RV Tire Safety: What does the pressure number on tires refer to?

5

By Roger Marble
A clarification about the pressure number on a tire might be of help.

The pressure number molded on the sidewall of tires is NOT the “Maximum Allowable” pressure. It is the Cold pressure necessary to support the Maximum Load capacity for that tire. In reality, the pressure number molded on the tire sidewall is the Minimum needed to provide for the support of that load.

Increasing the cold pressure above the number on the tire sidewall will NOT increase the tire rated load capacity per industry practice, standard and guidelines.

If the pressure increases because of increased Ambient Temperature or because the tire gets hot from being in the sunlight, or the tire gets hot from being driven on, that increase is considered and accounted for by tire design engineers. The increase is about 2% for each increase of 10°F in tire temperature. Even a temperature increase of 100°F (20°F to 120°F, for example) would only result in about 20% increase in tire pressure, and undamaged tires can tolerate a greater pressure increase than 20%.

Note: I am not saying that you can heat a tire to above 190°F and not have problems, but those problems would be the result of high temperature degradation of the rubber and not simply due to pressure increase.

 

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

 ##RVT974

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Russ De Maris (@russ)
15 days ago

Roger, perhaps you could also comment on elevation change effects on tire pressure. We got to learn about it when we went from Quartzsite (900′ el) to parts of Nevada (6,000′). Thanks!

WEB
15 days ago
Reply to  Russ De Maris

I would like to hear what you learnt, cuz I will speak from Roger’s site and say “No difference”. Well there is a +2 or +3 psi difference, but generally the at the higher elevation the ambient is cooler, so lower pressure. But 2-3 psi diff. I would not care.
https://www.rvtiresafety.net/2011/07/altitude-effect-on-tire-pressure.html

Roger Marble
12 days ago
Reply to  WEB

Thanks for reading my blog.

Stefan trestyn
15 days ago

My problem is not an increase in temperature, It’s a decrease in temperature which decreases pressure

Roger Marble
12 days ago
Reply to  Stefan trestyn

Stefan, Did you read the blog post where I provided the actual math used? In the example the pressure in the tire would increase by 2.7 psi assuming normal barometric pressure. While we don’t know the temperature change as we don’t know the conditions where you started travel or at the top of the mountain pass you are driving but if the mountain pass is about 15F cooler then the pressure would drop by about 2.7 psi so that gives a net change of zero.

Basically if you watch your TPMS and you are running a few psi above the minimum you need in your tires I doubt you will ever need to adjust pressure due to elevation but you may need to add a few psi when it gets a lot colder.