i want to start shoppin for some rims how big can i go in the back with 18 in rims

 

dude, there is wheel and tire section of the forum. Im sure you will have better results there. Just to answer your question a 10", depending on offset. Most would recomend a 9.5". Try looking at the price of a 285/30/18(very common for 10") .

 

I have 265's on the rear of my fc with wheel spacers. Nice and flush with the fenders.

 

285's on the back of my fd, 18x9.5 wheel