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Gas savings

Has there ever been a study that illustrates whether it is more gas-economical to run the air conditioner or drive with the windows down, given that the drag from the open windows reduces MPG?

GM ran some years back and found it was more economical with the A/C on. Your right,open windows cause drag.

The Mythbuster ran another one and if I recall corrctly found the same result.

Depends on the speed, of course - around town, windows down, no a/c, on the highway windows up, use a/c. Of course, it’s not a big difference, and I’m certainly not going to follow it here in Dallas in the summer!

Stdies have shown that it varies with the automobile and the driving. While the open windows have an effect on the aerodynamics, the AC compressor takes power directly off the crank. How much of an effect each has depends entirely on the vehicle and on its powerplant.

If economy is what you are after, then windows up, no AC, having the AC on will never improve your mileage, but its going to get hot.

I think a mistake is made when comparing the load put on a engine from a older generation compressor and those currently avialable, the older design compressors were bigger energy hog’s, I would like to quote when the more efficient compressors came into common use, I would have to do some reasearch.

It wasn’t GM…it was MT (Motor Trend) and they tested a Ferrari. Then EVERYONE took that test and WRONGLY applied it to every single vehicle made.

There are a LOT of factors to consider. Aerodynamics, engine-size, speed…etc. There is no ONE answer that will fit every single car in every situation.

The Society of Automotive Engineers studied this issue back in 2004. I have attached the study for your reference.

At high speeds, you use less gas with the windows up and the air conditioning on. The speed at which drag from open windows will affect fuel economy varies from car to car. With some cars you have to get past the legal speed limit before this drag hurts your fuel economy. Generally, in stop and go traffic, you use less gas with the windows open and the air conditioning off. The problem is that in summer heat, you really need the air conditioning more in stop and go traffic. So unless you want to punish yourself and your passengers, just run the air conditioning and don’t worry about it.

Here is an article from Slate magazine.

I mentioned GM because they gave the company which I worked for the details as to what the results were. At that time the company had a 15000 car fleet.