By Roger Marble
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, let’s be sure we all are using the same definition for “ambient temperature.” For our purposes, we should consider it “the outdoor air temperature in the shade.”
An RV owner noticed 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. 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.
There followed more than 100 posts – which is not uncommon when tire pressure 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 the increase in pressure 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 that 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. But they mentioned that a tire pressure can be set when the tire was not “warmed” by being in sunlight or having been driven on more than a mile.
Adjusting pressure when traveling
A few offered information on how to calculate the amount of air pressure that needed to be added, but this concept quickly turned into discussions of pressure versus temperature formulas.
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.
There are charts on the internet that cover how to adjust tire inflation under extreme conditions, such as the RV being in a garage heated to 65° F but the outdoor ambient is way below freezing. I posted a chart last March, but I bet that there are not many RV owners that need this information.
Read more from Roger Marble on his blog at RVtiresafety.net or on RVtravel.com.
I confess to being undereducated on tire pressure/ temperature. If morning temps vary 10-30 degrees from noon temps would it be viable to delay departure until the warmer temperatures return pressure to the proper range? (Given the shaded space scenario) And that makes me wonder about the bulk of the driving time being in the warmer part of the day too. Like I said, I’m undereducated.
Hi, Ozzie. You say you’re “undereducated on tire pressure/temperature.” But you are smart enough to ask questions, and that’s very important and how you get educated. Good for you! Take care, and stay safe and healthy. 🙂 –Diane
It is best to inflate your tires to the recommended level before you start driving. Do not worry about the temperature hours in the future. It’s better to be a bit high (+ 5 to 10%) rather than ever running low. Check out my blog for more tire information and knowledge. http://www.RVTireSafety.Net
I’ve never adjusted the tire pressure in my life due to temperature change. Like he said the temperature was back to normal after a few miles down the road.
So your “cold tire setting” was too low if you had to drive a few miles to get them to the recommended pressure.
Kenny, your post isn’t clear. By “back to normal” do you mean it is back to your minimum requirement? As mentioned in the post and many times in my blog http://www.RVTireSafety.net There is absolute minimum inflation required for all tires and that is the pressure needed to support the actual load on the tire. That pressure is measured when the tire has not been warmed up by driving or being in direct sunlight. RVIA recommends the tires be capable of supporting 110% of the GAWR but again this is when the tire is at Ambient and not warmed up. As soon as you start driving the temperature increases and this will result in higher pressure reading when you use a gauge or your TPMS. If you start out below the minimum you are doing some damage to the tire structure. This damage is small but tires never repair themselves and all damage just grows over time and can accumulate to the point that hitting a pothole that was no problem when the tire was new, can result in a sudden failure later.
I was talking about the RV owner who said his pressue dropped 7 psi and then his was back to normal after a few miles down the road. I have a tireminder that after a few years of false alarms, bad sensors, and a few blowouts the same time it warned me and one time a had a really low tire after a rest stop and the minder never even going off I haven’t used it at all the last few years.
Maybe I’m wrong but I usually run a little heavy, not over weight though. So I put 80 psi in my 80psi rated tires and my temperature from day to day only varies 10 to 30 degrees. Usually only 20 degrees at the most.