Fiction
You might recall being taught in school that as you travel to higher elevations atmospheric air pressure decreases. For those that can’t remember, the following provides a refresher course.
“As altitude rises, air pressure drops. In other words, if the indicated altitude is high, the air pressure is low.” Per the folks at National Geographic.
The folks at National Geographic go on to tell us, “This happens for two reasons. The first reason is gravity. Earth’s gravity pulls air as close to the surface as possible.
“The second reason is density. As altitude increases, the amount of gas molecules in the air decreases—the air becomes less dense than air nearer to sea level. This is what meteorologists and mountaineers mean by “thin air.” Thin air exerts less pressure than air at a lower altitude.”
Some effects of thin air at high altitudes
You have undoubtedly experienced the effects of thin air during your RV travels in one of the following ways:
- The engine propelling your RV struggles to produce enough power to get you up and over a high mountain pass. (This is due to less oxygen to support combustion.)
- You become easily winded while exerting yourself at high altitudes. (Less oxygen entering your lungs.)
- Your absorption refrigerator may not want to operate on propane, as outlined here. (Less oxygen to support proper combustion.)
- The plastic ketchup or mustard container that you haven’t opened since you left the lowlands becomes an artesian well automatically spewing out the contents when you open it in the mountains. (The air pressure in the container is now higher than the exterior air pressure, thus expelling the contents when opened.)
- The bag of unopened chips that you brought from your seaside home now appears 8 months pregnant. (The air pressure in the bag is now higher than the exterior air pressure, expanding the bag like a balloon.)
The last two examples clearly illustrate what happens with your RV tires when you gain altitude. As the atmospheric pressure surrounding the bag of chips, condiment container or your RV tires decreases, the air pressure measurement within those sealed items increases.
Verify increased PSI at high altitudes
This can easily be verified by filling your tires to the recommended air pressure at home, then recording the pressure with the use of a tire gauge, which typically displays PSI (Pound per Square Inch). Once you are atop a high mountain pass, measure the pressure again and compare it to the reading from home. You will likely see an increase of 2-3 PSI. It all boils down to pressure differential, as RVtravel.com’s tire expert Roger Marble explains here.
“I’d never thought about this until I had a P.O.S. sleep number bed. I had it set at a comfortable number halfway to full when I was camping in the prairies when I got into the mountains the bed was straining at its seams ready to explode.” Comment to the article mentioned above further illustrates that air pressure in sealed items increases as atmospheric pressure decreases at higher elevations.
While there are many more nuances that can be discussed about tires, pressure and altitude (Roger covers many of them in the article mentioned above), the fact is, tire pressure measured with a tire gauge increases at higher altitudes. They do not lose pressure in thin air.
Hope this clears the air (pun intended) regarding tire pressure changes with altitude.
To learn more about high-elevation travel in your RV and all that is affected, click here.
Now, some questions for you:
- Is there a reoccurring half-truth you keep seeing online that you would like to see addressed?
- Were you taught something by other RVers that turned out to be bad advice?
- Have you recently read something that left you wondering, is that true?
- Do you know something to be true, but none of your RVing friends believe you?
Please share your comments using the comment box below and we will do our best to provide the facts in a future Fact or Fiction entry.
Dave will be speaking at the 2023 America’s Largest RV Show in Hershey, PA, September 13th – 17th. He would love to meet RVtravel.com readers that are attending. Feel free to introduce yourself after one of his seminars. Breaking News – Those attending Dave’s Dry Camping Tips and Tricks seminar (10 a.m. daily) can enter to win a soft start device. One given away daily!
Test your knowledge some more with these previous Fact or Fiction questions:
- A propane furnace emits lots of moisture
- Your RV’s tank covers should never be removed
- If you see these on your RV, do not use it in winter!
- Outside temperatures can be too cold for an RV refrigerator to cool
- Never plug in with a 20-amp extension cord
- Doing THIS is the number one cause of RV fires on highways
- Propane gas has no odor
- New RV refrigerators are not designed to operate on propane above 5,500ft altitude.
##RVT1117
Dave you didn’t give me credit for using my quote
Hi, Seann. Do you want me to put your name in the post after your quote? I’ll do it if you want me to. Have a great day. 😀 –Diane at RVtravel.com
Ok so you are giving some confusing info here. To verify your tire pressure increase check it when you get to the top of the mountain. Well if you’re driving your RV then you will have higher tire pressure from the heat generated from the road. How can you differentiate the two?? Is it heat or higher altitude?? Or both? Just a thought..
Both…one would have to let the tire cool to the same ambient temp it was when originally checked to compare the altitude effect alone.
Technically all tires lose air, and thus air pressure, until they equal the outside air pressure. Thus we have to add air every so often. If the outside air pressure is higher they tend to loose air slower than if the pressure is lower.
We tent camped about 40 years ago. Brother-in-law took us to a fishing camp site well above Butte, MT. Not wanting to completely deflate our air mattress, we let enough air out to fit inside my brother-in-law’s topper equipped truck. We followed in our car. About 2/3 of the way up, the topper door popped open and camping gear began tumbling out! Yep. we didn’t remove enough air from that mattress!
In the case of vehicle tires, cooler air at elevation partially offsets the reduced air pressure outside the tire. Don’t let air out of your tires, or you better have a compressor on-board to restore the air on the way down!
I think there needs to be more/better explanation on hitch weights and towing. Russ and Tiña De Maris did an article about it not to long ago that I found confusing. Trying to apply the math ended in ridiculous results. Todd with NRVTA did one this week on YouTube that was pretty good. I have my scale tickets from my last trip and am going to check and compare that to the homework I’ve done. Since I’ve added Lectric bikes and Swagman carrier to the rear of the trailer sway has increased a little. It could be better. I think that addition moved a hundred pounds off the hitch. I may be wrong but I’m still working on it.
2017 s225rbs Shadow Cruiser by Cruiser RV.
Thanks
I don’t think the folks at National Geographic have it right. There’s really only one reason air pressure goes down with altitude. Air pressure is a measure of the weight of a column of air with a given cross sectional area above a given altitude/elevation. For us that’s a one inch cross sectional area column thus pounds per square inch, psi. Pressure gauges measure the difference in pressure between an enclosed vessel, the tire in this case and the outside or ambient pressure. Of course gravity causes the weight of this column of air. Density of air decreasing with altitude, though is just a result of this reduction of the amount of air above that altitude.
The temperature drop at higher altitude is in direct collation to the air pressure drop resulting in a net zero effect. Tires lose about 1 psi per 10 degrees of temp drop.
Air pressure does decrease with lower temps, 10% for a 27.3C / 49.1F temperature change, I.E. 0C / 32F <=> 27.3C / 81.1F. If you have high humidity air in the tires this will increase the change.