I know this was discussed on the show, problem is like some of you, I listened for 30 years or so… I did try searching the forums, but maybe not searching right, came up empty. (pun acknowledged, not intended.) My Dad, (who turns 90 in three weeks) claims that with a bigger engine (a V8, vs, a nice little 4 cylinder) at a certain point you get better mileage going 70 MPH on the highway than 55.
To me, this doesn’t make sense–fuel burns to produce momentum… the more momentum, the more fuel–and in fact that bigger V8 engine come with a couple thousand pounds more vehicle to push along, so I think going 55 MPH will get me better mileage than going 75.
(for the record, new-used '02 Suburban Beast trying to eek every mile I can out of that gas tank… )