Run-flat tire

A run-flat tire, comprising:

• a reinforcing rubber layer having a roughly crescent-shaped meridian cross-section and being disposed in sidewall portions at both sides in a tire width direction,
• a tread portion being provided formed of a tread rubber that comprises a cap tread rubber and an undertread rubber, the undertread rubber being disposed on an inner side of the cap tread rubber in a tire radial direction and having a higher hardness than the cap tread rubber,
• the undertread rubber comprising an undertread center rubber of a center land portion, and an undertread shoulder rubber disposed on an outer side of the undertread center rubber in the tire width direction,
• a hardness of the undertread shoulder rubber being higher than a hardness of the undertread center rubber,
• a gauge of the undertread shoulder rubber gradually decreasing from an outermost main groove located furthest outward in the tire width direction toward a tire equatorial plane, and
• a gauge of the undertread center rubber gradually increasing from the outermost main groove toward the tire equatorial plane;
• wherein
• a cross-sectional profile of the cap tread rubber is symmetrical across the tire equatorial plane and a cross-sectional profile of the undertread rubber is symmetrical across the tire equatorial plane,
• a whole of a boundary surface between the undertread center rubber and the undertread shoulder rubber is disposed on the inner side of the outermost main groove in the tire width direction,
• a ratio Ga_ce/GD of a gauge Ga_ce of the undertread rubber at the center land portion to a groove depth GD of the outermost main groove is from 0.2 to 0.4,
• a ratio Ga_sh/GD of a gauge Ga_sh of the undertread rubber at the shoulder land portion to the groove depth GD of the outermost main groove is from 0.4 to 0.6,
• the gauge Ca_ce of the undertread rubber at the center land portion and the gauge Ga_sh of the undertread rubber at the shoulder land portion have a relationship Ga_ce<Ga_sh,
• the gauge of the undertread rubber gradually decreases from the outermost main groove toward the equatorial plane,
• a ratio W1/Wg of a width W1 in the fire width direction of a portion of the undertread rubber where the gauge of the undertread rubber gradually decreases from the outermost main groove toward the tire equatorial plane to a groove width Wg of the outermost main groove is from 1.0 to 3.0, and
• the gauges of the undertread rubber Ga_ce and Ga_sh are determined by measuring groove bottoms of the outermost main groove and other main grooves using an imaginary line as a reference, and finding the average gauge within the land portion or a block, excluding the portion of the outermost main groove and the other main grooves.

A run-flat tire, comprising:

• a reinforcing rubber layer having a roughly crescent-shaped meridian cross-section and being disposed in sidewall portions at both sides in a tire width direction,
• a tread portion being provided formed of a tread rubber that comprises a cap tread rubber and an undertread rubber, the undertread rubber being disposed on an inner side of the cap tread rubber in a tire radial direction and having a higher hardness than the cap tread rubber, and
• in a meridian cross-section, a gauge of the undertread rubber on a shoulder land portion on an outer side of an outermost main groove located furthest outward in the tire width direction being thicker than a gauge of the undertread rubber of a center land portion closest to a tire equatorial plane, wherein
• a cross-sectional profile of the cap tread rubber is symmetrical across the tire equatorial plane and a cross-sectional profile of the undertread rubber is symmetrical across the tire equatorial plane,
• a gauge H of the undertread rubber on a tire equatorial plane side of the outermost main groove is larger than a gauge Ga_ce of the undertread rubber at the center land portion and smaller than or equal to the gauge Ga_sh of the undertread rubber at the shoulder land portion,
• a ratio H/GD of the gauge H to a groove depth GD of the outermost main groove is from 0.3 to 0.5,
• the gauge Ga_ce of the undertread rubber at the center land portion and the gauge Ga_sh of the undertread rubber at the shoulder land portion have a relationship Ga_ce<Ga_sh,
• the gauge of the undertread rubber gradually decreases from the outermost main groove toward the tire equatorial plane,
• a ratio W1/Wg of a width W1 in the tire width direction of a portion of the undertread rubber where the gauge of the undertread rubber gradually decreases from the outermost main groove toward the tire equatorial plane to a groove width Wg of the outermost main groove is from 1.0 to 3.0, and
• the gauge H of the undertread rubber is determined by measuring groove bottoms of the outermost main groove and other main grooves using an imaginary line as a reference, and finding the average gauge within the land portion or a block, excluding the portion of the outermost main groove and the other main grooves.