What is the widest wheel i can run in the rear ?

i m gettin some billet 18s for my 94 yota. does anyone konw how wide i can go with out rubbing frame ? i can also widen the bed flares to fit wide rims since i have an extra bed

You can go however wide you want. The backspacing is what counts. You can get away with about 6.5" backspacing without rubbing. I have +45 mm offset wheels, which is close to a 6" backspacing. I have about 3/4" on each side of the frame from the tires.

I'm running 17x10 w/ +45 offset.