Re: running outside duals only
Running the outer dual only is not a good idea. Other than the load bearing reasons, when you do this you put abnormal loads on the bearings. the setup is designed to have the two wheel bearings share the load, when you run just use one wheel, you move the load center outboard of the outer bearing. ( think leverage effect). this also puts a tremendous load on the spindle nuts.
Also think of this, when 2 tires share the load, they wear half as much as one. so your single would wear faster that duals. no savings there.
Think of this too, with duals, you still have one tire holding you up if you blow one. safer. With a single, you blow the tire you're stuck till you fix.