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Friday, March 18, 2022

Another post on Cold inflation. Is there just TMI?

A few times each week there are posts on various RV forums asking about tire inflation. There continues to be many  readers confused by the words "Max Cold Inflation" on the sidewall of many tires. This wording, while confusing, is mandated by regulation from DOT so don't blame the tire companies. You are more than welcome to write to      National Highway Traffic Safety Administration   at 1200 New Jersey Avenue, SE ,    Washington, D.C. 20590          and ask them why they require the marking say "Max xx psi" when they know that all tires warm up when in use and that many will have inflation above the stated "Max" soon after we start driving and that many people then bleed the tire pressure down to get below the stated "Max". This bleeding of hot air pressure has resulted in numerous tire failures.

As readers of my blog you know you should NEVER bleed down the pressure in hot or warm tires and the only time you might lower tire pressure is after you have been parked away from direct Sunlight and for at least two hours, and have moved to a location that is much warmer than where you were parked the day before your travels.

 Despite the information in my posts, some folks want to play the game of trying to adjust the tire pressure for the location they are traveling to. This is not the proper method of establishing your goal "set pressure" even if the expected "future" ambient is significantly different than the ambient where you are starting your travels.

 I'm not sure why this topic seems difficult to understand but maybe I'm just too close to the topic to see the confusion. I have over 25 blog posts that mention "Cold Inflation". THIS link will display a dozen of those posts if you need a review.

 I suppose one problem may be that with the introduction of TPMS many people are now getting a bit of "Information overload"  as they watch the pressure and temperature readings from each tire go up and down as they drive. This may be the TMI I spoke of in the title of this post.

I suggest you just stick to setting the pressure on the morning (before driving and generally before sunlight has hit the tires) of your travel day. Don't try and second-guess what the ambient temperature will be tomorrow and hundreds of miles away.

I have posts on how I suggest you learn what your "Set Pressure" should be. The procedure is a little different for motor vehicles (cars, trucks and motorhomes) vs trailers.

Generally trailers need to be running higher inflation and/or lower load levels than motor vehicles because of the higher level of Interply Shear that is inherent in multi-axle trailers.

For all users, I advise that the "set" pressure be at least the minimum in the load inflation tables for the measured load +10%.

For multi-axle trailers, I suggest you follow the inflation shown on the Certification sticker but you should confirm your actual axle load is no more than 85% of GAWR if you want a chance of getting better tire life.

Motorhomes should follow the Certification Sticker inflation until they have confirmed the actual loads on their tires, then consulting the load Inflation tables identify the MINIMUM tire pressure  they should ever run. I recommend you then add at least 10% to that inflation with a +15% Reserve load capacity being better.

Remember we are trying to always protect & prevent the tires from ever being in an overload or low inflation pressure condition when we are setting the temperature.

A tire with inflation higher than x psi will generate less heat than the same tire with the inflation lower than x. As you drive and your tire heats up, the pressure will rise but with the increase in pressure the amount of heat generated will decrease so the pressure will stabilize.


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