If you really don't want to trim at all, 275/70/17s would be the safest bet. With factory offset wheels, you could likely fit 285s with only removing the mudflaps + high caster. There may be some trimming needed on the front fender. I believe they trim the pros slightly to fit the more aggressive tires with the +7 offset (trail wheels are +15)
Here's a photo of my 285 MT01s on factory trail wheels. Full compressed. Just barely clears haha