CHEAT SHEET: Truth About Sky-High MPG Claims for Electric, Hybrid and Mini Cars

The battle of the MPGs kicked into high gear this week with General Motors making the bold claim that its upcoming Chevy Volt, an extended-range electric vehicle, will get 230 MPG for city driving. Nissan countered with an announcement that its 2011 all-electric LEAF sedan will get some 367 MPG — oh, snap! This banter of course raises questions about the validity and relevance of measuring the efficiency of cars that run on electricity in terms of how far they can go on a gallon of gasoline. (Check out the Atlantic, Consumer Reports, EcoGeek and Edmunds’ Green Car Advisor for some thoughtful discussions.)

Fritz Henderson Makes Volt Announcement

While we’re at it, how did GM really come up with that triple-digit MPG, and how does the company’s calculations compare with ratings for cars like the LEAF, gen-3 Toyota Prius, Smart Fortwo, Tesla Roadster and the Fusion Hybrid from Ford, which said earlier this summer that it’s making fuel efficiency improvements a top priority in upcoming lineups? We’ve put together a chart comparing fuel economy claims and methodology for these vehicles to help put them in perspective.

The EPA’s fuel economy rating system has plenty of critics (especially after a little revised number crunching by the agency disqualified some vehicles from the cash for clunkers program), but it does have relative transparency and consistency going for it. So even though real-world mileage varies from EPA ratings, numbers from the agency give us a sense of relative fuel efficiency of different vehicles on the market. The EPA isn’t vouching for GM’s 230 MPG claim, since it has not finalized the new rating system for plug-in vehicles and it has not tested the Volt, as the NYT Wheels Blog notes (GM’s Frank Weber says the model is slated for testing early next year).

In contrast with GM’s formerly-mysterious “230” ad campaign and focus solely on city driving, and Nissan’s unexplained 367 MPG estimate (in a talk at the Plug-in 2009 conference in Long Beach yesterday, Nissan’s Mark Perry said the company used methodology for “a zero emission kind of world”), we know that the EPA has two tests to simulate city and highway driving. In both city (a stop-and-go 30 minute test) and highway (a non-stop 10-mile test averaging 48 MPH) tests, MPG estimates are based on the amount of emissions generated during the simulation and then adjusted downward to reflect real-world conditions, such as aggressive driving or cold temperatures. For plug-in vehicles with zero tailpipe emissions, clearly this system is lacking.

If you have ideas for how the rating system should work (perhaps a total overhaul to measure and highlight gallons per mile?)  — or if you see ways to improve our chart below or would like to see other vehicles added, please let us know in the comments.

Vehicle Fuel Economy: City/Hwy/Combined How MPGs Were Calculated Estimated Costs
2011 Nissan LEAF (electric) 367 MPG equivalent/??/?? Unknown. EPA Rated? No. “Less than the cost of gasoline”
2011 GM Chevy Volt (extended-range electric) 230 MPG/??/”Over 100 MPG” GM says it used “tentative EPA methodology” for testing plug-in vehicles, a 51-mile urban driving cycle, and reportedly 40 miles of electricity and 11 miles on the gas engine. However the EPA says it has not published even a draft protocol for testing plug-in vehicles like the Volt. EPA Rated? No. GM claims $2.75 per 100 miles for city driving (Assuming: 25 kWh per 100 mi)
2009 Tesla Roadster (electric) 135 MPG equivalent/??/?? According to former Tesla Marketing VP Darryl Siry, the total energy used for a full charge of the Roadster’s battery is 62.3 kWh (assuming a 15 percent loss). That’s equivalent to 1.85 gallons of gas for the 244 miles that the Roadster can go on a full charge – 244 miles divided by 1.85 gallons gives us a little less than the equivalent of 135 MPG. EPA Rated? No. $2.81 per 100 miles for city driving (Assuming: 62.3kWh at $0.11/kWh = $6.85 per charge, which is supposed to deliver a range of 244 mi).
2010 Smart Fortwo (diesel) ??/??/69 MPG This model is slated for the European market, so has a rating from the EU’s New European Drive Cycle, or NEDC system, which combines city and highway drive cycle tests. It’s meant to reflect European driving patterns. EPA Rated? No. About $3.81 per 100 miles at U.S. diesel prices (currently averaging $2.63/gallon)
2010 Toyota Prius (hybrid) 51/48/50 MPG Standard EPA tests: 11 mile stop-and-go city cycle, 10 mile highway with average 48 MPH) EPA Rated? Yes. $5.28 per 100 miles (using EPA estimate of $1.32 per 25 mi, $2.65/gal gas); $795 for fuel annually (assuming $2.65/gal gas and using the EPA’s default 15,000 mi/year, 45 percent hwy, 55 percent city)
2010 Honda Insight (hybrid) 40/43/41 MPG Standard EPA tests: 11 mile stop-and-go city cycle, 10 mile highway with average 48 MPH). EPA Rated? Yes. $6.32 per 100 miles (using EPA estimate of $1.58 per 25 mi, $2.65 gal gas); $946 for fuel annually (assuming $2.65/gal gas, and using the EPA’s default 15,000 mi/year, 45 percent hwy, 55 percent city)
2010 Ford Fusion Hybrid 41/36/39 MPG Standard EPA tests: 11 mile stop-and-go city cycle, 10 mile highway with average 48 MPH). EPA Rated? Yes. $6.80 per 100 miles (using EPA estimate of $1.70 per 25 mi, $2.65/gal gas); $1,019 for fuel annually (assuming $2.65/gal gas and using the EPA’s default 15,000 mi/year, 45 percent hwy, 55 percent city)
2009 Smart Fortwo (premium gas) 33/41/36 MPG Standard EPA tests: 11 mile stop-and-go city cycle, 10 mile highway with average 48 MPH). EPA Rated? Yes. $8.08 per 100 miles (using EPA estimate of $2.02 per 25 mi, $2.91/gal premium gas); $1,213 for fuel annually (assuming $2.91/gal premium fuel and using the EPA’s default 15,000 mi/year, 45 percent hwy, 55 percent city);
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