Which consumes more fuel when driving at high speed: opening windows or turning on the air conditioning?
2 Answers
When comparing opening windows and turning on the air conditioning while driving at high speed, using the air conditioning is more fuel-efficient. The specific reasons are as follows: When a car is driving at high speed, the greater the speed, the greater the air resistance. The car's fuel consumption is mainly used to overcome air resistance. Many cars are designed with lower drag coefficients to reduce fuel consumption, such as lowering the body and improving the car's aerodynamics. The drag coefficient is at its lowest only when all the car's windows are closed. At speeds of 80 km/h, the difference in fuel consumption between opening the windows and using the air conditioning is minimal. If the car feels stuffy at this speed, you can open the windows slightly for ventilation. However, when the speed reaches 120 km/h or higher, opening the windows consumes significantly more fuel than using the air conditioning. Therefore, it is best to avoid opening the windows when driving at high speeds.
I've been into cars for years, paying special attention to fuel consumption details. Driving with windows down at high speeds increases wind resistance—the front of the car feels like it's being hit by strong winds, forcing the engine to work harder and burn more fuel, leading to a 10% to 20% spike in fuel consumption. Using the AC also consumes fuel because the compressor adds extra load, increasing fuel consumption by 5% to 15%. However, at high speeds (e.g., above 80 km/h), the additional drag from open windows is more significant, so using the AC might actually save a tiny bit of fuel. For example, I tested my own car and found that driving with windows down on the highway consumed 0.5 liters more per 100 km compared to using the AC. Additionally, open windows create more noise, reducing comfort and potentially prompting the driver to press the accelerator harder to maintain speed. Personally, I think using the AC is more cost-effective—when the engine runs efficiently, fuel consumption stays more stable, and over time, you might even save some money on gas.
