I have 225/75/17.5 tires, put in 120psi at 65 degrees after 300 miles with air temp at 80 degrees pressure went to 140 psi and temp was 90s; after a night a 7500 ft air temp was 45 degrees pressure was 116 psi drove 400 miles cruising at 70 mph outside air was 95 degrees, tire temp was 106 degrees and air pressure was 146 psi that is with my TST TPMS
That sounds like an extreme pressure change!
I would double check with a quality pressure gauge.
Down loaded from the web
The calculations for this change are based on the Ideal Gas Law. A good rule of thumb is this: For every 10 F degree change in temperature, the pressure will change by 1.9%. If a tire is filled to 32 psi at a temperature of 75 F degrees and the temperature drops 10 degrees, the tire pressure will drop to 31.4 psi; a difference of .6 psi. If a 100 psi tire is filled at 75 F degrees and the temperature drops 10 degrees, the tire pressure will drop to 98.1 psi; a difference of .9 psi.
