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Saturday, March 11, 2017

Question on Maximum tire pressure

Got an email stating the writer was concerned and a bit confused on the Maximum inflation a tire can have. He had heard about people having "Blowouts" and after installing a new TPMS and seeing the pressure increase was concerned his tires might explode.

I can understand the confusion as people read the tire sidewall and in some cases see the words 'Max Inflation". This is NOT the max operating inflation but in reality is the inflation needed to support the max load the tire is rated for. It is also important to remember that unless a tire engineer is specifically talking about "hot inflation" we are talking about the "Cold" tire inflation when the tire has not been warmed by either running or being in direct sunlight over the previous couple of hours. Technically this means the tire is the same temperature as the surrounding air or "AMBIENT" temperature.

I previously covered the effect of temperature on tire pressure and the "Ideal Gas law" so we know that for each change in temperature of 10F the tire pressure will change by about 2%. This means that when the tire temperature increases by about 50F we can expect the pressure to also change by about 10%. We need to remember that the TPMS sensor is being cooled by outside moving air so the hot spot on the tire is actually much warmer than the indicated temperature. This is one reason why we many times see pressure increase by 15% or more.

True tire "Blowouts" are usually caused by too low a pressure which flexes the tire sidewall and results in fatigue failure of the steel body cord or melting of the Polyester cord in LT, P, or ST type tires. The separation of the tread and belts is sometimes mislabeled a "Blowout" which leads to confusion. Separations have a different cause than simple loss of air pressure.

Back to the original question. Tires are designed to handle significant increase in pressure, most in the range of 200% of the pressure marked on the tire sidewall.

BOTTOM LINE Always ensure your tires are properly inflated and the use of a TPMS is, in my opinion, the best way to  not be surprised by a puncture or air leak.


Send your questions to me at  Tireman9 (at) gmail.com


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5 comments:

  1. and a TPMS is ....

    ReplyDelete
    Replies
    1. Tire Pressure Monitoring System -
      Either internal or external sensors relay individual tire pressures to a monitor in the vehicle (normally to the driver's position)

      Delete
  2. I understand the max pressure for the max load rating, but what is the correct pressure for normal minimum loads on a normally empty (pickup truck) tire?

    ReplyDelete
    Replies
    1. RTFM... In this case, open your driver door and look on the edge sticker for recommended pressure of each axle. This recommended pressure will often be less than the max safe pressure.

      Delete
  3. With many pickups the owner's manual has two inflation recommendations. A "Light" load and "Full" or "Heavy" load.

    ReplyDelete

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