Why do tires fail? Tire expert has the answers

 As an actual Tire Design and Quality Engineer, I know from my 50 years of tire experience, including 25 with a primary focus on failed tire forensic inspection, that tires fail from two basic causes:

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

Low air pressure

An active leak from a puncture or loose valve stem or valve core is the most common reason. Also, poor or no inflation maintenance contributes to low air pressure as all tires lose pressure at about 1% to 2% a month, excluding the pressure change due to changes in ambient temperature, and can lead to a sidewall flex failure, more commonly called a “blowout”.

The sidewall cord can melt (polyester) or fatigue (steel). Many travel trailer and fifth wheel owners fail to realize that they will never “feel” the results of a tire losing air until it is too late. Then 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. A tire pressure monitoring system (TPMS) can provide warning of air loss, so it is good insurance. A TPMS can easily pay for itself many times over.

Long-term degradation of rubber

The long-term degradation of the rubber at the edges of the belts in radial tires 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 in this case.

This degradation comes with age, as the rubber is always losing flexibility. Just think of those rubber bands you found in the back of the old desk drawer. Even in cool and dark they got brittle. However, running at, 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 with each increase of 18 F. Running a margin of at least 15% between tire capacity and measured load is a good first step. Running at higher speed will also generate excess heat. For ST-type tires, this means faster than 65 mph, no matter the Max speed rating.

Realizing that more than half of the RVs on the road have one or more tires 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. But many still have feelings along those lines when it comes to where a tire is made.

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 tire shopping tool available is comparing warranty and service support.

Can you get a 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? The answer to these questions may provide a better indication of tire quality than the opinion of other RV owners published on the internet.

There are some self-appointed “experts” out there who think that selling tires for a numbers of years qualifies them to make technical pronouncements on tire technology. I would suggest that people review "The Pneumatic Tire"   published by the US DOT before making a claim of being a “Tire Expert”.

 

 

 

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Weigh the RV each trip?

Was following a thread where some people were saying they adjust tire inflation each trip based on how much "stuff" they are carrying. I didn't think this was a good policy so offered the following: 

 

Unless you are making significant (1,000# or more) changes in what you pack in your RV, I see no reason to be messing with tire inflation once you have finished adjusting axle alignment and been on a scale to learn the actual load on your tires. The general advice for weighing is to have the RV loaded to the heaviest weight you expect to travel with. This means full of cloths, books, tools, water, fuel, food, spare parts and toys you might travel with. There is really only one inflation number you need to keep in mind and that is the MINIMUM inflation required to support your load. We are trying to protect the tire from failure and with data from RVSEF showing that over half of RVs historically have been running their tires in overload. Damage to the tire structure is caused by the rubber bending and stretching past an elastic limit at the molecular level. This stretching actually breaks some of the chemical bonds and once broken the resultant cracks never repair or reform themselves. They can start small as seen here.

 The cracks only grow. Once formed the cracks will just get larger and larger till eventually they get large enough to result in a failure of the structure which many times is in the form of a belt detachment from the body of the tire as seen here.

  It doesn't take too many miles for a tire in this condition to come apart and you may end up with a nice "Blowout" unless the tire is replaced before the crack gets too big. The inflation in the Load & Inflation chart is the MINIMUM you should run but heat, age and the tearing a tire experiences from hitting pot holes can result in the rubber cracks forming even if you are running the inflation found in the charts. Running higher than the minimum inflation, can offer some protection as the tire will run cooler and bend less which means less tearing of the rubber chemical bonds. If you look at the tables you can see that each increase of 5 psi gives you a few hundred pounds more load capacity and conversely each drop of 5 psi decreases the load capacity of your tires. Tandem axle trailers place some additional stress called Interply Shear, on the tires which result is more cracking and more tearing of the rubber bonds. I would recommend against lowering tire inflation once you have learned the inflation required to support your heaviest weight. I also recommend that you set your TPMS Low Pressure warning level to no lower than 5 psi below the minimum inflation learned from your scale reading as I can think of no reason or benefit to ever run an inflation lower that what is needed to support the load. In fact, on my RV, I run my inflation at a +10% margin over the inflation from the tables which allows me to set the TPMS low pressure warning level to the inflation requires to support my heaviest scale reading.

Simple question: Why do tires fail?

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 SLOWER. Now a side point about speed. I did a POST some time focusing on speed 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. Few people realize that ST tire loading is based on the assumption of 65 mph Max operation speed

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. 

 

##RVT1049

I just had a tire failure, for no reason

If you follow any RV forums you probably see a statement like this every few weeks. I can tell you that tires do not fail because of some RV-Magic. It comes down to actual Science.

Why do tires fail?

Simple question but as with almost every question about tires, the answer is not a one liner. This post. It's not short but it really isn't technical and I'm sure every reader will understand the concepts.

When looking at why tires fail we need to first exclude the obvious damage caused by external objects i.e. pot holes, curbs, chunks of metal, glass or rock or other trash and junk on the road. Second we'll exclude broken valve bodies, leaky valve cores, valve gaskets, extension hoses, and cracked rims.

What's left will be a structural failure which would almost 100 percent of the time will be either a detachment of different parts or components of a tire one from the other, OR a heat/fatigue failure in the mid sidewall due to driving with extreme low inflation.

Most tires are made up of 20 to 30 different components such as different steels (belts and bead are not the same steel) textiles such as Nylon, Polyester, Rayon, Aramid. Then there are the various different rubber components such as Tread, Sidewall, Innerliner, Steel skim, Wedge, Flippers, Chaffer, base tread, Inserts, and other bits and pieces.

Each component is selected for different reasons and contributes both advantages and disadvantages to the total. Each component must "stick" to its neighbors both in the un-cured and cured state. The interface between two different components is weaker than the individual components but it must hold together through millions of cycles over a 200F degree temperature range.

All would be just fine if a tire were made completely of inorganic materials such as metals, stone or even ceramics. There are numerous formulas for the strength and fatigue limits for these inorganic materials.

The issue with organics (wood, rubber or other materials made from oil such as plastics) is that their strength has a "T" or time function. If you build a bridge of stone, you can calculate the maximum load it can sustain and as long as the structure isn’t changed due to external damage its strength will be the same the day it’s built and 50 years later. If I build a pressure vessel of steel and put 150 psi in it and it doesn’t fail I would have every expectation for it to continue to hold that pressure for decades, again excluding external damage.

However, if I build a pressure vessel of organic materials (a tire) it might hold 150 psi the first day or maybe the first few days but at some point it can fail. This principle is not something many engineers think of today because they don’t design bridges of wood but 100 or 150 years ago when wood was common they learned that a bridge that was strong enough to hold a railroad train to drive across, it could fail if the train parked on the bridge.

I educated some fellow tire engineers about this “T” function when I proved, through lab experiments that it was possible to fail two tire with high pressure above its stated max 18 days after it was initially inflated.

The other condition that affects and changes the “T” in the equation is temperature. Organics experience constant change (loss) in properties as the temperature increases. The rate of change (aging) doubles about every 18 degrees F of increase in temperature, so it's not easy to calculate or predict the time it will take for an organic structure to fail unless you can control the temperature over time.

Bottom line. It’s a combination of temperature (heat) and time that causes tires to fail. A tire that spends its life in Flagstaff, Ariz., could probably last twice as long as a tire that spent its life in Phoenix if all other operating conditions were identical so even knowing the state where the RV was used isn't sufficient.

As the owner of an RV you can significantly affect one factor and that is the heat generated internal to the tire. When you run fast or overloaded or under-inflated you are running hotter. This means you are speeding up the rate of "aging" of your tires and can expect to see a tire fail before it wears out. You can also protect and shield your tires from the heat generated when in direct sunlight while your RV is parked. HERE you can read about an experiment I ran on the benefits of shielding your tires from Sun exposure.

##RVT1048

RV Tire warranty. How do engineers "read" tire conditions?

Read the following on an RV forum
"Carlisle Tire's warranty used to state "tires must be inflated to sidewall stated pressure or warranty is void"; I don't know about now though.
How in the world do they determine if the tires are inflated to sidewall pressure? Is there a little gremlin with a report card in each tire. Some manufactures just never get out of the box.
Unless it was a bad tire, had been run flat previously, and most likely a bunch of other possibilities.  At the time of a blow out there is no way they would know other than by assumption.
Yes, most probably operator error, but only assumptions."


Sorry, but there are ways to identify the probable inflation & load history of a tire. Just as a Medical Examiner can do an autopsy and identify the signs of bad diet and poor or no exercise, or years of smoking, it is many times possible to see the physical signs of low inflation and high load.


These signs can show up in the indentation into the tire left by the wheel.

Here are examples of improper inflation or a Run Low Flex Failure of a P type, ST or LT type tire.

Melted body cord is physical proof of extreme run low 

Also, the different flex markings can be seen on the interior of a tire. In extreme cases the Innerliner (special rubber that holds air in much like a tube did in tube-type tires)

Manufacturing "Defects" will usually result in early life failure i.e. <1,000 miles.  Tire failure is in itself not proof of some nebulous "defect" even though lawyers and those not experienced in failed tire inspection want to think so.
Once you examine, in detail, a few thousand tires from both controlled testing and from day to day use & abuse the conditions seen in tires tell a story of the tire's history.
Too often people simply think of the conditions (load, speed, inflation, road) at the moment the tire fails as the "facts" to be considered when trying to decide the "why" a tire failed. In reality, the damage might have been done hours, days or even months earlier.
See THIS post on a study of pot hole damage and how long it took for some tires to fail from the impact.


As I point out in my "RV Tire Knowledge" Seminars at RV Conventions, tires are like potato salad, putting the salad back in the refrigerator after it was left for hours in the hot sun does not "fix it" and make it good to eat the next day any more than taking the burnt hot dog off the grill and letting it cool down before serving it makes for a good meal. Adding the correct air in a tire after running it low for thousands of miles, does not repair the damage. Slowing down to 50mph after hours of speeds of 70 to 80+ over the preceding weeks and months does not "fix"  or heal the thousands of microscopic cracks that were formed in the overheated and overstressed belt rubber. Once a crack is initiated it does nothing but grow. If a person stopped his smoking addiction of 2 packs a day for 40 years a couple months ago, will his lungs be clean and clear today? Not a chance.

When examining a tire, I look at the physical condition of a tire and specifically what evidence there might be. Years of experience has taught me what to look for and allows me, as a court-certified "Expert", to form an opinion that is based on the examination of many thousand tires.

##RVT933

"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

Are sidewall cracks the cause of tire failure?

Read an RV forum post about sidewall cracks. From the picture, it appeared the tire had what I would call Ozone or UV cosmetic cracking. The owner was concerned about the tire durability as he had suffered a couple "Blowouts" previously.  I responded....

"Not being able to inspect the "Blowout" tires or even see some pictures, I have no idea for the reason for the tire failures as "blowout" is not specific enough to suggest a possible cause. They might have been run for a few miles while losing air. They might have suffered impact damage 10 or 100 or 1,000 miles prior to the ultimate failure. They might have been run overloaded or underinflated or over speed recommended by tire manufacturer or tire industry engineering guidelines for thousands of miles.

Yes, tire failures can be expensive if the failure is only discovered by operating the tires at speed and not during the regular detailed close inspection by a "qualified specialist" as outlined in the Michelin Tech bulletin on RV/Motorhome tire inspection.

It is also true that sidewall cracks, in my professional experience, are not in themselves the root cause of tire failure. Just as a person developing a temperature of 101F or 102F is not the cause of an illness but is just an external symptom. Tire sidewall cracks are an indication of extensive tire age with the cracks developing due to time, temperature, flexing and exposure to Ozone and UV. All of which are detrimental to tire life.

"Zipper" sidewall failures of steel body ply are the result of fatigue from operating for miles when significantly underinflated or overloaded or a combination of those. Sidewall crack inspection guidelines published on pg 8 of THIS guide, suggest a maximum depth of about 2/32" on large radial tires (22.5" sizes) which usually have rubber thickness closer or thicker than 0.10".

Tires "Fail" for two basic and different reasons:
1. Sidewall Flex failure from low inflation/High load
2. Belt separation from long term rubber degradation due to excess heat and age

I covered these in two separate posts in 2012  and again with a slightly different focus in 2014.

While I can conceive of someone running tires for many miles with sidewall cracks that get deeper than 2/32", those cracks would need to penetrate deeper and get completely through the sidewall rubber to the depth of the steel and then water would need to be introduced and enough time pass to allow a significant portion and number of steel cords rust and be weakened before a "Zipper" like failure could occur.

The above would, in most cases, take many months of operation and would require that no or improper or incomplete inspection take place before a tire would suffer a catastrophic failure.

So the bottom line is two-fold.

1. Ensure you are not overloading your tires and that they are ALWAYS inflated to what is needed  for your application by running a TPMS

2. Starting at 5 years (3 years in trailer application) from the DOT manufacture date molded on the tire sidewall and annually or every 2,000 miles whichever comes first, have them inspected.  I have covered the topic of inspection previously.

##RVT923

Remember: A tire is just a "tool" you use to get a job done

This in response to a report of tread cracking of some traction design tires placed on a custom heavy car hauler trailer. The owner was blaming the 4-year-old tires.

I do note that when there are tire problems, including actual "failure," it's common for some to say "My xxx brand tires failed, I will never buy xxx tires again".

Well, sorry to tell you but there is no such thing as "Fail-Proof" tire. This was even part of the testimony mentioned by DOT spokesperson during the Ford Explorer rollover fiasco of 2000.

Today's tires are amazingly robust. Even when they are made in Japan or Timbuktu, and we all remember how bad "Made In Japan" was when were growing up. As I pointed out in the thread, the subject tire an All season traction design was not at all appropriate for heavy trailer application. Both the tire type/size was wrong and the tread pattern was wrong.

Why is this the tire's fault?

If you put a truck tire with a heavy off-road mud traction tread design on the front of your 40' DP and had loud noise and vibration and harsh ride would that be the tire's fault? Would simply changing tire brands from say Bridgestone to Michelin solve the problems if you selected just another heavy off-road mud traction tread design? No of course not.
From my experiences as a tire engineer, I can tell you that I can probably "fail" any tire in under an hour and under 50 miles if you let me set the conditions.

A tire is just a tool you use to get a job done. If you don't select the correct tool that is appropriate for the job you want to be done why is it the fault of the tool manufacturer? Think of the absolute best tool company. Now select one of their flat blade screwdrivers.
 OK now start using it as a chisel and pound on it as you try and cut through some rusty bolts. After cutting through a few bolts would you blame SK or MAC or  Snap-On or ???? if the point of the screwdriver is dented and chipped?

Different tires are just tools with different intended usage.

Basically I would suggest "Rib" or "All position" designs for the front position and if you intend on occasional off-highway travel (a gravel road at a campground doesn't count) then you could select something with a bit more traction capability but I would consider any "Drive" position as not a great choice for Motorhomes or trailers.

WARNING - Super Technical Post Tire failure and Interply Shear

I have had some folks who seem to want to replace Science with what they term "common sense".
In my opinion, this is why some people still think the Sun and rest of the Universe rotate around the Earth or that believe the Earth is flat or the Moon landing is a hoax simply because they don't understand the Physics and Science behind the stated facts.

I mention this because I continue to get people claiming that because they checked their tire pressure last week or yesterday and had a tire failure today, some sort of "magic" must have happened to cause their 65 psi or 80 psi tire to suddenly go sky high in pressure to cause the tire to explode due to high pressure. You don't have to do the technical research yourself just as you don't go to medical school to learn about some ailment you have. You do have a choice. You can trust your Doctor or go to Medical School or in the case of tire failure, you can put your trust in those who have spent years working on and constantly improving tire design, or you can simply believe that tires fail because of some unidentifiable "defect" that was built into the tire.

I have previously posted on how Sidewall Flex Failures can easily mislead the inexperienced into believing they had a "blowout due to high pressure." I also have some who do not want to accept the Science behind the need for tires in trailer application to run lower speeds and higher inflation in an effort to lower (but not eliminate) the probability of Belt Separation.

So I decided it is time to get out the "Big Guns" and cite some actual tire Science.

Here is a question from someone who took issue with my recommendation to increase the inflation in trailer application.

Did you ever notice that the two rear tires on the tow vehicle are putting hundreds of horsepower to the road? Did you ever notice that the two front tires are steering the whole assembly?

Here is my reply:

Yes, I have noticed that. I also know that the internal structural forces are different for torque than for high "slip angle" which is the situation in trailer application. Front tires on cars, motorhome or tow vehicles do go through slip angle but usually in the 1° range while trailer tires are subject to angles in the 10° and greater range. The forces are NOT linear. 10° can generate significantly more shear than 1°.

If you want you can purchase the software package HERE for the vehicle response and handling. The results of this vehicle simulation show the vertical and side loads being applied to tires as you drive around a corner. These forces can then be used as the input into Finite Element software programs to determine the structural loads on tire components.

Here is is a technical paper on "Interply Shear Stresses and Coupled Deformations of a Folded Belt Structure Under Extension"


Personally, I prefer Dr. Song's paper on"FATIGUE OF CORD-RUBBER COMPOSITES FOR TIRES."
Here is the abstract.
Fatigue behaviors of cord-rubber composite materials forming the belt region of radial pneumatic tires have been characterized to assess their dependence on stress, strain and temperature history as well as materials composition and construction. Using actual tires, it was found that interply shear strain is one of the crucial parameters for damage assessment from the result that higher levels of interply shear strain of actual tires reduce the fatigue lifetime. Estimated at various levels of load amplitude were the fatigue life, the extent and rate of resultant strain increase (“dynamic creep”), cyclic strains at failure, and specimen temperature. The interply shear strain of 2-ply ‘tire belt’ composite laminate under circumferential tension was affected by twisting of specimen due to tension-bending coupling. However, a critical level of interply shear strain, which governs the gross failure of composite laminate due to the delamination, appeared to be independent of different lay-up of 2-ply vs. symmetric 4-ply configuration. Reflecting their matrix-dominated failure modes such as cord-matrix debonding and delamination, composite laminates with different cord reinforcements showed the same S-N relationship as long as they were constructed with the same rubber matrix, the same cord angle, similar cord volume, and the same ply lay-up. Because of much lower values of single cycle strength (in terms of gross fracture load per unit width), the composite laminates with larger cord angle and the 2-ply laminates exhibited exponentially shorter fatigue lifetime, at a given stress amplitude, than the composite laminates with smaller cord angle and 4-ply symmetric laminates, respectively. The increase of interply rubber thickness lengthens their fatigue lifetime at an intermediate level of stress amplitude. However, the increase in the fatigue lifetime of the composite laminate becomes less noticeable at very low stress amplitude. Even with small compressive cyclic stresses, the fatigue life of belt composites is predominantly influenced by the magnitude of maximum stress. Maximum cyclic strain of composite laminates at failure, which measures the total strain accumulation for gross failure, was independent of stress amplitude and close to the level of static failure strain. For all composite laminates under study, a linear correlation could be established between the temperature rise rate and dynamic creep rate which was, in turn, inversely proportional to the fatigue lifetime. Using the acoustic emission (AE) initiation stress value, better prediction of fatigue life was available for the fiber-reinforced composites having fatigue limit. The accumulation rate of AE activities during cyclic loading was linearly proportional to the maximum applied load and to the inverse of the fatigue life of cord-rubber composite laminates. Finally, a modified fatigue modulus model based on combination of power-law and logarithmic relation was proposed to predict the fatigue lifetime profile of cord-rubber composite laminates."


Let's see if I can help. Here is a key phrase "the fatigue life of belt composites is predominantly influenced by the magnitude of maximum stress."  Now, think of the tire side bending when you back a trailer into a campground site.

The video in THIS post shows the side loading during relatively low angle turns



I apologize for going so deep into tire engineering but sometimes the facts are needed to demonstrate that "common sense" doesn't always lead to the actual facts.  Before writing my posts on Interply Shear on trailer tires I had both vehicle simulation and tire structural shear forces run. We learned that for tires on multi-axle trailers, like RV trailers, the belt shear forces can be 24% higher than the belt shear forces of identical size, load and inflation tires on a motorized vehicle. This is why I suggest a different approach to tire inflation for trailer application than motorhome applications.


I will try and "lighten up" a bit in the next few posts.

##RVT862

How to prepare for and respond to tire failure

There are numerous posts on RV Motorhome forums on how the driver whould respond to a sudden tire failure (Do not stomp on the brakes but apply the gas for a couple seconds to be sure the driver has full control. THEN slow down and pull over.)
If towing a trailer you are less likely to lose control of the tow vehicle so you just need to slow down as soon as possible and pull over.

BUT the reason for this post is not to address vehicle control but to identify the actions you should take concerning your tires.

1. Before you have a tire failure you should be sure you have the full DOT serial for each tire written down somewhere.

2. With ANY failure, other than puncture or valve failure you should file a complaint with NHTSA. They need the FULL DOT tire serial and full vehicle VIN.

3. Take pictures.  In full sun, close enough so only half the tire fills the frame So more than a couple pictures are needed. Snapping a shot in the shade from ten feet away under the RV just isn't useful. Get tread, sidewall failed area, and non-failed area. Make sure the pictures are in FOCUS and at the highest quality possible for your camera.

4. Let NHTSA know you have pictures when you file your complaint.

5. Contact the tire dealer, RV dealer and RV MFG of the failure and the NHTSA complaint number.

6. KEEP THE FAILED TIRE. Tire company may be willing to compensate you but you must have the failed tire. Carry an HD trash bag if you must. A folded trash bag doesn't take space and is only a few ounces weight.  No tire = no possible compensation.

Note I have posts and video on how trailer owners, Class B and Class C owners can inspect your own tires each year for belt/tread separations. Running a TPMS will give you an advanced warning on Run Low Flex Failure.

Having the actual scale load on each tire as covered in the owner's manual will help substantiate your claim. Always run the tire pressure on the tire sidewall for your CIP if you are pulling a trailer. Motorhome owners need scale weight printout and a copy of tire load tables.

IMO if you don't do all of the above I am not interested in hearing your complaints.

Travel Trailer tire "Blowout" not quite.

Just got an email from a reader, in which he describes a recent tire failure he experienced on his travel trailer. He reported:

"Mr Marble,
I recently experienced a catastrophic tire blowout. I am 100% confident it was not due to low tire pressure (according to my tpms). My tpms did not alert me to an overheat or pressure issue. I was only 35 miles into my trip. It alerted to the blowout 3-5 seconds after the blowout, but I had already heard the pop and saw tire and fender shrapnel flying in my side view mirror. It was passenger front tire on trailer.
Tires are approx three ears old, around 5000 miles on them. We are weekend warriors plus 1-2 1000 mile trips per year. Rig sits 2-4 months of the year under shed cover with covers on tires on gravel.
Before I go in to details on rig and such, would you be willing to give me your opinion as to the cause of the failure? I have my suspicions but I'd like to hear from an expert.
I put the spare on and finished my trip and am sitting at ocean lakes family campground in Myrtle beach. Can take pics/video and provide whatever data you need.
Here's a couple of pics if it helps sway your decision.
RW-Myrtle Beach"

Here are the pictures he sent of his tire.

  Now many of you might think these are sufficient but for me to provide a better more accurate opinion of that went wrong I really do need better pictures.

In this case it was too late to get better pictures as RW informed me that he didn't have room to save the tire till he got home.

A few comments and observations.

The tire did not suffer a "Run Low Flex Failure" or what is normally called a "Blowout" by a non-tire engineer. The condition of the tire is more accurately a Tread or Belt Separation. The air loss came after the belts and tread had already separated from the body or carcass of the tire so that is why the TPMS did not provide any warning.

I did inform RW that the pictures were not close enough or of high enough quality to allow me to zoom in to see the details needed for me to establish a reason for the failure with a high degree of confidence but I did provide some comments.

A tire suffering a Tread Separation is simply not going to generate high enough temperature to trigger the TPMS.

It appears that this tire possibly suffered from some manufacturing or chemical problem as there are large amounts of steel cord with no rubber adhering to the steel cords. This could be because the tire had started to separate many miles prior to the external failure and the rubber was abraded from the steel cord. I would need to do microscopic examination to confirm this diagnosis.

I suggested that RW review the "Free Spin" tire inspection process that I outlined in my post on How to Inspect tires and in the post Why Blowouts are of special concern.

I also suggested that he include the Free Spin inspection procedure at least once a year so he would improve his chance of discovering an impending tire failure in the future.

A side comment about retaining the tire. If RW had wanted to file a warranty claim with the RV dealer or tire company he would need to be able to produce the tire for examination. It would also have been a good idea to be sure he had recorded the complete DOT serial and file a complaint with NHTSA for without complaints there will never be an investigation or a possibility of a recall or an improvement in the quality of tires produced for the RV market.

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HELP! We get tire "Flats" every year. or are they Tread Separations?

I got a question   "We have a 2012 43' 5th wheel Heartland Toyhauler, triple axle, have 235 80r 16 wheels and tires. Every year we seem to have at least 2 flats. This year we had 2 flats, going south, and by the time we arrived at our destination coming back north, (500+ miles) one of the tires were so rounded you could not stick your finger between the back and middle tire on the drivers side. We were very lucky they did not hit each other. We are wondering if we could put 12 or 14 ply tires on the same wheels? And if LT's would be better than the ST's?

Thanks for your help, 

Wife of very frustrated husband"

Dear "Wife of frustrated" I would be glad to help out. If you check my blog, you will see I cover a lot of different questions on RV tires.  My background is in the oldest post.

Now to your question.  I could use a bit more information.

You said you get a couple of "flats" but then describe a "rounded" tread which sounds like a tread or belt separation like

To me a "flat" just means you discover the tire has lost 20% or more of the correct inflation.

To be sure I have all the information I need, could you answer a few questions?

1. On your 5th wheel you have a tire placard (usually on outside of the RV toward the front of the driver side on the side of the trailer. This placard has tire size and inflation information similar to what is seen in attached Label. jpg. .There should also be some information from Heartland on the GAWR (Gross Axle Weight Rating) for your specific trailer in the stuff you got with your purchase. It might be 6,000# or similar number.

2. To confirm the tire size you are running you have "ST 235/80R16   LR-E"   The LR-E is Load Range E  The "ST" before the numbers is "Special Trailer" 

3. You might want to review THIS blog post on how to "read" a tire.

4. Is the tire inflation on your placard 80 psi?  Is that the inflation you set the tires to in the morning before travel?  You can learn more about inflation HERE.

5. Here is an important question. Have you ever had the trailer on a scale? The actual tire load is the 2nd most important thing to know with proper inflation being the MOST important.

6. What do you have for a tire pressure gauge. I prefer THIS gauge as I have tested them and found them accurate.

7 Do you have a TPMS to monitor tire inflation on your Trailer and Tow Vehicle?

LT type tires MAY be an option but we need to be sure that whatever tire you have can support the actual load on the tires.  The load on individual tires is NOT simply the load on an axle/2 and the load on an individual axle is NOT the total load/3.

Calculating the side to side load is something I can help with, and is needed if we want to know the actual individual tire load. BUT the individual axle load can be learned at any CAT scale or at most truck scales, or local gravel pits or grain elevators if you check Yellow pages or Google "Sacle Location"  where Location is your town or state.

================================

I hope the above is informative as it outlines the basic information needed if you have a tire problem and would like some help.  Some people are more than happy to simply jump in but as an engineer I need FACTS and DATA.

I will post the information received and hopefully a solution to "Wife of frustrated" problems.

What you need to do to get a tire failure replaced under Warranty

Along with this Blog I try and monitor a number of various RV forums. Some of you may have seen my posts. There have been a number of times when a topic comes up and I make a reply that I think would be a good topic for my blog but it is on a short side. I have decided that just because an answer to a question is not 600 words long, that should not stop me from sharing the answer so over the next few weeks I plan on posting a number of items where I provided an answer or comment on questions posed by other RV owners. As they say the Names have been changed to protect the innocent.

"John & Mary" wrote about the difficulty they had in getting a failed tire replaced. They were surprised that the tire company wanted to know the DOT serial, purchase date and to actually have the tire made available for inspection before a new tire would be provided. They said "When the tire company asked for the tire to be returned we were surprised. We dunno about everyone else, but we didn't keep the tires & didn't know until several months later what was required to file a report"

My response:

You are correct Mary, you can't get a tire replaced without providing a few items to the tire company. That's why I have advocated that everyone record the full DOT of each tire in the "Book of important RV Info" that we all keep, so if we ever have a tire problem and the DOT serial is destroyed we will have the information needed to file a complaint report to both NHTSA and to the tire company. We also need to keep the documents that show the date of purchase of the tire (if they were not new on the RV).

As far as keeping the tires, I understand that many RVs don't have space to store a tire but after reading this story where John & Mary were complaining that the tire company wanted the failed tire before it would issue a refund or compensation, I feel that people need to have a basic understand of their responsibilities in the event of a tire failure and wanting to make a claim so they can take the steps needed to increase their chance of getting a replacement tire when appropriate.

I have to wonder why people think that when the failed product and its serial number and some proof or purchase is required by every other company when requesting compensation or replacement, be it a toaster or refrigerator, that for some reason tire companies would be the only company to not ask for the failed product and Proof of Purchase..

Now if you don't have space to store the tire, then I would suggest that you need to contact the manufacturer at the number given in the warranty book you received when you bought the RV or tires and before you leave the tire service shop doing your changeover, you confirm what the tire company requires. You can then decide if the potential for a refund or adjustment is worth the effort and cost involved.

I do have space for a spare tire in my RV. That was a requirement when I was shopping for a new RV. I also run a brand of tires that has thousands of stores & dealers around the USA, another requirement when selecting a tire brand. So I am confident that I can always get to a store and would be able to process the paperwork needed to file a warranty claim as well as leave the tire at the store so a company engineer can inspect it or have the tire shipped back to the appropriate location if needed.