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Tuesday, October 13, 2015

TPMS don't prevent Blowouts

A reader wrote
"I'm a firm believer in a TPMS, but with that being said, I have a digital gauge. I set my pressure from that and then read from the TPMS I have installed. That has given me the plus or minus of the system which they claim can be plus or minus 1 or 2 PSI. Blowouts seem to happen no matter what precautions you take. I have been to the scales I know that I'm not overweight, I know that I have even wear. I know what my cold PSI is. So what then is a person to do more than that? I do not have control over the manufacture process, so you trust the dealer and data that they supply. So why are trailer tires so much more susceptible to blowouts than tow vehicle tires? A TPMS system cannot predict a sidewall blowout. To me that has to be the cord or construction of the tire itself. It will give me a pressure loss and then you still have to slow and pull off in a safe area that's where the damage occurs. So what are we to do or what do you recommend about that scenario. Thanks for all your help."

By "blowout" I will assume you are talking about "run low flex failure" of the sidewall and not the completely different "belt separation". As such if you can avoid driving at highway speed after the tire has lost significant inflation you can avoid having a run low flex failure, i.e., blowout. So it follows that if you stop driving on a tire after it has lost 30 to 50% of inflation or more, then you will avoid having a sidewall blowout.

I know of no part of the tire manufacturing process that can somehow manage to place "defective" material in a consistent circumferential line only in the upper mid sidewall. Also to my knowledge, no one has been able to identify exactly what the "defect" is that is located at the site of the melting.
Melting of polyester cord can occur no matter the size or number of cords if the sidewall is overstressed (bent) at a high rate. It does, however, take probably about 10 to 20 minutes for the temperature to rise to this level. This type of failure will and has occurred in all brands, so again, what is the exact defect.

In steel body tires we see the same circumferential line with signs of fatigue failure of the steel cords when they are run when significantly underinflated.

The reason trailers have a higher rate of sidewall flex failures than tow vehicles or motorhomes is twofold. First, a tire losing air on a tow vehicle provides the driver the opportunity to feel the change in ride and handling but provides no such tactical feedback if on a trailer. Second is the internal structural stresses that trailer suspension design place on its tires that are not experienced in as high a level in tow vehicle or motorhome applications. Interply shear is about 24% higher in trailer application than in a motorized vehicle.

I suggest you check the Label list on the left side of this blog and review the posts that have a label "Blowout" if you want to learn more.

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  1. I think the problem with trailer tires is that trailer manufacturers put marginally SIZED tires tires on their trailers - making them more susceptible to road debris. Going larger in size will help this.


  2. I've stayed with the original tire "size" (15") on our trailer but upgraded to Load Range E from D. So far, so good.

    1. When changing Load Range be sure you receive the advantages by also increasing the tire inflation which will give you extra load capacity margin and lower the Interply Shear.


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