The non-"S" Brooks saddles have much longer rails underneath. This enables you to move the saddle forward/backward much more than with the S models. I foun dI was way more comfortable when I got a non-S Broks and shoved my saddle back an additional 1 1/2" from what it was with the S model. With tthe saddle shoved back my center of gravity shifted back more and I felt more comfy and got better leg pedaling leverage too. The change also stopped that feeling that I was sliding forward too often. Just a few thoughts from one person's experience.