Originally Posted by
Kontact
You can follow Specialized guidelines and buy whatever width Specialized saddle their system recommends.
Otherwise, there is little to no connection between the sit bones and the outer saddle width. This is for two reasons:
Cyclists generally don't sit on their "sit bones", specifically the ischial tuberosities. These two bones are the widest in those arches of pelvic bone and you sit on them when you sit up in a straight backed chair. Cyclist actually sit on the ischial ramus, a narrower section of pelvic bone forward of the sit bones. The width of the ramus where you sit is a product of the angle of those bones and the forward tilt of the pelvis. So someone with wide sit bones and a lot of forward pelvic tilt can have very narrow pelvic bones where they touch the saddle.
The other reason is that the outer width of the saddle has little to do with the width of the saddle top where you sit. You can easily have a saddle with a narrow base but a wider seating area than a much wider saddle overall.
Imagine buying shoes by measuring your ankles instead of your feet, and then selecting shoes by with the dimensions of the sole. That's analogous to measuring bones you don't sit on and matching them to a saddle dimension you don't use. So I would caution you to not extrapolate Specialized's recommendations to other product lines.
The OP asked for a good starting point based on general rule of thumb guidelines for saddle selection. While there are subtle nuances to picking the right saddle, a good starting point doesn't have to be overly confusing.
IMO sit bone width matters. Riders (myself included) do actually use them while riding a bike. Yes, it is absolutely correct that in a forward-leaning position your hips hinge forward (at least they are supposed to) and we engage more with the ramus (which is narrower than the sit bones). Since we roll forward and back on the saddle as we change position, you ideally want a saddle shape and width that supports your sit bones and your ramus.
As a general rule of thumb I would start by looking at saddles around 130mm in width. You could probably tolerate a more narrow saddle, but options below 129mm are scarce.
As for the saddle shape, Selle SMP is the only brand I know of that makes saddles that properly support the sit bones, the ramus, and the natural curvature of the pelvis.
Check out the Composit if you like no padding, the Evolution if you like a little padding, or the Stratos if you like a little more padding. As a starting point this should give you some good options. Good luck!
