Why Your Car's Tires Lose Air During Winter

When Air Temperature Drops, So Does Tire Pressure

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It's happened to you before. You crank up your car on a cold fall or winter morning and find its orange tire pressure monitoring system (TPMS) light greets you on your dashboard! Do your tires really need air? Or can you blame the reading on the weather?

What does weather have to do with it, anyway?

Air Contracts When Cooled

The simple reason why your vehicle's tires deflate during the cold season is because air contracts whenever it is cooled. As air temperature drops, it's individual molecules slow their speed and don't take up as much space within the tire well. By taking up less space, the air molecules exert less of a force against the tire walls -- hence, a drop in your tire pressure.

According to the Rubber Manufacturer's Association, the air pressure inside tires drops by 1-2 PSI for every 10-degree Fahrenheit drop in outside temperature.

Even if you think cold weather alone is the culprit, it's still a good idea to go ahead and top off those tires. If cold weather lowers your tire pressure reading enough to trigger a TPMS alarm, 9 times out of 10, it was already borderline low before the cold wave settled in.

Always Check Tire Pressure When Your Car Is "Cold" 

When you do check your tire pressure and get ready to add air, just make sure to do it when your car is "cold" -- that is, before you start driving. Just like air contracts when it cools, air also expands when it is warm, so anything that causes your tire temperature to rise -- including driving your car, which causes friction (heat) with the road -- can give you an inaccurate tire pressure reading. (If you've ever heard that it's best to check tire pressure after a vehicle sits for an hour or more, this is why!)

A Risk of Blowouts in Hot Weather?

Just like tire psi drops in colder months, it also rises (assuming no other air loss) when the weather turns hot. But this occurrence isn't as talked about because most TPMS only sense when tires become significantly under-inflated, not overinflated.

All the more reason to routinely (or at least seasonally) check your tire pressure!