i figured out some new ex-math to help you improve your ex-miles-per-gallon in you vehicle.  the way i see it mileage is the number of miles that it takes to get you from one place to another.  it takes me 17 miles to get to work.  if i ride my bike one day that is 34 miles i didn’t drive my car…i can add it to my car’s total mileage.  if i go out for a 100 mile weekend ride, i can not add it to my mileage.  however if i ride out to a bike trail and ride the trail, i could arguably add that to my car’s total.    here are some rules:

1. only add miles that you used to replace a car drive.

2. do the calculation after each fill up.  don’t just drive a mile and fill it up after a really long commute and get like infinity miles per gallon.

3. do it for a long period of time, just to see how much you save.

sample calculation for this tank:

miles driven = 420

miles ridden=  102

total miles = 522

total gallons= 11

ex-miles per gallon= 522/11=  47.5 emg!!!  [note this is with only 3 days of bike commuting]