Originally Posted by Tim-H
If you're comparing how car manufacturers have adapted to the added weight of their vehicles(which is what that chart does) it's just fine.
All you can do with the data is what the OP originally stated about mpg increasing/maintaining while vehicle weight increased. Other's have posted wondering how they've adapted. For instance what makes the biggest difference? Is it engine efficiency or aerodynamics.
You can't compare how the manufacturers adapted because there are too many variables, which was BOY's point as well.
shikataganai, do you have data that covers a single model that kept the same size engine over several years? That would be an interesting one....