I'm looking to get some 18's, but I don't want to have to modify the fenders or suspension to get the clearances. What is the widest I could go without changing anything and avoid rubbing?? Would 18x8 work or 18x7.5? What tires would be right for this setup as well?

 

with stock suspension, id guess around a 18x7.5 with a 225

 

i don't have a wagon, but i had 18x7.5 with 225/40's with quite a bit of space left. i know wagon fenders aren't as wide, but i'm pretty sure they will fit without any rolling.

 

I had 18's at one time on my wagon, had a little rub with 18x7.5, but only when loaded in the back with people or cargo. This was with 225 tires as well.