MPG drops like a rock after 55mph.
The peak is at about 40-45mph for a large truck or SUV.
MPG drops like a rock after 55mph.
The peak is at about 40-45mph for a large truck or SUV.
One, the speed vs economy curve is different for every vehicle. That particular vehicle does best at 55mph and 25% worse at 75, but that doesn't mean every vehicle will.
Two, that graph is a textbook example of how to lie with statistics. The range begins at 15mpg, so a roughly 25% drop in real numbers (from 30 to 23 mpg) is represented by a roughly 50% drop on the graph (from 15 units above the X-axis to 8 units.)
Three, a 100 mile trip in this hypothetical car at 55mph and 30mpg takes 1 hour and 49 minutes and burns 3.3 gallons of gas. At 75mph and 23mpg the same trip takes 1 hour and 19 minutes and burns 4.3 gallons of gas. $2.50 of gas to save half a hour sitting in a cramped car is a good trade off to me.