I ran across a series of posts on an RV forum on the need to adjust tire pressure because of changes in ambient temperature.
First, it is important to understand that we are talking about the “Cold Inflation Temperature,” or CIP, and not the temperature reported by our TPMS (tire pressure monitoring system) when the tire is running down the road. That would be the “Hot Inflation Pressure.”
There is almost no reason for the average user to be concerned with or talking about the Hot Inflation Pressure. The Load & Inflation tables are ALWAYS referring to the CIP. Also, let’s be sure we all are using the same definition for “ambient temperature,” which, for our purposes, is “the outdoor air temperature in the shade.”
An RV owner said that his tire pressure had dropped based on his TPMS readings, almost 7 psi when the temperature dropped to the 40s. He did not provide his “normal” pressure or temperature, but he did claim, “But within 10 driving miles they are back to normal pressure.” He asked if he needed to add air when it is cold to bring pressure back to normal.
Lots of posts in reply
There followed more than 100 posts, which is not uncommon when tire pressure or temperature is the topic. As expected, some offered correct information on the need to adjust pressure to accommodate the normal drop when it gets cold, or increase the CIP when the ambient temperature rises. This immediately led to various suggestions on the amount of adjustment needed.
I was heartened to read the comments from many that knew it was important to adjust tire pressure to compensate for changes in ambient temperature. There were a couple of people who thought there was some special temperature for adjusting pressure. Replies to these people were quick and correctly pointed out that there was no special temperature such as 68 F or 72 F when tire inflation could be set. It was noted that tire pressure can be set when the tire was not “warmed” by being in direct sunlight or having been driven on in the prior couple of hours.
A few people offered information on how to calculate the amount of air pressure that needed to be added. However, this concept quickly changed into discussions of pressure versus temperature formulas.
Bottom line
Tire inflation pressure will change about 2% for each change in ambient temperature of 10°F (6°C).
I advise that you use your TPMS to check inflation at the start of each travel day. This might be in the morning, but whenever you check you need to ensure that no tire has been warmed from being in direct sunlight for the previous couple of hours. Then set your tire inflation when the tires are at ambient temperature. It’s just that easy. I have found that TPMS pressure readings are reasonably accurate at +/-2%.
There are charts on the internet that cover how to adjust tire inflation under extreme conditions. An example is the RV being in a garage heated to 65° F but the outdoor ambient temperature is way below freezing. But this would be a special situation that almost no one needs to consider. I posted information on this extreme situation HERE, but I bet that there are not many RV owners that need this information
Roger Marble
Check out my Blog www.RVTireSafety.Net
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Another fact based excellent article from Roger. We need more like this.
Interesting information, thank you.
Thank you, Roger! 🙂 Have a great week, safe travels, and safe stays! 🙂