Is it impact damage to your tire or a defective tire? How can a fishing line help explain which it is?
Many times the root cause of a “blowout” is impact damage. While there are many variable conditions such as speed, size of the 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 when you hit a pothole if the right combination of factors occurs.
Impact may be too small to remember
Many times you hit something or drop into a pothole 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 be to the tread and belts. The main reason you don’t always have an immediate loss of air due to the impact is that 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.
Think of a fishing line
The best way to think of how you “snap” body cord is to think of a fishing line.
I think that many can understand it is possible to “land” a 10# fish while using a 5# line if you are gentle when pulling on the line. It’s also possible to break the 10#-rated line when you hook a 5# fish if you jerk the line.
Fishing line comes in different strengths just as tire body cord comes in different strengths. There are a number of tradeoffs with going to a 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 the 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, as also mentioned, it is 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.
Above is an example.
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 where the tire was forced down over the rim, leaving black marks on the rim, so I did the additional investigation. I discovered a broken body cord on the inside of the tire, as seen below.
Here, is a close-up showing damage to the outside of the tire at the exact location of the broken cord on the inside.
Delay in noticing apparent damage
Once the cord is broken, the tire may continue to hold air with the remaining unbroken rubber, as seen in the above picture. Only sometime 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 until the rubber sidewall tore open.
Tire engineers experienced in root cause analysis can sometimes find evidence that established that there was an impact that ultimately lead to the sudden loss of air. Other times the less experienced 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 a 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.
Have a tire question? Ask Roger on his new RV Tires Forum here. It’s hosted by RVtravel.com and moderated by Roger. He’ll be happy to help you.
Read more from Roger Marble on his blog at RVtiresafety.net or on RVtravel.com.
 ##RVT1097
Hit a tire gator with our RV years ago, with. brand new tires that had less than a thousand miles on them. The day was over 100 degrees heading into Vegas. After hitting the gator we pulled over, inspected the tire and RV. We thought had no damage, and finished our two week tour of the Southwest.
A month after we got home, the damage to the tire began to rear its head. It began with a rhythmic thumping noise at freeway speeds. At first the noise was almost. imperceptible, but became more and more pronounced as the mile accumulated.
We finally retired that brand new tire a couple weeks later. I have no doubt that we would have experienced a rapid tire deflation within a few hundred miles later.
Mr. Marble
I wrote you a question months ago about the potential cause of my blowout with no indicator from my TPMS. With your latest article, I now think this may be a causative reason for the blowout. Don’t know if I related the possible contributing reasons for the blowout, but I’ll never forget I-40 traveling west was 100+ degrees east of Barstow California. I noticed my TPMS showed the tire temperatures were averaging 114 degrees. I don’t recall any pothole damage, but now I understand that could have contributed to my catastrophic blowout and the ensuing damage. I may now spend the necessary hour to inspect all tires following every days drive!
Hey Roger great information, for some reason when I click on your photos they don’t enlarge like they should. Is there a way to correct this on my end or your’s?
Thanks for all your information!
Snoopy
Hi, Snoopy. This time the images that Roger used were all small, so there’s no way to click on them to enlarge them (from the stored larger image in our Media Library). I’ll ask him to include larger images in the future so that they can be enlarged by clicking on them in the post, like usual. Sorry. Have a great day. 😀 –Diane
Used two fingers to spread photos on my phone
Great! Thanks, James. Usually we have the larger image stored in our Media Library, so folks can click on the image in the post and see the larger image, if desired. That way the images don’t take up so much bandwidth when opening the post. Your way may come up with a slightly blurrier image but, hey, whatever works! Have a great day! 😀 –Diane at RVtravel.com
Good article, but I wish there would have been more picture examples of what to look for when inspecting one’s tires. Cuts and bad scuffs are obvious. A big bulge as well. But what are some subtle things we should be looking for that might indicate a pending failure?
I love Roger’s articles and appreciate him taking the time to spread his vast tire knowledge. I have been on his website but unfortunately find it difficult to quickly navigate to what I want or need to see.