Mr. Green Car: Chevy Volt—fuzzy math?

By Allen Penticoff

Free-lance Writer

There seems to be a lot of excitement over the prospect of the new Chevy Volt arriving. This is a four-door hybrid car with aggressive styling and technology galore slated to appear in 2010.

General Motors (G.M.) is waving the green flag with this car—but it will be a while before we see one on the streets. G.M. still depends a great deal on selling us cars that get fuel economy ratings in the 20 to 30 mpg range. So the Volt, at this point, is “green-washing.”

G.M.’s offerings have always lacked a good small-car line-up. Small cars, often imports, were a side show—something to get you to buy a Chevy, then trade up later, rather than a lifestyle car in themselves. Remember the Vega and Chevette (I saw a cream puff silver Chevette in Rockford recently—I was so amazed, I took a picture of it. Most have been crushed long ago).

But the Volt is more promising. The General has been awakened, and knows it can’t bet its future on SUVs and pick-up trucks. G.M. is claiming fuel economy of 230 mpg for the Volt. I find this mileage rating to be somewhat suspect. Real-world Priuses are getting 50 to 60 mpg. Custom-made plug-in Priuses, which are very similar to the Volt, are getting fuel economy of about 130 mpg. Both the Volt and the plug-in Priuses can claim to use no fuel for the first 40 miles operating as pure electric cars.

In the case of the Chevy Volt, the engine is really just a flex-fuel generator that kicks in to recharge the batteries as needed, or, I suppose, to supply enough amps to power the electric motor on the highway. The Prius is similar, but the engine can drive the wheels directly when the electric motor is not in use—or use the electric motor in conjunction with the engine.

Why I am suspect of the Volt’s mileage claim? I think fuzzy math may be involved. What course are they driving? If you drove 45 miles, and the generator engine kicked in and used little more than two pop cans full of fuel for the last 5 miles—is that fair math—even though you did go 45 miles on 25 ounces of fuel (230 mpg).

Take the same Volt out on the freeway, when the engine must run constantly to keep up with the demand, and the fuel economy will plummet. It is a law of physics that the faster you go, the more power it takes, and, therefore, more fuel.

It’s a bit more complicated than that, but in general, it is true. For the same size and weight vehicle, unless there is remarkable aerodynamics, and the Volt does not appear to be breaking any new ground there, fuel economies should be comparable for similar-sized engines.

To be fair, the plug-in Prius drivers are using the same sort of fuzzy math—blending electric miles with fuel-powered miles. No independent testing of a Volt has been done yet—so we’re still at taking G.M.’s word for its performance at this time. I think a fair test for plug-in hybrids will be a standard city/highway course loop—and see just how far a gallon of fuel will take you. Despite the fuzzy math, both are much better for the environment and our balance of trade with the world’s oil producers.

While seeing a short-lived demand for hybrids at their higher price during the $4 per gallon days, with so many manufacturers rushing to build hybrids and electric cars, a potential shortage of the rare-earth metals for the high-performance magnets is looming. It is predicted that engineers will need to revert to heavier, less exotic metals for the magnets in the electric motors that drive these cars. Weight up, performance down, unless some pretty sharp pencils find a way around these things.

We can bypass much of this issue. Buy the smallest vehicle that can transport you for your needs, and it will get better fuel economy, release less CO2 and cost you less—hybrid or not.

From the September 26-29, 2009 issue

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