Common sense is often wrong, though. As Jan Heine has shown in a series of articles in Bicycle Quarterly, under real world conditions, wider tires run at lower pressures are just as fast as narrower tires at higher pressures. The ride is smoother, but not necessarily slower, because you're not losing as much energy to vibration. The most important factor is how supple the tire sidewalls are; there's a huge difference in efficiency between different tires of the same size.