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Friday, January 24, 2014

Tires and Burst Pressure, What causes Blowouts?

Recently saw a post on another blog Tires and Burst Pressure, What causes a "blowout". 



Now there was nothing really wrong with what was posted, it was just not as accurate as it could have been.
I have many posts on tire blowouts and their most likely cause, but as long as I continue to hear people claim or read blog or forum posts on blowouts followed by partially correct information I will continue to try and provide the facts based on the thousands of tire autopsies I have done in my career.

Tire Maximum Pressure
Many times people incorrectly think the pressure molded on the tire sidewall, similar to what we see in this picture,


to be the maximum tire pressure a tire can tolerate, when in reality you should consider it the minimum pressure needed to carry the load indicated 
Tire companies design and test their tires to tolerate pressures much higher than the number molded on the sidewall. For regular passenger tires it is probably close to or above 150psi. Light truck tires will probably be a bit higher and truck tires higher yet. In almost all cases I am aware of, there is a good possibility that the wheel might fail from high pressure before the tire simply explodes from high pressure.

SAFETY WARNING  DO NOT TEST THIS YOURSELF. The explosive force can take out concrete block walls and could kill you.


The correct terminology for the pressure on the tire sidewall is: The tire pressure molded on the tire sidewall associated with the maximum load capability for the tire. Now this is admittedly a real mouthful so I can understand it being shortened to "Tire pressure associated with max load" or even Tire pressure molded on the tire sidewall. but it is incorrect to say or think that the pressure molded on the tire is the maximum the tire can stand.
Now it is important that you not confuse "The tire pressure molded on the tire sidewall associated with the maximum load capability for the tire." with the number that might be part of the tire "Safety Warning" 



many passenger and light truck tires have a separate warning about tire pressure not associated with the tire load capability. This has to do with the pressure used to "seat" the beads. This is the "pop" you hear in the tire store when the tech is inflating your new passenger tires.

Important Tire Safety information. If you do not understand the safety warning you should never be inflating tires from flat. Leave that job to the professionals.

Bottom Line
Tires can handle pressures higher than the number molded on the tire sidewall that is associated with the maximum tire load, so do not bleed down your tires when the hot tire pressure increases above the number molded on the sidewall. Pressure increases of 10 to 20% are not uncommon. Always inflate your tires to specified pressure when they are "cold". That means at air temperature, not having been driven on or in sunshine or even partial sun for at least two to three hours.

3 comments:

  1. Exactly....we run our 28ft class C tires with the max pressure of 80 psi in the rear duals and 75psi on the front tires. The pressure monitor sometimes show in the high 90 psi and high temps in the summer time. Never had an issue with good solid tires. We travel at 60 65 mph and have not seen any problems.

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  2. Sounds like you have a good plan. Your numbers are similar to mine.

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  3. Exactly said, it is always safe to observe the recommended tire pressure in hot temperatures. Most people have this doubt, is there any warning signs to recognize whether your tires require a substitute?. I too had that doubt, but I found a vehicle maintenance blog which has all the information we need to know regarding tire replacement. I think it will be a great help for people who really care for their car.

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