On Wed, 19 Jul 2017 12:34:29 -0700,
Bob F wrote:

Actually read the article. They are changing from a 15" to a 19" tire.

I completely misquoted the article.

I agree with you that they lost about 25% in torque going up in four
inches, not one inch.

That's a 26% increase in diameter. The torque goes down 26%, the engine
RPM goes down 26%. The power required to go THE SAME speed stays
virtually the same. But now, the engine may be operating at a lower part
of it's efficiency curve. Or maybe not.

That's what the Cooper Tire article said.
http://www.dunntire.com/blog/Do-larg...ve-gas-mileage
"the vehicles which stand to benefit from a larger diameter tire are those
that produce more torque than they need to in order to maintain
speed...[but] There are just too many factors to consider to make general
statements that larger or smaller tires are more fuel efficient."

These days, cars are geared for efficiency generally, with possible
choices to change the shift points for performance. So changing tire
O.D. is not likely to help mileage.

This Consumer Reports report says that the OEM tires are designed for fuel
efficiency where the replacement tires can have a few mpg impact, so, that
seems to back up the claim that too many things change even if all you do
is change the tire diameter.
http://www.consumerreports.org/cro/n...nomy/index.htm
"Consumer Reports recently tested a few all-season tire models with low
rolling resistance and found that those tires can improve fuel economy by
an additional one or two mpg."