1 . WeightLow weight is the cornerstone of a fuel-efficient vehicle because the amount of energy required to accelerate a car is directly proportional to its mass. Plus, lightness has a cascading effect. A lightweight body doesn’t require a stout chassis, heavy-duty suspension components or large brakes. And the tires can be smaller, reducing rolling resistance. 2. Aerodynamic dragThe power—the rate of energy consumption—required to overcome aero drag is a product of the speed and the car’s aerodynamic resistance. Lowering the resistance requires a two-pronged strategy: reducing the frontal area (the product of the car’s height and width minus about 15 percent) and the drag coefficient, which is a measure of how easily the shape glides through the air.3. Mechanical EfficiencyHow much of the car’s onboard energy makes it to the road? Electric powertrains are more efficient in this regard but require large and heavy batteries, which hurt overall vehicle efficiency. Internal combustion engines and liquid fuel are lighter but convert only about 30 percent of chemical energy to motion. Hybrids attempt to bridge the gap by capturing normally wasted braking energy. 4. Rolling ResistanceDrivetrain and bearing friction play a role here, but so does the rolling resistance of the tires. The less rubber on the road, the better, but beware of handling instability. And weight is the enemy of low rolling resistance (see No. 1, above).X-Prize Entrant: FVT Racing eVaro »>Media Platforms Design TeamJohn Pearley HuffmanContributing EditorJohn Pearley Huffman has been writing about cars since 1990 and is getting okay at it. Besides Car and Driver, his work has appeared in the New York Times and more than 100 automotive publications and websites. A graduate of UC Santa Barbara, he still lives near that campus with his wife and two children. He owns a pair of Toyota Tundras and two Siberian huskies. He used to have a Nova and a Camaro.
