Originally Posted by
idcruiserman
Not much in my experience. Slicks matter over knobbies, and aero position is better than upright, but fat versus skinny doesn't matter much (in tires).
In commuting/biking for transportation, yes. In racing, no. Difference in race times due to rolling resistance on a 40k TT can be as much as the difference between using areobars and not using aerobars. While I put on the most bullet proof tires I can find when commuting caring about little else, I choose my racing tires (and tubes for that matter) very carefully.