Chevy Volt Designers: Shape, Not Weight, Is More Important
December 11, 2007

By Bill Visnic

WARREN, Michigan –- General Motors Corp. designers and engineers say they will have to figure out ways to seriously cheat physics if a production version of the company’s Chevrolet Volt plug-in hybrid-electric concept car is to deliver on the promised driving range of 40 miles propelled solely on battery power.

GM designers revealed at a media event here they have embarked on an all-out battle to minimize efficiency-reducing aerodynamic drag. And the company recently commissioned a new studio and a 45-strong staff dedicated to developing hybrid and full electric vehicles using its E-Flex “modular” propulsion system. Right now, that means the full staff is working on just one vehicle: the Volt.

Frank Weber, global chief engineer and vehicle line executive for the E-Flex system, shows surprising data that indicates aerodynamic drag is a much greater enemy than mass when it comes to limiting how far the Volt will be able to travel solely under electric power. So the Volt design team is working overtime to optimize the plug-in hybrid’s styling and shape –- and Ed Welburn, vice president of global design, reveals the engineers and aerodynamicists already have cut aerodynamic drag of the original Volt concept car by more than 30 percent.

And they insist the new shape is more appealing.

“It’s a fresher, newer design than what the Volt concept was,” Welburn confidently says.

Bob Boniface, director of design for E-Flex vehicles, agrees, saying particular changes from the first Volt concept car center on the crucial front and rear areas. But he says the latest Volt bodywork doesn’t just achieve a markedly better drag coefficient –- it also is more aesthetically appealing.

“To me –- and I worked on the [original Volt] show car -– I like this front end better,” Boniface says. To back him up, GM releases a “teaser” image of the latest Volt styling showing a smoother, rounder front corner.

To help achieve the 40-mile electric-only driving range for Volt, Boniface tells AutoObserver that GM engineers have decided on a target coefficient of drag, but “I’m not going to tell you.” He also is quick to say stylists will not let the aerodynamicists completely have their way with the shape, or else it would be boring and bland.

Discussion of hybrid and pure-electric vehicle development often focuses on reducing mass, because for conventional vehicles powered by internal-combustion engines, more mass typically means less fuel efficiency. But Weber says adding extra weight in hybrids and fully electric vehicles -– particularly when that much of that mass is dedicated to battery capacity -– is not such an engineering no-no, because it enables increased levels of electricity-producing regenerative braking when the vehicle decelerates.

Cutting aerodynamic drag, meanwhile, has a markedly more positive effect on driving range. Weber’s data shows reducing vehicle weight by as much as 400 pounds delivers just two more miles of range in city driving, and so-called “sensitivity to mass” is even less vital on the highway, where the same kind of massive weight reduction would yield just one extra mile of driving range.

A proportional decrease in aerodynamic drag, meanwhile, could take the Volt from 37 miles of highway driving range to 42 miles. And more surprising, aerodynamic optimization has even more impact in city driving.

Boniface, who recently helped design GM’s widely acclaimed Camaro concept car, says the “new” shape of the Volt will not be revealed anytime soon. And he is careful to remind the Volt remains a concept and has not yet been formally approved for production.

Photos by GM
1 – The restyled Chevy Volt in the wind tunnel
2 – Designer Bob Boniface, who worked on the Volt concept, heads styling for the production Volt.

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