I have heard that the more upright one rides, the wider the saddle should be . But many of the hybrids seem to have very narrow saddles. Why is that?

I'm not sure if it's really true. In any case, the sit bones are the points that carry most of the weight that rests on the saddle, and their width is fixed anyway. In my experience, wider saddles can be comfier for shorter rides, especially if your bum hasn't gotten used to long hours in the saddle. But on longer and faster rides a wider saddle can attribute to excess rubbing and chaffing in the groin area.

Not strictly true, the bones that support your weight are curved and set at an angle, so they are closer together at the front. When your pelvis is leaned forward, the contact points are laterally closer together than when it is upright.



google "pelvic bone ischial tuberosity and greater trochanter"

^ duly noted.