[kipps]

Keep in mind that fuel savings won't pay for an overdrive unit.

Assuming $4000 installed cost, $3.00 gas, and raising your mpg's from 11 to 14.

.273 cost per mile at 11 mpg.

.214 cost per mile at 14 mpg.

With a savings of about six cents per mile, you'll need 67,000 miles to pay back the purchase price.

I'm not saying don't do it; just don't think of it as a cost-saving measure. Only pursue this if you personally want the extra gears.

Also, if your wife is handy with a calculator, don't use mpg gains to convince her of the purchase.

P.S. Just in case math is not your idea of fun-- To get the cost per mile, divide 1 by the mpg to get gallons per mile. For example, 1 divided by 11 results in .09 gallons per mile. Multiply that number by the cost of gas($3.00), and you get 27 cents per mile.