I recently read in a car book that modern cars will actually get better mileage on the highway if the windows are up and the AC is on vs windows down and AC off. The reasoning was that the increase of drag on the car decreases the mileage more than having the AC on. I've always heard the AC just devours gas. What do you think?

 

Ive heard both stories as well. I prefer using windows through cities and AC on highway. Wouldnt know the real answer though.

 

There was another thread recently that touched on this subject:

https://my350z.com/forum/2003-2009-nissan-350z/121961-increased-mpg-by-2-for-50cents.html

It makes sense that the drag on the car would have more effect than the A/C. The A/C draws the same amount of power no matter how fast you're going. The drag on the car increases by a power of 2 as the speed increases (i.e. as your speed doubles, the drag goes up 4X). At highway speeds the drag could be significant enough to make a difference and offset the AC loss.

 

Yep, I'm sure there is a theoretical speed where your car gets enough drag to make the engine have to work just as hard as it does to spin the A/C compressor. The bottom line is that it barely matters and you should do whatever you want. I always do windows unless it is raining or I can't take the cold or heat anymore.

 

If you ever watch that dumb show myth busters, they had two identical ford excursions going around a super speed way at 55 one with all the windows down and the other with the AC on full blast, the windows last almost 2 MPG better, however when they did instantenous reads it was showing AC winning. So the answer is there is no answer, but I would say at higher speeds AC would be better.

 

they did a myth busters on this one... i think the ac won...

I am such a baller if i am just going around town I will do AC on and windows down.

 

That show is pretty dumb... I don't think either of those guys have any scientific background and they often totally botch the scientific method like when they did that chicken gun... they cared more about making a cool toy than actually making a scientific study...

<rant>
If i remember correctly before they re did the chicken gun "experiment" they were able to shoot both a frozen and a non frozen chicken though the glass of an airplane... which doesn't prove anything b/c the glass they shot it at wasn't rated for bird impacts and if both go through the glass there is no way to tell which one went through harder, they simply concluded that since they both went through the glass they both were the same. Also when they re did the experiment they were getting results that were so varied its nearly impossable to tell if the fact the frozen chicken went further though the panes of glass was just part of the normal standard deviation of the amount of force produced by the gun they made... I would hardly say 2 shots through the glass with a variance of ammo can lead to a very scientific conclusion unless you were 100% sure that gun always shot with the same amount of force (which I am not)
</rant>

 

Windows up and no AC > Windows up and AC > Windows down

 

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