| CPC B60C 15/06 (2013.01) [B60C 15/0607 (2013.01); B60C 2015/0621 (2013.01)] | 13 Claims |
|
1. A pneumatic tire comprising:
a pair of bead portions each with a bead core embedded therein, and
a carcass extending between the bead cores, and comprising a carcass ply,
the carcass ply comprising a main portion extending between the bead cores, and a turnup portion turned up around the bead core in each bead portion from the axially inside to the axially outside and extending outwardly in the tire radial direction,
wherein
at least one of the bead portions is provided with a reinforcing rubber portion adjacent to an axially outer side of the turnup portion,
the reinforcing rubber portion comprises an inner rubber layer, and an outer rubber layer adjacent to an axially outer side of the inner rubber layer,
wherein
a loss tangent δ2 of the outer rubber layer is 0.12 or more but 0.25 or less,
a loss tangent δ1 of the inner rubber layer is 60% or more but 90% or less of the loss tangent δ2 of the outer rubber layer,
a complex elastic modulus E*2 of the outer rubber layer is 60 MPa or more but 140 MPa or less, and
the complex elastic modulus E*2 of the outer rubber layer is 60% or more but 200% or less of a complex elastic modulus E*1 of the inner rubber layer,
wherein
a radially outer end of the outer rubber layer is positioned radially outside a radially outer end of the inner rubber layer,
a radially inner end of the outer rubber layer is positioned radially outside a radially inner end of the inner rubber layer,
the inner rubber layer and the outer rubber layer closely overlap with each other from the radially inner end of the outer rubber layer to the radially outer end of the inner rubber layer,
wherein
a thickness T1 of the inner rubber layer is 0.5 mm or more but 2.0 mm or less,
a thickness T2 of the outer rubber layer is 0.5 mm or more but 2.0 mm or less,
each of the inner rubber layer and the outer rubber layer consists of a radially outer reduced-thickness portion, a radially inner reduced-thickness portion, and a constant-thickness portion therebetween, wherein
the constant-thickness portion has a constant thickness,
the radially outer reduced-thickness portion has a thickness decreasing toward its radially outer end,
the radially inner reduced-thickness portion has a thickness decreasing toward its radially inner end, and
the radially outer and inner reduced-thickness portions each have a length Lc of not more than 5 mm,
wherein
a radial height H1 of the radially outer end of the outer rubber layer from a bead base line is 25% or more but 75% or less of a tire cross-sectional height H,
a radial height H2 of the radially outer end of the inner rubber layer from the bead base line is 25% or more but 60% or less of the tire section height H,
a second distance Hb in the tire radial direction between the radially inner end of the outer rubber layer and the radially inner end of the inner rubber layer, is 5% or more but 15% or less of a difference (H1−H2) between the radial height H1 and the radial height H2,
wherein
the radially inner end of the inner rubber layer is located at a position in the tire radial direction between a radially outer end and a radially inner end of the bead core,
wherein
the axially inner surface of the reinforcing rubber portion is directly adjacent to the carcass ply turnup portion from the radially outer end to the radially inner end of the reinforcing rubber portion, and
the axially outer surface of the reinforcing rubber portion is directly adjacent to a clinch rubber forming a tire outer surface in the bead portion and a sidewall rubber forming a tire outer surface in a tire sidewall portion,
wherein
the loss tangents are measured in accordance with the provisions of JIS-K6394 under the following conditions:
Initial Strain of 10%
Dynamic strain amplitude of +/−2%
Frequency of 10 Hz
Deformation mode is stretch
Measurement temperature is 70 deg. C.
|