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Capri,
Keeping everything else the same, but just changing tread width, would you agree that the contact patch will keep the same area, but change shape becoming shorter and off course wider?
Most of the rolling resistance in a tire comes from the flexing of the sidewalls (~80%). When you shorten the contact patch by going to a wider tire, you will flex less sidewall but more tread. The impact of the reduction of sidewall flexing will outweigh the penalty taken on the tread flexing.
In real life though, everything else rarely is the same.
Choosing a rim/tire combination is always a matter of compromise. It would be easy to make a recommendations if you were always driving down the highway at 85 mph (skinny and tall), or cruising along country roads at 40 mph without ever stopping (midsize and tall), or driving 100% city with stop and go all the time (short and wide). But that's generally never the case.
Also, I would like to comment on pressure and rolling resistance. Higher pressure reduces hysteresis, which is the main variable determining rolling resistance. There's hysteresis between pressure and RR.
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