Here is a post I read recently about tire pressure and temperature changes:
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 temperature 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. If I am going to adjust tire pressure, I will only adjust it when I am done traveling for that day. Usually the next morning 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 driven 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.
Read more from Roger Marble on his blog at RVtiresafety.net or on RVtravel.com.
 ##RVT1060
I have always set tire pressures to the spec provided by the vehicle manufacturer and have had no problems. I don’t understand all of the constant discussion. Has the non engineering public been provided with too much information and they now think they are experts?
This is harder than Japanese arithmetic.
Let me know what you need translated, Impavid. My sister’s granddaughter, grandson-in-law, and brand-new great-grandson live in Japan. I’m sure Jessica could help you with your Japanese math.🤔 Have a good afternoon/evening. 😀 –Diane
Thank you, Roger!
Set pressure to door sticker specs when tires are cool and shaded.
Plus 10% at beginning of day. Monitor with TMPS. Know your load. Simple enough.
Question how many people out there calculate their minimum cold inflation?
Roger. I really appreciate your expertise and information. But please change your picture. For years I’ve thought you looked like you were sitting on a cactus.
This is all wrong!
Tire manufacturers set a Max pressure (cold) I run 5 psi under that, there is expansion figured into the max cold pressure from the manufacturer adjusting pressure every day or more than once a day is a waste of time and energy.
What part is all wrong? The original post or Rogers comments? Roger engineered tires. Do you have tire expertise that you care to share? I would say inflating tires to 5 psi below cold inflation pressure is not a good idea on a multiple axle trailer. I have no tire expertise but that opinion is based on Rogers posts.
Sorry Chris but someone gave you incorrect information. The information on a tire sidewall is in fact the Maximum load capacity of that particular tire. The inflation number is the inflation required to support that load. Increasing that inflation will NOT result in any increase in load capacity. Also, don’t forget that the inflation number is for when the tire is at ambient temperature and not warmed up by either being driven on or placed in direct sunlight for the previous 2 hours. We tire design engineers do account for the pressure increase seen when tires are run fully loaded in the Sunlight so you should never run lower inflation and depend on the increase in operating pressure to get up to the pressure required to support the load.