How Fuel Economy Is Measured (And Why You Get Different MPGs)
 

Although a little technical, it's a fascinating read and was written by a former FCA engineer.

How Fuel Economy Is Measured (And Why You Get Different MPGs)

City figures are often criticized for being too optimistic, especially on turbo cars, but it's fairly easy to beat EPA highway figures for most cars. And I hear manual transmissions are underrated due to the EPA measurements requiring certain (prolonged) shift points.

The US tests are far more realistic than the NEDC tests, which are highly flawed and easily manipulated. Some manufactures are now rolling out their "fuel economy calculators" where you can select your car/engine, driving style, average trip distance, whether you carry passengers etc and they give you an estimate. Pretty cool. Example below based of Peugeot 308 station wagon 1.6 HDI:

"Estimated average real-world fuel consumption 57.6 MPG"

You can even change the wheel size, as this makes a difference, percentage of rural/urban/highway driving etc. Check them out here:

Consumption Calculator

Consumption based on usage

Vehicle consumption | Real use figures | - Citroën UK

Tesla did that years ago :)

And I understand a range/fuel economy to speed graph is standard in aircraft manuals.