MPG estimates are NOT linear: please replace your SUV now

June 20, 2008 by Rob.

NPR did an interesting report about bad MPG analysis based on research from a Duke Professor (my alma mater) . The crux of the report is that small MPG improvements (e.g. +5 MPG) at the bottom have a much bigger impact on actual fuel used ($$$) than the same improvement at the top. So replacing a 30 MPG car with a 35 MPG car is a much smaller real consumption difference than replacing a 15 MPG one for 20 MPG.

This is not surprising. If fact, it’s painfully obvious if you present the data as a percentage (33% vs 17%) but we’ve gotten so used to looking at the just the MPG #s.

(sourc: http://www.dotnetcharting.com/)
So, take everything back to $ for your estimations and you’ll be fine. That same analysis may point you away from a hybrid into a small ICE. But now we’re assuming that you can make a logic based decision about buying a car. Most of the research out there says that car buying is a emotional decision for most of us.

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