On the outside, Ecsta SPT tires feature Kumho's High Dispersion Silica tread compound (that broadens the tread rubber's temperature operating range) molded into a directional tread design that features large, independent shoulder blocks, four straight circumferential grooves and three solid center ribs to combine wet grip, responsive handling and high-speed stability. Rotation Wear Indicators (R.W.I.) are built into the Ecsta SPT to let drivers know the time has come to rotate tires to maintain more even wear and lower noise levels into the later stages of the tire's life. On the inside, Ecsta SPT tires feature twin steel belts reinforced by a spiral-wrapped, jointless nylon cap ply to enhance ride quality while providing high-speed durability.