Tuesday, September 21, 2021
Tuesday, September 21, 2021

RV Tire Safety: How cold does it have to be to set tire pressure correctly?

By Roger Marble
With thousands of new RV owners out there, the answer to the question of “How cold does it need to be for me to check tire inflation” continues to come up. This will be new information for some and a refresher for others.

Some people want to refer to a temperature compensation chart and go through some calculations to learn the “correct” tire inflation when it is 82 F or 62 F outside. This is not what you should do.

Tire pressure is not based on any laboratory standard temperature (some claim 70 F or 68 F). It is based on the tire not being warmed from either use, i.e., being driven in the previous two hours, or from being in the sun for the previous two hours. Even partial sun can affect the reading.

Classical “temperature in the shade” is the “ambient” temperature we tire engineers are talking about. Not temperature in a theoretical laboratory.

When is the best time to check cold inflation pressure

It is correct to say, “The BEST time to check cold inflation pressure, or CIP, is the FIRST thing in the morning BEFORE the day’s temp has had a chance to increase and BEFORE the sun has had a chance to shine on the tires and BEFORE you have used the vehicle.”

With many people installing a tire pressure monitoring system (TPMS) that provides a temperature reading to the driver for the first time, some are surprised when they see that both temperature and pressure increase as they drive. Please remember it is NOT correct to bleed pressure from a “hot or warm” tire after you have started that day’s travels.

As I have covered in other posts, the tire pressure will change by about 2% for each change of 10 F. There are some pages on the internet that say 1 psi for 10 F, but those are talking about standard 36 psi passenger tires, not 80 or 100 psi RV tires.

I suggest a +10% “cushion” on the required inflation

Now, if you are driving from a campground, let’s say, on top of Pike’s Peak and stop for lunch for two hours in the shade in Flagstaff where it is 90 and check your air, you might find a change of a few psi. You could adjust your pressure before continuing to Phoenix, where it is 120 F. But I don’t bother to adjust inflation by the 1 to 3 psi variation I observe day to day. In my mind that is too much work. This is one reason why I suggest a +10% “cushion” on the required inflation as that eliminates the need to chase inflation with every change in ambient of 15 to 20 F. We tire engineers know that tire temperature and pressure will increase and we have taken that into consideration when we design and test tires.

What I run my tires at

NOTE: My personal CIP is 75/80 F/R on my Class-C MH. Both of these pressures are more than 15% above the minimum pressure needed to support the measured load on each tire – so I have a nice “cushion.”

I usually wait till I am home and am getting ready for the next trip before I adjust my inflation to my personal CIP. So I simply monitor the running inflation pressure. It goes up and down as ambient temperature, driving and sun exposure changes the inflation. My TPMS will warn me of air loss – so all is good as I motor down the highway.

I hope this info helps some of the first-time RV folks out there. If you are an “ol’ timer,” you might direct the “newbies” to this post when they ask about setting tire pressure.

Have a tire question? Sign up for Roger Marble’s new Facebook Group: RV tire news, information and discussion, hosted by RVtravel.com and moderated by Roger. He’ll be happy to help you.

Read more from Roger Marble on his blog at RVtiresafety.net or on RVtravel.com.

 ##RVT1014

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Tsippi
30 days ago

Very good article. I just want to be sure I understand. If the manufacturer recommends using the pressure stated on the door — in the case of my Class C, 67psi in front and 64psi for the duallies — you would generally run them at a higher psi? I’ve always just run them at 62 and 67, but it means that at high altitude after a cold night, especially if I’m up on legos, the TPMS warns me that my pressure is more than 7% too low. Frankly, I’ve always just ignored those low pressure situations, since the tires will warm up soon and changing tire pressure every time I change altitude seems like way too much work. I would love to hear your advice.

Michael Galvin
30 days ago

There is no campground on top of Pikes Peak.

— Michael, Colorado Springs

Admin
RV Staff (@rvstaff)
30 days ago
Reply to  Michael Galvin

Ha ha. Thanks, Michael. I think Roger was just using that as a possible scenario, if there were such a thing. It’s been reworded. Have a good night. 🙂 –Diane

Luke
30 days ago

Great refresher, Roger. Now, let me run this past you… During our travels, if we’re going to stay at an RV spot for more than a few days, I’ll release the towing pressure of my tow rigs tires down to 60 lbs in the morning all around. I then remember this setting. When I’m ready to move to our next destination, I’ll check the pressure again and most often find (because it’s usually in the afternoon or after we’re all done with our side trips) that all the tires have increased in the area of 5 pounds or more. While towing our 5th wheel, I run the suggested pressure of 80 lbs in the rear. I then add that 5 pound or more difference onto the 80 lbs and inflate the rear tires to that 85 pounds or more, assuming that when they cool, they’ll be right at or near the target 80 pounds. Your thoughts? Good, bad or indifferent?

Roger Marble
30 days ago
Reply to  Luke

Sounds like a bit of work. BUT as long as you re-inflate the tires back to a pressure that ends up at 80 when the tires are not warmed up I don’t see a problem.

Carol
1 month ago

I’ve heard a lot of this discussion on a FB page for a particular Class C. Many people insist that the tire pressure is based on the actual weight of the vehicle and should be changed based on that. So if you are carrying a full load of water vs empty, etc. the psi should be adjusted. Any thoughts? Thanks!

Roger Marble
30 days ago
Reply to  Carol

A 40 or 50 gal water tank can add 500# weight. I feel it’s better to get weighed when the Rv is at its heaviest and with those numbers consult the inflation tables. DO the appropriate math as I have outlined in my blog and have a single set of inflation numbers. If you can keep it simple you are more likely to keep the tires properly inflated.

Jim
1 month ago

Could you explain how you use your 10% cushion? Do you bleed the tire pressure if the TPMS shows 10% above your CIP? Or are you saying the RV manufacture recommends a CIP of X so your personal CIP is within X to X +10%? Or are you saying when traveling each morning you check the CIP and don’t change the tire pressure if it is within your personal CIP to CIP+10%?

Roger Marble
30 days ago
Reply to  Jim
  1. I do not adjust my inflation each day. 2. I established my minimum cold set pressure to be the pressure from the tables + 10% 3. I only think about adjusting inflation when I get down to the minimum cold set pressure + a couple of psi. 4. Knowing what the weather was (Ambient temperature) and what I expect it to be the next day I can either leave things as they are or if I expect ambient to stay cool I might add 3 to 5 psi to get closer to my cold set pressure goal. I try to not make setting pressure a daily task. The +10% will fluctuate +/- 5 psi and I leave things alone. The tires can handle the extra few psi. What I really want to do is to protect and prevent running at the minimum inflation specified in the tables.

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