First thing I thought of was wheels/tires as to the feel of the ride. I have done more handlebar changes than any other thing though, so I think that handlebar changes necessitate a saddle change or at least an adjustment. For example, right now I have a Brooks B67 on my mountain bike drop bar conversion (1995 Trek 820), because it's the only saddle I have at the moment that is "free". I definitely feel & know that this is NOT the right saddle for me on this bike, and it will be changed once I acquire another black Brooks B17. However, if I had different handlebars on this bike I could likely use this saddle, so again....boils down to handlebars. Interesting topic. Interested to see what others say.