This is the smallest all terrain tire Tire Rack has listed that I could find by just messing with numbers. Diameter comes out to 26.16. If you're on stock suspension and your shock are good you probably wont have a problem. At stock height there is plenty of room in our wheel wells.
Other then that you could go to a gravel rally tire but that wouldn't be cheap and you would have to go down to 15 inch wheels. Hopefully someone else will chime in with other suggestions.