The Finer Points of the Chevy Volt


Chevy’s upcoming electric vehicle the Volt — highly anticipated, and crucial to GM’s future — has gotten a lot of press for its fully integrated hybrid drivetrain, but relatively little attention has been paid to the car’s aerodynamics. In a blog post on GM’s FastLane, Bob Boniface, director of design for the Volt, points out the various streamlined features, even including a few new sneak-peek photos for good measure (see below).

After drivetrain efficiency, aerodynamics is the second most important factor in a car’s overall energy consumption. As Boniface writes, “When you’re driving down the road, it takes energy to slice through the air that is pushing against the car. That force is known as drag and it can account for up to 20 percent of the energy consumed in an average vehicle.” And for hybrids and electric vehicles, efficiency is paramount.

Boniface says that GM spent hours experimenting with various angle designs, which they tested in the wind tunnel (see video below), before deciding on the “rounded and flushed front fascia, tapered corners and closed grille” shown in the photos above.

In a world of least air resistance, the teardrop is the ideal aerodynamic shape — look at Aptera’s Typ-1. That’s one way Aptera gets such stunning MPG figures; a vehicle like that will cut through the air like a knife through water.

Not every vehicle maker is willing to go to such lengths on design to cut down on drag. But the Volt needs to be a mainstream vehicle, one that not just early adopters will buy. So there has to be both an aesthetic reason for every line and form, as well as sound aerodynamic reasoning behind those lines and forms.

And the Volt needs to be able to produce considerable speed. Not like a race car, but to meet the expectations of a mid- to high-end car. Increasing a vehicle’s speed does horrendous things to the aero drag on it. When the car speeds up to 20 miles an hour from 10, the drag doesn’t double, it quadruples. When you increase your speed to 40 mph, it quadruples again. Every time you double your speed, you quadruple the drag. This is known as the inverse square law, and you can see why it takes so much energy to push a race car down a track at, say, 200 mph.

When the Volt eventually comes out, it will be up to the customers to decide if they like the aesthetic decisions vs. the aerodynamic ones. And it could be another reason why the Volt looks a little different from the standard. But as Boniface notes: “When you’re trying to extend gas-free driving of the vehicle, you’ll take all the efficiency you can get.”



Power required of a vehicle to offset aero drag is proportional to the velocity cubed. (The drag force is proportional to the velocity squared.)

Cd of certain cars (Coefficient of drag)

Prius .26
GM EV1 .195
Aptera .11 (claimed)

Bernie Haverkamp

Inverse square law has nothing to do with drag. Inverse square law applies to forces which decrease over distance such as gravity. Drag is a simple sqaure rule not an inverse square rule.

Comments are closed.