As others have noted, speed kills MPG. Even 60 is faster than the ideal--which is why they cut the speed limit to 55 back in the 1970s.
Wind resistance increases at the cube of speed. It takes eight times as much energy to go twice as fast.
In general engines lose efficiency big time over 2,400 rpm.
So, at what speed is the engine turning 2,400 rpm?
It's why we ask for average speed on our real-world fuel economy survey:
Real-world Volkswagen Jetta / Golf / Rabbit / GTI gas mileage
Wind resistance increases at the cube of speed. It takes eight times as much energy to go twice as fast.
In general engines lose efficiency big time over 2,400 rpm.
So, at what speed is the engine turning 2,400 rpm?
It's why we ask for average speed on our real-world fuel economy survey:
Real-world Volkswagen Jetta / Golf / Rabbit / GTI gas mileage