For those curious, go to

http://www.fivethirty.com/misc/gears-tires-rpm-mph-conversions.xls

and download or run the spreadsheet I've put together. Keep in mind that I'm not an expert on this, this info is just what was passed on to me. <img src="/forums/images/graemlins/baby.gif" alt="" />

For those without the ability to run Excel spreadsheets:

(transmission X diff X t-case X 336 X MPH) / Tires (inches) = RPM

Transmission gears
First: 3.918
Second: 2.261
Third: 1.395
Fourth: 1.000
Fifth: 0.829
Reverse: 3.925

Diff gears
4.625
4.88
5.29

T-case gears
1.925
2.850
1.000 (to get RPM for 2WD or 4-HI)

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Stay the Trail!