On Wed, 19 Jul 2017 19:20:49 -0400,
wrote:

If I drive very conservatively I CAN get a bit better mileage than
with the original small tires, but generally speaking, in normal
driving there is little if any improvement -and around town, it is
slightly worse. The truck works harder every time it starts from a
stop or accellerates at low speed. I'm willing to put up with that on
a 21 year old truck with about 350000km on it, to have the "look" I
wanted. It is not a "performance" look - -

I'm just curious how close do you think you can get to "accurate" gas
mileage calculations using the classic odometer plus fill it up to guess at
the gallons used method?

I've read that nobody can accurately get the sig figs closer than +- 1 mpg,
despite the fact that most people I've seen do it try to calculate it down
to the tenth or even hundredth of a gallon, which, even for computers, is
impossible given there are no controls.

So 20mpg is really from 19mpg to 21mpg, which makes calculation difficult
(when I was looking up the wheel size stuff earlier today, Consumer Reports
said as much so that's why I'm curious how close you think you can get to a
repeatably precise figure (yes, both repeatable, and precise).