PNEUMATIC TIRE
A pneumatic tire includes a shoulder land defined by a circumferential groove having a width of ≥3 mm on a tread and width-direction grooves in the shoulder land. The width-direction grooves include lug grooves having a width at a position at a center of the shoulder land in the width direction of ≥1.5 mm and a depth of ≥50% of a maximum depth of the width-direction grooves on a circumference. Blocks defined by the lug grooves have circumferential lengths varying at the position. A maximum-to-minimum ratio of circumferential lengths of the blocks is ≥1.2 and ≤1.8. The number of blocks on the circumference is N, the circumferential lengths of the blocks are sequentially P 1 , P 2 , . . . , P N , the circumferential length of any block is P i (i=1 to N), the number of blocks satisfying P i /min(P i−1 , P i+1 )≤0.95 is M 1 , the number of blocks satisfying 2P i /(P i−1 +P i+1 )≤0.95 is M 2 , an index R satisfies 0≤R=((M 1 ·M 2 ) 1/2 /N)≤0.2.
1 . A pneumatic tire, comprising:
a shoulder land portion defined by a circumferential groove having a groove width of 3 mm or more on a tread portion; and
a plurality of width direction grooves provided in the shoulder land portion and extending in a tire width direction;
the width direction grooves comprising a plurality of lug grooves having a groove width at a reference position at a center of the shoulder land portion in the tire width direction of 1.5 mm or more and a groove depth of 50% or more of a maximum groove depth of the width direction grooves on a tire circumference,
a plurality of block-like land portions defined by the lug grooves having circumferential lengths varying at the reference position,
a ratio of a maximum to minimum circumferential length of the block-like land portions being in a range of 1.2 or more and 1.8 or less,
the number of block-like land portions on the tire circumference being N, the circumferential lengths of the block-like land portions being sequentially P 1 , P 2 , . . . , P N along the tire circumferential direction,
the circumferential length of any block-like land portion being P i (i=1 to N),
the number of block-like land portions satisfying P i /min(P i−1 , P i+1 )≤0.95 being M 1 ,
the number of block-like land portions satisfying 2P i /(P i−1 , P i+1 )≤0.95 being M 2 ,
an index R being R=(M 1 ·M 2 ) 1/2 /N, and
the index R being in a range 0≤R≤0.2.
2 . The pneumatic tire according to claim 1 , wherein the index R is also in the range 0≤R≤0.2 at any position of a specified region of from 30% to 70% from an inner edge in the tire width direction toward a ground contact edge of the shoulder land portion.
3 . The pneumatic tire according to claim 1 , wherein a ratio M 1 /N of the number M 1 to the number N of the block-like land portions is in a range 0≤M 1 /N≤0.15.
4 . The pneumatic tire according to claim 1 , wherein
the number of levels of the circumferential lengths of the block-like land portions is 3 or more,
a maximum value of the circumferential length of the block-like land portions is P max ,
a minimum value of the circumferential length of the block-like land portions is P min ,
a sum of circumferential lengths of block-like land portions satisfying P i <P min ·(P max /P min ) 1/3 is PL,
a sum of circumferential lengths of block-like land portions satisfying P i >P min ·(P max /P min ) 2/3 is PH,
Mathematical Formulas (1) and (2)
0.2
≤
PL
∑
i
=
1
N
P
i
≤
0.7
(
1
)
0.2
≤
PH
∑
i
=
1
N
P
i
≤
0.7
(
2
)
are satisfied, and
a relationship of 0.4≤PH/PL≤3.0 is satisfied.
5 . The pneumatic tire according to claim 1 , wherein
narrow grooves having a groove width of 1 mm or more and 2 mm or less and a groove depth of 10% or more and less than 50% of the maximum groove depth of the lug grooves are disposed in the shoulder land portion at an angle of 35° or less with respect to the tire circumferential direction.
6 . The pneumatic tire according to claim 1 , wherein
at least one sipe which extends in the tire width direction and has a groove width of less than 1.5 mm and a groove depth of 50% or more and less than 100% of a maximum depth of the lug grooves is disposed in each of the block-like land portions of the shoulder land portion.
7 . The pneumatic tire according to claim 6 , wherein
a ratio P max /P min of the maximum value P max to the minimum value P min of the circumferential lengths of the block-like land portions is 1.4 or more, and
the number M i of sipes disposed in the block-like land portions satisfying P i >P min ·(P max /P min ) 2/3 is larger than the number M min of sipes disposed in the block-like land portions having the minimum value P min .
8 . The pneumatic tire according to claim 6 , wherein
m i (m i ≥2) sipes are disposed in any block-like land portions crossing the reference position,
the block-like land portions are partitioned into three or more small land portions by the m i sipes,
circumferential lengths of the small land portions at the reference position are sequentially S 1 , S 2 , . . . , S mi+1 along the tire circumferential direction, and
relationships min(S 1 , S mi+1 )≥0.95·max(S 2 , S 3 , . . . S m ) and max(S 1 , S mi+1 )≤1.5·min(S 2 , S 3 , . . . , S mi ) are satisfied.
9 . The pneumatic tire according to claim 2 , wherein
the number of levels of the circumferential lengths of the block-like land portions is 3 or more,
a maximum value of the circumferential length of the block-like land portions is P max ,
a minimum value of the circumferential length of the block-like land portions is P min ,
a sum of circumferential lengths of block-like land portions satisfying P i <P min ·(P max /P min ) 1/3 is PL,
a sum of circumferential lengths of block-like land portions satisfying P i >P min ·(P max /P min ) 2/3 is PH,
Mathematical
Formulas
(
1
)
and
(
2
)
0.2
≤
PL
∑
i
=
1
N
P
i
≤
0.7
(
1
)
0.2
≤
PH
∑
i
=
1
N
P
i
≤
0.7
(
2
)
are satisfied, and
a relationship of 0.4≤PH/PL≤3.0 is satisfied.
10 . The pneumatic tire according to claim 9 , wherein
narrow grooves having a groove width of 1 mm or more and 2 mm or less and a groove depth of 10% or more and less than 50% of the maximum groove depth of the lug grooves are disposed in the shoulder land portion at an angle of 35° or less with respect to the tire circumferential direction.
11 . The pneumatic tire according to claim 10 , wherein
at least one sipe which extends in the tire width direction and has a groove width of less than 1.5 mm and a groove depth of 50% or more and less than 100% of a maximum depth of the lug grooves is disposed in each of the block-like land portions of the shoulder land portion.
12 . The pneumatic tire according to claim 11 , wherein
a ratio P max /P min of the maximum value P max to the minimum value P min of the circumferential lengths of the block-like land portions is 1.4 or more, and
the number M i of sipes disposed in the block-like land portions satisfying P i >P min ·(P max /P min ) 2/3 is larger than the number M min of sipes disposed in the block-like land portions having the minimum value P min .
13 . The pneumatic tire according to claim 12 , wherein
m i (m i ≥2) sipes are disposed in any block-like land portions crossing the reference position,
the block-like land portions are partitioned into three or more small land portions by the m i sipes,
circumferential lengths of the small land portions at the reference position are sequentially S 1 , S 2 , . . . , S mi+1 along the tire circumferential direction, and relationships min(S 1 , S mi+1 )≥0.95·max(S 2 , S 3 , . . . S m ) and max(S 1 , S mi+1 )≤1.5·min(S 2 , S 3 , . . . , S mi ) are satisfied.