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Monday, April 21, 2014

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.

14 comments:

  1. Roger, this makes sense... Taking things 'forensically' and scientifically is the only fair way to approach these 'failures'.. or as above, 'breakage' of an item...in this case, a tire. All things can be 'broken'...it is incorrect and sometimes dangerous to ignore this reality. I am guilty of "reasoning" my way out of situations I shouldn't...

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  2. Channing Thanks for your comment and taking the time to learn and understand.

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  3. I have become very tire sensitive. It scares me when I see cars with bald tires. It really scares me when I see RVs with bald or old tires.

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  4. I agree with your research , but still think a better made U.S. tire would have less problems. I work in the construction industry and our drivers of everything from pickups to road tractors run their tires low , run over curbs and rocks , potholes ,lumber and anything else that gets in their way and we do not have as many tire problems with quality U.S. made tires as we do with Chinese made tires. The U.S. tires take the abuse and when aired back up , last the life of the tread normally.
    Just my opinion. Thanks for your research. I would like to see a side by side comparison of U.S. and Chinese tires put to the same reallife abuse on an RV and see the outcome.

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    Replies
    1. There is a standard Government "Plunger" test where a 3/4" steel rod is driven into a tire. All tires sold in the US are certified my the manufacturer to pass this test. This includes tires made in USA, Japan, China, Germany etc. So there is a "side by side" controlled test.

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  5. The Tire failures that I have had in the last 20 plus years with ST Tires has been my own fault because of one or more of the following Items.
    1. under inflated tires.
    2. Overloaded.
    3. Driving to fast for tire speed rating. (over 65 MPH) on ST Tires.
    4. Not inspecting tires after running over object in road.

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  6. I wish I had bought a TPMS when I first bought my trailer. It would have paid for itself within the first year that I went Full Time travelling. Trailer tires are expensive, especially when you have to buy one at a gas station along the freeway somewhere.

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  7. I watched a trailer go by with a severely underinflated tire. I later passed the same trailer pulled over, changing that tire. I stopped to let the owner know what I had seen, but he immediately launched into a dramatic story about his blowout. He heard a bang when it blew. Raved about how he would never by Goodyear Marathons again. Then I told him that I had seen his tire almost flat a few miles back. Made me think differently about blowouts.

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  8. What about wrong valve installations. I purchased six tires US made, and with 2013 dates of manufacture, from a reputable dealer. Metal stems were removed during the tire changes and rubber stems with brass valves were installed. Tires had less than 1200 miles when the rightside duallies blew out. Upon inspection, tires were not at fault...valve stems blew out of the rims as a result of heat expansion. The duffus that installed the rubber valves was fired from his job, the dealer made good on the tires plus other costs. Note: look at the valve stems, they all should be metal, and sized for the usage and weight of your rv.

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    Replies
    1. High Pressure valve stems ARE REQUIRED in anything over 45 PSI! I know if you check the placard on your drivers side door it's going to suggest 65-80 PSI in the rears. I'm sorry about your problem and I would not suggest going back to that tire place.

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  9. Not sure I am posting this in the correct place?
    I see the article about winter storing tires,if possible, but you also say "do not use tire dressings". Please comment on why not as they are touted as UV protect-ant and keep rubber pliable?
    The shinny part is just a by product.

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    Replies
    1. RE tire dressing. Too many of these products seem to add a lot of shine but I'm not sure if the UV protection is meaningful.
      It is well documented that some of these products contain petroleum distillate that can damage a tire sidewall. I am inclined to believe that a coating of oil or brake fluid which would partially dissolve the tire rubber does offer some shielding from UV light.
      If the "dressing involves scrubbing of the tire sidewall then you are probably removing some of the protection provided by the tire manufacturer, which certainly isn't a good thing.

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  10. I had a tire failure on our new trailer while towing on a winding and steep mountain road. This prompted me to do some sanity checking on the tire load rating versus actual load.

    The load rating of my factory tires is 1760lbs. Multiplying by four tires, the total combined load rating is 7040lbs. This assumes that all four tires share the load exactly equally, which won't ever happen in practice.

    The GVWR of my trailer is 7715lbs. So the combined load rating of my tires is less than the fully loaded trailer weight by almost 700lbs.

    The dry hitch weight of my trailer is 715lbs. Subtracting this from the GVWR of 7715lbs, the static load on my tires is 7000lbs. So the margin between tire load rating and tire load is 40lbs, or 10lbs per tire.

    This is standing still on flat ground with perfectly balanced cargo and axles that have perfectly identical force constants. This isn't real life.

    So then I asked myself what happens when the trailer is moving. It's hard to quantify the lumps and bumps that will add stresses to the already fully loaded tires. However it's not too hard to figure the amount of weight transfer to the outside wheels on curves.

    Using the government guidelines for setting 'advisory speeds' on curves, a guestimate of the height of the center of mass of my trailer off the ground, and the wheel to wheel width of my trailer, I've estimated the increased loading on my outside tires on curves.

    The numbers are astonishing.

    When I take a curve that is posted with a 20mph advisory speed, the load transferred to the outside tires can be about 580lbs each. Since there is no margin of substance in the tire rating, this is an overload of 580lbs. What happens when I hit a bump at the same time?

    To withstand the forces repeatedly encountered on curves, I think I really need tires that have substantially more load capacity than those provided by the factory. Going from LRC to LRD helps, but doesn't completely eliminate the risk of overload.

    So, perhaps the problem with 'China Bombs' is that they're pushed beyond their ratings as soon as a trailer starts to move. In that case, some people will have problems while others don't, depending on driving style, locale, and a host of other variables.

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  11. Some of what I am about to say may already been have been said, but I didnt have time to read all of the replies. I agree with this article 100% as I took a trip about a year and a half ago where I lost 3/4 of my tires on a trailer that was only 6 mos. old. Incidentally, the failures were during the roughest roads of the trip. The manufacture (Rockwood) reimbursed me for the new tires I put on. In ever case of a blow-out over a two day period, I had checked and double checked inflation. While one could argue that the factory tires were probably not the best application for my trailer, the tires were in good shape. I replaced two of the tires at a local walmart in Little Rock, AR as we were driving through, the other two I replaced back home with Goodyear Marathons. The next week I took another 300 mi trip and when I arrived at my destination two of the new tires were under-inflated. I was perplexed. After investigating, I found that one of the walmarts replaced the valve stems and the other did not. The two tires with old valve stems were the ones that were losing air. The tires were not bad, the factory valve stems were dry-rotted. When you buy a "new" trailer, either replace the tires and valve stems are insist that the dealer do it.

    I have since invested in a TPMS system for the piece of mind and it has made my travel experiences much less stressful.

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