elastomer coupling instead of rigidly welded (or bonded for carbon joints). The intent is to decouple the vertical vibrations (from a rough road) from the seat, and thus, the rider. The result is the frame is a little more compliant in general. The hope (or marketing point) is that it's compliant vertically when it comes to road vibrations, but still stiff laterally when it comes to putting a lot of torque into pedaling. When I road one, the seat would sometimes start bouncing up and down with my pedal strokes. Found that if I concentrated on having a smooth stroke (like you're supposed to) it wasn't bad. That's what I meant by forcing you to have a smoother pedaling motion.