On Wed, 28 Jan 2009 19:38:42 -0800 (PST), Chalo
wrote:

Instrumented tests have shown that for tires of equal construction,
wider tires have slightly less rolling resistance at the same
pressure. Narrower tires have slightly less aerodynamic drag. While
these factors mostly offset each other, all other benefits (rim
protection, ride quality, wear life, pinch flat resistance, traction)
give the advantage to the wider tire.

This depends on how much one weighs and what sort of roads the person
is riding on.