WUT? How could no one have said this yet? The correct answer to this question depends almost entirely upon the rider's preferred cadence when cruising on flat ground. The answer for someone who spins at 100 rpm is surely different than for someone who pedals at 60 rpm. I pedal at 90-100 rpm except when climbing so I spend most of my "flats" time on the small ring. If I pedaled at 65 rpm, I would be on the large ring instead.