How large of a tire can I put on a 92' F-150 stock 15" rim? Stock tire size is 235-75-R15, and I want something larger without going to a larger rim.

It is best to talk it over at the tire shop, the guys will have section width numbers to refer to for each tire size you talk about. From one MFR to another, the same supposed tire can vary in actuality when mounted and aired up. too big, too tall, too wide can cause issues on the same wheel. with one brand but not the other. P tires come out different than LT tires. Get the benefit of the persons experience for do's and donts, they learn it by book but know it by trying it to see. You can also view the brands in person to select tread design and play with ideas about the appearance using their simulators. You do not have to buy anything and getting a quote is customary.