Neggytive
Well-Known Member
Before you drive the car and add heat to the tire by friction, Heat causes pressure to go up, by way of Boyle's Combined Gas Law
That is why you get a low pressure warning when the tires you filled at 75 degrees ambient sit outside on the first cold night of fall or winter and drop to 40 degrees
Normally your pressure will go up about 3 degrees when you drive the car and get some heat in the tires.
Set the TP hot, the car cools off, the pressure drops 3 PSI or more, and we are looking at the Ford / Firestone fiasco of the 90's, which is why we have Federally mandated TPMS monitors
If you notice the TPS monitor comes on at about 2 to 3 pounds below its target pressure.
So my answer is... when the car has sat for a while, overnight is better, and has no added heat that would cause the pressure to be higher than it would at static rest
https://chem.libretexts.org/Bookshe...The_Behavior_of_Gases/14.06:_Combined_Gas_Law
That is why you get a low pressure warning when the tires you filled at 75 degrees ambient sit outside on the first cold night of fall or winter and drop to 40 degrees
Normally your pressure will go up about 3 degrees when you drive the car and get some heat in the tires.
Set the TP hot, the car cools off, the pressure drops 3 PSI or more, and we are looking at the Ford / Firestone fiasco of the 90's, which is why we have Federally mandated TPMS monitors
If you notice the TPS monitor comes on at about 2 to 3 pounds below its target pressure.
So my answer is... when the car has sat for a while, overnight is better, and has no added heat that would cause the pressure to be higher than it would at static rest
https://chem.libretexts.org/Bookshe...The_Behavior_of_Gases/14.06:_Combined_Gas_Law
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