The more athletic and forward leaning the sitting position, the more the supporting points on the seat move towards one another and away from the actual seat bones to the pubic bone, allowing the bicycle seat to be narrower.

The support surface for a very forward leaning sitting position is critical. It should provide relieve not only in the middle but also at the pubic bone area.

In general, the more upright your sitting position, the wider your seat has to be.