2008 stx f-150 stock
 

I have stock tires and they look way to small for my truck I was wondering how big I can go without lifting at all just want bigger tires

Welcome to the site..

Can't answer your specific question, but what I used to do was talk to our tire rep first, get a general fit recommendation, then on specific brands considered, wheel offsets, may determine sizing. Some manufactures sizes may vary slightly, and if your going for a critical fit and have a brand/vendor in mind most will mount up a tire and check clearance prior to purchase if any doubt. I'm sure someone here may have some recommendation.