Hybrids, small turbos often fall short of EPA mileage estimates

Hybrids get great mileage, but some leave their owners disappointed because their window stickers promise better fuel economy than the cars deliver.

We analyzed more than 315 cars and compared the results of our own tests with EPA window stickers. While most cars in our study fell within one or two mpg of their official estimates, two groups stood out as not living up to the claims their window stickers' promise. (See our full report on "The mpg gap.")

Here's what we found:

• The vast majority of hybrids fell short of their EPA estimates in our tests. As a group, hybrids missed their estimates by 10 percent on average. The most egregious were the latest hybrids from Ford and Volkswagen. The Lincoln MKZ Hybrid, rated 45 mpg overall in EPA tests (with identical city and highway ratings), returned just 35 mpg in our tests, a discrepancy of nearly 25 percent.

• The latest wave of cars with small, turbocharged engines also fell short. In our analysis, more than three quarters of cars with these small, turbocharged engines missed their EPA estimates. Some cars fell short of the advertised figure by as much as 15 percent.

These types of cars are much more sensitive to how they're driven, says Mike Duoba, a test engineer with Argonne National Laboratory who works on fuel economy testing. So the old adage about "your mileage may vary" holds doubly true for these types of cars.

See which vehicles have the best fuel economy by category.

And the type of driving the EPA uses to test fuel economy looks a lot different than the normal traffic. EPA tests are run in a laboratory on a rolling treadmill called a dynamometer. The EPA's two main fuel economy tests were developed in the 1970s as emissions tests. And the simulated routes drivers follow on them are designed not to exceed the safety parameters of the dynamometer technology of the day.