I thought this listing of gas saving tips was somewhat interesting and informative, but I was especially surprised to read #27. Everything I have read lately still touts 55 mph as the optimum fuel efficient speed. I have had my doubts. I tend to drive 65-70 on the highway, mostly with cruise control on since I drive most of the way to work on a rural highway.
27. Do you need to slow down to 55 mph to save fuel?
Not really... every vehicle has its most efficient speed in the highest gear. It differs depending on the design of the car, and things like tire pressure, open windows, bike racks, etc. The 55 mph speed limits come from the 1970s, when a nationwide speed limit was established in an attempt to reduce gas consumption at the time of an energy crisis. This attempt failed miserably by the way, but that's another story. Which does not mean speed does not matter... it does. For modern aerodynamically enhanced cars, the most efficient average speed is more in the range of 65 mph or even higher. You don't want to exceed that speed if you are trying to maximize gas mileage. At higher speeds, the main gas eater is aerodynamic drag, which is proportional to the square of your speed. That means your car needs four times more fuel to overcome the drag when you double your speed.