(WHTM) — Have you noticed your gas mileage has gotten a little less efficient recently? There are several reasons why your car’s fuel economy may have worsened since winter started.

One of those reasons has to do with aerodynamics or the way the air moves around a vehicle. Cold air is much denser than warmer air, which causes drag on a vehicle. According to energy.gov, this drag increases at highway speeds. Cold air also has an effect on tire pressure. Because of this, the rolling resistance on a vehicle is increased. More drag and more resistance mean your car gets fewer miles to the gallon.

Another factor has to do with the gasoline itself. Energy.gov states that winter blends of gasoline have less energy per gallon when compared to summer blends.

The difference in these blends has to do with something called the Reid Vapor Pressure, or RVP. This is the measure of how easily the fuel evaporates at increased temperatures.

Winter fuel requires an increase in this RVP. If the fuel doesn’t evaporate readily in cold temperatures, the engine will start hard and run roughly when it is cold outside, according to The Inside Track.

Other reasons gas mileage drops in the winter include idling your car for too long, and how the engine and transmission friction increases in cold weather due to the cold engine oil and other drive-line fluids.

So, what can you do to maximize your mileage in cold weather? Energy.gov provides some tips:

  • Minimize idling to warm up the car. Most manufacturers recommend driving off gently after about 30 seconds. The engine will warm up faster being driven, which will allow the heat to turn on sooner, decreasing fuel costs, and reducing emissions.
  • Don’t use seat warmers or defrosters more than necessary.
  • Check tire pressure regularly.
  • Use the type of oil recommended for cold weather driving by the vehicle manufacturer.
  • Remove accessories that increase wind resistance, like roof racks, when not in use.