I know check the tire pressure more often in the cold since the air contracts and PSI's go down. My question: Is the air simply contracting and not escaping ? So say i have 35 PSI normal temps, it drops down to freezing conditions and the tire is now reading 28 PSI. If i add 7 PSI to bring it back to the 35 PSI mark does that mean i now have a total of 42 PSI in the tire ? If i were to warm the tire would it become overinflated ?

 

^^ +1 thats a good question! Never really crossed my mind.

 

air pressure contracts under lower temps. to be specific, the pressure of air decreases with lower temps and that causes the lower reading. Same goes for warmer temps where the pressure increases. Volume of air is the same, but that volume is compressed (cold temps outside) or expanded (hot temps outside) which affects the pressure readings.

for every 10 degrees of temp change = about 1psi of pressure change

example : 50 degrees temp @ 35psi
same tire/same volume but lower temps
30 degrees temp = 33psi

new scenario:
30 degrees temp @ 35psi
same tire/same volume but warmer temps outside
50 degrees temp = 37psi

so yes the tire would be overinflated, ride harder, etc but only at that temp, if the temps fell back to the original level, the air pressure would return to what you installed it at.

hope that helps you understand, and you had the right ideas just needed some clarification

The other thing that I've found is nitrogen filled tires have been less affected by temperature swings/changes. When I had just regular air in I was finding the temps were always messing with the tires. Now that I have nitrogen in them, those swings/changes are less noticeable and I'm finally able to just not have to mess with the air pressures much! Might be something that could help. Luckily my tire shop doesn't charge anything for nitrogen fills, some places use it as a money maker.

also if you filled up a tire at 35psi @ 30 degrees outside, and drove around warming the tire, the tire based on friction due to it being rolled/moving, usually goes up about 3-4psi, that interaction is acceptable. Cold tire temps is the rule of thumb to set air pressures at.

edit:
just found this link, here's some of the physics behind the pressure/temperature interaction which is Ideal gas Law in physics.
http://www.arden.org/misc/pressure.html