what tire sizes should i run (stretched) on 20x8.5 and 20x10 AWD

I have an AWD gs300 with 20x8.5 and 20x10 wheels, I am currently running 245/35 and 285/30 falken fk452s. I am about to put coilovers on and want to drop it pretty low and push the wheels out more. to do so, I am going to need to stretch some rubber (obviously), the problem I am running into, is that the tires have to have the same rolling diameter. so when they are stretched, I would assume that the rolling diameter changes right? can someone recommend a set up that would have the same rd F&R or extremely close? I didnt realize what a mess I was getting myself into buying an awd vehicle. :pat: 

Thanks for the help guys. 

Anthony

you have to do some math with this on... the overall diameter between the front and rear tires have to be very, very, very, very close to each other.... because you have AWD, there i a center diff, with gears in it. if the front tires are smaller than the rears, the center diff does more work than its supposed to, meaning those geasr are constantly moving... wearing out faster, and youll have a moaning noise coming though the cab... kinda like a FWD car that has a space saver spare tire on one of the front wheels, and the other a normal size tire, one side is turning faster than the other. just like your AWD, if the front tires are smaller than the rears, the front tires will turn faster than the rear.... 
 
in conclusion..... haha.... do your math with what tire sizes you choose, front and rear diamters have too be super close to each other, something like no more than 1/4" difference or smaller....
 
google those tire size calculators....

2% difference in rolling diameter

[QUOTE=mista808;269845]you have to do some math with this on... the overall diameter between the front and rear tires have to be very, very, very, very close to each other.... because you have AWD, there i a center diff, with gears in it. if the front tires are smaller than the rears, the center diff does more work than its supposed to, meaning those geasr are constantly moving... wearing out faster, and youll have a moaning noise coming though the cab... kinda like a FWD car that has a space saver spare tire on one of the front wheels, and the other a normal size tire, one side is turning faster than the other. just like your AWD, if the front tires are smaller than the rears, the front tires will turn faster than the rear.... 
 
in conclusion..... haha.... do your math with what tire sizes you choose, front and rear diamters have too be super close to each other, something like no more than 1/4" difference or smaller....
 
google those tire size calculators....[/QUOTE]\

I understand that part, the problem with those calculators is, they dont account for wheel width and stretching. i have a setup that is very close right now, but my tires are pretty large, so no stretch at all.

If you want to stretch them a bit, go with 225/35-20 and 255/30-20.

I've done this on an AWD Audi TT before and it worked great.

If you don't want them stretched, you can go shorter with 245/30-20 + 285/25-20.

thanks, what width wheels were you running? got any pics of the stretch?