Tire Pressure and Temperature
You’ll notice that the stamp on your tire’s sidewall specifies inflation for HOT tires. Why is that?
Pretty simple physics, really. Gases expand with heat, meaning both the temperature of a friction-heated tire and ambient temperature of outside air. A rule of thumb is that for about for about every ten degrees Fahrenheit change in air temperature, your tire’s inflation will fluctuate by about one PSI. In most parts of the United States, the difference between winter and summer temperatures can be as much as a 50-degree spread, meaning a potential fluctuation of five PSI. That’s not even thinking about the 20-degree spread between hot afternoon temperatures and cooler nighttime or early morning temperatures in summer.
Tires that are low by 5 psi will hurt traction, steering response, control and fuel economy. So, keeping this all in mind, this means that fall and early winter are probably the most crucial time to keep an eye on your tires’ inflation, as ambient temps get colder, nights get longer and days get shorter. Also bear in mind that rubber is porous, and the Schrade valve stem on your tires, while a great design, will still very slowly lose air. Check your tires’ inflation level at least once a month, and make sure that the inflation of warm tires corresponds to the manufacturer’s recommendation on the sidewall.