tires & cold weather

[jack_w]

I am driving a 2010 9-3 Aero here in Nashville, TN. It was 4° two days ago and suddenly my dashboard warns me of low tire pressures all around. I checked all four tires. They are each at 30 lbs. I guess the recommended pressure is 35 lbs. I wonder if this sudden cold snap has caused the warning, where there hasn't been any problem before. No hints of tire pressure problems.

[nordwulf]

When the temperature of the air (in your tires) decreases, the pressure decreases as well. So there is nothing wrong with your car, tires or sensors. The sensors just did their job and warned about the low tire pressure.

Temperature vs pressure is also the reason why you have to check tire pressure when your tires are cold before driving. When you drive, tires warm up and pressure will be higher.

When you inflate your tires to the correct pressure now, the pressure will be too high when it warms up again.



http://www.tirerack.com/tires/tirete....jsp?techid=73

[jack_w]

Thanks, Frank. It puts my mind at rest. I had thought that, but not being familiar with the Saab "check" system, I wasn't sure. Golly this Saab is a dream, Been up and down the East Coast and the Appalachians as well since we got it in May.

[Paamf]

I read there can also be a difference in how fast the alloy wheels and tires cool which causes the tire to pull away from the rim enough to cause a small loss of pressure. I had an issue with this on a GTI I had and the high performance Michelins.

[tunnanxwd]

It happens with both our Saab cars and even with my Corvette this time each year.

[Tom]

For those of us who endure ice and snow have learned that every 18 degrees F (10 degrees C) change the tire pressure will change 2 PSI. So if the temperature drops by 54 degrees F (30 degrees C) the tire pressure will go down from 35 to 29 PSI. The science geeks will know it by the Ideal Gas Law.

[Paamf]

54 degrees F is quite a drop. The difference between summer and winter in my neck of the woods.

[Tom]

It is quite a drop and not one we typically get in a day but something to think about especially if you check your tire pressure in a warm garage then park outside for several hours.