Originally Posted by Six jours

JFWIW, it was Jan Heine/Bicycle Quarterly that got this ball rolling. His research showed pretty conclusively that narrower does not necessarily mean faster, and also that higher pressure does not necessarily mean faster either. A decade later, the mainstream bike press is catching on. Unfortunately, the main stream bike press is still using steel drums to calculate rolling resistance, which makes the data meaningless for anyone not riding on a steel drum.

At least part of the reason wider can be faster (or not slower, anyway) is that wider can be run at lower pressure. That seems counterintuitive (and don't forget that higher pressure can feel faster, because it gives the higher frequency vibrations that the rider equates with going fast) but the idea is to allow the tire to absorb shock, rather than transmitting it to the bike and rider. The human body can absorb a lot of wattage, depending upon the road surface. On anything less than perfectly surfaced road, a relatively wide, soft tire is not only more comfortable, but also rolls better - unless the rider has fouled things up by pumping it up too hard.