Learn how fuel usage correlates to CO2 despite…
Fuel consumption vs speed
by Alex
Expert answer:
Quick answer
Fuel consumption typically rises sharply at high speeds because wind resistance grows exponentially. Moderately lower speeds often achieve better mpg.
Detailed answer
In most vehicles, the optimal speed for best fuel efficiency sits around 45–60 mph. Above that range, aerodynamic drag increases significantly, causing the engine to consume more fuel per mile traveled. Meanwhile, extremely slow speeds can also be inefficient if lower gears are used or if stop-and-go is frequent.
Because drag grows with the square of speed, driving 75–80 mph can drastically reduce mpg compared to 60–65 mph. Some modern cars mitigate this with low drag coefficients or advanced transmissions, but physics still holds. So if you can drive 5–10 mph slower on highways, you often save a good chunk of fuel. Monitoring real-time mpg readouts or manually calculating after fill-ups can highlight the difference.