excerpted from: The Steering Column: After 30 years, the EPA finally comes up with realistic fuel-economy estimates.
The Steering Column
BY CSABA CSERE, April 2007
The changes will have a major effect on the estimates appearing on new-car window stickers. On average, estimates of city mileage will decline by about 12 percent and highway estimates will fall by roughly 8 percent. But some vehicles, particularly those that enjoy extremely high fuel-economy estimates under the current system, will suffer mpg cuts of 25 to 30 percent.
Hybrids will take the biggest hits. Measured by the new procedures, a 2007 Toyota Prius's city fuel economy would drop from 60 mpg to about 48. Its highway figure would shrink from 52 mpg to about 45. Those reductions will bring the mileage estimates of the Prius way closer to reality. In a Prius road test in February 2004, we got 42 mpg during our usual speed-limits-be-damned driving, and even when feather-footing a Prius to get the best mileage [C/D, September 2004], we only achieved between 50 and 54 mpg. The new EPA figures will fall between those extremes.
Cars with lower mpg numbers will typically take smaller fuel-economy hits because vehicles with bigger engines will be less affected by the harder accelerations and higher speeds in the new procedures. A BMW 328 six-speed sedan will likely go from 20/29 city/highway mpg to 18/27. A Corvette Z06 will go from 16/26 to 15/24. A Nissan Altima four-cylinder with a CVT will change from 26/34 to 23/31. And a Chevy Tahoe 4WD will get a 13/19 label, down 2 mpg in each test. Remember, these are my estimates. Come the 2008 models, automakers will be doing their best to incorporate hardware and calibration changes to maximize mileage on the new tests.
During 2007, you'll need to keep close tabs on these fuel-economy labels because, as early 2008 models are introduced, their labels will reflect the results of the new procedures, yet existing 2007 models parked next to them will still be labeled with the outdated, higher-mpg figures. The EPA has come up with a formula that can approximate the change between the old and new fuel-economy numbers, and it can be found at CARandDRIVER.com/2008fueleconomy.
None of this changes the fact that we all drive different routes, at different speeds, with different driving styles. In other words, your mileage will still vary. But with these new EPA mileage estimates, it will vary a lot less than it used to.
Reprinted with permission from Car and Driver Magazine. Copyright (c)2007 Hachette Filipacchi Media U.S., Inc.