This is in response to an excellent NMA article about the folly of thinking that “55” saves gas.
In 1986 I bought my first brand-new car, a Mercury Sable with the hard-to-find electronic display dash. Turned out to be a huge mistake, of course; the first model year for an American car is really just the beta-test version, and it had too many defects to live beyond a couple of years, even with lots of time in the shop. But I digress.
For the first time, I could see a readout of my MPG, but over time and instantaneously. It didn’t take me long to find that for this cutting-edge car, with a powerful fuel-injected engine, lockup & overdrive transaxle, and very slippery low-drag design, the best MPG was betweeen 74 and 77 MPH! 55 mph was WAY down the curve and cost me $$$ as well as time.
Every car is going to have a different $/mile sweet-spot based on many, many design and environmental factors, but “55” was designed to save with big 1060’s boats with “3 on the tree”, not modern sleek OD cars.