There's been some discussion on this. From what everyone is saying, the factory doesn't recomend dual wheels because of the possibility of overstressing the wheel motors if you would get up on the edges of the outside wheels. Some folks think it is your machine and you should do what you want with it.
Personally, if my slopes were that steep, I'd start looking at a different machine, as the Kohler is only rated for 20 or maybe 25 degrees due to its oiling system. Prolonged use at greater angles could cause engine damage.
I've seen pictures of early Power Tracs that were similar in size to the current 400 series. They had dual wheels, but the wheels were much narrower than the current wheels.
