AC vs Windows Down

The debate between turning a vehicle’s air conditioning on and rolling the windows down when the thermometer rises is unquestionably…heated.

Devotees of the MythBusters television series might think they know the answer (Windows down, baby!) but, as much as I like MythBusters, they are sometimes unreliable in their testing.
So let’s go to the experts!
As with most things in life the answer is… it depends.
The gas use/savings between air-conditioning and rolling down windows depends on two factors:

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How fast is the vehicle traveling?
According to Consumer Reports auto testing department, windows should go up at 40 mph. OakRidge National Laboratory, the nation’s largest Department of Energy lab, gives the cut off at about 60 mph.
The wind drag created by an open window at lower speeds is not enough to affect gas expenditure and AC does reduce miles per gallon. However, as MotorTrend also notes, if using the AC at 60 mph and above, “there’s likely to be no fuel economy penalty versus driving with the windows down”.

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How aerodynamic is the vehicle?
Modern cars are made to be aerodynamic. Car companies depend on this when figuring the vehicles miles per gallon. If one creates holes in the vehicles aerodynamic-ness by opening windows, mpg will be reduced.
In contrast, larger vehicles like SUVs are not primarily made to be aerodynamic. Therefore, rolling windows down in these vehicles will have less of an impact on their fuel efficiency.
According to a study by the Society of Automotive Engineers, windows down in a sedan reduced fuel efficiency by 20% but rolling the windows down in an SUV only impacted it by 8%.

So..
if you’re in an SUV and city driving, roll your windows down.
if you’re in a sedan on the freeway, roll up your windows and turn on the AC.
Of course, if the gas savings, open windows will be affecting your hair in a negative way, all bets are off.

Just do what you want and have a great summer!

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