Originally Posted by SCutchins
This is absolutely incorrect!! Use the bicycle analogy, pedal in top gear at the slowest speed you can go and you're really cranking on the pedals to keep going. Cranking = energy expenditure which in a car = fuel consumption.
Absolutely incorrect? Let me clarify, throw out any RPMs which will cause your car to crank, and it's still your top gear. Anything else would have more rolling resistance. So, for a WRX, it's 2000 RPMs in fifth, or about 52 mph. Almost every street car is geared so that it's lowest normal operating speed in it's highest gear puts it around 55 mph, the most fuel efficient speed. Why do you think a Corvette gets 28 mpg highway?
To use the bicycle analogy, standing on the pedals isn't "going", making full revolutions is. Same as your "lowest speed" in a car... you'll use the least energy if you can turn the crank easily in the highest gear.