On Wed, 19 Jul 2017 13:56:02 -0600,
rbowman wrote:

Many manufacturers use low rolling resistance tires as OEM equipment to
improve their CAFE numbers. One of the best is the Bridgestone B381
which has a 65 profile. Low profile is usually considered to be 50 and
under.

The Consumer Reports reference I already quoted said there were a few miles
per gallon to be had from changing the tire and nothing else (not the size
or anything else but the tire).

So it's more complex, but no reliable source yet says that most cars will
benefit in fuel economy from larger diameters alone, and in fact, all the
reliable sources say the opposite.

Here is another source from Dunn Tire.
Does tire size affect gas mileage?
http://www.dunntire.com/blog/Does-ti...ct-gas-mileage

That source talked about truck tires when it said
"It is probably not worth switching to smaller tires, since any gains in
fuel economy would be offset by the added cost of re-gearing to keep your
engine operating in its most efficient rpm range. Remember, power and
economy are affected by transmission, drive axle ratios and tire size
(revolution per mile). Change one, and you throw the equation off. With
today¢s new tires, there is virtually no difference in mpg due to tire
size."