Pain in the Rear
I have been a Professional Fitter and student for biomechanics for longer than I care to admit. The one aspect of riding that continues to amaze me is when someone is riding a saddle he or she hates and tells me it is because “No saddle is comfortable”. Nothing could be further from the truth. Assuming an individual has a proper fit and their pelvis properly rotated, there is a saddle that will be comfortable, and as amazing as it sounds, probably several saddles. There are 2 main components of a saddle that determine the comfort - the shape and the rail.
Shape
The shape of the saddle is the major determinant of whether a saddle is going to work with one’s body biomechanically. There are 4 general shapes of saddle, and once a person finds which shape works for them it becomes easy to find other saddles that may be comfortable.
Shape 1 - The original “Saddle” shape (I call it the saddle shape because it is the mathematical definition of a saddle i.e. z=x²-y²). This shape is characterised a dip in the middle when looking at the saddle from the side, and rounded profile when looking at the saddle from the front/back. A few examples of this shape are the Selle Italia Flite, Selle San Marco Concor, Fizik Aliante, Prologo Scratch, and the Specialized Ronin. In my experience, this shape tends to be the least popular for an aero fit due to the fact there is not much room to move around.
Shape 2 - The Flat-Flat saddle. This is a pretty straight forward shape in that the saddle is flat from front to back and side to side. A few examples are the Selle Italia SLR, Fizik Antares, Cobb Fifty-Five, Prologo Zero, and ISM PN1.1.
Shape 3 - The Flat-Rounded saddle. This saddle is flat when looking at it from the side, and is rounded when when looking at it from the front or back. Some examples are the Fizik Arione, Fizik Volta, Prologo Kappa, and Cobb Randee.
Shape 4 - The Dipping-Flat saddle. This saddle has a dip in the center when looking at it from the side and is flat when looking at it for the front or back. A few examples are the Cobb VFlow, Cobb G2, ISM PS 1.0, WTB Rocket.
Rail
The rail of the saddle is also a determinant of comfort, but one of the most over looked. While rails come in several different materials (steel, titanium, and carbon), the length of the rail is what tends to be the most important. While the length of the rail is important for fitting purposes, it is also directed related to the amount the saddle is able to move in relation to the bike. Meaning the rail acts like a shock absorber. The longer the rail, the more shock that can absorbed and allowing for a more comfortable saddle.
Other Things To Consider
As a fitter, I have discovered that there are other aspects of the saddle that influence comfort:
Cut-outs - Cut-outs may provide perineal relief, but is important to remember that a narrow saddle with a large cut-out will have very little surface area for actual sitting causing more discomfort.
Padding - The squishier a saddle is the less comfortable it will be for long rides. It is a little counterintuitive, but the softer and deeper the padding the more the sit bones can sink into the saddle causing the padding to press more against the soft tissue ultimately leading to numbness.
So, if you are unhappy with your current saddle, or are like me and try new things in the off season, try some different saddle shapes and see which one works the best for you.