On Wed, 19 Jul 2017 21:19:40 -0700, Bob F wrote:

On 7/19/2017 7:59 PM, wrote:
On Thu, 20 Jul 2017 01:45:19 -0000 (UTC), Mad Roger
wrote:

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?
With my scanguage calibrated to my GPS, over a 2 or 3 tank run I can
be accurate to tenths

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.

I used to have a gas milage tester that could be accurate to way less
than a tenth - fuel consumption measured to within less than a cc.

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).
With the fuel mileage rig I had (for carbureted vehicles) you could
see the differnce made by changing tire pressure by a few PSI if the
wind didn.t change. You could see the difference from winding down a
window.



Maybe you can answer a question I've long wondered about.

Many cars claim in the owners manual that opening the window uses more
gas than turning on the AC. My 1987 Nissan van even claimed this, with
its almost square front and back. However, if I was going up a steep
hill in hot weather with a full load, it would slow down a lot more from
running the AC than from opening the window. Have you ever tested this
with your test rig? On what kinds of vehicles, and what did you find?
Windows or AC better?
Back when I had the use of the unit, AC was not as efficient as it is
today, but at low speeds it was more efficient to open the windows,
although a lot less effective here where relative humidity is quite
high. At highway speeds the extra drag from open windows and all the
bufetting inside the car made the AC more efficient. I strongly
suspect the same is still true today with more efficient AC - perhaps
the "transition speed" is lower today.

I know running with the windows open at 60 MPH across Kansas and
Oklahoma back in 1976 did NOTHING to make the cab of my 1957 Fargo
more comfortable, so whatever the mileage hit for AC, IT WAS ON!!!!