what causes the air pressure to fluctuate in the tire

Temperature. Get an empty 2L bottle, open it and run it under hot sink water for about 20 seconds. Quickly put the lid on it and put it in the freezer for about 1 minute. Then remove the lid and fill it with freezer air and then close it and run it under the hot sink water.

a week ago, i had 35 psi. i came back from vacation, it was 33 psi. temperture dropped from 80 degrees to 66. activity lowers at decreasing temps.

for ev ery 10 degree difference pressure changes about one pound per square inch (PSI) is the general rule of thumb increase in temp causes increase in pressure decrease in temp causes decrease in pressure thats why everyone should check tire pressure periodically