I recently test drove a 128is and then a mini clubman sport. The difference in ride quality was a very noticeable between the two. Both were quick and handled curves and maneuvers with great composure. But, the 128 sport suspension was smooth as butter compared to the jarring, panel-rattling suspension on the mini. I've also noticed this whenever I drive an E39 and then get back to my E34 with bilstein HDs. The E34 will communicate every bump, and in this case will feel more alive and engaging but also uncomfortable, while a 540i sport E39 will be way faster and flatter through the curves, but it will feel calm and smooth. So, I wonder, what is the difference? What is it about newer BMWs that allows for this "smooth stiffness"? Is it the design of the frame? The extra weight?