I admit that I have nothing but subjective opinion to support my claim that they ride more smoothly. But, if we look at the physics of the question, we see that a tubular rim is an elegant, lightweight solution that because of its strong cross section can be made to be strong and still somewhat flexible, whereas a clincher needs extra mass to clinch the tire to the rim. The complicated cross section must preclude flex or the bead clinch runs the risk of failing. It is this more rigid rim design that makes the dang thangs ride like a skyed 87 Dodge Ram Pickup.