What's the largest size tire I can put on my f150 XL with stock rims, 17inch? Also if I want to put bigger rims on, how large can I go before the tires rub?

 

If you know the rim width, you can go tire rack and look up recommended rim widths for larger tires. If you truck is a 2wd it won't take as large a tire as a 4x4.

265/70x17 is the stock size for my 02 F150 FX4. 285/70x17 is the largest that fits into the recommended rim width for my 7 1/2" rims.