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GM asking for trouble with Volt mileage claims
AP photo
GM claims fuel consumption of 230 mpg for its Chevy Volt.
Last week, General Motors revealed that the figure represents, in American measure, the gas mileage it claims for its Chevy Volt – the plug-in hybrid intended to drag the company from bankruptcy to showroom-shiny future.
But will the corporate smile morph into a dreary frown?
GM's marketers opted for flash rather than a figure likely to represent the fuel economy that real drivers (who will pay around $40,000 U.S., minus government rebates, for the Volt) will achieve.
The company won't say how it and the U.S. Environmental Protection Agency arrived at 230 m.p.g. for city driving or even their backup claim in which, as GM Canada spokesperson Stew Low put it: "We expect the majority of Volt drivers who plug-in for a full charge once per day to achieve triple-digit fuel economy during typical daily commuting." That's 100 miles per American gallon, or 2.3 litres per 100 kilometres.
Electric vehicle enthusiasts are filling the information vacuum by circulating the following formula on the Internet: (I'll use American measures; converting into Canadian metric is head-spinning.)
They begin with GM's claim that the Volt's range will be 40 miles (62 kilometres) on battery alone – enough, the U.S. Bureau of Transportation says, to fuel the daily commute of 78 per cent of American drivers.
The fuel-economy test added 10 miles during which the small gasoline engine kicked in to keep the battery charged. Those 10 miles consumed 0.2 gallons. So 50 miles of travel, using 0.2 gallons of gasoline, translates into 250 miles per gallon. Adjusting for energy consumed by the battery produces the glittering "230."
The calculation assumes that with the gas engine running, fuel use would remain at 0.2 gallons for every 10 miles, or 50 m.p.g. So, the more you drive between plug-ins, the worse your fuel economy.
For a 160-mile trip, the Volt would use 2.4 gallons, for about 67 m.p.g. A 300-mile drive, using 5.2 gallons, would achieve around 57. With this calculation, "triple-digit" fuel economy would be possible only for trips of less than 80 miles. This would cover 90 per cent of Americans' presumed daily use, but seems to make the Volt mainly a costly commuting car.
Using this Internet calculation, when a drive between charges exceeds about 225 miles the Volt's fuel economy is similar to the Toyota Prius or other non-plug-in hybrids likely to cost much less.
GM cautions against the formula: "It is inappropriate to extrapolate these test results as a means of estimating overall fuel economy," Low says. But the company hasn't described its own calculation or estimated the mileage over longer distances.
In any case, the "230" claim appears arbitrary. Had GM focused on commutes under 40 miles it could have advertised infinite gas mileage. Using 45 miles, it could have proclaimed 450 m.p.g. Increasing the commute to 60 miles would reduce the mileage to 150.
And all this likely overstates the performance at any distance because the promise of 40 miles on battery alone is open to question.
As I've written before, the EPA test omits many real-world conditions – such as extra passengers, air conditioning, wind and hills – that reduce the all-battery range.
This isn't to say the Volt will flop. But GM is courting trouble by trumpeting dubious performance claims.
Chances are, by the time the car comes to market nobody will take "230" seriously. But the attempt to feed it to us could leave a lingering bad taste that makes the entire project unpalatable.
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