Ok, so I did some digging and came up with the following equation.

Do the math to solve for the variable you need to.

Here are the variables:
MPH = MPH
RPM = RPM
pi = 3.14159
d = Tire true diameter (inches)
g = rear end gear ratio
od = final gear reduction for overdrive

The equation:

MPH = (RPM*pi*d)/(12*88*g*od)

Example:
My truck with 35" treads and the NV5600 transmission:

MPH = (RPM*pi*34.9")/(12*88*3.55*0.73)

So, driving at 60 MPH I see an RPM of: 1498 (rounded up).

This is a useful tool when determining the outcome of new tires on your truck. I am leaning hard toward the Toyo MT 35x12.5 (315x75x16)

Cheers,

 

thanks for the info

 

just go here....
https://www.dieselbombers.com/calculators.php

 

fair enough but seeing the formula is better for me.

 

yep its always nice to know the formulas when the calculator craps out on ya....