Silent Groove Design (Nokian zLine A/S) Silent Groove Design is an innovation on the walls of the tire's longitudinal ribs that improves driving comfort. The hemispherical indentations that resemble the surface of a golf ball control the air flow of the tire. The indentations cut out any sounds induced by the edges of the transverse grooves and prevent any unpleasant howling sounds. The design reduces noise levels both inside and outside the vehicle, which makes driving pleasantly quiet. Silent Groove Design reduces air resistance, which cools the surface of the tire. This improves the wear resistance of the tire and provides the driver with more kilometres.