By Eric Johnson
TechnoRV
In the past 5 years there’s been a large increase in RVers who monitor their tire pressure with a tire pressure monitoring system (TPMS). When you have a TPMS and you can see your tire pressures in real time you start to realize very quickly that tire pressures can vary over a 24-hour period.
Let’s say it is travel day and you check your tire pressure at 8 a.m. and the ambient temperature at the RV park is 70° F. The pressure measured using your TPMS or calibrated gauge is exactly 100 psi. For this example, let’s say that 100 psi is the correct tire pressure that you should be running in your tires.
Now you are on the road and within a few minutes you are on the interstate traveling at 65 mph. Within five minutes of leaving the RV park, you notice that your TPMS is showing your tires at 107 psi. You keep driving and within 20 minutes your tires are now reading 112 psi while the outside temperature is still 70 degrees. Thirty minutes later the tire pressure is still 112 psi, but as the outside temperature rises, you notice even more rise in PSI and now you are up to 118 psi.
Interestingly, the side of the RV that the sun is shining on has pressures that are a bit higher than the side without the sun shining on it. At this point your tires have reached a steady state condition, but will they stay at this pressure assuming the outside temperature remains the same? We have already established that the outside temperature will affect your tire pressure, but what else?
The road surface you are traveling on will have an impact on the tire pressure as well; for instance, the difference between concrete and asphalt. The surface temperature of asphalt is usually hotter than concrete and may increase the tire pressure another one or two psi.
VEHICLE SPEED CAN INCREASE the tire pressure even further. Running at 75 mph versus 65 mph will generate even more heat and the tire pressure will rise even more. If you have dual tires, then you may also notice that your inside duals can run a little higher on the pressure side. This is because the inside duals have less air flow and therefore run a little hotter, and that increase in temperature can have a small effect on the pressure.
So, the big question here is should you be concerned that your tire pressure increases 15%, 20% or even 25% from your cold tire pressure? The short answer is NO. Tires are designed to take all these load, speed, and temperature variables into account when a commercial radial truck tire is designed, developed, and tested.
THIS IS THE REAL WORLD and is why all tire companies clearly state in their literature to never check a hot tire for pressure because you will think that the tire is overinflated when the air pressure is exactly where it should be. Don’t take air out of a hot tire. A truck tire can take four to six hours to revert to its original pressure. You simply do not know where in the cycle you are checking the tire pressure. The recommendation is to check your tire pressures first thing in the morning after the tire has cooled down overnight.
We have talked about tire pressure increasing, but what about tire pressure decreasing? Cold weather can create a different challenge as it relates to tire pressure. As an example, a tire that has cooled down after running all day and measures 100 psi at 70° F will lose pressure if it sits out overnight and the temperature drops to 20° F. When the tire is checked in the morning, you will find only 90 psi in the tire because when the temperature drops, so does the tire pressure. Every loss of 10° F equals a loss of two psi. Remember, tire inflation charts are based on ambient temperature of 68 degrees and do NOT include any inflation pressure build-up due to vehicle operation.
Another obvious reason your tire pressure may go down is because you have a leak. This low-pressure situation is among the most serious that you can encounter. Heat is a tire’s worst enemy. It is when a tire is running underinflated that an excessive amount of internal heat is generated due to the increased sidewall flexing and longer tire footprint (more rubber on the road). An underinflated tire is always much more serious to the tire’s health than a tire being a few psi over-inflated. Excessive heat will eventually lead to tire failure. Once a tire goes north of 200 degrees then the compounds in the tire start to break down and this is when a tire blowout can occur.
This is why we 100% strongly recommend every RVer run a quality TPMS. A good TPMS will monitor temperature and pressure. Since high temperature and low pressure are the two leading indicators of a future blowout, by monitoring these points of data you can be warned of problems to hopefully give you time to pull over and prevent the blowout. We recommend the TST Tire Pressure Monitoring System and have used this system for the past 5 years. Check them out if you do not already have one.
I have checked my tires when cold or at ambient temps in the mornings and have found that the tires on the sunny side always are a little higher pressure than the ones on the shady side. What to do, or how do you compensate.
Essentially the ambient temperatureon each side is different causing the pressure differential. So no need to do anything.
No. You should not do anything to lower the pressure on the sunny side tires. Our advice is to check your pressure when tires have not been driven or and have not been in direct sunlight for the previous two hours. There are a number of posts with more details on setting and adjusting tire pressure on http://www.RVTireSafety.net
This was indeed a very useful and informative article. Clear, well written and easy to understand, without all the ‘engineering speak’.
Thanks folks!
I totally agree, Tony.
Glad I read this. I set my pressure to 80 psi and then watch it go to 90/92. Always worried that’s too much. I guess now I can quit worrying.
Traveled from Discovery Bay, CA [elevation 10′] to Truckee, CA [elevation 7,200′]. RV tires in the morning were at 70 psi in Discovery Bay. The next morning in Truckee they were under 60 psi. combination of altitude and colder morning temperatures. Added air from portable pump. Altitude and temperatures can change pressures. Daily morning check when traveling is VERY important.
The altitude doesn’t change your tire pressure but it does effect the gauge accuracy. There are charts to show how much accuracy is affected per thousand feet. There are special, expensive gauges that work at altitude.
For those that want the details and “Engineer Speak” you can check THIS blog post.
Do you adjust the air pressure every morning in order to attain the proper tire condition? If you awake and find that your tires have lost air pressure due to air temperatures dropped to 20 degrees, do you increase the tire pressure back to the 100 psi you were describing?
Are you supposed to increase/decrease your tire pressure when the temps are above or below 68?
Are you supposed to set them when the temps are 68 and leave them alone or adjust them?
68F is not a magic number. You should adjust your pressure “each travel day” when the tires are at “Ambient” temperature. Ambient means the air temperature in the shade.
Why do I pay for subscription? This is just a lame advertisement for a sales link.
Sorry it upset you so much, Chet. Chuck found that useful and informative article, and has to give credit where it came from. It’s not one of our advertisers, and we have nothing to do with them, except borrowing their article and acknowledging it came from them. If you don’t like it, don’t click on the link to the author’s website. —Diane at RVtravel.com
I will add – first, we see comments on FB and the blogs all the time about the thousands of dollars in damage that a blown tire has caused and 2nd, is the danger blowing a tire causes to you and those around you. Chuck may have recommended a certain brand, probably because they offer some support, but there are several good system available. TPMS systems are just another weapon in our arsenal to improve our experience, stay safe and save money. Does you vehicle have a tire monitor system? I have on the truck and added one to my 5er and it is not the brand advertised. A little extra cost is cheap insurance to provide safety for my family. Especially compared to the cost of my camper. Not trying to throw rocks, but this was a good article.
That was mean… it answered several questions I didn’t know the answer to… you sound like my dad at thanksgiving .. always bumming the table out with negative vibes… and I’m almost 70 yrs old…so I’m not picking on old people… just cranky ,mean old people… haaa… ya better laugh A bit.. this is not a real long ride we are on…jim,,,, Boone nc.
Thank you for your comments, Jim. We’re glad you found the information useful. Like I mentioned in my response to Chet, it wasn’t an actual advertisement (we have nothing to do with the group that posted the article) but Chuck had to give credit where credit was due. I’m glad not everyone is cranky like, well, you-know-who. And, from someone even older than you, I hope you have a long and healthy and happy ride (in your RV?). 😀 —Diane at RVtravel.com
You should be asking your questions to the manufacturer, not to RV Travel. They are just pointing out the benefits of a TPMS.
I didn’t think it was lame at all. I totally agree with Tony above. I can use info like this, written in ‘laymen-speak’ without a lot of engineering lingo. I still don’t have a TPMS system on my trailer, though my truck came with one.
I bought a wireless tire pressure monitor for my 1998 class C. It took all the worry and fuss out of tire pressures all for $122.00. I am very happy.
Thanks for that tip on checking pressure when it’s cold out. I just need to remember 10 degrees = 2 psi.
When I bought my class A last year one of the very first items I purchased was a TPMS sensor kit. When your driving 26 thousands pounds down the highway at 70 you want to know what your tires are doing for your own safety.