Juat haven't stopped long enough to think about it and work
out the math, which by the way, I'm reallllll bad at.
But...I've kept a running record of every fill up
since I brought me truck home.
With different sized tires, different rear end gear ratios
it's bound to throw the speedo/odometer off by some factor.
It's easy enough to check how much with a GPS and in my
case it comes out to be right around 5 mph slower than
he actual speed.
In my mileage calculation I've always just used the odometer
reading without correction, so....it's really not that
accurate. Mostly I keep the record just so I can tell if
a mechanical problem seems to be headed my way. I've
never been all that concerned with the actual fuel economy.
I never would expect to get good mileage with a car/truck
that was dang near as old as I am, I mean my mileage is
down now a days also.
So the question that has been sitting on the shelf for
a while is, how would you make the correction for a
mpg calculation if your speedo read 5 mph slow??
DG
