On another forum dedicated to MPG
, a Dodge Ram dude gets fabulous MPG
, but he rarely drives more than 40 MPH.
He does appreciate the effect of what automotive engineers call the "road load equation." This equation calculates the HP a vehicle needs to maintain a given speed with various other factors involved. Weight, grade, tire, wheel bearing and drivetrain rolling resistance, etc. All that HP has to be made good by engine fuel burn.
With one exception, each factor's road load HP goes up proportionately with road speed.
That exception is aero drag which goes up with the cube of road speed.
It does not take an expert in differential calculus to tell you road load HP is minimum (zero) at V=0. to achieve this you've made what pilots call the "no-go decision."
But most of us have a truck to go somewhere. If a guy has the luxury of being able to drive around twenty under the limit, well good for him.
Myself I feel a MPG
reached by driving slowly is a dishonest comparison. Very few people can get away with driving like granny.
On the other hand, if you drive as much as I do "driving it like you stole it" gets you tickets. The law of probabilities will catch up to you sooner or later.
So for MPG
testing purposes there is only one rational and honest speed for comparison - the posted limit.
But if fuel cost is important to you and you have the time and patience to drive slow, by all means do so. It will increase your MPG
, all else equal.