Mark,
I am a long way from being an expert on tires, but here are my thoughts.
Your bus has a front slide-out and therefore it carries an extra 1100# or more. My coach also has a front slide and Newell recommends changing the front tires every 3 years. They recommend changing rear tires every 5 years (I have a rear slide).
I follow this regiment for one simple reason: I am too young and beautiful to die!
Just kidding!