Many drivers notice that a car can burn fuel very differently even on the same stretch of road.
Many drivers have seen it firsthand: one day the fuel gauge barely moves, and on another the tank seems to evaporate. The automotive outlet Auto30.com decided to find out how much your cruising speed really affects fuel economy.
To conduct a clean test, researchers chose a 100-mile highway stretch—flat, with no traffic jams or sharp curves. The test vehicle was a 2022 Ford F-150 with a 3.3L Ti-VCT V6. The route was divided into three equal segments, and on each run the driver maintained a steady speed. After every loop, the team recorded the fuel consumption.
The results were clear: driving too slowly isn’t a magic solution. When the engine spends a long time in low gears, fuel is burned slowly but continuously. However, at higher speeds the engine starts “drinking” gas much faster, and aerodynamic drag rises dramatically.
Another finding surprised many: the common belief that air conditioning always hurts fuel economy isn’t entirely accurate. With the windows down, the body loses aerodynamic efficiency and drag increases. On the highway it’s often more efficient to close the windows and use the A/C—the vehicle may actually burn slightly less fuel than with the windows open.
The experiment began with a steady cruise at about 52 mph (≈84 km/h) on a 19-mile segment. The truck drove smoothly, and the onboard computer showed a solid result of about 23.1 mpg (≈10.2 L/100 km). The data was reset before the second run.
Next, the driver increased speed to 58 mph (≈94 km/h). It doesn’t sound like a big jump, but fuel economy dropped to 21.6 mpg (≈10.9 L/100 km). Even a small bump in speed noticeably affected fuel consumption.
The third run averaged 65 mph (≈104 km/h), and fuel economy fell further to about 19.9 mpg (≈11.8 L/100 km). Higher revs, more drag, more stress on the engine—no surprises here.
To complete the picture, the test was repeated in city conditions. Stop-and-go driving, lights, traffic, and constant accelerations pushed fuel consumption above 18 mpg (≈13 L/100 km)—a typical outcome for urban trips.
After all the measurements, the conclusion was simple: the most fuel-efficient cruising range for most vehicles is about 50–56 mph (≈80–90 km/h). In that window, the engine runs smoothly and burns the least fuel.
For vehicles with larger, more powerful engines—say, a 5.0L V8—the numbers will be higher, but the principle remains the same: a moderate cruising speed is almost always the most economical.