It depends on the weight capacity of the axles and how firm you want the ride & handling. For the fronts I would say 40-50 psi as a starting point, but the heavier suspensions can actually go up quite a bit higher. For the rear I would say 20 psi and adjust from there.
Former owner of 2004 American Tradition and several other RVs
Home is in the Ocala Nat'l Forest near Ocala, FL
Summers in Black Mountain, NC