Quote:
Originally Posted by bambooshoots
Let's say Plus is about 15 cents more than Regular. It's more like 1012 cents more here in Texas, but lets use 15 cents for the nationwide average.
A fill up of 20 gallons would be 20gal * $0.15 = $3.00 more if you use Plus, or also $3.00 saved if you use Regular over Plus.
Let's say that using Plus gets you 1.5mpg more than regular. Could be as low as 1, could be higher.
So, 1.5mpg * 20gal = 30 miles more per tank. Most of us get ~18mpg, mixed driving (don't kid yourself with lifted with heavy off road tires).
So 30mi/18mpg = 1.667 gallons worth of "extra" gas if we had used plus. Well, currently gas averages $3.65 (Reg) nationally, so 3.65 * 1.667 = $6.09 more than would have to been spent using Regular to travel as far as when using Plus. So, $6.09  $3.00 saved earlier when using Regular = $3.09 saved when using Plus.

I looked at it a different way....
Using Chris's original figures of 20cents more (per say) for 91 versus 87.
87 Costs $4 a gallon (for example) He's getting 15.5mpg. That's $.2581 cents per mile.
91 Costs $4.20 a gallon. He's getting 16.6mpg. That's $.2530 cents per mile.
We'll say you're getting 350 miles per tank  which leaves you with a total cost of:
$90.335 for 87 for 350 miles
$88.55 for 91 for 350 miles
That's only $1.79 savings for 350 miles.
If you drop the gas price to $3.50 & $3.65  then the difference is only $2.06 per 350 miles.
The cost per mile will probably vary a lot between one truck to the other and how we drive etc. You'd probably have to run your own tests to see how your own results end up.