Rick's Free Auto Repair Advice

Tire Pressure in Cold Weather

Correct tire pressure in cold weather

When the weather turns cold you often see the TPMS light light up on your dash. Tire pressure sensor set the TPMS warning light when tire pressure falls below the recommended level by at least 25%. But if you filled your tires in the Fall, what’s causing the dramatic drop in pressure now? Here’s the deal.

All tires lose pressure due to permeation

That’s right, Air can permeate through the layers of the tire and escape. This happens to new tires as well. The permeation rate is usually 1-2-psi. per month.

Tire pressure drops 1-psi. for every 10°F drop in outside temperature

If you filled your tires when outside air was 70°F and you park your car outside where the temps have dropped to -10°F, your tire pressure has dropped by 8-psi. (if the recommended pressure was 32-psi. and you lose 8-psi, that’s a 25% drop in pressure; enough to trigger the TPMS light).

Refill tires to the recommended psi when they’re cold

The recommended tire pressure listed on the placard located in the driver’s door area if for cold tires; tires that haven’t been driven in at least 4 hours. If you see a TPMS light on first thing in the morning when your car is parked outside in the cold, simply fill the tires to the pressure listed on the placard.

If your vehicle is parked inside a heated garage, refer to the chart below and use the following calculation to determine the proper inflation pressure.
1) Measure the temperature inside the heated garage (Let’s assume 70°F)
2) Determine the lowest expected outside temperature in your area. (Let’s assume 14°F)
3) Subtract the lowest expected temperature from the heated garage temperature (70°F – 14°F = 56F)
4) Refer to the chart to determine the proper inflation pressure to add to the tire’s recommended pressure (from the placard). In this case approximately 4.8psi.
tire temp versus pressure
If you’ve driven the car to the tire shop, refer to the green dotted line.

If you’ve driven the car on the highway for at least one hour, refer to the blue dashed line.

©, 2022 Rick Muscoplat


Posted on by Rick Muscoplat

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