Car care · Elgin Auto Sales & Service Center · Elgin, IL
What Is the Best Speed for Gas Mileage?
Every car has its own most efficient speed, but the U.S. government fuel economy site, fueleconomy.gov, says gas mileage usually drops quickly once you go faster than about 50 mph. Here is what fueleconomy.gov and the Department of Energy's Alternative Fuels Data Center say about speed, driving style and cruise control.
50 mphabove this, mpg usually drops quickly
15% to 30%lower mpg from aggressive highway driving
10% to 40%lower mpg from aggressive stop-and-go driving
10% to 25%lower mpg from a large roof box at 65-75 mph
The short answer
There is no single best speed for every car. Fueleconomy.gov says each vehicle reaches its best fuel economy at a different speed or range of speeds, but gas mileage usually decreases rapidly above 50 mph. It estimates that each 5 mph you drive over 50 mph is like paying about 29 cents more per gallon, based on its assumed fuel price of 4.15 dollars a gallon. Driving smoothly, using cruise control on the highway and observing the speed limit all help.
Why gas mileage drops at higher speeds
Fueleconomy.gov puts it this way: while each vehicle reaches its optimal fuel economy at a different speed or range of speeds, gas mileage usually decreases rapidly at speeds above 50 mph. The Alternative Fuels Data Center (AFDC) says the same: gas mileage typically decreases significantly at speeds above 50 miles per hour.
Part of the reason is wind resistance. Fueleconomy.gov explains that open windows add aerodynamic drag, an effect that is quite small at low speeds but increases at highway speeds, and that roof-top cargo also increases drag and lowers fuel economy, most of all at Interstate speeds. Fueleconomy.gov also offers a calculator on its driving tips page that estimates the speed penalty for your own car.
From Driving More Efficiently (fueleconomy.gov), Fuel Economy in Hot Weather (fueleconomy.gov) and Efficient Driving to Conserve Fuel (Alternative Fuels Data Center), read November 9, 2026.
Speed and driving habits compared
Here is how fueleconomy.gov and the AFDC describe the effect of common habits on gas mileage:
| Habit | Effect on gas mileage |
|---|---|
| Driving faster than about 50 mph | Gas mileage usually decreases rapidly; each 5 mph over 50 mph is like paying about 29 cents more per gallon at fueleconomy.gov's assumed fuel price |
| Aggressive driving: speeding, rapid acceleration and braking | Roughly 15% to 30% lower at highway speeds and 10% to 40% lower in stop-and-go traffic |
| A large, blunt roof-top cargo box | Around 2% to 8% lower in the city, 6% to 17% on the highway and 10% to 25% at Interstate speeds (65 to 75 mph) |
| Windows down | A small effect at low speeds that increases at highway speeds |
| Idling | A quarter to a half gallon of fuel per hour, depending on engine size and air conditioner use |
From Driving More Efficiently (fueleconomy.gov) (driving habits, cargo and idling), Fuel Economy in Hot Weather (fueleconomy.gov) (windows) and Efficient Driving to Conserve Fuel (Alternative Fuels Data Center) (aggressive driving), read November 9, 2026. Your results depend on your vehicle and conditions.
Does cruise control save gas?
Usually, on the highway. Fueleconomy.gov says using cruise control on the highway helps you maintain a constant speed and, in most cases, will save gas.
On hot days, fueleconomy.gov suggests rolling the windows down at lower speeds and using the air conditioning at highway speeds. For more, see our guide to how often to rotate tires and how to check tire pressure.
From Driving More Efficiently (fueleconomy.gov), Fuel Economy in Hot Weather (fueleconomy.gov) and Efficient Driving to Conserve Fuel (Alternative Fuels Data Center), read November 9, 2026.
Service at Elgin Auto Sales & Service Center
Mileage dropped and you are not sure why? Schedule service or see our service specials.
Our service department at 1200 E. Chicago St. in Elgin is open Monday to Friday 8 a.m. to 5 p.m. and Saturday 8 a.m. to 4 p.m., and is closed Sunday. Get directions.
Best speed for gas mileage FAQ
What is the most fuel efficient speed?
It depends on the vehicle. Fueleconomy.gov says each vehicle reaches its optimal fuel economy at a different speed or range of speeds, and gas mileage usually decreases rapidly above 50 mph.
How much does speeding hurt gas mileage?
Fueleconomy.gov estimates that each 5 mph you drive over 50 mph is like paying about 29 cents more per gallon at its assumed fuel price. Aggressive driving can lower gas mileage by roughly 15% to 30% at highway speeds.
Does cruise control save gas?
In most cases, yes, on the highway. Fueleconomy.gov says cruise control helps you maintain a constant speed and, in most cases, will save gas.
Is it better to drive with the windows down or the AC on?
Fueleconomy.gov suggests rolling the windows down at lower speeds and using the AC at highway speeds, because open windows add drag that increases at highway speed.
Does a roof box hurt gas mileage at highway speed?
It can. Fueleconomy.gov says a large, blunt roof-top cargo box can reduce fuel economy by around 10% to 25% at Interstate speeds of 65 to 75 mph.
What are your service hours?
Monday to Friday 8 a.m. to 5 p.m. and Saturday 8 a.m. to 4 p.m. We are closed Sunday.
Shopping for a used car?
Visit us at 1200 E. Chicago St. in Elgin.
Sources
Speed, driving habit, cargo, window and idling information is from fueleconomy.gov, the U.S. government fuel economy site administered for the Department of Energy and the EPA, and from the U.S. Department of Energy's Alternative Fuels Data Center, read November 9, 2026. This is general information; your owner's manual is the authority for your vehicle. Our address and service hours are from our own website, checked the same day. Photo is of our dealership.
- Driving More Efficiently (fueleconomy.gov), U.S. Department of Energy and U.S. EPA, read November 9, 2026
- Fuel Economy in Hot Weather (fueleconomy.gov), U.S. Department of Energy and U.S. EPA, read November 9, 2026
- Efficient Driving to Conserve Fuel (Alternative Fuels Data Center), U.S. Department of Energy, read November 9, 2026
- Service page: address and service hours, Elgin Auto Sales & Service Center, read November 9, 2026