For those cyclists who have ever wondered why there are so many different sized tires out there, I hope the following explanation will help you with part of the equation. For instance, why do I need a 23c as opposed to a 25c tire?
The 23c tires are the norm. They are the ideal size with considerations for weight, aerodynamics, size of contact patch, rolling resistance and comfort. Unfortunately, this is also assuming the road surface is paved and kept. The less perfect the road, the worse a 23c tire is for you to ride on. In many cases, a 25c tire will provide LOWER rolling resistance and increased comfort.
Personally, I usually ride on a 23c tires "just because" but often train my longer miles on the more comfortable 25c tires.
If you were to ride a kilo bike on a Velodrome on a mahogany wood surface, which is as smooth as a baby's bottom, then those 20c tires inflated to 150+ psi would be the right choice. Or, if you were to ride the cobbles of Belgium or even the fractured chip seal roads in the United States, then 25c or 28c tires would be best.
There are three variables when choosing a tire; 1) Tires width, 2) Tire pressure, and 3) ROAD SURFACE. For some reason, everyone seems to forget the latter. It also depends what you want from your ride. Those 23c tires are preferred as they are perhaps the ideal compromise of all things. Another way to look at this is with pressure. A 25c tire inflated to 120psi on a rough road IS NOT going to roll better than a 23c tire inflated to say only 90psi.
Those 23c tires work very well for most situations, but a 25c tire is often just more comfortable.
I hope this information is helpful. If you have any other questions, please submit them via a "Comment' and I will ask a Bike Shop Mechanic.