At the heart of these audits is a procedure known as the "coast-down" test; the very same test that keyed officials in on problems with Kia and Hyundai window-sticker mpg numbers last year. The coast-down test involves bringing a car up to around 80 miles per hour and letting it coast to a stop. The process is used to measure overall vehicle aerodynamics, rolling resistance and drivetrain friction; the goal being an accurate calibration of the EPA's dynamometer, which is then subsequently used to run test cycles and estimate mpg data.
The coast-down test is used to measure overall vehicle aerodynamics, rolling resistance and drivetrain friction.
Christopher Grundler of the EPA's Office of Transportation and Air Quality has declined to comment on the audit results with the official report due out sometime this fall, but he did tell AN that the results "will be very interesting to some people."
The EPA has only begun regularly auditing this sort of test data submitted by automakers for about three years now, and Grundler believes that reports like the one upcoming are important information for the public at large. The actual results from this coast-down test are "coefficients from a mathematical formula" that are not easy to parse for your average car buyer, but Grundler said in his interview that the reports findings would be delivered in "plain English."
Apparently the test is neither easy nor cheap for the EPA, as it requires a level two-mile stretch of straight track. This year the agency paid to use the Chrysler proving grounds in Chelsea, MI, along with two unnamed tracks in Arizona.