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Men in Green step back from GM's 230mpg Volt claim

E-car not tested by us, warns EPA

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Leccy Tech The US Environmental Protection Agency has cast a shadow over General Motors' bullish claim that the Chevy Volt - aka the Vauxhall Ampera - can do 230 miles on a single US gallon of fuel.

In a statement released last night, the organisation said: "The EPA has not tested a Chevy Volt and therefore can't confirm the fuel economy values claimed by GM."

To be fair, GM didn't say the EPA had tested the Volt. It simply said it had used the Agency's draft extended-range plug-in hybrid fuel economy testing methodology to calculate a figure of its own.

Certainly, GM's claim has been met with plenty of scepticism, among Reg Hardware readers' comments and elsewhere on the web.

But why the 230mpg claim has caused so much beard stroking, hair pulling and all around consternation is a bit of a mystery here at Vulture Central.

EPA test cycles are designed to replicate likely real-world day-to-day use, and in the case of the Volt day-to-day use in an urban environment is certainly going to involve regular re-charges of the 16kWh battery pack by the driver either at home, at work or at public charging facilities where such exist.

That's why the EPA has had to cook up a new test cycle. The existing ones make no sense when applied to a car which can technically achieve an infinite number of miles per gallon as long as you never venture more than 40 miles from a power socket.

So no, the Volt won't do 40 miles on a charge then 190 on a gallon of petrol. What it will do – and here we admit we are speculating on what the EPA unpublished test cycle consists of – is drive 40 miles on a charge, then another ten using its on-board petrol-powered electricity generator, then another 40 after a re-charge and then another ten or 20 using the range extender, and so on.

If we're generous and assume the Volt's range-extender 1.4l engine can get 60mpg then the car will travel 170 miles on power from the grid and 60 miles on power generated by its petrol engine and only use one gallon of gas in the process. If you are trying to re-create actual driving conditions that seems to us a reasonable way of getting to the 230mpg figure.

GM has said that the EPA methodology uses kilowatt hours per 100 miles travelled to define the efficiency of plug-ins, and that GM expects the Volt to consume as little as 25kWh per 100 miles in city driving. Fair enough, but that doesn't tell us where those 25kWh of power come from – visits to a power socket or the generator hooked up the engine.

To add (ahem) fuel to the fire, Nissan has Twittered that its e-car, the Leaf, can get 367mpg. Apparently, that had been calculated using a formula – of truly brain-strangling complexity no doubt - from the US Department of Energy.

If there is a point to all this it's that in the age of the electric car, we are all going to have re-think our assumptions on how fuel-economy figures are determined and what they actually mean. And that is surely no bad thing. ®

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