I’m stating the obvious here, but finding the right saddle is very important for rider comfort. Every person is different, so it can take some experimentation to find a good fit. You know you have a good fit when your weight is supported by your ischial tuberosities, or what are called “sit bones”, and little to no pressure is placed on the soft tissues between the bones. We’re naturally accustomed to supporting our weight on our sit bones, so it only makes sense to do so when we’re on our bicycles.
Handlebar height in relation to saddle height affects saddle fit. As a general rule, the higher the handlebars in relation to the saddle, the wider the saddle needs to be. High bars place the rider in an upright position, rolling back the hips and placing more weight on the wider portion of the sit bones. Low bars place the rider in a forward leaning position, moving the pressure points to the narrower, front portion of the sit bones. A wide saddle combined with low handlebars is likely to cause chafing between the thighs, while a narrow saddle combined with high bars is likely to place too much pressure on the soft tissues between the sit bones.
I wish I could say there’s a simple method for finding the perfect saddle. Unfortunately, it’s been my experience that a fair amount of expensive trial-and-error is required. Even among the bikes I ride on a regular basis, each requires a different saddle. For example, the Brooks B67 that works so well on my Surly set-up with North Road bars doesn’t work well at all on my Civia with its lower flat bar, and conversely, the Selle An-Atomica that is so plush on my Civia is too narrow (for me) on my Surly.
The goal is to identify the saddle that works best for your physique, on a particular bike, with a particular build. Taking into consideration the relationship between saddle height and handlebar height will get you there quicker and greatly simplify the search, saving you time, money, and maybe even some discomfort in the process.