Tire
A circumferential narrow main groove extending in a circumferential direction in a tread of a pneumatic tire. The circumferential narrow main groove includes a narrow portion opening to a road contact surface of the tread and a widened portion having a wider groove width than the narrow portion. The widened portion is at a groove bottom. A groove width ratio (W 2 /W 1 ) of a maximum groove width W 2 of the widened portion to a groove width W 1 of the narrow groove portion is in a range 1.5≤(W 2 /W 1 )≤4.0, and a cross-sectional area ratio (A 2 /A 1 ) of a groove bottom-side cross-sectional area A 2 to a groove opening-side cross-sectional area A 1 in a meridian cross-section is within a range 1.2≤(A 2 /A 1 )≤4.0 when the circumferential narrow main groove is divided into two parts at 50% of a maximum groove depth of the circumferential narrow main groove. The cross-sectional area ratio changes along the circumferential direction.
1. A tire comprising a circumferential groove extending in a tire circumferential direction in a tread portion, wherein
the circumferential groove comprises a narrow groove portion opening to a surface of the tread portion, and a widened portion having a wider groove width than the narrow groove portion, the widened portion being provided at a groove bottom,
a groove width ratio (W 2 /W 1 ) of a maximum groove width W 2 of the widened portion to a groove width W 1 of the narrow groove portion is in a range of 1.5≤(W 2 /W 1 )≤4.0,
a cross-sectional area ratio (A 2 /A 1 ) of a groove bottom-side cross-sectional area A 2 to a groove opening-side cross-sectional area A 1 in a tire meridian cross-section is within a range of 1.2≤(A 2 /A 1 )≤4.0 when the circumferential groove is divided into two parts at a depth position of 50% of a maximum groove depth of the circumferential groove, and the cross-sectional area ratio (A 2 /A 1 ) continuously changes along the tire circumferential direction, and
a height of a widening starting point of the widened portion or both the height of the widening starting point and the groove width of the widened portion are changed with changing of the cross-sectional area ratio (A 2 /A 1 ).
2. The tire according to claim 1 , wherein in the circumferential groove, the groove width W 1 of the narrow groove portion is in a range of 1.0 mm≤W 1 ≤4.0 mm in a region where a groove depth from the surface of the tread portion is less than 30% of the maximum groove depth.
3. The tire according to claim 2 , wherein the maximum groove width W 2 of the widened portion is in a range of 3.0 mm≤W 2 ≤8.0 mm.
4. The tire according to claim 3 , further comprising a land portion defined by a plurality of the circumferential grooves, wherein
the land portion comprises a block divided by a plurality of lug grooves or sipes that intersect the circumferential grooves, and
the circumferential grooves have at least one local maximal value and at least one local minimal value as the cross-sectional area ratio (A 2 /A 1 ) changes within a range of pitch length of the block in the tire circumferential direction.
5. The tire according to claim 4 , wherein
a plurality of lug grooves or sipes opening to the circumferential groove are provided in the tread portion, and
a first cross-sectional area S 1 of the widened portion that is cut by a tire meridian cross-section at an opening portion to which the lug groove or the sipe is opening, is smaller than a second cross-sectional area S 2 of the widened portion that is cut by the tire meridian cross-section at an intermediate portion in the tire circumferential direction of an adjacent pair of the opening portions.
6. The tire according to claim 5 , wherein the ratio (S 2 /S 1 ) of the second cross-sectional area S 2 to the first cross-sectional area S 1 is 1.2≤(S 2 /S 1 )≤2.5.
7. The tire according to claim 6 , wherein the first cross-sectional area S 1 is the smallest cross-sectional area of the widened portion, and at least one of a plurality of second cross-sectional areas S 2 is the largest cross-sectional area of the widened portion.
8. The tire according to claim 7 , wherein the circumferential groove has a widening starting position of the widened portion displacing within a range of 30% or more and 65% or less of the maximum groove depth.
9. The tire according to claim 1 , wherein the maximum groove width W 2 of the widened portion is in a range of 3.0 mm≤W 2 ≤8.0 mm.
10. The tire according to claim 1 , further comprising a land portion defined by a plurality of the circumferential grooves, wherein
the land portion comprises a block divided by a plurality of lug grooves or sipes that intersect the circumferential grooves, and
the circumferential grooves have at least one local maximal value and at least one local minimal value as the cross-sectional area ratio (A 2 /A 1 ) changes within a range of pitch length of the block in the tire circumferential direction.
11. The tire according to claim 1 , wherein
a plurality of lug grooves or sipes opening to the circumferential groove are provided in the tread portion, and
a first cross-sectional area S 1 of the widened portion that is cut by a tire meridian cross-section at an opening portion to which the lug groove or the sipe is opening, is smaller than a second cross-sectional area S 2 of the widened portion that is cut by the tire meridian cross-section at an intermediate portion in the tire circumferential direction of an adjacent pair of the opening portions.
12. The tire according to claim 11 , wherein the ratio (S 2 /S 1 ) of the second cross-sectional area S 2 to the first cross-sectional area S 1 is 1.2≤(S 2 /S 1 )≤2.5.
13. The tire according to claim 11 , wherein the first cross-sectional area S 1 is the smallest cross-sectional area of the widened portion, and at least one of a plurality of second cross-sectional areas S 2 is the largest cross-sectional area of the widened portion.
14. The tire according to claim 1 , wherein the circumferential groove has a widening starting position of the widened portion displacing within a range of 30% or more and 65% or less of the maximum groove depth.
15. The tire according to claim 1 , wherein the widening starting point refers to a height position at which the groove width is widened to be equal to or greater than a predetermined value which is a smaller one of 1.2 times the groove width W 1 of the narrow groove portion and the groove width W 1 +0.5 mm.
16. The tire according to claim 1 , wherein the cross-sectional area ratio (A 2 /A 1 ) continuously changes along the tire circumferential direction in a sine wave shape or a triangular wave shape.