Mod Payback Distance
 

I was looking to see if there was a formula for figuring how far one would have to travel to save enough money to cover the price of a mod. I only found a spreadsheet that tells time for payback, so I figured I would create a formula for distance till payback.

Variables:
C = Cost of Mod
A = Avg Gas Price
N = New MPG
O = Old MPG

First we would have to figure out how much gas we would have to save to equal the cost of the mod. So we divide the Cost of Mod by Avg Gas Price and that gives us gallons:

C = Gallons of Gas
A

Then we have to figure out how much gas is saved per mile.

1 mile.._..1 mile = Gas Saved per Mile
...O...........N

Then it is just gallons of gas divided by gas saved per mile and that gives you distance till payback.

Gallons of Gas = Payback Distance
Gas saved/Mile

A simplified equation using only the first 4 variables is:

C*N*O = Payback Distance
A*(N-O)

Where (N-O) is the Change in MPG

Example problem:

Mirror Delete (not attempted yet)

C = $18
A = $4.00
N = 33 MPG
O = 25 MPG

$18 * 33MPG * 25MPG ... =... $14850(MPG^2)...=..464 miles
$4.00/G*(33MPG-25MPG).........$32/G*MPG

$ cancel, One term MPG Cancel, G cancel with remaining MPG, leaving only Miles.

For the Old, I used EPA Est. I'm Not sure if That is what I should use, or if it should be actual MPG.

Your entire formula becomes nothing more than an estimate if you use Old EPA as "before"... unless you were actually getting exactly Old EPA.

Before should be your actual before mileage.

Yup, use your actual mileage before. In my case, I dropped the gas motored car and purchased a TDi. It payed for itself, $5K, in 140K miles of driving. Now I'm driving a free car... right?