Hi all - I've found some calculators for tire size/gear ratios that I've found useful and just wanted to share. They're not new by any stretch, but they work great. Here they are:

Tire size comparisons:
http://www.csgnetwork.com/tireinfo4calc.html

Gear ratios:
http://www.4x4wire.com/tech/applications/gearandtire/
It will even figure overdrive in autos - just use 4th gear.

Transmission ratios:
https://www.f150online.com/forums/sh...d.php?t=211867

Good luck!