The Cars.com True Mileage Index

With gas mileage figures posted on the window sticker of just about every new car sold in America, it's easy to see where an individual model stands. Rating where each automaker stands, though, is trickier. The closest thing to an official ranking is the federal government's corporate average fuel economy program, established in 1975 and regulated by the National Highway Traffic Safety Administration. Suffice it to say the program has major implications for automakers — especially with a recent mandate that mileage standards increase over the next dozen years — but these numbers can be misleading to car shoppers.

Case in point: For 2007, CAFE rated Honda's domestic passenger-car fleet at 33.5 mpg; Honda's imported cars averaged 39.6 mpg, and its light trucks averaged 25.0 mpg. Given those figures, you'd think a typical Honda dealership would be teeming with cars with combined city/highway gas mileage in the mid-30s. You'd be wrong. Aside from the Civic Hybrid, no Honda has combined mileage (meaning a combination of city and highway mileage) of better than 31 mpg.

That isn't a knock against Honda; it's largely the same story across the industry. The underreported truth about CAFE is that even though its figures are regulated by the EPA, those numbers, according to NHTSA spokesman Eric Bolton, have nothing to do with the ones posted on new-car window stickers. CAFE rankings are subject to a number of adjustments, such as whether a car can use E85 or other alternative fuels.

As such, the idea that the auto industry will be required to achieve an average of 35 mpg by 2020 is misleading. Strictly speaking, that's 35 mpg by CAFE calculations. It doesn't mean, as it might suggest, that in a dozen years the window stickers on most models will have mileage figures in the mid-30s.

That's why we've created Cars.com's True Mileage Index. Our index analyzes a number of factors — combined city/highway EPA gas mileage ratings, vehicle sales, an automaker's lineup of vehicles and more — to determine major automakers' average gas mileage across their lineups. The True Mileage Index offers a snapshot of the sort of mpg ratings you'll actually see reflected on new-car stickers.

True Mileage Index
AutomakerMPG
American Honda Motor Co.
Honda
Acura
24.4
24.9
19.8
Toyota Motor Sales U.S.A.
Scion
Toyota
Lexus
24.3
25.2
24.8
21.0
Hyundai-Kia Automotive Group
Hyundai
Kia
24.1
24.6
23.6
Nissan North America
Nissan
Infiniti
23.2
23.8
18.8
Volkswagen Group of America
Volkswagen
Audi
Bentley
Lamborghini
Bugatti
22.2
23.2
20.1
11.8
11.2
9.9
American Suzuki Motor Corp. 21.8
INDUSTRY AVERAGE21.7
Daimler AG
Smart
Mercedes-Benz
Maybach
21.5
36.2
18.8
12.0
Fuji Heavy Industries (Subaru) 21.3
Mitsubishi Motors North America 20.7
BMW Group
Mini
BMW
Rolls-Royce
20.6
28.3
18.9
13.3
Ford Motor Co.
Mazda
Ford
Mercury
Volvo
Lincoln
20.5
23.0
20.2
20.1
18.9
18.5
General Motors
Pontiac
Saturn
Chevrolet
Saab
Buick
Cadillac
GMC
Hummer
19.9
22.0
21.5
20.3
20.3
18.7
17.7
16.5
14.9
Chrysler LLC
Chrysler
Dodge
Jeep
19.0
19.8
18.7
18.7
Porsche Cars North America 18.3
Tata Motors
Jaguar
Land Rover
15.4
18.3
14.7

Due to low sales volumes and non-affiliation with any of the above brands, Aston Martin, Ferrari, Isuzu, Lotus and Maserati were excluded.

On the strength of high-mileage sellers like the Civic and Fit, Honda's 24.4-mpg average clinches the top overall spot by a hair. Toyota follows closely behind, with its Lexus division nabbing the most-efficient title among luxury brands. Rounding out the top five are Hyundai-Kia, Nissan and Volkswagen. With a product mix that's heavier in trucks and SUVs, Detroit automakers post comparatively lower numbers, but there are a few bright spots: Ford-controlled Mazda earns a respectable 23.0 mpg, while GM's car-heavy Pontiac division comes in at 22.0 mpg.

Not surprisingly, the top individual rankers include a number of small-car niche brands: Mercedes' Smart division averages 36.2 mpg, while BMW's Mini and Toyota's Scion come in at 28.3 and 25.2 mpg, respectively. Of the mainstream marques, Honda, Toyota and Hyundai are at the top of the heap. At the opposite end is Indian automaker Tata, whose recent Jaguar and Land Rover purchases have a predominance of powerful but gas-guzzling luxury cars and SUVs.

Editor's Note

The True Mileage Index gauges average fuel economy for a brand based on numbers from the EPA. We calculate mileage using the most efficient stuff you can pump in, so there is no allowance for cars that can use E85, which typically gets about 25 percent fewer miles per gallon than regular gas. We studied mileage for all drivetrain variants — including different engine and transmission combinations — across a model line, factoring in (whenever possible) sales figures for any variants in mileage. We also look at how many of each model are sold. We try to analyze only sales of the model year in question, but automakers rarely break out sales by model year. For example, a given brand's September 2007 sales could include an even mix of '07 and '08 models. Thus, we track sales during several months where the current model year is the predominant seller, but we also account for any early changeovers to the next year or late changeovers from the previous year.

In a perfect world we'd have sales volumes broken out by model year and product ratios for every drivetrain variant. Unfortunately, most automakers won't reveal that sort of data. As it stands, Cars.com's True Mileage Index shows average sales-weighted mpg across a lineup from a mix of public sales figures, mileage numbers and internal automaker data. Sources include the EPA, automaker data and Automotive News.

© Cars.com 7/31/08