Question

Using the temperature-pressure relationship, why you should check your tire pressure when the temperature changes?

Answer 1

Gas pressure is directly proportional to Kelvin temperature, so when the temperature of the air drops, the pressure in a tire will drop as well.

Explanation:

Here are some numbers to back this up.

From the `P-T` relationship,

`P_1/T_1=P_2/T_2`

Which can be rearranged to give

`P_2/P_1=T_2/T_1`

Lets say the temperature changes from 5°C to-25°C (we had a situation similar to this only a few weeks ago in Winnipeg, where I live). Expressed in Kelvin, this is a change of 278 K to 248 K.

The resulting change in pressure (expressed as a fraction) would be

`P_2/P_1=248/278 = 0.89`

So, this is better than a 10% drop in pressure within a tire. Not enough to make it go flat, but enough to cause it to wear improperly and waste fuel.