TT tire pressure increase while on the road

[Lloydg]

I have a Tire Minder TPMS and my baseline pressure is set at 65 psi. The Tire Minder is set to sound its alarm at 15% over the baseline or when the tires reach ~75 psi. I expect to see some alarms in a couple of weeks after leaving Michigan for Florida. It'll be quite cold in Michigan when I leave and the tire pressure will be adjusted accordingly. As I get farther south and it starts to get warmer, I'm sure I'll have to let some air out.

[Blackhat6mike]

I also have the TST 507RV system. I run 15" tires at 78 psi as this keeps me below the 93 psi set as the alarm pressure.
We left Marathon Key when it was 81* and headed North where the next morning, it was 50*. The next morning, I had to ADD air as all tires showed 73-73psi with the lower temps. When we got home, the pressures were at 85-86* and all around 94-96*
IMHO, you should change your pressures relative the ambient temps or you will go over your 15% max increase when going from cold to warmer weather. Going from warmer to colder temps, you will be under inflated.

[D_B Travelers]

Originally Posted by Blackhat6mike

We left Marathon Key when it was 81* and headed North where the next morning, it was 50*. The next morning, I had to ADD air as all tires showed 73-73psi with the lower temps. When we got home, the pressures were at 85-86* and all around 94-96*
IMHO, you should change your pressures relative the ambient temps or you will go over your 15% max increase when going from cold to warmer weather. Going from warmer to colder temps, you will be under inflated.

Amen. When I parked the TT here in Fort Worth the first week of November, we had 65# in the tires, but it was about 95 degrees out. I checked them the other day and they were all in the mid-50's now, but so was the weather. Tire pressure isn't check them and forget them; we have seen those guys on the side of the road with one side of their rig missing or dragging. All good comments and observations on this subject!

[Blackhat6mike]

Originally Posted by Blackhat6mike

I also have the TST 507RV system. I run 15" tires at 78 psi as this keeps me below the 93 psi set as the alarm pressure.
We left Marathon Key when it was 81* and headed North where the next morning, it was 50*. The next morning, I had to ADD air as all tires showed 73-73psi with the lower temps. When we got home, the pressures were at 85-86* and all around 94-96*
IMHO, you should change your pressures relative the ambient temps or you will go over your 15% max increase when going from cold to warmer weather. Going from warmer to colder temps, you will be under inflated.

Sorry, I meant 85-86 psi and 94-96 degrees. My bad.

[Timtation]

Originally Posted by johntaylor

Not true. All gases respond identically to temperature changes. It's Gay-Lussac's pressure-temperature law: P1 / T1 = P2 / T2

The only difference with nitrogen is that it is dry. Air contains water vapor. If you start out below the dew point temperature, some of that water vapor will be condensed out. As the tire warms, it will evaporate and increase the pressure, but only very slightly.

For the facts on nitrogen inflation, read this. Now I'll just sit back and wait for the nitrogen police.

You probably can use the psi numbers for pressure but for temperature you must use the Kelvin temperature scale which starts at absolute zero. For this exercise use 0 centigrade (32F) as 273 then adjust temperatures as needed, in centigrade.
60 psi @ 60F, 15.6C would increase to 63.5 @90F or 32C in a perfect world. I find my imperfect gauges show more like a 5 degree change.
I also would like to take credit for the nitrogen change but doubt that it would be well supported. In the late 1980s touring pit row at a NASCAR event I asked the head of a pit crew why they used bottles of compressed air rather than compressed nitrogen. He asked why I would ask that question. The compressed gas was used both for tire air and air wrenches. My reply, "Nitrogen is cheaper, it is nearly 80% of the distillation process and is essentially a by-product and cheaper than all other compressed gasses."
yrmv

[emm-dee]

I'll never figure out this tire pressure stuff. In my pre-retirement life operating a business jet we have checked tire pressure in the morning with an ambient temperature of -20f (northern Canada in the winter) and it was at 207 psi. Non-stop to southern Florida, ambient temperature 85f, and the pressure was 210 psi. Next morning, 70f, pressure still at 210.

Go figure.

[Lefty59]

Our Load range E tires are set cold at 80 PSI and I set the high pressure alarm at 96 PSI per the users guide on my TPMS (quoted below). Typically our tire PSI hot settles in around 88-94 depending on ambient temperature, which side is sunny and also wind direction. We did have one occasion where PSI went to 97 on one tire, but it was a hot day running in Wyoming.

Here's the excerpt from the users guide on my TPMS:

STEP 1: SETTING YOUR SYSTEMS ALARM PARAMETERS
(By Sequence)
Refer to the diagram on the last page of this manual where you wrote the sensor number for each tire.
1. Next to each axle write down what your tire pressure is by axle and calculate what your alarm setting will be.
2. High Pressure setting will be (20% above axle tire pressure).
3. Low Pressure setting will be (10% below axle tire pressure).
Example: Front Axle Tire Pressure is: 100 psi
High Pressure Alarm Setting will be: 120 psi (100 psi x 1.20 (or 20%) = 120
Low Pressure Alarm Setting will be: 90 psi (100 psi x .9 (or 90%) = 90
These are industry standards for the initial set-up, some adjustment may be
needed after your first trip. Every brand of tire operates differently, when
some brands reach operating temperature the psi will increase 5 psi, other
brands may increase 20 - 22 psi. During your first trip you will see if you need to increase your High Pressure Alarm setting. For the temperature it is
recommended leaving it at the factory default of 158 degree F.

Safe travels!