Why tire pressure drops in cold weather
Air contracts as it cools. Because a tire's volume barely changes, the pressure falls with the temperature: roughly 1 psi for every 10°F (about 0.07 bar for every 5.5°C). That is why the low-pressure warning light often comes on during the first cold morning of autumn, even though no air has leaked.
Tire pressure temperature formula
Pressures in psi (gauge), temperatures in °F. 14.7 psi is atmospheric pressure; 459.67 converts °F to an absolute scale.
Worked examples
- Set to 35 psi at 70°F in the garage, the tire drops to about 31.2 psi at 30°F outside: 3.8 psi low, enough to trigger many warning lights.
- The same tire on a 95°F afternoon reads about 37.3 psi before driving.
- 35 psi is 2.41 bar or 241 kPa.
PSI, bar and kPa
| PSI | bar | kPa |
|---|---|---|
| 30 | 2.07 | 207 |
| 32 | 2.21 | 221 |
| 35 | 2.41 | 241 |
| 38 | 2.62 | 262 |
| 41 | 2.83 | 283 |
| 44 | 3.03 | 303 |
Tire pressure tips
- Check monthly and before long trips, with the tires cold.
- Use the door jamb number, not the "max press" on the sidewall.
- Do not let air out of hot tires; the pressure rises when driving and that is accounted for in the recommendation.
- Under-inflation costs money: it raises fuel use and wears the tire edges. Track the effect with the gas mileage calculator.
Changing tire size? Compare dimensions with the tire size calculator.
Frequently asked questions
How much does tire pressure drop in cold weather?
About 1 psi for every 10°F drop in temperature. A tire set to 35 psi at 70°F reads about 31 psi at 30°F.
Should I add air to my tires in winter?
Yes. Check pressure on a cold morning and add air to reach the number on your door jamb, because pressure falls as the temperature drops.
How do I convert PSI to bar?
Multiply PSI by 0.0689. For example, 35 psi equals about 2.41 bar, and 2.5 bar equals about 36 psi.
Why does my tire pressure light come on when it is cold?
Cold air lowers the pressure inside the tire, often by 3 to 5 psi overnight, which can drop it below the warning threshold even without a leak.
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Last updated October 2026.