Autos, driving: tire pressure change with temp

Self-tutoring about autos: the tutor mentions a pressure change he noticed.

The following is my understanding.

As mention in my post here, I check the autos’ tire pressures about once per month.

A couple days ago, I found a tire gauge I’d misplaced long ago, so checked a tire to see how accurate the found gauge might be. I was surprised: a tire I’d thought to be around 35psi, the found gauge reported as 28psi. Yet, the found one is a digital gauge, and perhaps to be taken seriously. I got out the gauge I normally trust, and measured the tire pressure: 31psi, it said.

I’m aware tires can lose pressure gradually, but not that much. I wondered if the recent season change could play into it. Within the last few weeks, the average temperature has fallen around ten degrees Celsius.

It turns out that temperature does affect tire pressure, by perhaps 1psi for every ten degrees Fahrenheit. A drop of ten Celsius suggests a drop of about eighteen degrees Fahrenheit, implying a drop in tire pressure of around two psi.

So, to explain the reading of 31psi from 35psi, the drop might be two psi because of the change in temp, then another two psi because of gradual loss over time. As for the new gauge, I’ll have to do more testing to see which one is to be trusted.

Source:

consumerreports.org