Metro

It’s cold. You should check your tire pressure

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Did you see a strange warning light on your dashboard as you shivered into the driver’s seat this morning?

If it looks like an exclamation point between parentheses, it means your tire pressure is way too low. Like other gases, air contracts as it gets colder — and that means there’s less of it in your tires.

Tire pressure (per square inch) drops between one and two pounds for every 10-degree decrease in temperature, and that can make a big difference to a driver who hasn’t filled up since summer.

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On a day like today, when the low temperature was 24 degrees, your tires could be 5 to 10 pounds per square inch lower than they were on a 74-degree morning.

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So even if you filled up to a comfortable PSI of 32 in August, your tires could have dropped as much as 25 percent by today — which in most cars is enough to trigger a warning.

Tire manufactures say the onset of winter weather is a good time to make sure your tires are properly inflated. Air pressure can affect steering, handling, gas mileage, and the life of the tires themselves.

“If you simply use [the light] that as a crutch to say, hey, I need to put air in my tires, then you’re already down a certain threshold,” said Jim Davis, a spokesman for the tire maker Goodyear. He suggests that people check in using a pressure gauge once a month or before any big trip.

Every vehicle has its own ideal PSI. It’s usually written on the driver’s side door jamb, and in the owner’s manual.

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That rating might not be the same as what’s listed on the wall of the tire, which is the maximum amount of air it can hold, rather than the best amount for your particular car. It also might be the difference between an unexpected flat and a smooth ride.

Your tires are the only part of your vehicle touching the road. Try to keep it that way.

How temperature affects tires

Gas expands with heat and contracts with cold. So when winter arrives, it's best to check in on your tire pressure for safety.

Tire pressure drops by one to two pounds per square inch for every 10 degrees. Type in two temperatures to see the minimum effect on your tires as the temperature cools.
Summer (Temperature in F)
Winter (Temperature in F)
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SOURCE: Tirebuyer.com

Globe Staff

Andy Rosen can be reached at andrew.rosen@globe.com. Follow him on Twitter at @andyrosen.