Biggest overachievers and underachievers in real world highway MPG
Car and Driver tested 100 cars for their real world highway MPG by doing a 200 mile loop of Michigan's I-94 maintaining 75 mph (120 km/h). Here are the results ranked by percent difference between real world and EPA numbers (slide show format):
Interesting to see mostly trucks and SUVs for the underachievers. Could it be that the testers had more offroad accessories and the EPA ratings are from base models with, say, lower rolling resistance tires?
Note how MPG isn't linear - The BMW 330i EPA rating was 34 MPG highway, but achieved 41 MPG real world (+ 7 MPG; 21 % difference) while the Maserati Levante is rated at 19 MPG highway and achieved 24 MPG real world (+5 MPG; 26% difference).
Not huge differences there, in the MPG Marathon this year, the V8 Mustang got a 75% improvement over it's "already over-rated" NEDC figures, although this was hypermiling, probably no considered "real World" enough for the average user.
Why the gasoline bias? No doubt some of the diesels would have trumped all of those shown. Shame. Still seems kind of odd praising cars that still have low MPG figures in this day and age though.
Ok well just for good measure, here are some UK findings, best real world MPG for various categories including small cars, SUV'S, 4 wheel drives, family cars etc. Plenty in there getting 60-70 MPG too.
It looks like a number of Porches are doing a lot better in the real World than reported by the manufacturer. The rumor is that since they are owned by VW, and they don't want any more trouble with the EPA, they are very conservative with their fuel mileage for the new cars. Hyundai had to send monthly gas cheques to owners because they advertised larger mpg's than it was possible and pissed off a lot of people. Better be safe than sorry.
You often find it's the sportier cars get close to their ratings. This is mainly because they are "Sports" cars, so many don't have the functions that normal cars do, such as stop start etc, which boost the numbers in the test cycles. The same can be said for older cars, and basic cars, the gap between the test cycle and the real world has increased here from about 10% to over 25% in the last decade or so.
Also, Sports cars are very low, aerodynamic etc, what makes them cut through the air to make the quicker also helps fuel economy.