Maintaining the Speed Limit

Improving Your Fuel Economy – Maintaining the Speed Limit

Driving the speed limit will save you money. Besides not receiving speeding tickets and higher insurance premiums, driving the speed limit generally keeps your vehicle in an RPM range that is ideal for maximum performance and fuel economy.

Studies have shown that speeds in excess of 55 miles per hour (90 kilometers per hour) decrease fuel economy at an exponential rate. The difference between driving 55 miles per hour and 65 miles per hour may only be four or five minutes of travel time but it may cost you an extra $5 in gas. Consider that driving the speed limit is like being paid $5-$10 per to take that trip.

The Mechanics Behind Slower Speeds and Fuel Economy

There are many different variables which affect fuel economy: engine efficiency, operating temperature, the drag coefficient of the vehicle (dictated by the aerodynamics of the vehicle’s design), the type of fuel being used and the elevation of the driving environment. Phew – that’s a lot to consider.

Driving at slower speeds directly affects the drag coefficient of the vehicle. Though the actual coefficient value doesn’t change, the resistance placed on the vehicle by the ambient air or wind does change based on speed. The faster you are moving, the more resistance that the air will place on the vehicle.

Imagine that the ambient outside air, the environment in which your vehicle must drive through, is a gigantic bowl of water; the moment that you remove your foot from the gas your vehicle immediately begins to slow down. Have you ever noticed that coasting at slower speeds lasts longer than coasting at higher speeds? This is because when you are driving at high speeds your vehicle must slice through the air.

Variables, such as wind resistance and even temperature/air density will affect your vehicles ability to do this efficiently. When cruising at 20 miles per hour, less resistance is placed upon your vehicle. This is due to the fact that the air has more time to channel around the vehicle, as opposed to colliding with it. When cruising at 80 miles per hour, the air has substantially less time to channel around your vehicle meaning that the result is a 100% difference in fuel economy from 40 miles per hour when compared with 80 miles per hour.

In Closing

The need to get wherever you’re going quickly can overcome your desire to get optimum efficiency from your vehicle. However, the faster you drive the more fuel you will burn. Next time you go for a long drive on the highway, try cruising at the speed limit as opposed to 5 miles per hour over. You will notice a definite difference in fuel consumption.