Oversize tires

I own a 1986 bronco II with 2.9/4wd and 5 speed.(Plain Jane), The Bronc II has 15" rims. What is the largest tire I can run on this truck without lift kits??

A good tire shop can answer that. That's how I found the answer for my '92 Bronco. If you find out let me know because a friend of my just picked up an '88.