Got this information as a part of an email from one of my bike part suppliers...........
The skinnier and higher pressure the tires, the faster the bike, right? Well, no, actually. Speed comes down to a variety of factors, and even many pro road riders these days are choosing wider rubber for training and racing.
So what should you be considering when you're weighing your tire width options? First up is, well, weight. A 20mm or 23mm tire is just plain less rubber than a 25mm tire -- so it will weigh less than the wider tire, resulting in lower rotational weight, which means you'll be able to spin your wheels up to speed that much quicker.
But weight isn't the only thing to consider. Rolling resistance, aerodynamics, grip, and ride quality all play an important role in how fast you ride. 23mm tires still have 25mm tires beat in terms of aerodynamics, but with the newest aero rims, which tend to be wider than previous incarnations, that advantage is negligible, and 25mm tires perform better in pretty much every other way.
You mean 25mm tires actually offer less rolling resistance than 23mm tires? How does that work? Yes, it's true! A 25mm tire at slightly lower pressure has a wider contact patch that actually allows the tire to conform to imperfections in the road surface much more effectively than a hard, bouncy 23mm tire, resulting in lower frictional forces and, yup, a faster roll. That greater contact patch also gives 25mm tires better grip through corners, meaning you can roll through them at higher speeds with greater confidence. And, of course, wider tires provide a softer, more comfortable ride -- which doesn't seem related to speed until you consider that the better you feel, the harder you can push.
So consider widening the gap between you and the competition by widening your tires. Our favorite racing and training tires are all available in 700c x 25mm sizes.