I'm looking in to changing the tires and rims on my LUV because i just installed 3.70 gears (posi Ford 9") The truck still cooks the tires so i need to take action to get the thing to hook up.
I found a calculator that shows what 2 different tire/rim combinations compare to one another
http://www.rimsntires.com/specs.jsp I can see how my exsisting tire/rim setup compares to any different combo. So with a tape measure, I can figure out how much bigger and wider i can go with tire size, rim size and back space.
It helps to actually see what you want. It takes alot of the guesswork out of tire configuration.