Chevy Bolt: A Drag on Aerodynamics

General Motors Co. concedes its upcoming Chevrolet Bolt electric car lags several key competitors when it comes to aerodynamic efficiency.

The vanlike hatchback, which is due this autumn, has a drag coefficient of 0.32. That compares with a far more slippery 0.24 for the Toyota Prius hybrid and Tesla’s Model S and Model X full-electric vehicles. Next year's Tesla Model 3 is expected to boast an even sleeker 0.21.

GM says the Bolt’s design was heavily driven by GM's goal of squeezing a C-segment interior into a B-segment platform. The goal was to maximize the car’s interior space, trunk capacity and drivetrain performance while maintaining its hatchback proportions. The resulting roomier interior was enabled by widening the wheelbase, flattening the floor and pushing the windshield forward.

But the result, project lead designer Stuart Norris tells Automotive News, also was a "disaster for aero."

Still, designers at GM’s studio in South Korea, which took the lead on the program, did add numerous design elements to help improve airflow around the car. The effort integrated interior and exterior design teams.

Exterior tweaks include a rear spoiler, underbody paneling, air dams and active grille shutters that automatically close at certain vehicle speeds. The car’s A-pillar, side mirrors and tires were reconfigured to streamline airflow. Results were checked by conducting six sets of full-size wind tunnel tests, according to AN.

Interior enhancements include the use of thinner asymmetrical seats, a compact electric motor, improved HVAC packaging and a unique center console design that extends from the dashboard rather than connecting to the floor. To increase trunk size, the taillights were built into the liftgate rather than the side body panels.