Why Does Fuel Consumption Increase on Highways?
2 Answers
The reasons why fuel consumption increases on highways are as follows: 1. Drag coefficient: Air resistance is the largest and most significant resistance encountered when a car is moving. The size of the drag coefficient depends on the car's shape and speed. The larger the windshield area and the higher the speed, the greater the drag coefficient. A higher drag coefficient leads to greater air resistance and consequently higher fuel consumption. Currently, the drag coefficient of cars generally ranges between 0.25-0.5, with that of sedans being about 0.28-0.4. 2. Impact of driving speed: A car's engine has its own characteristic curve, and its thermal efficiency is not constant. Under medium to high load and medium to low speeds, the thermal efficiency is at its highest; under low load and low speed conditions, the thermal efficiency can drop by half compared to its peak. Therefore, every car has its own economical speed, typically designed between 70-100km/h for sedans.
When I was younger, I was obsessed with mechanical details and found that increased fuel consumption on highways is quite common, mainly because air resistance surges with speed, forcing the engine to work harder. Driving above 100 km/h, wind resistance doubles directly, consuming a lot of fuel, whereas at low speeds in the city, wind resistance is minimal, making it more economical. I tested this with my own small car—once the engine RPM soared on the highway, efficiency dropped immediately. Add to that underinflated tires or carrying heavy loads, and fuel consumption would rise sharply. The solution is to maintain a speed between 80-100 km/h, avoid blasting the air conditioning, and regularly check the vehicle's maintenance status, which can save a lot of money and reduce environmental impact. Also, be cautious during high winds or uphill sections on highways, as these can unexpectedly increase fuel consumption.
