Chevy Volt -- 100 mpg, or 48 mpg?

Posted: September 8, 2008

Chevy Volt Spy Shots

Chevy Volt Spy Shots

General Motors and the Environmental Protection Agency have apparently begun an argument over just what, exactly, GM's upcoming plug-in hybrid Chevy Volt is.  The point isn't just academic -- it could determine whether the Volt receives a jaw-dropping EPA rating of over 100 mpg -- -- making it by far the most fuel-efficient car sold by a major automaker -- or a rather Prius-like 48 mpg.

GM considers the Chevy Volt an electric car.  The EPA wants to classify it as a hybrid.

PC Magazine explains, "Its drivetrain is entirely electric, since the companion gas engine powers a generator, not the car itself. The Volt is not a hybrid in the usual sense, in other words. GM claims it can run 40 miles before the gas engine even kicks in."

The car uses its batteries to provide most of its power, activating the electric generator only when they are depleted to a certain point.  According to, "The car is designed to arrive to destination at roughly 30%-35% of the battery's state of charge."

According to Motor Trend, "Reports suggest the Volt can make it through the EPA test cycle -- which from 2008 includes high speed running, air conditioning load, and cold start tests in addition to the city and highway cycles -- with the internal combustion engine running about 15 percent of the time."  That result would give the Volt "an EPA fuel consumption rating somewhere north of 100mpg. But the EPA apparently wants to certify the Volt differently."  Because it includes a gasoline engine, the EPA considers the Volt a hybrid -- even though that gasoline engine doesn't power the transmission, acting only as a generator.  EPA hybrid testing rules require that the cars finish the full suite of tests with their batteries fully charged -- not at the 30 percent the Volt is designed to retain at the end of most drives.   If the Volt were required to finish the tests with its battery fully charged, its fuel consumption rate would instead be "just under 48mpg, because the internal combustion engine would have to be run essentially all the time to keep the batteries near full charge."

"While not a bad number," Autoblog Green notes, 48 mpg is "no where near reflective of what the Volt could achieve in the real world for most drivers."  If GM's claims about the car are true, the 100mpg number would be closer to most people's actual experience of driving the car.  If the Volt is in fact an entirely new technology, AG comments, "the EPA needs to work with manufacturers to change the testing methodology and come up with something that more closely approximates real world conditions for plug-in vehicles. Insisting on something else would force automakers to calibrate plug-ins to meet those requirements at the expense of real world efficiency, helping no one."

It also can't be overstated what that 48 mpg rating might do to Volt sales.  The next-generation Prius is expected to achieve more than 90 mpg.  Even the current Prius is rated for 48 on the highway.  GM clearly doesn't want to have to market the Volt in 2010 and later as nearly as fuel-efficient as  a 2008 Prius.

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