Accurate tire pressure readings can only be taken when tires are cold, often understood as any time before you’ve driven on them. But, really, what IS cold tire pressure, and are you sure your readings are accurate even if you haven’t driven on your tires yet today? Don’t be too sure!
Most RVers, especially us DIY types, are very careful about maintaining the correct tire pressure in our RV’s tires. But even if you understand cold tire pressure vs hot, and you’re diligent about checking your tires before every trip, you could still accidentally run them under their proper pressure. And since under-inflated tires are the primary cause of tire blowouts, this is essential information.
We realized this after we first started RVing when we confirmed our tire pressures and then rechecked them a few hours later, finding a dramatic difference between tires… even though we hadn’t moved the RV.
Today, we’re sharing the critical details because we know that if it never occurred to us, it may not have occurred to other RVers either.
What Temperature Is Cold Tire Pressure?
We want to start our answer to the question of what cold tire inflation pressure is by sharing our own experience:
We were getting ready for a long day of driving, so we were up early doing our PTI (pre-trip inspection). Before the sun came out, we checked the pressures of all eight tires on our motorhome using a quality tire pressure gauge — a standard part of any PTI.
We confirmed that all of our rear tires were exactly as they should be, including 85 PSI (pounds per square inch) on the drive and tag axles, the correct pressures for our axle weights (find out more here: RV Tire Pressure: You’re Probably Doing it Wrong!).
Our departure ended up getting delayed by a couple of hours, and when we were finally ready to roll, we did a second quick walkaround, including spot-checking tire pressures. We were shocked to find that some of the rear tires were way over 85 PSI!
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One side of the RV had been in the shade the entire time. The rear tires on that side of the RV remained at exactly 85 PSI. We also checked the temperature of the tire’s surface using our infrared thermometer and got a reading of 57° F.
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The other side of the RV had been sitting in bright sunshine for the past couple of hours. We used our infrared thermometer to measure the surface temperature of the rear outer dual, and the tire was 107.5° F even though it was a pretty comfortable day out.
We wanted to know what effect that dramatic surface temperature increase had on tire pressure, so we measured that outside tire that had been in the sun. We found that the pressure in that tire had jumped a full 5 pounds per square inch to 90psi. The same thing was true with the tag axle tire just behind it, which had also been sitting in direct sunlight.
Here’s the problem: Had we checked our tire pressure a couple of hours later than we initially did that day (after the sun was already shining on the tire), we may have mistakenly concluded that those tires were overpressure, and we would have let out 5 PSI. This would have left us driving on under-inflated tires, which is the number one cause of tire blowouts.
Do Tire Manufacturers Account for Temperature Changes With Their Recommended PSI?
Tire pressure recommendations account for some temperature fluctuations. Tire manufacturers factor some buffer into their recommended tire pressures to support each load. But the PSI settings listed on your door jamb, DOT placard, or owner’s manual aren’t necessarily the correct pressures to set your tires to. More important info on that below.
Cold tire pressures reported from a tire pressure gauge or TPMS (tire pressure monitoring system) will also FALL as the ambient temperatures drop (for instance, in the fall and winter). That means Spring and Fall are the most common times that RV owners may see tire pressures needing much adjustment up (in the Fall as it gets colder) or down (in the Spring when air temperatures start to rise).
But once you’ve set your cold tire pressures correctly, you’re unlikely to need to add or release air very often unless there’s a fair amount of change in outside temperature. Elevation changes also cause tire PSI to change, but not as significantly as temperature changes. If you see any significant reduction in PSI, especially in only one tire, it may be a sign of a slow leak. Stay on top of that!
Here’s the video we shot the morning our departure was delayed:
Here are a few tire pressure tips we use where changing temperatures and elevations are concerned:
- When we check our tire pressures in the Fall (as the ambient temps are beginning to drop, with average temps down to the 40s instead of the 70s or 80s, for example), we’ll add a little bit more air into the tires and bring their cold pressures up to about 3-5 PSI higher than normal. As long as you stay below the maximum PSI stamped into the tire’s sidewall, there’s no harm in airing the tires up several PSI above their recommended pressures. That counteracts continuing pressure drop due to continuing temperature drops.
- Suppose we’re briefly traveling through a colder climate (for example, climbing up into the mountains where temperatures can be much colder than at lower elevations). In that case, we don’t alter our tire pressures. If you checked your tires at a lower elevation and warmer ambient temperature and they were fine, leave them alone if you’ll shortly be returning to similar conditions. They should be fine all day and correct when you reach a similar elevation on the other side.
- If you’re driving into colder weather and will be staying (and driving) in those lower temps for a couple of days or longer, check and set your pressures on the first morning you spend in those colder conditions and continue to monitor them.
How to Get Accurate Tire Pressure Readings
The next time you take cold tire pressure readings, remember that pressures can rise from more than just driving.
To get an accurate reading, check your tires early in the day before the sun hits them to be sure you’re not getting artificially inflated readings.
Proper tire inflation not only impacts fuel economy and ride comfort but it’s also a critical safety issue. Under-inflated tires can lead to tire blowouts due to increased flexing of the sidewalls, which increases the temperature of the tire rubber.
And if you need a tire pressure monitoring system, you can check out our post on the EEZ Tire TPMS.
BONUS: If you want to read our eBook “How To Inflate RV Tires Correctly,” subscribe to our newsletter! As part of the process, you’ll receive a link to read the eBook online.
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To see which portable tire inflator we use, check out our post about why we love our Viair compressor.
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