DENVER (KDVR) — Tires naturally lose air pressure over time, but each year as the weather gets colder, tire pressure lights turn on and drivers everywhere begin to look for the nearest air compressor.

For many motorists, this is the first sign that cold temperatures are coming and that they need to winterize their vehicles, according to AAA Regional Director Skyler McKinley.

McKinley said the reason for this annual, widespread decrease in tire air pressure is just fundamental physics.

Tire pressure low? It’s physics

Boyle’s law is a gas law which McKinley summarized as the pressure of a gas at a volume is proportionate to temperature. It means that air pressure in a space will drop when it is cold, and increase when it is hot.

Air molecules in tires bounce around. In the heat, there is more energy and those molecules bounce faster, resulting in higher air pressure. The opposite is true when the ambient temperature goes down.

“With a loss of temperature comes a loss of energy, and that tire pressure is going to go down,” McKinley told FOX31.

For every 10 degrees that temperatures go down, tire pressure will fall by approximately one PSI (pound-force per square inch).

“We see this when you’re driving, your tires will heat up as the rubber meets the road and your tire pressure will be more after a long drive than before one, this is fundamental physics,” McKinley said.

The physics goes beyond the inside of the tires to even affect fuel efficiency. According to the U.S. Department of Energy, underinflated tires can lower gas mileage by 0.3 percent for every 1 PSI that a tire is below its optimal pressure.

Plus, low tire pressure can make driving less safe, so McKinley recommends filling up tires as soon as the light comes on, or even before the light comes on with regular manual tire pressure checks.