Is your Low Tire Pressure warning on? Here’s why
Here in New England the temperature has dropped about 70 degrees in the past week and a half. Last night it was well below 0F here. Just days ago we were all out in T-shirts. These extreme temperature swings are hard on every piece of automotive equipment in our lives. Batteries are unhappy, the windshield washer fluid freezes on contact with the window, and worst of all, the seats are just so cold! If your dashboard just told you that your tires are underinflated you should check, but chances are you are just a victim of physics.
Tire Pressure Drops With Temperature
Back when the Pilgrims and Mayflower were still in Europe, Charles, Boyle and other scientists were making big discoveries and backing those discoveries up with sound, repeatable experiments. This was way before “consensus" replaced the scientific method. For many centuries, we have known that gasses expand when heated and they take up less volume when the gasses are cooled. Another part of this is that if the temperature goes down in a sealed vessel, the gas inside a vessel has a resulting drop in pressure. This is what is happening to your tires.
Where Did the Air Go?
You could have a flat, but if you check your tire pressure either using your car’s dash display or with a gauge, you are more than likely going to find that all of the tires are lower than the suggested set point. The gas (air) didn’t go anywhere; it just lost pressure. How much? In practical measurements, the pressure inside a tire goes down about one psi for every 10 degrees F. So if you had 32 PSI last week, you now have just 25 due to the temperature drop. A drop that extreme can trigger the TPMS system in some cars. Nothing is broken.
Fixing a Low Tire Pressure Warning
What can be done to make that dash light go off? It might go off itself. Tires heat up a coupe degrees F when the car is driven. You could also add air. You can find the proper amount to put in listed on the driver’s door jam. Note that your car's proper setpoint is NOT the pressure mentioned on the tire itself.
Nitrogen won’t help you. Car dealers sell this, and it is worthless in passenger cars. One of those laws (Boyle’s) that I remember from my hazy days back in engineering school is “All gasses expand at the same rate.” For our purposes, this applies nicely.
If you are part of the nitrogen conspiracy feel free to expound below in the comments. We welcome all opinions, but you are not entitled your own set of physical properties.