2007 F150 XLT supercab, need help on what size tires to buy. I do not have a leveling kit on the front. Looking to replace 265 x 60 x 18 with 20" wheel and tires. How big of a tire can I put on my truck by keeping the 18" or going with 20" wheels?

 

When my truck was stock i was able to put on 265/75/R16 on them with no problem. that comes out to be almost a 32'' tire