Would a 16" wheel fit? I think that a 16" wheel and R16 tire would be better, if a 16" wheel will clear your brakes. Look for a load C tire. There are a few load C tires in R16 sizes. If you can't fit a 16" wheel, then a 17" wheel.
For tire, I recommend Cooper AT3. I use them every week in conditions similar to what you describe. They are doing great on steep rocky roads, steep muddy roads, muddy creek bed, and are excellent on highway.
Cooper AT3 is aggressive enough for mild to moderate off road, and mild enough to be excellent on highway.
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