I am buying a leveling kit for my 03 z71. I current ly run 285/55/20 tires. And am wondering how big of tires I can go with

 

the 285's fit with no leveling kit? do they rub at all?

 

I used to run 285/75-16's on my truck without doing any work at all to the suspension...they were almost 33" tall...

 

Don't buy one of those $200 leveling kits, just get the ford f150 torsion keys off ebay for about $70. I cranked my torsion bars about 2" and kept the factory rear blocks to level my truck. I'm running 305/50/20's on a 10" wheel with a pretty wide offset. I trimmed the inner plastic fender well a little but it still rubs some if you have the wheels cranked all the way in reverse. Also, drive your truck for a couple of days before you get it realigned because it will settle some after you crank on the torsion bars. You might crank them some more if it settles to much and I also have my driver side just a hair higher because it will squat some as soon as you sit in it.

Here's how she sits..

 

get the ford keys. and new longer shocks. fronts for sure.you can fit 33's depending on the rim backspacing

 

Like has been said, how big a tire you can fit really depends on your wheel width and offset. The wider, and less back spacing you have, the smaller a tire or more lift you need to keep them from rubbing when you turn.

I fit 305/55/20 Nitto Trail Grapplers on 20x9.5s with 5" BS (-6 offset) on my truck with ford keys, longer shocks, and a little trimming of the valence and inner fender plastic. It's stuffed, and I want a 1.5" Body lift to make it look a little less so, but it doesn't rub.

If I went to a 20x10 wheel with 4.5 BS and the same tires, I would rub like crazy right now. It's something I would like to do eventually, so I'm hoping the 1.5 BL would allow me to clear that set up.