Originally Posted by s14sh3r
The mileage test also needs to be long term to get an average. I think that would be more accurate than driving 200 miles and comparing.
Needs more science!
Exactly. It is also human nature to try to produce the results, often subconciously, that you expect or desire. Some will install some product that claims better mpg... so after they install it, they drive the vehicle in such a way that often they will see better mpg & then scream to the world how it improved their mpg. But without realizing it overtly, they had been driving differently, sometimes subconciously, to produce those results. Driving a little slower, accelerating a little more easily, on a highway trip instead of around town, etc.