# Thermal - why check tire pressure when it's cold?

1. Aug 30, 2011

### accountkiller

1. The problem statement, all variables and given/known data
Why should we check pressure in a tire when the tire is cold?

2. Relevant equations
...

3. The attempt at a solution
After Googling around, I found a statement saying that when a tire is "cold," it means that it is at 'room' temperature, or the surrounding air in this case. Therefore, when a tire is "cold" it is in thermal equilibrium and thus will give an accurate reading of tire pressure, is the answer I want to go with. However, why on earth would "cold" translate to "room temperature?" Isn't cold... well, cold? If they said 'cool,' it would have made sense. What's up with this?

2. Aug 30, 2011

### Dick

I think 'cold' in the question can also be taken as 'cool'. That's fine. I think the point is that the tire manufacturer gives you a recommended pressure for the tire at somewhere near room temperature. If you measure the pressure when the tire is very hot from driving and you get a pressure that's too high, should you deflate it to get the recommended pressure? Why not?

3. Aug 30, 2011

### accountkiller

Well, no, because the pressure increases with heat, so when the tire cools down again, the pressure will decrease and eventually come into equilibrium. I get what you're saying though. Thanks for the reply :)

4. Aug 30, 2011

### Dick

I'm not sure what 'equilibrium' quite has to do with it, but when the tire cools down, now it will be underinflated, right? I think the point is just that pressure varies with temperature.