I don't know if they will help this time but here are a couple of speed, rpm, gear ratio tire size calculators to play with.
The first is the Advanced EV calculator that you can plug in three knows and get the fourth.
https://www.advanced-ev.com/Calculators/TireSize/
The second one is the Pur Performance that only gives rpm when you put in the other factors but will let you see the difference between tire sizes and or gear ratios in both the trans and the rear end.
The last is the tire size dot com page that lets you compare two tire and wheel combos side by side. It will tell you the speed differences between two tires such as a 225-60-15 and a 225-75-15. Throwing a set of low profile tires on a rig can mess with your speed a lot.