Noise-reducing tire

A noise-reducing tire comprising:

• side walls on both sides of the noise-reducing tire;
• a tread portion connecting outer circumferences of the side walls;
• a longitudinal groove defined in the tread portion along a driving direction;
• and
• a lateral groove defined from the longitudinal groove towards one of the side walls in a lateral direction,
• wherein the lateral groove expands in width towards the one of the side walls,
• wherein the lateral groove comprises a lateral expansion section having two or more sidewall steps on at least one of both sidewalls of the lateral groove, the two or more sidewall steps expanding the width of the lateral groove in a stepwise manner towards the one of the side walls of the noise-reducing tire,
• wherein each of the two or more sidewall steps defined in a length direction of the lateral groove increases the width of the lateral groove sequentially within a range of 0.01 mm to 0.1 mm from the lateral groove without the lateral expansion section towards the one of the side walls of the noise-reducing tire,
• wherein the lateral groove includes a tie bar connecting inner walls of the lateral groove, the tie bar being disposed in the lateral groove adjacent to the longitudinal groove,
• wherein the tie bar has a height lower than a surface of the tread portion,
• wherein the lateral groove includes one or more lower surface steps, each lower surface step having a height different from a height of another lower surface step,
• wherein a height of each of the one or more lower surface steps is lower than the height of the tie bar.