hansshanks

so i have a backspacing/tire size question. i am thinking about going up to 33x9.50 or 10.50 tires. or the metric =. so is getting wheel with more than stock offset needed to run this width? is it a tire diam problem or a tire width problem. i currently have 31x1050R15 on it now. and it rubs at full lock and in the rear on bumps with my boat hooked up. I am planning to lift 4 inches when iget home and then cut from there. the wheels i have now are not stock. they have some backspacing but how much i am unsure but it is more than stock. So i guess after all this reading i am trying ot clear up in my head exactly how much back spacing do i need.