"I never hit a pothole"

The title for this post is a direct quote made by many people who have suffered some tire failure. If you think about this claim for a moment and then think about the road conditions we all see in our day to day driving experience one has to wonder just where these people are driving.

In our life as drivers, I am sure that all of us have hit some objects other than simple 1" deep pot hole. Some objects could include bricks, lumber, railroad tracks, curbs, and puncturing or cutting objects such as nails or screws.

Here are some examples of tire damage I discovered in my work. The first three were each submitted with a written claim that the tire was "defective" so I can only assume the driver made little or no effort to inspect the tire or wheel for evidence of what might really have happened.

The last tire, with the wooden stake through the tread was submitted with a claim that the tire was defective because it was "making noise". IMO the noise would have been from the wood hitting the pavement at speed.

I have no expectation of changing the minds of those who want to make a claim of never hitting a curb or pothole or another object. I do want to relate the findings I recently discovered in a technical paper on tire forensics and impact damage.

In the paper, the reference studies involved a process of obtaining a couple dozen both new and used tires P type, LT type and sizes appropriate on Some Class-A RVs. The rim diameters ranged from 14" to 19.5". Tires came from 8 different tire companies. Each tire was inspected and no externally visible signs of damage were found.  Each tire was run on the appropriate DOT laboratory tests to confirm the tire was in good condition. Each tire was then mounted and hit with a heavy pendulum to simulate hitting some object or pothole on the road using a machine like this from STL company

 The tires were again visually inspected and any evidence recorded. Finally, every tire was run on a drum durability test under a load until failure occurred.

RESULTS:
Failure Rate  100%
Miles to failure for new tires   1,826 mi  to  41,400 (avg. 11,586)
Miles to failure for used tires  5  mi      to    7,458   (avg. 2,092)

Can anyone here list every object they knowingly or unknowingly hit over the past 2,000 miles?

I know that I have posted a number of times that tires do not always fail at the instant of impact or damage. Clearly, these above studies confirm these observations.



Some reference material for those interested:
Price, V & Follen,G (2019). Road Hazard Impacts: Their Influence on Radial Passenger Tires and the Forensic Signs They Leave Behind
Bolden, G. C., Smith, J. M., & Flood, T. R. (2001). Impact Simulations in the Lab. Tire Technology International.
Bolden, G. C., Smith, J. M., & Flood, T. R. (2005). Impact simulations - what happens when a tire/wheel impacts a road hazard. Tire Technology International, 44.
Bolden, G. C., Smith, J. M., & Flood, T. R. (2006). Structural Impact Damage Under Varying Laboratory Conditions. Tire Technology International, 10.
Gent, A. N., & Walter, J. D. (2005). The Pneumatic Tire. Washington: National Highway Traffic Safety Administration, U.S. Department of Transportation.
Giapponi, T. R. (2008). Tire Forensic Investiagation Analyzing Tire Failure. Warrendale: SAE International.
McClain, C. P., & DiTallo, M. A. (2001). Tire Examination After Motor Vehicle Collisions. In K. Baker, Traffic Accident Collision Investigation (9 ed.). Evanston, Il: Northwestern University Center for Public Safety.
Tire Industry Association. (2005). Passenger & Light Truck Tire Conditions Manual.

##RVT930

Sidewall "Bubble" or ? A Tire Autopsy

Took the wife's Miata down for an oil change and tire rotation. Contacted by the store, that they had discovered a "Bubble" in the sidewall and wanted to know what I wanted to do.
After a quick look at the location of interest I concluded that we were looking at a Sidewall Impact Break. I had the store replace the tire with a new one and asked that the allow me to do a "Failed Tire Inspection".  Here is what I found.

Picture 1 is of the inflated LF tire on the car.
You can easily see the "Bubble" on the sidewall under the molded word"OUTSIDE". What tipped me off to the damage being an impact and not a sidewall bubble or blister was the shape (more radial in nature than round) and the gradual nature of the rise of the shape. Sidewall blisters are normally more abrupt.



The interior picture is what we see inside the air chamber at the location of the sidewall "bump".

I have an arrow pointing at the stress marks of the body cord on the inner liner rubber.






Picture 2 is of my initial examination cuts.   Note I did not cut directly through the area in question as I did not want to destroy or contaminate the "evidence" that I suspected would be found in the area of interest. This is an important point that many inexperienced investigators sometimes miss.

In picture 3 we see the location of interest. I added an arrow that points to area os special interest. If you look closely you will see a short dark line. This is a depression where the interior rubber has been "sucked" into the damaged area of the sidewall,




After removing the section of the tire, close examination revealed some of the initial Innerliner cracks / tears.  Here is a close-up shot.

These cracks would grow and could eventually result is air loss through small cracks in the sidewall. It is important to consider that the cracks will not grow in just a couple of miles or maybe not even in 100 miles but if driven long enough would most certainly result in an air loss. The driver would have no recollection of ever hitting a bad pothole or road debris so in all likelihood simply claim that the "Blowout" was due to some tire defect.

 Finally, we can see the separation of the body cord from the surrounding rubber. It is possible for this type of separation to allow the cords to move independently from the rubber next to the cord and the rubbing can generate heat which under the right circumstances could lead to a cord failure.
Again this could take weeks or months to progress to a loss of air but is another example of why few drivers connect the effect of a tire losing air to the real cause of suffering a sidewall impact break.

This break was actually quite minor. A more severe impact was covered in THIS post.

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

22.5 tire inspection. Confusing answer from dealer

Got this Private Message (PM) about sidewall "Bulges". Will keep it "private" redacting any identifying details but think there is a good learning experience for others here.

===========
 Thanks for sharing your knowledge, and I do like your blog!

I have 5 1/2 year old xxxxxxxxxxxx Mich XZE* tires on our coach. No cracking, and have performed well.

I found sidewall 'bumps' on two tires ("Tire store" 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 "tire store" 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 store" 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. When asked if he would drive on them with his family, he said from what he could see, yes. 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, that it was at risk for a catastrophic failure?

The tire was not unmounted for inspection, but if it was a 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?

(I have a thread on Class A, asking for ride opinions between the XZA2 and the Cont HSL1 in 315/80R size. These are the two I'm currently considering to put on the steers. But, open for input on others to consider too!)

Hope you don't mind the PM, but, I was just a bit uncertain on which way to go.

Best,
zzzzzzzzzzzzzzzz
=======================
Here are more pictures of the feature of concern. You can see the small bulge right above the "M"

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 "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 TBR tire there is basically the thin innerliner then the 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 if full sunlight of smooth sidewall tires you will see depressions than might be about 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. The depressions will run a radial direction from the wheel to the tread and seem to dispensary 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 to help people understand.

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

Now 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 near-by larger community, should give you a number of options.
Are you dealing with a TCI  "Passenger/Light truck center" or a "Commercial Truck Center"  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 identifies on their RV tire page for a suggested location with people sufficiently trained in tire inspection to pass judgment on your tires.
you can tell them that your not happy with the inspection you got from "tire store" as they don't seem to understand the basics of tuck tire construction.



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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 Bulge. Defect? or Damage

Sidewall bulges can be difficult to diagnose. Sometimes it is even possible to misinterpret a depression as a bulge so lets start off today's lesson with clarifying the words.

According to Dictionary.com  bulge means a "rounded projection, bend, or protruding part; protuberance; hump".  I think we can all agree that this is a sidewall bulge.





A depression would be the opposite, or "sunken place or part; an area lower than the surrounding surface". Sometimes I may use the terms "Bulge in" and "bulge out"just to be sure people have a clear understanding.
Look closely at this shot and I think you can see that this is a depression in the sidewall.

 Here are a couple of other shots showing sidewall depressions.






OK So now you are probably asking why are these two conditions in tires and are they defects or what? Lets step back for a moment and consider how tires are made.







The basics apply to all tires, be they small 10" or 12" as seen on micro cars or 22.5 or even large mining tires like this one.






In this post there are some links with videos showing the basic process of wrapping layers of fabric (or sometimes steel cord) that is in a sheet of rubber, around a drum. The place where the builder starts and stops has a "splice". Now the goal is to have a strong enough joint to keep the uncured rubber together till the tire is cured. In some constructions this means a small overlap of one to maybe 4 cords. If the overlap is larger than desired there is a doubling-up of the cord and this is what creates the depression. I know this is counter-intuitive but you need to remember that when a tire is inflated the rubber stretches and the textile cords stretch a slight bit. However if the splice is "heavy" or larger than desired the forces from inflation are resisted by twice the normal amount of cord and rubber so the stretch is less than in the rest of the tire. There is nothing wrong here other than a visual depression.

Now a bulge is just the opposite. If the splice is "open" or there are cords missing then that area will stretch out more as there is only sidewall rubber resisting the air pressure so the sidewall stretches out just like a balloon. A bulge from an open splice is noticeable as soon as the tire is inflated. If you see this on a new tire point it out to the tire dealer right away and confirm the bulge is below the level of concern for that make of tire. This will probably be less than a tenth inch above the surface of the rest of the tire and less than 1/2" wide. If larger I would request a different tire unless the dealer is willing to put in writing that the tire is safe.  Get a nice close picture of the tire for your records and be sure the bulge does not get any larger.

The other thing that can cause a bulge is broken body cord from some sort of impact such as a curb, pothole or from hitting something on the road. Here are a couple shots of a 22.5 that suffered an impact.

.One thing to point out how I know this was not a factory defect. I have yellow arrows pointing to the small amount to irregular tread wear. You will note that this level of wear is fairly uniform around the tire. If the defect had been in the tire from when new I would expect the sidewall bulge to affect the tread wear. Since it didn't, that indicates to me the break of the body cord is recent.

In case you are wondering what broken cord might look like here are a couple shots of broken Polyester cord from a smaller tire.

.I hope everyone now understands the difference between a cosmetic depression and a bulge due to a tire impact.


If you have a Bulge that looks anything like the examples above I would not drive on the tire. If we are talking about a high pressure tire (75 psi or higher) I would not even stand near the tire while waiting for service. A tire explosion can be damaging or even injure people.



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Tire Blowout - China-Bomb or Pothole?

Hardly a week goes by without someone posting that they had a "Blowout" and since they had checked the tire air that morning, they "knew" the blowout must have been caused by a defective tire. Many times they jump to the conclusion that because the tire was not made in the USA, that fact seems sufficient in their minds to establish certainty.

I have posted replies that just because they had checked their tire a few hours prior to the failure, that is not sufficient proof that the failure was due to a defective tire. In my experience the vast majority of so-called "Blowouts" are actually "Run-Low-Flex" failures. A tire can loose air for any number of reasons such as puncture or valve leak or even an impact.

I am a strong advocate of TPMS as they can warn of air loss but even the best TPMS cannot provide warning of a catastrophic air loss that can occur after impact damage.

Those that have attended one of my seminars may remember my story of the two impact failures my then fiancee had and how both tire failures occurred some 20 miles after the actual impact. I am sad to report that I suffered an impact on my personal car. I do not remember hitting a specifically large or deep pot-hole with the LF tire but luckily for me I noticed a bulge on the outer shoulder of that tire.

When I saw the bulge I knew at once I had a failed tire and it was only a matter of a few miles before there would be a sudden rupture of the sidewall and the air would rush out the 1" plus hole. Too fast for my TPMS to provide a warning. I recognized the signs of an impact because I have inspected hundreds of tires with similar damage. Some were hard to find as the damage was not even visible after dismounting the tire while others had "blown" while the vehicle was parked so there was no damage from running on a tire with zero psi.

The silver lining to this is that it gives me an opportunity to show the results of my step by step examination. Hopefully this will allow you to have a better understanding of how proper failed tire inspection is done and note that simply jumping to conclusion that since the tire was not made in the USA the country of origin played no part in causing the failure.

Here is the dismounted tire.

 Note the signs of damage are essentially invisible BUT since I did a complete examination before dismounting the tire I can show the physical evidence on the rim that shows the marks left by the tire as it was severely deflected and bent down over the rim even though fully inflated.

  The small lines were left from the sidewall decoration on the tire where it contacted the rim.

Here you can see the break in the interior where the body cord failed under the shock load.

Before I dissected the tire I continued my visual inspection and noted marks on the interior opposite the fracture. You can see where the tire was bent and over extended but did not fail.

A close-up showing the failed body cord. This "crack" measures about 0.6" long

.





Here is a video.

Watch the rubber to the left of the break. See how it stretches in a strange manner. The body cord under this rubber is also broken but not visible as the interior rubber has not failed yet. Sometimes all I find are signs of this stretching that indicates hidden failed body cord.

Hope this helps some understand what can happen. If I hadn't happened to see the bulge I definitely would have suffered a rapid air loss with possible vehicle damage or even loss of control and worse.

Impact damage or Defective tire? How can fishing line help explain which?

Many times the root cause of a "blowout" is impact damage. While there are many variable conditions such as speed, size of object being hit, tire inflation, spring rate, shock absorber stiffness, angle of attack, tire size and many others, I think we can all understand that it is possible to damage a tire if the right combination of factors occurs.

Many times you hit something or drop into a pot hole and don't know it because the impact is small. Other times you may feel the impact but if nothing happens right at the instant of the hit, the event seems to get erased from your memory. While it is true that most of the time when you hit something no significant damage occurs, sometimes there has been damage and you may not see the result of the damage for many miles, hours or even days so you may not link the impact event with the tire failure.

If there is damage to the tire, many times the damage is limited to the tire sidewall and could be in the side under the RV so you would not observe it unless you removed the tire from the RV. Sometimes the damage can damage the tread and belts. The main reason you don't always have an immediate loss of air due to the impact is because the damage occurs to the structure buried deep within the tire. In the case of sidewall damage it is the body cord that suffers a shock load and "snaps".

Sometimes when it is the steel belts that are damaged you might have managed to bend the steel beyond its yield point so now it is kinked and experiencing a concentrated load at the location of the bent steel.

The best way to think of how you "snap" body cord is to think of fishing line. Fishing line comes in different strengths just as tire body cord comes in different strengths. There are a number of the tradeoffs with going to higher strength cord than what you expect to need. Cost, weight and flexibility are some obvious examples so the tire manufacturer just like the fisherman tries to find a balance between stronger cord and the other measurable or desirable characteristics. Even if you don't fish you may know someone that does so you can check with them on this example.

You can confirm that it is possible to catch a 10# fish using 5# rated line but it is also possible for a 5# fish to break a 10# line if the fisherman doesn't play the fish properly and there is a shock load because the fish jumped or the fisherman jerked the line too fast. The same thing happens with the cord in the tire. A cord that would normally be more than strong enough can be snapped if all the conditions as named above happen to result in a shock load.

Here is an example to the left. This tire was labeled "defective" as the owner saw the bulge in the sidewall but did not remember hitting anything. However I noted the witness marks on the rim (arrow) where the tire was forced down over the rim, leaving black marks on the rim, so I did additional investigation. I discovered broken body cord on the inside of the tire, as seen below right

Here, below left, is a close-up showing damage to the outside of the tire at the exact location of the broken cord on the inside.
 



Now once the cord is broken the tire may continue to hold air with the remaining unbroken rubber as seen in the above picture. Only some time later when the rubber is heated up from driving at highway speed does the force of the inflation air exceed the decreased strength of the rubber. This delay can easily occur if the damage occurred shortly before you parked the RV for an extended stay at a campground. Days later as you pull out you would have completely forgotten about the deep pothole you hit as you turned off the freeway a mile from the campground. The result is a rapid loss of air. This event is often considered a "blowout" by the driver. A TPMS will not provide advance warning of the sudden failure because there was no loss in pressure till the rubber sidewall tore open.

Tire engineers experienced in root cause analysis can sometimes find the evidence that established that there was an impact that ultimately lead to the sudden loss of air. Other times the less experiensed will jump to the erroneous conclusion that the tire was "defective" because they do not know the tell-tail signs to look for or really aren't inquisitive enough to make a sufficiently detailed examination.

I hope this example demonstrates how it is possible for the owner to arrive at the wrong conclusion of what really caused the tire failure.

BOTTOM LINE
Discovering the real "root cause" of a tire failure requires detailed examination of all the evidence. Seldom is the RV owner in the mood to spend an hour or so examining the tire or he may not have the equipment needed to examine it in sufficient detail to arrive at the real answer.

A Tire Autopsy "Root Cause" Part 1

Many  people make statements about a tire "blowing out" or being defective but few post any facts about the real condition of the tire other than it came apart. There is a major difference between simply reporting a condition and providing information on the "Root Cause".
Examples of Conditions would be "the tread came off' or "tire lost air" or "tire went BOOM".
Examples of Root Cause might be "tire had a puncture" or "tire had an impact break" or "tire was run low and the sidewall had a flex failure". If you don't know the "WHY" of a tire failure then whatever actions were taken after the failure may or may not help to prevent a re-occurrence.

To help you understand this concept I want to take you through some real life examples. In many of these examples it was initially claimed that the subject tire was simply "defective" however as we review these examples I think you will ultimately agree that most tire failures occur because of some outside cause.

Here are three examples of damage done through the use of a high pressure power washer.

In each case someone claimed there was a defect built into the tire that caused a blister to form as seen in the pictures.

I know and proved that the damage was in fact caused by the use of a power washer as I did a quick cut tire examination (autopsy) to examine the layers of the sidewall. No internal contamination was observed.

A theory was formed and an experiment done to confirm or refute the theory. A tire that was sound was selected and using a pressure washer similar to what any of us could buy at a big box hardware store, we were was able to duplicate this damage.

Sidewall Impact Breaks occur under a combination of variables that have a very complex interaction. These include speed, load, inflation, shape and size of the item impacting the tire, angle of impact and even the condition of the shock absorbers. Change one or more of these and you may avoid the damage.

What usually happens is the pot hole or road debris is hit but if the tire doesn't immediately fail the incident is forgotten. Miles later the now damaged and weakened sidewall ruptures with no advance warning. Even if you have a TPMS you will probably get only a few seconds advance warning as the now hot rubber will rupture very quickly and the tire will many times shred which destroys the evidence.

Sometimes the sidewall bulge is observed before the sidewall ruptures. The inspection of tires with this body ply damage allows us to identify the sequense of events. In fact if you attend one of my tire seminars I relate the story of my then fiance and her experience of traveling over 17 miles after the impact before the tire ruptured.

Next time I will cover Belt Detachments

                      and Punctures

Why Do Tires fail #2

We need to have a better understanding why tires fail if we are to prevent or decrease the probability of another failure occurring in the future.

In the first post of this series, I said we need eliminate punctures or impacts when we investigate a claim of "defective" tire, as these external forms of damage have little or nothing to do with tire design or manufacturing process.
Some punctures are easy to identify.

This puncture was made by a piece of aluminum which based on its shape appears to be a piece of an aluminum rim from a broken truck rim.

Or when a chunk of wood goes right through the steel belts





Or small piece of metal








Now the above examples are relatively easy to find but here is something I found only by learning that the tire was loosing about 3 psi a week


This appeared to be a piece of steel like a straight pin that was only 0.01” diameter. If I hadn’t been checking my tires frequently (before I had TPMS on my car) I would not have know I had a puncture or was losing air. I could have suffered a run low failure.

Some externally caused damage is not found till someone takes a closer look




here is a puncture that caused a slow leak but in this case the owner probably just kept adding a little air each week rather than pay to have it properly fixed. In this case the sidewall did not flex enough to melt the cord but the tire did run hotter than normal for many miles. This extra heat degraded the rubber which ultimately resulted in a loss of enough strength that the belts detached from the body.



In this case the initial inspector decided the tire was defective. However I think you will agree that a tire being punctures and the owner not repairing the puncture was the real reason the belts came off the body of this tire and not the fact that the tire was built in &X%*$ or the tire builder spoke in C*!%@@+.

Impact damage can be masked by subsequent damage but here are a couple examples.
Looking at the interior of this tire

shows that this impact was so severe the bead area of the interior of the tire (right side) was folded enough to rub against the interior under the tread.

In this case the impact broke a number of body cords in the sidewall due to the sudden impact.

I hope I have shown that failed tire analysis takes a detailed inspection if you are going to learn if the tire suffered external damage or had some other cause for the failure.