Tire pressure fluctuation when hot

[locster]

Via my tire pressure monitor kit, I noticed that my tire pressures in all 6 tires increased uniformly by as much as 18psi from cold pressure on a long trip thru the desert. Is this normal?

I drive a 21ft Coachman with just normal full weight loading. I typically set the tires at 68psi in the front and 75psi in the rear.

[jhp124gr]

I have a 21 ft class c and the door sticker states psi 65 single and psi 55 dual. I run what the door sticker states. I am taking it as the front single tires run 65 and the rear duals are 55. big difference then max laod of 80.

[rjstractor]

Perfectly normal IMO. My rear tires would get up to 95 psi from 80 cold running through 100 degree temps in Eastern Washington. Having said that, with small wheel wells that inhibit airflow, the inside duals are prone to getting too hot and failing from tread separation especially when loaded to max. I learned the hard way to use quality tires.

[BarryG20]

on our fifth wheel just a few weeks ago the pressure started out at 64psi and 66 deg temp. The highest pressure I saw was 77psi at 134 deg temp, ambient temp was 105 deg and sunny all day, running 60-68mph. Tires were well within their load range running at approx. 2100lbs out of 2520lbs capacity.

Ambient air temp may have been 105 but road temp could have easily been 115-120

[Sandia_Man]

It would be abnormal if they didn't rise in psi once warmed up. An 18psi increase is a bit on the high-side but I've seen our psi increase nearly that much on a couple of occasions. As long as they return to cold psi setting more than likely all is well. Many worry excessively about the psi increase but engineers have factored in this normal occurrence when designing the tire. It's the main reason why psi should only be adjusted when tires are cold.

[Tal_IL]

I typically set the tires at 68psi in the front and 75psi in the rear.

What is the max weight/pressure given on your tire sidewalls? Are you running at or near the max pressure?

[fla-gypsy]

Run the recommended pressure and quit over thinking it. This is a great example of technology creating a mythical problem.

[Sam_Spade]

locster wrote:

Yes, they all dropped to my cold setting pressure after cooling down. I've confirmed the readings from the TPMS on a few occasions with my manual gauge as well.

So are YOUR cold settings also the settings recommended by the coach maker ??

18 PSI does seem like a lot unless you are starting out at 50 F and ending up at 110 F maybe; in which case the pavement and tires might be at 150F or more for a swing of 100F or more.

If you are in an unusual situation like that, I think I'd drop my cold pressure a couple of PSI and then not worry about it.

If you have jacked up the cold pressure from the recommendation without a good reason (weight increase), you should consider putting them back.

[darsben1]

The bottom line is if the pressure goes up hot and returns to normal when cold you are fine unless you are running overloaded. If the increase bothers you weigh the rig fully loaded and make sure you are not overloaded if not overloaded then just enjoy the ride.

[CapriRacer]

Old-Biscuit wrote:
...... Thanks for pointing out 1 psi per 10*F increase....that is the 'standard' on charts.

To increase 18 psi the temp would have had to change 180*F :H

:S:S:S ........

Except that the 1 psi for every 10 degrees F is for passenger car tires that operate at about 30 psi. If you are operating a tire at 60 psi, then the change is doubled.

To get around this, think in terms of percent - 3% for every 10 degrees.

[Ivylog]

A +18 psi from the 70s seems a little too much. I do not see that much starting at 100. I go 5 over what the chart calls for the weight as a strong cross wind can shift that much weight to one side.

[locster]

Old-Biscuit wrote:

locster wrote:
Thank you for the reassurance.

I expected them to increase once heated up, but not by that much. I've read somewhere to expect 1psi increase for every 10 degrees F change. Even my tire monitor sounded the alarm with these numbers. I had to manually override the threshold to shut it up, but was afraid that I shouldn't have ignored them.

Thanks for pointing out 1 psi per 10*F increase....that is the 'standard' on charts.

To increase 18 psi the temp would have had to change 180*F :H

:S:S:S

All tire 'monitors' indicated same 18 psi increase in ALL 6 tires....suspect tire monitoring system error.

YES-tire pressures will increase from COLD to HOT
But you are correct to suspect an 18PSI increase.

So did all 6 tires drop 18 psi when they returned to COLD temp??






TPMS are neat but I still prefer 'old school'
Digital Pressure Gauge (not old old school pencil gauge :B )

Yes, they all dropped to my cold setting pressure after cooling down. I've confirmed the readings from the TPMS on a few occasions with my manual gauge as well.

[Old-Biscuit]

locster wrote:
Thank you for the reassurance.

I expected them to increase once heated up, but not by that much. I've read somewhere to expect 1psi increase for every 10 degrees F change. Even my tire monitor sounded the alarm with these numbers. I had to manually override the threshold to shut it up, but was afraid that I shouldn't have ignored them.

Thanks for pointing out 1 psi per 10*F increase....that is the 'standard' on charts.

To increase 18 psi the temp would have had to change 180*F :H

:S:S:S

All tire 'monitors' indicated same 18 psi increase in ALL 6 tires....suspect tire monitoring system error.

YES-tire pressures will increase from COLD to HOT
But you are correct to suspect an 18PSI increase.

So did all 6 tires drop 18 psi when they returned to COLD temp??






TPMS are neat but I still prefer 'old school'
Digital Pressure Gauge (not old old school pencil gauge :B )

[locster]

Thank you for the reassurance.

I expected them to increase once heated up, but not by that much. I've read somewhere to expect 1psi increase for every 10 degrees F change. Even my tire monitor sounded the alarm with these numbers. I had to manually override the threshold to shut it up, but was afraid that I shouldn't have ignored them.

[Old-Biscuit]

Not only normal but expected.

Tire engineers have already 'planned' on those pressure increases so do NOT adjust tire pressures when HOT.

Set pressures when tires are COLD.......
Cold is not driven on and before the SUN heats them up