31" tire backspace specs

[cooldrool]

i have a 1999 sport.....stock suspension...id like to put on 31" tires...ok ..no problem....ive looked up many threads on the tire upgrades...but cant find a definitive backspace/offset specs for what i need....but id like to know the offset and backspacing for the 31" tire/wheel combo....should it be like the stock backspace.....or is more positive offset going to hit the fenders.....ill be using either 7 or 8 inch rims so the backspace will have to be the same...thanks for the help...

 

[cooldrool]

can i use my stock wheels ?...which are 4" neg....and 3" pos.....where aftermarket rims are 4" pos...3" neg.[ or 4" on 8" rims]