Toyota Cars Best Fuel Economy - A/C On or Windows Down

With rising gas prices in the summer, many drivers wanting better MPG wonder if it is better to turn on the a/c or roll down the windows. Researchers have concluded that yes, it is. Confused? It matters what you are driving.

Toyota Cars Best Fuel Economy - A/C On or Windows Down

Is it better for fuel economy to drive with the a/c on or the windows down? Researchers say it depends.

A group of researchers at Oak Ridge Laboratory took some time and conducted an experiment to find the answer to this often asked question. Most people think that running the a/c is bad for MPG because you are causing the engine to work harder. While others believe that opening windows creates more drag which reduces MPG.

For the experiment, a 2009 Toyota Corolla and Ford Explorer were tested on a “Burke Porter 300-hp (224-kW) two-wheel-drive dynamometer” inside a laboratory that is “climate-controlled, and the testing was done at 95°F (35°C),” according to a SAE article. At first they wanted to do the test on public roads, however, they thought there would be “too much variation from such factors as humidity, wind direction, and grade (and the resulting transmission shifting activity) over the period of time necessary to provide enough data.”

Researchers reported that:

  1. Driving at speeds below 75mph, it is more efficient to roll down the windows of both cars.
  2. Driving at speeds above 75mph, it was more efficient to run the a/c in the Corolla. But, the Ford Explorer (larger SUV) was not more efficient. The reasoning is that the larger cabin space of the Explorer made it harder to keep cooled down.

At the end of the day, there is no perfect answer to this question besides it depends. If you are driving a small car, you can probably drive with the windows up to maximize fuel economy at highway speeds. If you are driving a larger vehicle like a truck or SUV, you can probably drive with them down.

What do you think? Do you agree with the researchers?

Written by Tim Esterdahl