Why Your Car's Tires Lose Air During Winter

When Air Temperature Drops, so Does Tire Pressure

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

And what does weather have to do with it, anyway?

Why Do Tires Contract in the Winter?

The reason why your vehicle's tires deflate during the cold season is simple: air contracts when it is cooled. As temperature drops, individual air molecules slow their speed. As a result, these molecules 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 tire pressure reading enough to trigger a TPMS alarm, in most cases, it was already borderline low before the cold wave settled in.

Always Check Tire Pressure When Your Car Is "Cold"

When you check your tire pressure and get ready to add air, make sure to do it when your car is "cold" — which means before you start driving. Just as air contracts when it cools, it also expands when it is warm. 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.

Risk of Blowouts in Hot Weather

Just as tire psi drops in colder months, it also rises when the weather turns hot, assuming no other air loss has occurred. This occurrence isn't as noticeable because most TPMS displays only sense when tires become significantly under-inflated, not overinflated. This is all the more reason to routinely (or at least seasonally) check your tire pressure.

Source:

Rubber Manufacturers Association. "Comments of the Rubber Manufacturers Association on Advance Notice of Proposed Rulemaking on Tire Sidewall Labeling Requirements." Steven Butcher (Staff Contact), National Highway Traffic Safety Administration, U. S. Department of Transportation, January 30, 2001, Washington, D.C.