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Friday, July 8, 2022

Another question and post on adjusting pressure due to temperature changes

 Reviewed another comment on tire pressure changes due to temperature changes:

The original post
Very informative thread. If I may throw in my recent experience...

One thing I do not see mentioned is how outside temperatures can affect tire pressures. Last Nov-Dec, I had a R/T excursion from upstate SC to the Keys.

Outside temperatures ranged from the mid-30's to the 90's and I found myself either adding or reducing air not only prior to every trip, but on a few occasions during mid-travel. The tires on the side of the trailer facing the sun would increase by 2-3 lbs. alone. This was worrisome as I was constantly attempting to monitor and maintain a constant psi in the tires.

The point I'm trying to make and what I've discovered is that having a margin of safety, especially in temperature extremes cannot be understated.

My reply:

I have covered the effects of a change in Ambient temperature in great detail in this blog with some 40 posts on Cold Inflation pressure or similar related topics. I have also covered my reason for recommending that people run a +10% margin on inflation over the minimum needed to support the load so they do not have to worry about adjusting pressure every time the Ambient changes a few degrees.

Bottom line: Once you have learned the MINIMUM inflation to run on your RV based on actual scale measurement of the heaviest loading expected and consulting the load inflation tables, you simply add 10% to that  pressure number. With tire pressure changing at about 2% for each change in Ambient of 10°F, that 10% margin should cover you for a drop of as much as 40 or 50 degrees.

Using the readings from my TPMS in the morning of each travel day, I can monitor my pressure change and know if I need to plan on adding pressure if there has been a significant temperature drop or just keep an eye on the pressure if it has gone up. Most days I make no adjustment at all.

You do not need to worry about a change in pressure of + a few psi as long as you know you are still above the MINIMUM inflation and have not seen a pressure increase of 20% or more.

I don't see myself ever adjusting pressure in the middle of a travel day. I am going to adjust tire pressure, I will only adjust it when I am done traveling for that day. Usually the next AM when the tires have cooled down to the surrounding Ambient temperature.
Remember that the inflation pressure in the tables or on your RV Certification sticker are when the tire is not warmed up from being driver or in direct sunlight for the previous 2 hours.

In my post on how I program my TPMS I cover the margins by setting the Low pressure warning level to protect the tire from ever being lower then the minimum required. My high pressure warning is set to +20 to + 25% as undamaged tires can easily tolerate that higher pressure assuming they were set correctly in the first place.


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