In cars that have optional wheel sizes, generally the tire's outside diameter is the same for 18", 19", or 20" wheels. The thickness of the sidewalls is less on the larger wheels, of course. The heavier weight of the larger diameter wheels results in more unsprung weight, and add to that the stiffer sidewalls of the lower profile tires, and you get a harsher ride. Braking and range can be impacted, too. I have seen a test that compared 18", 19", and 20" wheels on VW GTI's, and the 18" gave the best ride comfort, but the 19" wheels gave the best overall result of the three in handling and ride.