Don't forget to factor in tire size, the actual outside diameter, a few inches makes a significant difference in effective gear ratio.
All of the above suggestions and comments mean nothing without knowing what tire size they have in mind.

For example, a truck with 26" tires and a 3.73 ratio is equivalent to having 4.16 (an imaginary ratio) and 29" tires. You can see in this example a 3" taller tire requires about one step up in gear ratio, 4.11 would be the closest available ratio.

This will help you figure speeds and rpm with tire size and gear ratios.
http://www.onlineconversion.com/bigger_tires.htm

If you like how it drives now, then compare the final drive ratios and gear it so you get the same thing, the same engine rpm for a given road speed.
Or if you feel the engine needs to run faster or slower at a given road speed then correct for that by changing gears and or tire size.

Grigg


Last edited by Grigg; 12/13/2008 4:10 AM.
•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-