how big of tires can i fit on my stock 18 inch rims on my 06 ford 150 4x4

 

You can fit a 35x12.50-18 tire if you install one of the 2 or 2.5 inch leveling kits. Most tire manufactures recommend an 8 to 10 inch wide wheel for a 12.50 inch (305mm or 315mm) wide tires, but many members here and at FTW have run 12.50 inch wide tires on the OEM 7.5 inch wheels for thousands of miles with no problems.