You can use this Spreadsheet to change the Gear ratio and tire size on your Cummins powered Truck You will see the typical peak power RPMS in green on the chart.
To use this tool, enter your Trucks values into the Yellow Highlighted Fields.
Tire Size is inputted into Field B5-D5
Truck type should be inputted to match the truck ( not useful yet) Options are "4wd Quad" "2wd Quad" "4wd Single" "2wd Single"
Tire Type can be Offroad or Road ( not useful yet)
Truck Weight can be any value ( not useful yet)
Rear End Ratio can be any value
Trans Type can be any trans from fields A:22 - H:22 **Spelling is critical** Use "47re" if you have a 48re
Transfer Case can be "High" or "Low" for range select, Use this to edit the MPH values per gear.
High can be any value to define Transfer case gearing
Low can be any value to define Transfer case gearing
Download HERE: mopar1973man gearing calc.xlsx
This Spreadsheet will cover rear end gears of any custom amount, trannys listed are nv4550, nv5600, 47re, 48re, g56, 68rfe, as69rc. Thsi will so you the comparison between the gearing, tire size and tranny.