How to drive for better fuel economy

Fuel economy is about wasted energy

A car burns fuel to get moving, push air out of the way, and overcome the rolling resistance between tires and road. During everyday driving, though, much of the energy you paid for is thrown away as brake heat. Accelerate hard and then stop sharply at a red light, and the fuel you used to speed up becomes nothing but warm brake pads. Driving for economy is mostly about cutting that waste. It is why two people in the same car on the same road can get very different mileage. Changing your habits is more reliable than any gadget or additive, and it costs nothing.

Gentle starts and early slowing

Press the accelerator gradually when pulling away, and lift off early when you see a light turn red or traffic bunching up ahead. Modern fuel-injected engines are designed to reduce or cut fuel when you coast with the car in gear and your foot off the pedal. Rolling toward a stop and braking lightly at the end saves fuel and brake wear at the same time. That only works if you leave a generous gap and watch the traffic two or three cars ahead.

• Pull away smoothly and build speed without strain
• Lift off early when you see a stop ahead
• Leave a generous gap to avoid hard braking
• Never coast downhill in neutral

Speed and air resistance

Aerodynamic drag grows with the square of speed, and the power needed to overcome it rises even faster. That is why driving a bit faster on the highway costs more fuel than most people expect. The most efficient speed varies by car, but a steady pace generally gives the best mileage. Cruise control can help on flat highways. On hilly roads, though, holding a fixed speed can mean frequent hard acceleration, so use it with judgment. Roof boxes and racks also add drag, so take them off when you are not using them.

Idling and warming up

When the car is stationary with the engine running, your fuel economy is effectively zero. Leaving the engine on while waiting for someone or loading the trunk simply burns fuel. Many local governments restrict idling, so it is worth checking the rules where you live. Long warm-ups are also unnecessary for most modern cars. Waiting a moment after starting and then driving gently for the first few minutes brings the engine to operating temperature faster. Cold-weather warm-up advice can vary by model, so follow what your owner's manual says.

Weight and tire pressure

Anything you leave in the trunk makes the car heavier every time you accelerate. Sports gear, tools, and cases of bottled water that you are not using are worth taking out. Underinflated tires flatten more against the road, which raises rolling resistance, lowers mileage, and can damage the sidewalls or lengthen braking distances. Check pressure about once a month with the tires cold, and set it to the value on the placard inside the driver's door. The tire guide in this topic explains the details.

Air conditioning or open windows

Air conditioning draws power from the engine, so it uses extra fuel. That does not mean switching it off and opening the windows always wins. At low city speeds, open windows may be the better choice, but at highway speeds they disturb the airflow and add drag. In summer, open the windows briefly after you set off to let hot air out, then turn on the air conditioning so it has less work to do. A driver worn down by heat loses focus, so suffering through the heat to save fuel is not a good trade.

Measuring your real mileage

The average fuel economy on the dashboard is handy but can be off. For a more accurate number, fill the tank, reset the trip meter, and at the next fill-up divide the distance by the amount of fuel you added. Repeat this a few times and you will see the effect of changing your habits. Once you know your monthly distance and mileage, a fuel cost calculator can estimate your monthly spending. Official ratings come from standardized test conditions, so a gap between them and real roads is normal.

• Fill the tank and reset the trip meter
• At the next fill-up, record how much fuel went in
• Distance divided by fuel used equals real mileage
• Repeat a few times and look at the average

Safety comes before mileage

Focusing on economy can tempt you to drive far slower than traffic, coast downhill in neutral, or tuck in close behind another vehicle to cut wind resistance. All of these are dangerous. Coasting in neutral takes away engine braking, and tailgating leads to rear-end collisions. The core of economical driving is a generous following distance and anticipating what comes next, which is exactly what safe driving asks of you too. When conditions turn risky, forget about mileage and keep a safe speed and distance.