On the outside, Ecsta SPT XRP 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 XRP to let drivers know the time has come to rotate tires to maintain more even wear and lower noise levels as the tire approaches the later stages of its treadlife. The Ecsta SPT XRP tire's structure includes twin steel belts reinforced by a spiral-wrapped, jointless nylon cap ply to enhance ride quality while providing high-speed durability. Rubber run-flat inserts are molded on the inside of both of the tire's sidewalls to provide temporary continuing mobility in the event of a puncture causing air loss.