This thought is not original with me, but the fuel savings you get from an overdrive swap will take years to cover the expense -- particularly with the $3000+ Gear Vendors OD.

Here's a chart of fuel costs per 1000 miles with gas prices of $2 and $3 per gallon:

10 mpg and $2/gal = $200 per 1000 miles

15 mpg and $2/gal = $133

20 mpg and $2/gal = $100

25 mpg and $2/gal = $ 80

10 mpg and $3/gal = $300

15 mpg and $3/gal = $200

20 mpg and $3/gal = $150

25 mpg and $3/gal = $120

An overdrive will only bump you about 5 mpg, and only at cruising speed. So take a 15 mpg car and bump it to 20. Assume 10,000 miles per year, all at cruising speed (generous assumptions). The fuel costs at $2/gal are $1333 and $1000 respectively -- a savings of $333. At $3/gal the annual costs are $2000 at 15 mpg and $1500 at 20 mpg, for an annual savings of $500.

And this is without factoring in the opportunity costs of spending that money on an OD tranny rather than on an investment portfolio compounding at 10% per annum.

With a Gear Vendors and $3/gal gas it would take you seven years at 10,000 miles/year to recoup the outlay. With a T-5 or AOD -- assuming a $2000 "all in" installation expense -- it would take four years.

At $2/gal the Gear Vendors takes 10 years and the T-5 or AOD takes six years.

So while OD might be great for bragging rights, it doesn't make much economic sense.

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