Windows Down Below 40 MPH, AC Above 40 MPH

The Problem

You can't decide: windows down (hot but free) or AC on (cool but costs fuel).

The Hack

Below 40 mph: windows down is more efficient (AC compressor load > minimal drag). Above 40 mph: AC is more efficient (window drag > AC compressor load).

Why It Works

At low speeds, aerodynamic drag from open windows is minimal. At highway speeds, open windows create significant drag that the engine must overcome — costing more than running the AC compressor.

Pro Tips

• City driving: windows down, AC off
• Highway: windows up, AC on
• This is confirmed by multiple SAE engineering studies
• The crossover point is roughly 40-45 mph