The car industry has kept a dirty little secret for years: The widely publicized Environmental Protection Agency fuel-economy ratings overstate the miles per gallon you’re likely to get.Those of us who calculate our mileage at every fill-up already knew the truth. The general public began to notice when the redesigned Toyota Prius hit showrooms several years ago. Although the EPA said the Prius got an astronomical 60 mpg in the city and 51 mpg on the highway, Prius drivers — and the news media — registered miles per gallon in the 40s.Toyota and other car makers acknowledge that the EPA numbers often overstate fuel economy, but the testing process and window-sticker ratings are controlled by reams of regulations. Now, new tests for 2008 models will more closely reflect real-world fuel efficiency. Look for the revised numbers on the window stickers of 2008 vehicles. For now, check out Kiplinger’s new tool that gives estimates of what fuel economy would be for hundreds of 2007 models under the new tests News source: MSN Money Driving like Grandma Mileage tests were developed when we more or less channeled our grandmothers’ driving. For years, cars have been run in a lab on a treadmill with the air conditioners turned off, with conservative speeds and without any fast starts. In 1985, after an EPA study found that drivers were achieving lower fuel economy than predicted by the tests, the agency concocted a formula on paper to lower the official figures. But the formula didn’t bring the numbers down far enough, and in 2002, the environmental group Bluewater Network, a division of Friends of the Earth, petitioned the EPA to update its procedures.More from MSN Money and Kiplinger’s Personal Finance MagazineHow would your 2007 rate on mpg?Paying too much for car insurance?MSN Autos: Tips for maximizing your mileageMSN Autos’ Green Vehicle CenterCars that last a million milesThe new standards will get closer to reality by factoring in higher speeds, stop-and-go driving, more-aggressive acceleration, use of air conditioning and driving in colder weather. Mileage will still vary, but the tests will reduce estimated city mpg by 12%, on average, and highway mpg by 8%, according to the EPA. Hybrids’ fuel economy is likely to get a haircut of up to 30% for city driving and 20% for highway.Fuel-economy confusion Car makers generally approve of the new tests because they have heard enough grumbling from buyers. “It isn’t good for anybody” when customers don’t get the fuel economy shown on the window sticker, says Edward Cohen of Honda North America. But given the lower mpg estimates, car makers have a tricky marketing problem to reassure buyers that the 2008 models aren’t less efficient. You can expect to see advertising that addresses the differences.One of the first car makers to face that challenge is Mitsubishi, which introduced its redesigned Lancer sedan in March. The 2006 Lancer (Mitsubishi skipped the 2007 model) gets EPA-rated fuel economy of 27 mpg in cities and 35 mpg on highways. The numbers for the 2008 model will fall to 22 and 29 mpg, respectively. On lists of top fuel misers, the new Lancer will be a no-show, at least until the other 2008 vehicles debut. One fix, at least for the Lancer, will be listing miles per gallon under both the new and the old testing procedures, says Moe Durand, the product public-relations manager for Mitsubishi.Video on MSN Money Video: Should you buy a hybrid?Gas-electric hybrid cars get better mileage and help the environment. But are they worth the higher price?The window sticker for all cars is undergoing a slight redesign, to allow annual estimated fuel costs to be more prominently displayed. For more information about the new fuel-economy labels, see Mileagewillvary.com.