The first cold morning of the year has a familiar soundtrack: the car starts, and a yellow tire symbol lights up on the dashboard. Nothing has punctured anything. The air in your tires simply got colder overnight, and cold air takes up less room.

This is one of the few tire questions with a clean physics answer, so let us do the physics, then the practical part.

The short version

Michelin’s rule of thumb is that each 10°F drop in temperature costs about 1 psi of tire pressure. A tire set correctly on a mild autumn afternoon can easily be 3 to 4 psi low by a frosty morning, without losing any air at all.

Chart showing tire pressure falling as air temperature drops, from 35 psi at 70°F 35 psi at 70°F 31.2 psi at 30°F 28.4 psi at 0°F 2530354070°F50°F30°F10°F0°F Air temperature (°F); gauge pressure (psi) starting from 35 psi cold at 70°F
Pressure falls roughly 1 psi for every 10°F, with no air lost.

Why it happens

A tire is a sealed container of air. When you cool a fixed amount of gas in a container that cannot shrink much, its pressure falls in proportion to its absolute temperature. That is the gas law you may remember from school.

There is one trap. Your tire gauge shows gauge pressure, the pressure above the surrounding atmosphere. The gas law works with absolute pressure, so you have to add atmospheric pressure (about 14.7 psi at sea level) before doing the sum and subtract it again afterwards. Temperatures also have to be absolute, in kelvin.

A worked example

Say you set your tires to 35 psi on a 70°F afternoon, and the temperature falls to 30°F overnight.

  • Absolute pressure at the start: 35 + 14.7 = 49.7 psi
  • 70°F is about 294.3 K and 30°F is about 272.0 K
  • New absolute pressure: 49.7 × 272.0 ÷ 294.3 ≈ 45.9 psi
  • New gauge reading: 45.9 − 14.7 ≈ 31.2 psi

That is a drop of about 3.8 psi for a 40°F swing, or a little under 1 psi per 10°F, which matches the rule of thumb. If the same tire meets a 0°F morning, it reads about 28.4 psi.

In metric terms: a tire set to 240 kPa at 20°C reads roughly 217 kPa at 0°C and about 205 kPa at −10°C.

Why the warning light comes on

In the US, cars are required to have a tire pressure monitoring system (TPMS). The federal standard requires the warning to come on when a tire falls to 25 percent below the vehicle maker’s recommended cold pressure, or to a minimum value set in the standard, whichever is higher. For a car with a 35 psi placard, 25 percent below is about 26 psi.

So a cold snap alone usually is not enough to trigger the light on a tire that was set correctly. If the light comes on, the tire was probably a bit low already, and the cold pushed it over the line. Either way, the fix is the same: check and top up.

How to check pressure properly in winter

Flowchart for checking tire pressure correctly in cold weatherTires cold?At least 3 hours sincedrivingRead the placardDriver door frame orowner manualTop up to placardAt the current outsidetemperatureRe-check next cold morningOne tire dropping faster= look for a leak
Check cold, fill to the placard, then check again.
  1. Check cold. Michelin advises checking when the tires are cold, at least three hours after driving. Driving warms the air inside and makes the reading look higher than it really is.
  2. Use the number on the vehicle placard. It is on the driver’s door frame or in the owner’s manual. The number molded on the tire sidewall is the tire’s maximum, not the pressure your car needs.
  3. Top up to the placard value at the outside temperature you are actually driving in. Do not add extra “to allow for the cold”; the placard value is meant to be measured cold.
  4. Re-check the next cold morning. If one tire keeps dropping more than the others, that is not the weather, so have it checked for a leak.

Tires also lose a little air anyway

Even with no temperature change, tires seep air slowly. Michelin says tires lose some air pressure, 1 to 2 psi, over a month or so, which is why it recommends checking pressure once a month. In autumn, that slow loss and the falling temperature add up.

What about hot weather?

The same physics works in reverse. Pressure rises as the tire warms up, whether from summer sun or from driving. That is why you should not let air out of hot tires to bring them down to the placard number; once they cool, they will be underinflated.

FAQ

How much does tire pressure drop in cold weather?

About 1 psi for every 10°F drop in temperature, according to Michelin. A tire set at 35 psi on a 70°F day will read roughly 31 psi at 30°F, using the gas law with absolute pressure and temperature. The tire has not lost air; the air inside has simply contracted.

Should I add air when it gets cold?

Yes, if the cold reading is below the pressure on your vehicle’s placard. Check when the tires are cold, at least three hours after driving, and fill to the placard value. Do not overfill to compensate for future cold, and re-check after the next cold night.

Why is my tire pressure light on in the morning but off later?

Overnight cold lowered the pressure in a tire that was probably already a little low. As you drive, the tires warm up and pressure rises, so the light may go off. The underlying problem is still there, so check all four tires cold and top them up to the placard pressure.

Use our tools

Convert between psi, bar and kPa with the tire pressure calculator, and read more about compound behaviour in the science of winter tires.

Sources

Checked on 23 October 2026.