Appeal No. 94-3608
Application 07/844,980
tires tend to wear irregularly and wander. Narrow-
width grooves can be employed to improve wear and
decrease wandering.
In such a tire, with a tread having a pair of
upper and lower rubber layers with different moduli of
elasticity, deforming stress concentrates in the
boundary surface bordering the two rubber layers when
the tire rolls normally or rides on a curb stone.
The appellants go on to describe their discovery that the
deforming stress which concentrated in the boundary surface
adversely affected the bottom of the fine groove, causing cracks
to occur, and that their invention solves this problem by a tire
construction having a plurality of features.
The following requirements manifest the appellants'
invention in both of the independent claims:
(1) Upper and lower tread layers having different moduli of
300% elasticity at room temperature with the layer located
on the tread surface side having a smaller modulus than the
other layer.
(2) Plural circumferential main grooves on the tread surface
side of the tire.
(3) A narrow-width fine circumferential groove in the layer
on the tread surface side of the tire and having
(a) a radius of curvature of its bottom of 1.5mm or
less, and
(b) a width in a range of not less than 15% and not
more than 30% of the width of one of the main grooves.
(4) The shortest distance between the bottom of the fine
groove and a boundary surface bordering between the pair of
upper and lower layers being within a range of 1mm and 3mm.
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Last modified: November 3, 2007