At first, I was getting unacceptable wear on my round-profile tire (fairly smooth tread, of course). All of my drives power was being focused on a thin strip down the center of the tread.
Once I took EVTodds suggestion and switched to a square-profile beach cruiser tire, everything improved. The roller was engaging across the entire tread face, instead of just in the middle of the rounded tread. My occasional slippage went to NO slippage, even under hard acceleration.
As Todd said, my rear tire seems to be wearing at the same rate as the front tire now...check the pics of his drives to see the type of square-profile I am talking about.