Cold temps and tire pressure

Now that its actually winter where I live I have a question about tire pressure and cold weather. I store my bikes indoors. Going from room temp to -30C or colder is a big change in temp. I am curious if there is a way to figure out how much psi I will lose based on temp. For example if at room temp I am at 35psi how much pressure will I lose at -30C. Or could someone point me toward a formula?

Re: Cold temps and tire pressure

You could use the ideal gas law.

p*v = n*r*t

It's pressure times volume equals molecules times a constant times temperature.

You don't really need to know a bunch of the values because they don't change. Basically what it's telling you is that tire pressure is proportional to temperature. In fact, if you do a little algebra to put pressure and temperature on one side and the constants on the other, you can derive exactly the formula you're asking for.

The 't' term is in Kelvin. That's important because for someone in a fairly temperate place, it means that the changes in temperature a bike is likely to experience don't matter all that much. For example, I'm unlikely to ride in temperatures below 40° F, which is a few degrees above 0° C, which means the 't' term in that formula changes less than 10% when I go outside.

If you're really riding in -30° C weather, I guess you could anticipate a pressure change on the order of 20%.