It's become a common part of road testing: Get the car up to speed, then roll down a window to see how bad the drumming and buffeting gets.

Never experienced it? Try it on your own car sometime.

Now, it turns out, there's an aerodynamic add-on fix available to cure the worst of the thrumming vibrations in the Chevrolet Volt, the best-selling plug-in electric car on the U.S. market.

2014 Chevrolet Volt

2014 Chevrolet Volt

Carmakers routinely spend hundreds or thousands of hours in the wind tunnel with every new car design, working to smooth airflow over the car's body.

Above about 40 mph, the energy required for the car to push air aside while moving through it starts to mount significantly. That's what's called "wind resistance." On the highway, it takes far more energy to displace the air than it does to keep the car moving at a steady speed.

Every time an aerodynamicist can eliminate turbulence along any part of the car, its wind resistance falls slightly--requiring less fuel to push the car through the air.

And with electric cars--whether range-extended like the Volt or battery-electric like the Nissan Leaf and Tesla Model S--every last point of drag coefficient counts to extend range just that much more.

The challenge seems to be that often carmakers don't test what happens with one or two windows open, or presume that with modern climate control, few people drive that way.

And frequently the drumming and pulsing when a passenger opens a window can be remarkably unpleasant for all passengers.

Now, courtesy of EVworld, we learned that Chevrolet dealers can order a kit that contains aerodynamic add-ons that reduce the pulsations.

"The fix must be done by the dealer and involves replacing both mirrors plus adding modified wind deflectors on the window trim," wrote San Diego Vectrix Guy.

(We give Vectrix Guy huge credit for his genius headline: Mirror, Mirror on the Car, You're the Loudest Noise By Far.)

"The mirrors have small wings to redirect the air flow, and must be painted to match each car," he wrote, "which added an extra day to the installation."

Vectrix Guy reports himself entirely satisfied with the results.

If you're a Volt owner, and you'd like to keep a window or two open at speed, your solution is at hand: See your local Chevrolet dealer.


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