Volt's coefficient of drag

[Dr Mordrid]

Link....

GM has talked tirelessly abut how aerodynamic the Volt is, how its shape was born from the wind tunnel, and how important aerodynamics are for the car to achieve its 40 miles all electric range.

Yet for all that talk, the company has never released any official figure for the vehicle’s coefficient of drag (CD). This is the numerical measurement that indicates how slippery a car is, and unlikely to be slowed by wind resistance.

Bob Boniface who is chief of Voltec design finally provided us the details that were obtained when GM measured the Volt and its competitors on its own wind tunnel.

“We had the comparably-equipped 2010 Prius with 17 inch wheels, and the new Insight,” he said.

“The Prius came in at .30,” said Boniface. “That was a number that was verified in our tunnel, in Chrysler’s tunnel, and in Ford’s tunnel.”

“The Insight was 0.32, and the Volt was .28,” he said.

“I’d like to test the Volt in the same tunnel where Toyota got their 0.25 value,” he teased.
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[Brian Ellis]

This is a thorny subject and empirical results in tunnels can vary ±0.05 due to tunnel design, tolerance in wind speeds, tunnel wall turbulence etc.

The average modern automobile achieves a drag coefficient of between 0.30 and 0.35. SUVs, with their typically boxy shapes and larger frontal area, typically achieve a Cd of 0.35–0.45. A very gently inclined windshield gives a lower drag coefficient but has safety disadvantages, including reduced driver visibility. Certain cars can achieve figures of 0.25–0.30, although sometimes designers deliberately increase drag in order to reduce lift.

Some examples of Cd follow. Figures given are generally for the basic model. Some "high performance" models may actually have higher drag, due to wider tires and extra spoilers.

From here

This gives a long table, presumably derived from manufacturers' data.

The current Prius is given as 0.26 and next year's model as 0.25. Next year's Volt is given as 0.26.

I wouldn't set too much store on the tunnel figures. It is easy to fudge them. Just a slight (1 mm) misalignment of the car will alter the value, or pseudo-passenger weight, or steering direction, or tyre tread depth, or size of body gaps etc. Obviously, makers will give their best results.

[Fluff]

Wonder what % the wing mirrors add...