Ask The Fit RV: Are Our Tires OVER-inflated?!?


We got a really good question on our RV Tire Inflation post, and I thought it deserved an answer in video form.  So, without further ado, here it is:  an “Ask The Fit RV” first:

 

I should confess that the reason I really liked this question is because I once asked it of myself.  I did the research and answered it to my own satisfaction, but apparently I wasn’t the only one asking the question.  The basic thought behind the question is:

“If you inflate your tires cold, and then they heat up, will they then be OVER pressurized?”

The answer is, in a nutshell, no.

The research I did told me one thing over and over again.  Every source I looked at, from tire manufacturers to the NHTSA, was always referring to a “cold” tire pressure.  And this wasn’t because they weren’t aware that your tires might heat up.  Quite the opposite – they knew about it, and were counting on it.  So, long story short, just remember this rule and you’ll be fine:

All official references to tire pressures are to “cold” tire pressures.  This means the tire pressure when the vehicle hasn’t been driven for 3 or more hours.

 

Yes, your tires will heat up, and yes, the pressure will increase.  But everyone in the tire industry knows about this, and they’re not likely to go over pressure and burst.  It’s actually far more dangerous to have under-inflated tires than over, so don’t under-inflate and count on the heat to bring the psi up.  That’s a recipe for disaster.

There’s some other useful info in the video as well, so give it a watch!

 



James is a former rocket scientist, a USA Cycling certified coach, and lifelong fitness buff. When he's not driving the RV, or modifying the RV (or - that one time - doing both at once), you can find him racing bicycles, or building furniture, or making music. In his spare time, he works for a large IT company.


    23 thoughts on “Ask The Fit RV: Are Our Tires OVER-inflated?!?

    1. Karen

      We are looking at an ERA, but my concern is the shower for my husband. He is 6’1″ and 220. Do you have enough room in your shower. We love it.

      Reply
      1. James - Post author

        Plenty of room in our shower!
        (I mean, that’s not an invitation or anything. I just mean there’s plenty of room in there for me…)

        Reply
    2. Derrick

      James and Stef
      Thanks for answering my question. Really appreciate it.
      Now my wife officially calls me a nerd and is completely agreeing with you two! 🙂

      Reply
    3. Dave Andrews

      Tire pressure is also part of your vehicles suspension setup. I always drop my pressure to half the recommended psi (for more traction and comfort) when going off road at less than 20 mph. Once I get back to the pavement I re-inflate to spec with my onboard air compressor and top off the next morning.

      Reply
      1. James - Post author

        We don’t do any off-roading, so I can’t comment on running with pressures that low in those situations.

        Clearly though, tires at half psi aren’t safe at all for over-the-road travel at speed.

        Reply
    4. JJ

      James, I LOVE that you brought up the Ideal Gas Law (and was sad that you were shot down for the nerdiness). More science, please!

      Reply
    5. Edith R. Northam

      OMGoodness! THANK YOU times a million! I’ve worried about this for years!!! And I’m absolutely serious about that! I’m 77 y.o. and have been checking my tires pressure & filling them when necessary for at least 50 of those years! But EVERY SINGLE TIME I DID, I alway wondered – & worried – that I might be overfilling them. At present I have a ’97 Ranger, PSI 35 (door jamb) and, yes, I realize it’s not an RV!!! – but now I know the “why” and “when” about tire pressure. (I don’t get up at 4:30 a.m. but I always – intuitively – thought I should ck. pressure in the coolest part of the day!) Thank you WAY more than I can say!

      Reply
      1. Stefany

        Awww so nice, Edith! Look James, you did some good! And Edith I’m with you, I had no clue underfilling was the big danger, not overfilling. Learning something new; LOVE IT! xoxo

        Reply
    6. Mike

      Great video!

      Do you have a link to the tireminder?

      How often do you typically have to add air?

      What are your thoughts on traveling with a portable tire inflator?

      Reply
      1. James - Post author

        This is the Tire Minder that we use: https://amzn.to/2wuxVHu

        I don’t find that I’m adding air very often. I will have to add air a couple times as the seasons shift to colder temperatures though.

        And we *always* carry a portable tire inflator. (Meaning, we always travel with a bike pump…)
        We also carry the inflator/sealant package that was provided with the new RV. But we’ve never used that one. I just use bike pumps on the road.

        Reply
    7. Dan

      I usually check my tires early in the morning after letting it sit overnight too. The tires are guaranteed to be as cold as possible, and I’ve also found that late afternoon on a hot day, the side facing the sun will have 1-2 PSI more than the shady side just due to the sun heating up the tire.

      Reply
      1. Stefany

        Would you think less of me if I admit I didn’t even know it was a real thing? I THOUGHT HE MADE IT UP!!!!! #ihaveotherstrengths

        Reply
    8. Sam Pellegrino

      1. I was always told to never “bleed your tires down” when they are hot. Some of us might get alarmed at the pressure rise on a hot day, and think bleeding the tire(s) might be a good idea. Your thoughts on that?

      2. So, if you are driving east-to-west, for example, and the Driver’s Side tires are in direct sun all day, do you find those tires have much higher pressures and temps than those that are running “on the shady side?” Does it matter if they do?

      3. Lastly, how much of a part does “pavement temperature” play in increasing the internal tire pressure? Is it a concern? There’s always this fear of “crossing the desert in the heat of the summer.” We see blown tires and retreads strewn all over the place.

      Reply
      1. James - Post author

        1. Correct. Never “bleed your tires down”. That’s a recipe for under-inflation, and a bad idea.
        2. I have noticed sunny-side/shady-side temperature differences. This is not usually more than 15-20 degrees at the most, which translates into less than 5psi difference. (7% on a 65psi tire)
        3. Pavement temperature will certainly help heat up the tire. Air temperature, friction, pavement temperature… they all play a part. Those retreads you see on the side of the road were more likely from a defective or under-inflated tire than from one that overheated and blew because it was too hot out.

        Reply
    9. Nathan

      When I was younger I worked as a lot guy at a Toyota dealership. When we would get new cars in, strait off the truck, they would have their tires inflated to like 90-110 psi. Sometimes we had to drive them to the storage lot a few blocks away with the overinflated tires and it did feel weird. I guess the idea was to keep the tires from flatspotting while waiting to be sold. It was on out checklist 3 times to set the correct tire pressure before they got out to the sales lot.
      Since then I always get a kick out of people that worry that their tires will explode if theyre set 5psi past the recommendation.

      Reply

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