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Friday, October 21, 2022

"Optimal Inflation" or not?

 Many think the RV sticker (aka tire placard)








or in tire Load & Inflation tables







PSI number is an "Optimum" pressure when it is in fact, it is the MINIMUM pressure needed to support the GAWR which assumes a perfect 50/50 side to side split which is unrealistic.

We tire engineers want to ALWAYS protect the tire from overload. We know that pressure will change with changes in the Ambient (air temperature in the shade). We also know that tires will always get warmer when they are driven.

The pressures found in the Load & Inflation tables are almost universal across all tire companies (a handful of Michelin sizes differ by 5 psi or so, so not significantly different) and they are not playing games with tire engineering science.

Unless there is a specific reason, which should be mentioned in a post, we are ALWAYS talking about "cold" inflation pressure as we know that tire pressure changes by about 2% for each change in temperature of the tire as I covered in these posts.

The Short answer to all tire inflation questions.
1. Get the weight on each RV axle from a truck scale (or similar)

2. If you do not get individual tire position weights (aka 4 Corner weights) assume the heavy end of each axle is supporting 51 to 53% of the axle total.

3. Consult tire Load & inflation tables to learn the MINIMUM inflation to run based on the heavy end of each axle.

4. I suggest that your cold inflation on all tires on that axle, be _at least_ 110% of the MINIMUM psi found in the table in #3 above, but do not exceed the max inflation rating for your wheel. (number may be on the wheel or you may need to consult RV company).

5. *Always* run a TPMS with the low pressure warning level set to the pressure in #3 above ( this might take some calculation effort as different TPMS have different ways of setting the warning level.



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