The Importance of Fuel Efficiency


Fuel efficiency, defined by gallons of gas per 100 miles, can make all the difference when shopping for a new vehicle. Sources like Wikipedia and the MIT School of Engineering note that automobiles account for 60 percent of oil consumption and 25 percent of greenhouse gas emissions in the U.S.


Size and Weight

As an energy source, fuel has a limited supply, and the more a vehicle weighs, the less distance it can travel on a gallon of fuel. The relationship between vehicle weight and fuel efficiency is well known, with the curve-fits for city and highway mileage versus curb mass revealing a clear inverse correlation.

But the weight of a vehicle is only one factor in its overall efficiency. Other factors, including engine and tire maintenance, as well as wheel and roof rack weight, can also reduce fuel economy by requiring the vehicle to work harder to keep itself moving.

Even simple changes in vehicle spec can have a big impact on fuel efficiency. For example, using lighter paper in a corporate jet can save 643,000 kilograms of fuel per flight. Fleet managers can also lighten the load by eliminating unnecessary equipment, storage bins and accessories, such as tools or extra shelving, or simply carrying less in the trunk and back seats. This can easily add up to several thousand pounds in savings. Similarly, when shopping for vehicles, consider selecting the lightest option within each class.


The way a vehicle moves through air affects fuel efficiency. A more streamlined car produces less drag, which requires less engine power to overcome. This is especially true for highway speeds, where a larger portion of the fuel consumed is used to overcome aerodynamic forces.

For example, the Toyota Prius gets very good fuel economy because its frontal area is extremely low, with a Cd of just 0.26. Pickup trucks and SUVs, on the other hand, have a higher Cd because they are taller and need to accommodate large cooling systems.

Engineers in motorsport use aerodynamics to generate downforce, which increases a car’s grip and stability during high-speed cornering while also reducing drag. They do this by minimizing 방문운전연수 the frontal area and designing efficient air ducts for brakes and engines.

Truck manufacturers are working hard to improve aerodynamics to increase their fleet’s fuel efficiency. These efforts can save drivers money, lower their carbon footprint and align with broader sustainability goals. Trucking regulations are increasingly demanding that truckers make significant aerodynamic improvements to reduce their fuel costs and emissions.

Engine Efficiency

A vehicle engine converts chemical energy from fuel into kinetic energy your car uses to move. But the engine’s thermal efficiency—the rate at which it converts fuel into usable power—also contributes to a vehicle’s overall fuel economy.

The tractive energy requirements of your vehicle are the result of its wheels and axles pushing against the road, air resistance (the product of the tire’s aero coefficient and its frontal area CDA) resisting motion, inertia, hill-climbing forces, and engine and drive line losses. It is important to consider these factors when assessing a vehicle’s fuel efficiency.

Some of the fuel’s energy must be used to induct intake and exhaust gases into the engine, overcome friction between sliding surfaces inside the engine, and drive engine auxiliaries, such as oil and water pumps. This is accounted for with the gross indicated engine efficiency and the net gas exchange and mechanical efficiency of your engine. In addition, some of the fuel’s energy is wasted as heat through the exhaust and in combustion losses. The brake thermal efficiency of your engine is the sum of these various losses.

Transmission Efficiency

A transmission’s main function is to multiply the rotational power of a vehicle’s engine via changing gear ratios. This allows the engine to function within a narrow range of revolutions per minute (RPM) while still delivering the performance required by a Federal Test Procedure drive cycle.

In addition to enabling optimum engine speeds, transmission design also reduces fuel efficiency losses by reducing shift change steps. This is achieved by using a larger gear ratio spread with smaller change steps.

Finally, transmissions that allow a driver to downshift during a normal driving cycle can dramatically reduce fuel consumption. However, fleets considering this type of technology must be sure that their driver pool is made up of experienced and efficient drivers capable of operating the truck correctly.

Lastly, one of the most overlooked ways to improve fuel efficiency is simply to avoid prolonged engine idling. Idling burns a significant amount of fuel and generates a significant amount of pollution in the process. Fleets that can eliminate idle time are likely to see an immediate improvement in their fuel efficiency.


In addition to wasting fuel, excessive engine idling also damages the engine. In the case of a diesel truck, this is especially important because idling increases the amount of wear on the internal components. This can result in a shorter engine life and increased maintenance costs.

In a trucking fleet, idling can take many forms: waiting at traffic lights, keeping the engine running to pick up passengers, or idling while drivers make deliveries or sleep during rest stops. Regardless of the reason, idling is expensive and creates emissions that damage the environment and contribute to climate change.

To reduce the impact of idling, some companies have installed auxiliary power units to allow trucks to turn off their engines when not in motion. While these solutions are effective, they also increase the cost of the vehicle and limit driver flexibility. Other options to consider include installing onboard energy systems that can provide heating and cooling to the cab and sleeper, as well as electrical power for accessories and electronic devices. These are more cost-effective and environmentally friendly solutions.