One of the more interesting issues to come out of this subject is some of our government's attempts to artificially control fuel economy.
In seemingly another lifetime (the early 1970's), I had not yet learned the benefits of buy American, and still was driving small import vehicles. Some of the import manufacturers DID publish charts such as these, and I calculated approximate gearing necessary to maximize fuel economy at 70 MPH (then Missouri's speed limit). I special ordered the vehicle and then played a few tricks with the carburetor, exhaust, and distributor curve. After a break-in of 1000 miles, highway mileage was 39.3 (I corrected the odometer, and kept a complete record of all fuel entering the tank). Somewhat later that year, the national 55 MPH speed limit took effect. I wasn't really happy about the reduction in speed (more time on the road), but was curious about fuel economy. Imagine my chagrin when a 300 mile road trip DROPPED my fuel economy to 33.6! Worse, I had absolutely NO power. I found by driving in fourth gear rather than fifth, I gained back the power, but the mileage still stayed around 33~34. I ended up selling the car in disgust!
Very easy to put in O.D. tranny and numerically low final drive, and get both less power AND less economy.
Jon.
