Need some gear ratio help

I am currently workin on an AWD 33 3 window, and i have to keep all of the tires the same diameter which means the gears have to be the same front and back, UNLESS i can find out how to do the gear ratio to over all tire hieght math. I know there is a way to figure out by switching gears and going with a different size tire, you can keep them spinning at the same speed for the transfer case not to blow out. If anyone knows the formula or knows where i can get my hands on a program, i would be greatly appreciated of the information.
Thanks Mike

I know this is not exactly what you wanted but I think you could use this calculator to do what you want by matching the tire and gear size to the same engine rpm value. Nobody else has answered you so far so play around with this until you get a better answer. To use this you would start by calculating the rpm for a given rear gear ratio and tire size and then play around with the gear ratio and tire size for the front until you get the same rpm at the engine. However, it is not clear to me that you will be able to find exactly the right combination because the tire sizes and gear ratios come in steps and you may not be able to get a match within 100 rpm and then it is up to whatever clutch or torque converter slippage saves the transfer case. What happens if you go over a bump off road and lift front or rear wheels off the ground and then come down hard? Anyway I approached your problem from the point of view as a math problem and do not have the experience to know how much rpm difference the drive line will take, but anyway here is a start.

http://home.tampabay.rr.com/1bking/c...calculator.htm

Don Shillady
Retired Scientist/teen rodder

This calculator actually helps out a lot, i think i have a formula somewhere for it that i have to find. And as far as hitting a bump or something like that, i am hoping the transfer case can take a beating, lol. Thanks A Lot!!!

First, you're gonna have to find out what ratios are available for the differentials.

I remember that Fords (can't say about the others) used to have the front diff running a SLIGHTLY lower numerical ratio than the rear. Ex: 4.09 front 4.10 rear. I think I would approach the switching tire diameters thing very cautiously