Originally Posted by
huerro
All things being equal, skinnier tires will offer less rolling resistance and will be faster, but all things are never equal. Gearing, aerodynamics, and weight all make a big difference. Perhaps you could let us know which bikes you are considering and then we could give you a better idea.
Actually, all things being equal, wider tires will offer less rolling resistance. As you indicated, however, all things are never equal. Virtually everybody uses more air pressure in skinny tires. That generally repays the rolling resistance penalty but it makes them ride more harshly.