Big Car Small Car

There are still a lot of big cars in America. A colleague in charge of certain North American automotive metrics today pointed me to a recent study from Duke University's Fuqua School of Business that proved the regularly quoted mpg figures are often misleading.

Simple numerical facts. As usual here, considering my own example instead of copying that from the study:

First car is a typical one, one that does 30 mpg. Could increase by 10 mpg to give 40 mpg.
Second vehicle is a large SUV. It does 15 mpg. Could increase by 10 mpg to give 25 mpg.

Where is the bigger benefit? Both increase by 10 mpg so benefit is the same, right? Wrong.

First increases mpg by 33%, second increases by 67%, so the second gives twice as much benefit, right? Wrong.

Say the SUV increases only by 33% like the first case, 15 up to 20 (corresponding to 30 up to 40). The benefit is the same, right? Wrong.

If the SUV increases only from 15 to 18 mpg, it still saves more fuel than increasing the car's mpg from 30 to 40. I've said it before: However far the journey.

The Europeans have been using litres per 100 km for years. It just makes more sense.