It’s a chilly morning. You’ve bundled up for your drive and your thermos of coffee or tea is piping hot next to you in the cupholder. You place the key in the ignition and start your car, ready to go. But all of the sudden, your “low tire pressure” light comes on in your vehicle.

You may feel a quick jolt of annoyance but if it’s the first time that temperatures have dropped 10 to 20 degrees overnight— check the forecast for latest temperature — everything is likely fine with your tires. It’s just chemistry! Why does this happen when it gets cold?

Depending on the amount of heat in the air, the molecules are either very spread out or crowded together. When the air is heated, the distance between the molecules expands. However, when heat is removed from the air, causing temperatures to drop, the distance between the molecules is less and the air contracts, thus bringing the pressure down.

The air in your vehicle’s tires reacts this same way. As temperatures drop, the air in the tire contracts. This means the air takes up less space inside the tire and leads to the tire becoming more flat than firm. According to Erie Insurance, tires can drop between 1 and 2 PSI, or pressure per square inch, for every 10-degree decrease in the outdoor temperature. You’ll find an even lower PSI reading if you are also parked in the shade on a cold morning.

The great news is that if your tires are in good shape and temperatures are forecast to increase throughout the day, simply driving will help! The air in the tires expands as friction from driving on the road helps to heat the air inside the tires. The molecules within the air inside the tire will spread out bringing your tire pressure back to a normal reading.

However, if temperatures are forecast to stay cold, the air inside the tires may not expand much even if driving on them. The best thing to do is to inflate them to the proper PSI to your vehicle’s standards.

The tire pressure standards can be found on the driver’s side door panel or in your vehicle’s user manual.