Gears & Axles - Needing to find out some gear info. Bigger tire and biggger gear.

Ok to start off I'm used to f-bodies with 26-28 tires and 3.23-3.42 gears. I can pretty much judge what gears are needed if a person need to go up or down in gears. Here is one out of my league and I can't find the right calculator on google to calculate it.

My buddy has 4.88 gears with 31" tires and I'm trying to see what that would be equal to. 3.73's and 27"? 3.90's and 27"?

Help me out guys or just give me a link to a calculator

http://www.4lo.com/

Look on the left side of the screen.

Al 95 Z28

http://www.wallaceracing.com/Calculators.htm
good luck,Johnny