll survive. Stay safe, stay warm.

 

 

My answer:

Where / how did you get the information that the tire with the sidewall problem had some "inferior" compound?

Without a lot more data it's hard for me to pass judgment on tires made in the early 80's. I can however relate a personal experience that I have written about previously. This may shed some light on tire quality.

By late 2000 my primary job responsibility had become doing forensic tire inspection and analysis. I came across one almost new (weeks old) passenger tire with the steel in the belt having lost all adhesion to any rubber. There was only one tire and at the time no report of other similar tires. Many times single tire issues get set aside as a "single data point" is hard to establish any trend.  A few weeks later I was presented with two more tires with belt issues and upon conducting an autopsy discovered these tires had steel in one of the two belts, BUT NOT BOTH, having no adhesion to the rubber. The other belt had normal levels of adhesion. Recalling the single earlier tire I dug deeper.

Eventually, after some investigation and some test results from the chemistry lab, it was confirmed that a single batch of approximately 145 lbs of the rubber had been improperly labeled in the factory and built into about 150 tires. I notified the VP of Corporate QA and a recall was initiated with the permission of NHTSA (the agency like NTSB but dealing with automobiles, not commercial vehicles such as buses or airplanes). The recall covered some 6,000 tires as the effort required the recovery of all tires that were cured the week when the factory mistake was made.

Technically we knew that with only 145 lbs of rubber involved and the specific process used in that plant that a maximum of 150 tires could have been affected but since tires are recalled based on the DOT serial and all tires made in any one week carry the identical serial that was the only option.  It turns out that most of the tires were still in the warehouse which made completing that recall easier as many times even when recall notices are published a significant portion of the public does not pay attention.

Your suggestion that some inferior material was intentionally used in your LT tires just doesn't seem plausible as NHTSA would have ordered a recall of all suspect tires if there was data that supported the idea that some substandard material had been used.

In modern tire manufacturing, most rubber compounds are used in many different sizes and types of tires. I would say that the sidewall rubber in the Light Truck tire would probably have been used in most if not all LT tires being made at that time which would have involved millions of tires.

It is also true that tire store dealers do not get detailed training in tire forensics so sometimes they tend to simplify the explanation for a problem. When tires are "adjusted" and replaced however those tires are sent to be inspected, in detail, by engineers with the necessary training and experience. If manufacturing errors, as found in my example, are confirmed, appropriate action is taken as there are serious financial fines for knowingly allowing tires that do not pass DOT requirements to be sold or used.

All tires sold for highway use are certified by the tire manufacturer to be capable of passing the DOT test requirements and the data I have seen, including a number of tires made in China, shows that the tires meet the DOT requirements. The "China Bomb" concept is a combination of improper use and improper understanding of statistics. It is a known fact that a majority of tires on RV trailers are overloaded. Also, some 90+% of the tires applied to RV trailers were for a number of years were made in China. With these known facts is it any wonder that there were tire failures on RV trailers and that most of those failed tires had been made in China? Many people jumped to the incorrect conclusion that since very few tires failed on their passenger cars or pick-ups and that the tires on their cars and pick-ups were not made in China. That the China-made tires must somehow be "defective" even while never being able to identify any specific "defect".

A side issue. You mentioned a desire to "perform an autopsy of sorts" immediately raises the question in my mind of how and what you thought you would do when doing your first tire autopsy? I suggest you read these blog posts where I mention "Autopsy" and ask yourself if you would have noticed or been able to identify the evidence I pointed out in these examples. And if you had noticed the details do you think you would have reached the same conclusions I did?

Hope this gives you something to read and think about on a cold day in March.

 

##RVT990

 

Why does a sidewall "blow out" when you run on low inflation?

The title for this post is essentially the exact question I was asked.
"Tireman9, can you explain why, when the tire pressure drops below a rating for a tire, that the sidewall of the tire blows out with great force? What pressure drop will cause this type of damage? When the tire blew it had enough force to damage the motorhome with the rapid escape of air that made a large bang when it blew."

My answer:
OK, let's see if i can cover the details of why and how a tire sidewall fails due to being run without proper inflation.

The mechanics are essentially the same, be it a textile (usually Polyester) tire as are most P, LT, and ST type tires, or for tires with steel body cord as most commercial grade LT tires and "TBR" Truck-Bus Radial" tires. These cords are referred to as the "body ply".

I think we all realize that tire sidewalls bend when loaded. This can be observed by simply looking at the bottom (near the road) vs. the rest of the tire sidewall. The amount of bending is essentially just a function of tire size, load and inflation. This bending includes some stretching of the outer surface of the tire and of the rubber surrounding the body ply. This stretching results in some heat being generated. You can test/experience this heat generation yourself with a simple test of holding a rubber band against your lip and stretching and releasing the rubber band rapidly. Your lip is sensitive enough to feel the temperature rise of the rubber band.

Now the rubber used in tire construction can tolerate some temperature rise. The heat generated can transfer to outside air at about the same rate it is being generated. This is what happens for hopefully tens of thousands of miles and hundreds of thousands of revolutions, i.e., sidewall flexes.

So what happens if there is a leak of inflation air? Or if the tire was not properly inflated in the first place? With lower air pressure the amount of bending increases and with an increase in bending we see more heat being generated. Increased heat generation means increased temperature of the rubber internal to the tire structure. Since rubber is a good insulator, heat transfer can be slower than heat dissipation to the outside air so the temperature can continue to rise ever faster.

The strength of the rubber decreases with an increase in temperature which allows more bending. With slower heat transfer from the internal structure to the outer surface and increased heat generation as more air leaks out, I think you can see how it is possible to get to a point where there is something like a chain reaction or "runaway" temperature increase.

The above heat generation can also result in the polyester experiencing a rise in temperature with the associated loss of strength. You have seen the effect of high heat by holding a match near the end of a piece of Nylon or Polyester rope and see the textile melting. In the steel body ply tire the increased bending can result in a fatigue failure of a steel cord. You can test the fatigue with a steel paperclip. Simply bend the paper-clip a few times and it will break. In the case of a tire the number of bends to failure can easily be in the thousands.

So what you are seeing when the sidewall fails is the result of dozens, hundreds or thousands of miles of excess rapid flexing of sidewall rubber and sidewall cords. If the bending is great enough the materials that are being bent simply fail. An explosive loss of air can occur if/when the force of the remaining inflation exceeds the strength of the body cord. Since there is an almost infinite combination of load, inflation, bending and speed involved, it is impossible to give an exact answer as to when the sidewall will finally fail.

If we have a large tire we can have significant force involved even at relatively low pressure. 20 or 30 psi can easily generate over 30,000 pounds of force.

##RVT809

Question on Sidewall "bumps"

This topic concerns a potential SAFETY issue so is a bit more involved as it is important that everyone understands the situation.

Smitty asked:
I have 5 1/2-year-old 12R Michelin XZE tires on our coach. No cracking, and have performed well.

I found sidewall 'bumps' (Tire Center gent, said they're not 'bulges', as they're so slight). One maybe 3/32" of a protrusion, the other much less. The gent said they could be belts that are misplaced or broken. But he also said the XZE's have a thicker sidewall, and that the outer layer of the tire could have separated.

I know it's hard to give advice based upon a description, but I wanted to ask your thoughts on the opinion given to me by this tire gent.

He suggested that I monitor the size of the 'bumps' daily, and if they don't grow, he felt that they were safe to drive on. He commented that the tire was so overrated for what it was carrying weight-wise on my RV, that it was not working hard.

I've always thought that once a tire starts to break down, it was at risk for a catastrophic failure?
 
The tire was not unmounted for inspection, but if it was an outer layer separation, as he said it could be, how would they be able to see this?

Opinion? At 5 1/2 years of age, is it worth even considering monitoring and watching for growth? Or just replace and move on? 

+++++++++++++++++
Here is my reply:

First off, I do not feel that sidewall "bumps," "bulges" or "protrusions" occur because of misplaced or broken belts. Belts are under the tread not on the sidewall so I have to wonder what training, if any, the "gent" at the tire store has received on tire construction or inspection procedures. Also not sure what he is talking about as the "outer layer" of the sidewall. In a truck tire there is basically the thin innerliner (a bit like having a tube as part of the tire), then body ply, then the sidewall. So, if he thinks the sidewall has separated, then the tire has failed and should be replaced.

Now, some fact-based observations on sidewall bulges or outward protrusion vs. depressions that are inward toward the air chamber and are indications of two completely different causes.

The inward depressions can occur once or twice around almost any radial tire. If you take a close look in full sunlight of smooth sidewall tires you will see depressions that might be about 1/16" deep and 1/4" to 1/2" wide in the circumferential direction. These are caused by the lap splice of body ply material that provides more resistance to the slight growth seen in all radials due to inflation. These depressions will run a radial direction from the wheel to the tread and seem to disappear as you get near the tread or near the wheel. These are normal and I would only consider them minor cosmetic features of a tire.

An outward bulge may be 1/2" or as large as a couple of inches in the circumferential direction. The larger or more distinct, the more concerned I would be about the durability of the tire. Usually bulges are the result of some impact damage done to the body cords that resulted in a few being broken due to shock loading.

Here is a blog post I did with pictures of bulges and depressions to help people understand.

Here is a post on an Impact Failure I had on my personal car.

Now on some with small features, the eye plays tricks as to it being a bulge out or a depression in. I have even seen instances of two depressions being close together such that the normal sidewall between the depressions gave the appearance of being a depression. The simple tool to use is a ruler or straight edge and to lay it across the area of interest. This will quickly identify if you have a bulge or depression.

What to do:
Review my blog posts above.

You might also find a different dealer. A simple Google for "Truck Tire Dealer Town" where "Town" is a nearby larger community, should give you a number of options. For 19.5 and larger size tires I would only deal with a Heavy truck Center.

You might also contact Michelin at their Customer Contact on their RV tire page for a suggested location with people sufficiently trained in tire inspection to pass judgment on your tires.
http://www.michelinrvtires.com/reference-materials/
You can tell them that you're not happy with the inspection you got from the tire guy as they don't seem to understand the basics of rtuck tire construction.

##RVT787

"Why do so many RV tires seem to be failing?"

 Well, that may seem to be a reasonable question but in my opinion it is based on what is often inaccurate failure analysis. In reality, tires fail for a relatively small number of Root Cause reasons that can be discovered, but it does require detailed and sometimes exhaustive investigation. By "Root Cause," I mean the initiating feature or condition that eventually led to the failure. Too often people confuse the tire's ending condition with the initiating or "Root Cause" reason for the tire to end up in the condition they are observing.

For the last few years of my 40-year career as a tire engineer, my primary job duty was to investigate failed tires that had conditions that were hard to understand or provided confusing and sometimes contradictory evidence as to the Root Cause for their condition. With that background, I have developed some guiding principles for the most likely reasons for tires to fail.

These are, in no special order:
1. External Damage. These include punctures, cuts, impacts, wheel and valve failures and similar conditions.
2. Run Low Flex Failure. This is best described by the failure of the tire sidewall due to excessive flexing. The flexing is the result of operation when the tire is significantly under-inflated.
3. Belt & Tread Separations. This is when the belts of a radial tire detach from the body or from each other and/or when the tread rubber detaches from the top belt.
4. Manufacturing Defect. For the purpose of this discussion this would be when components of a tire were not manufactured to intended specification.

The "Why" for some of these are obvious, such as the External Damage category.
Others can be further traced to various contributory reasons.

Run Low Flex Failure This is a more accurate description of what some incorrectly call "Blowout". When a tire looses significant inflation air they flex much more that the body cord can tolerate. Excess heat is generated which can, in extreme cases, result in the Polyester actually melting. I showed examples of what this can look link in THIS post. Polyester is used in most Passenger, ST type and LT type tires. Steel body tires are used on most Class-A RVs, the steel can fatigue. I covered "Zipper" failures and steel fatigue in THIS post.

Belt & Tread Separations occur primarily because the rubber around the belt cords or between the belt rubber and the tread rubber isn't strong enough. Now it can be weak for a variety of reasons. Some might be design, some might be manufacturing and some weakening can be caused by cumulative improper service conditions.

Now let's talk about tires made by a reputable company, i.e., one that has tire stores and dealers with physical stores and sells tires that have a warranty of two or more years.
If this tire is subjected to thousands of miles of lower inflation or higher loading or operation at higher speeds or stored is full sunlight it is reasonable to expect the strength of the belt & tread area rubber to loose a good portion of its strength primarily due to the increased operating temperature of the tire. If this tire is in service on a tandem axle trailer then there is also increased Interply Shear which can overload the belt area rubber. The combination of the above may result in a belt or tread separation.

Another possibility is a Manufacturing Defect. These usually occur in small numbers as tires are built in batches so the substitution of the wrong type of rubber may cause tires to fail. It is important to understand that in almost all cases this type of "defect" usually shows up at early life of the tire. It is also very important to understand that unlike some lawyers, engineers deal in facts and logic. Simply having a tire fail is not in it self proof of a defect but all to often that is the position that those in the legal profession seem to jump to. That approach may result in a nice payout to the lawyer but will not result in product improvement as there has been no determination or identification of the actual initiating "defect".

Finally there is the possibility of a design weakness. Now I do not believe that anyone is intentionally designing tires to fail but this sometimes may occur when the performance goals of the manufacturer are limited to meet the bare minimum for strength and durability and the focus is primarily on low cost. There is no absolute way to identify these tires but I do believe there are indicators when looking for tires that are made to a higher standard of quality and durability.
I would consider a tire company reputable if it had a chain of stores across the country. If the tires carry the name of the manufacturer and have a multi-year warranty the longer the better then they probably have higher durability requirements than those established by DOT.

 For ST type tires I would look for tires with a Speed Symbol of "L" (75 mph) or faster. Now a side point about speed. I did a POST a little while ago on the topic and strongly recommend you read it. I do not think I would recommend any tire for general use that does not have a speed rating molded on the sidewall.

I do hope this post will help some to have a better understanding of what can contribute to tire failure and consider what you can do to lower the chances of having such a failure.

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Understanding Tire Failure

Yes, when a tire fails there is almost always evidence left behind that points to the Root Cause. I have shown this in tire "autopsy" posts on my blog.

Some "causes" are easy to see or understand:
Punctures, cuts and external damage from hitting potholes or other "road trash" can lead to leaking air (fast or slow) or in some cases broken body cord (see my blog post on sidewall bulges).

"Blowouts" with sidewall flex failures are most likely the result of air leak, not just low air pressure due to poor maintenance. The leak could be caused by puncture, cut, leaking valve, cracked wheel or the like.


Other failure modes are harder to detect, such as:

Belt separations come from long-term heating of the tire belt/body interface. This heating comes from a combination of insufficient air pressure for the load and excessive speed.

Now while separations may be harder to detect, many can be found if a little effort is made by the person doing the tire inspection.

I previously published a video showing one way to "measure" a defect.

Sometimes you don't need to "spin" or rotate the tire but just get a good look at it and roll it across the floor for a full revolution as one part may look OK while another portion clearly would only look straight to a drunk.

If any of your tires look like the above, I would bet $$ that they had a belt separation similar to what is seen here.

Driving on a tire in this condition is simply asking for trouble as it could come apart when you least expect it as you drive down the road.

As we move out of Winter and you "DE-Winterize" your RV, especially trailers, Please take the time to do a thorough tire inspection.  Spin or off-the-vehicle inspection is much better than a stationary on-the-vehicle "Look At".




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Tire Crack or Cut ? CSI - Akron

More than once I was presented with an almost new tire with a claimed "defect crack". I believe that the owner was many times asking for a refund. While the decision to refund the price of the tire or to replace the tire or to deny the claim was not my job. My job was to do a detailed "autopsy" and issue a report. Here is one such case.

A tire was presented with the identified area of concern as seen in this picture. You can see the area of concern does appear to be a jagged crack about 1.2" long.


TIP. To enlarge the pictures to see the "Witness Marks" left by the cutting object right click and select open in new  Tab or New Window. Then you can close the Tab or window and return to this post.


Looking down into the "crack" I noted what appeared to be "witness marks" that would be left by a cutting object. You can think of these much like Ballistic fingerprints left on a bullet by the rifling of the gun. as seen in this picture of a bullet.

For examples and detailed explanation see pg 8 of THIS presentation.

If some object cuts a tire it will leave straight line marks much like those seen on the bullet. If there is simple rubber tear or a molding defect, there will be no such straight lines.



 After deciding where to cut so as to not destroy the evidence, I was able to spread the area open to confirm the presence of the witness marks. There have the appearance of small ridges or lines in the rubber.
Here is the piece I dissected out of the sidewall. You can easily see the lines of the witness marks left by the knife I used to remove this piece.



In this picture you can see the witness marks in the "cut"..







Then I looked at the side of the area and discovered that at its deepest point the body cord was cut.







Cracks in a tire can grow through the rubber but not through body cord.

 The external cut would be in the top of this picture and the "examination" cuts I made are from the bottom.




Closer examination confirm the body cords were cut from some external sharp object and not from any manufacturing defect as seen in these final pictures.

I think you will all agree that there was no defect and that some sharp object cut the tire sidewall.

BOTTOM LINE
Tire inspection is a real science and knowing what to look for and how not to contaminate or destroy the evidence as an inspection is done is what takes years to learn. I think you can also see that having pictures of the whole tire cannot provide sufficient detail to arrive at the "Root Cause" of the tire condition.

What is involved in doing a tire inspection?

 Some of you may wonder how I can provide an opinion on what caused a tire to come apart when all I see is a picture or two. 

For many decades my primary job was to perform tire inspections and "autopsies." I estimate I did more than 20,000 inspections, so I was able to build a good experience base for my observations.

My findings were many times presented to a customer that did not want to accept responsibility for the failure, so I needed to be very thorough and to provide an easy to follow explanation.

 Here is an example of just one such inspection.

The tire was reported to have "blown out on a local road” The lack of facts and data did not help in the analysis of the tire.

However I was able to establish that the tire suffered a sidewall puncture, lost air and after running significantly under inflated at highway speeds for a number of miles the cumulative damage to the tire resulted in a flex fatigue failure.

Photo -1 above

                Shows the 2 piece condition, which is indicative of, flex fatigue failure.

Photo -2

Shows the result of melted body cord – Body Cord melts at 350°F to 400°F

Photo Tire-3

Shows the abrasion on the interior from running a few miles at essentially zero inflation

 Photo 4 shows a larger portion of the interior. Here I noticed the location of a possible small sidewall puncture.

 

Picture 5 is a close-up of the area of interest

  

 Picture 6 is what the outside looks like.

The question is ... How do I prove there was a puncture?  If I used a sharp probe like an awl some would think I might fave made the "puncture" myself. Over the years I learned a trick. If you take a paper clip and straighten it out, you can use it like a probe. The un-bent clip isn't strong enough to hold and doesn't allow you to force the end of the clip through the sidewall of a tire but if there already is a hole, the paper clip can be guided through the already made puncture.

Pictures 7 shows the clip on the inside

Picture 8 shows the clip on the outside at the suspect location.

               

Findings

                The tire was not defective but failed due to being operated significantly under inflated. The under inflation was caused by the small sidewall puncture.

Corrective Action:

                Use a TPMS. Instruct driver to be more attuned to ride & handling degradation, as this tire should be operated with 80 psi under normal conditions. A slow leak would have taken some time and resulted in significant changes in handling and vehicle response.

BOTTOM LINE

Some punctures are hard to find. Sometimes the puncture occurred in the heavily damaged portion of the tire so it is impossible to demonstrate the puncture. Melted polyester body cord is physical proof that a tire was run with only 10% to 20% of the proper inflation.

"Blowout" A Real Life Experience

In the previous post, I covered Run Low Flex Failure, RLOF, and how there were telltale signs or physical evidence that while each taken individually are just circumstantial in nature but when taking as a whole make a very strong case for the tire having been operated for a number of miles at very significant air loss. In this post, I want to walk you through the thought process of a forensic analysis of the evidence that is available and show how an opinion or conclusion is reached.

First I need to tell you that I have not had the opportunity to personally inspect the subject tire, but there is a YouTube video and I will show you some shots from the video and tell you what I see in these shots. Second I cannot tell you about the individual as I have had only limited correspondence about this tire failure but according to statements in the video they called it a "Blowout", said they had checked the air pressure in the morning and had only driven about 45 miles before the loss of air occurred.

So lets see what the pictures show. I have highlighted the area of interest in each picture. In pic #112 we see in the yellow area signs that the interior of the tire was worn from abrasion on the inside of the tire under one side of the tread rubbing on the inside of the tire above the wheel. This occurs at 0 psi but takes more than the half mile it takes to come to a stop to wear this much. Also the tire must still be in one piece such that the tread can uniformly contact the lower interior of the tire so the wear occurred before the tread part of this tire broke away. In the red area we can see a few dark holes where the body cord has melted and shrunk back into the tire structure. This occurs when the body cord exceeds 390°F. To put this temp in perspective properly loaded and inflated tires may get to 160°F and ultra high speed tires such as seen at the Indianapolis 500 may see 200° to 210° but rubber starts to come apart an just a little more than that.


In pic 108 is another view of the same location of melted body cord. If the cord had simply failed due to high pressure the cord would be frayed. Also note the nice circumferential line the failure took. More on that later.


 Moving on to picture 057 note the areas circled in red. An alternate view is seen at the arrow in pic 426. Now if we compare the loss of the ridge that is easily seen in pic 121. What this means is that the upper sidewall was in contact with the road surface for a number of miles and the outer edge of the sidewall "Scuff Guard" raised rib has been completely worn down. What we do not see is the lettering of the "Scuff Guard" worn away so we know that the wear was not due to the trailer being repeatedly parked against a curb.


+++++++++++++++++++++++++++++

Now I am sure some are wondering how I can tell the difference between running a tire at 5 psi vs 0 psi. Well here are some shots from an experiment I ran myself a few years ago.


  This first picture here on the left shows the wear of the upper sidewall that occurred in only 3.9 mi while the tire had a minimum of 5 psi cold inflation. This is a bit like the wear on the RV tire sidewall

The next picture is of the interior of the same tire. You can see the nice circumferential crease/crack that has formed. This tire did not generate enough heat to melt the body cord as I was driving at less than 10 mph for the 3.9 mile test. That crease is at the location up the sidewall similar to where we see the circumferential failure in the "Blowout". Note there is no contact between the inside of the tread and the inside of the tire above the wheel as seen in the RV tire.

If you look at some of the examples shown in the previous post you will note that many show the same nice circumferential failure line.

Here are some examples that I use as ref pictures to help me understand the Root Cause of a tire failure.

Here are pictures of melted body cord, broken body cord and the holes sometimes left when the cord heats up and shrinks as it melts.
I hope this helps you see how easy it is to be mistaken when you think the failure is because of a defective tire when in fact the evidence shows the tire lost air, the Rv continued down the road at normal highway speed and after a few miles the tire "blew out". The only way to have some warning and to protect yourself against this all too often type of failure is to have a TPMS which will warn you as soon as the tire loses 10% of its air.


Bottom Line: I do not think this tire was "possibly defective" or a "crap tire". It did not "fall apart for no apparent reason". It came apart because it lost its air and the operator did not know till too late. 

“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.