I want to give CR
some credit for making claims in a somewhat controlled fashion. They're at least doing track driving only, at set speeds, and correcting for temperature variation.
The government’s tests vs. ours
Quote:
Road tests. Consumer Reports’ fuel-economy tests are conducted on our track and on public roads. Testers splice a precise fuel meter into each test car’s fuel line to measure how much gas is consumed. Each car is then run through highway and city drive loops, with each performed multiple times by two drivers.
The city test is conducted on a loop that’s set up on our track to reflect driving in a suburban area. It’s marked so that a driver must maintain specific speeds in certain sections and stop the car at specific points for set idling times. Highway mpg is measured by driving on a particular stretch of sparsely used freeway near our test track at a steady pace of 65 mph.
Each driver runs the test in both directions to compensate for wind and the slight difference in grade.
Our raw results are corrected for temperature using a formula established by the Society of Automotive Engineers. But we don’t test if it’s too hot, too cold, too wet, or too windy. Our overall mpg is a weighted composite of city and highway mpg measurements.
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From:
https://www.consumerreports.org/cro/...-gap/index.htm
An interesting trend from their conclusions (I believe this refers mainly to city driving):
