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Ambient air temperature affects your tire pressure: the hotter the weather, the higher your psi climbs. But according to Firestone, you’re usually safe if you check your psi right before driving. Read on for the only situation in which you might want to factor the weather forecast into your psi.

For every 10 degrees Fahrenheit the ambient air temperature climbs, your tires’ pressure will also go up about 1 psi. So if you have carefully set your tires to 35 psi on a cold, 30 degree spring morning, then on a hot 80 degree summer day they could read 40 psi. How? The ambient temperature expands the air that’s been in the tires. It’s a good idea to recheck your tires as the seasons change.

Your tires will heat up even more while you’re driving. This is because the act of driving makes the rubber sidewall flex and this movement heats the tire up. Luckily for us, your tire manufacturer calculated this temperature change. So if your tire calls for 35 psi, that is 35 psi before you begin driving. But because most of that psi change comes from the tires’ movement, not the ambient air temperature, this recommended psi doesn’t change throughout the seasons.

Man uses a tire pressure gauge to check his psi in hot summer weather.
Tire pressure gauge | LoveTheWind via iStockPhoto

There is one scenario you should consider. If you were to check your tire pressure first thing on a cold morning, then to drive through an increasingly hot day, you may end up with a psi a bit higher than the factory recommendation. This temperature swing can be even worse if you are driving from a cold place to a hot place. Let’s say you wake up early in the morning, after a ski vacation in the Sierra Nevada Mountains and drive down to Malibu. In one day, you could travel from a 10 degree location to a 90 degree location, and your tires could climb 8 psi.

Again, it’s safe to assume your 1 psi increase for every 10 degrees Fahrenheit the temperature climbs. Your recommended psi is a range, so on most days you will probably remain within the range. But if temperatures climb dramatically you might consider letting a few psi out of each tire.

What happens if your tire pressure gets too low? Under-inflated tires hurt your mpg, may blowout, and will wear quicker. What about if a hot day pushes your tire pressure too high? Overinflated tires have less traction, which can make them dangerous when you slam on the brakes. What’s more, they can also wear out quicker. If your tires are way overinflated, you also risk a blowout.

Some folks like to overinflate their tires, hoping to improve mpg. See why over-inflating your tires doesn’t actually help fuel mileage. Or learn how to properly check tire pressure from a mechanic in the video below:

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Henry Cesari

Henry Cesari joined MotorBiscuit in 2021 and brings his deep interest in vintage cars, trucks, and motorcycles to the site. Having restored his first classic car at just 16 years old, Henry has wrenched on everything from overland campers to Japanese motorcycles and even pre-war Bugattis. Henry is also an avid attendee at local car shows and genuinely enjoys connecting with fellow auto enthusiasts.

Henry earned a Bachelor’s in Anthropology and English from the University of Vermont. He has since incorporated his love of the written word with his admiration of classic cars. While Henry is interested in vintage cars, he believes the golden age of cars is yet to come. He is confident journalists will play an important role in this revolution by exposing the industry as it is now and envisioning its possible future.