A studless tire with a tread pattern comprising blocks that are defined by longitudinal and transverse grooves and having at least one row of blocks that extends in the peripheral direction of the tire. The peripheral rows of blocks are such that at least one sub-block is provided within one pitch of the tread pattern outside an adjacent block in the tire's rotating axle. And the sub-block is separated from the block by a sub-groove less deep than the longitudinal and transverse grooves and has the longer side in the peripheral direction and the shorter side in the direction of the rotating axle.

BACKGROUND OF THE INVENTION 
The present invention relates to a studless tire that assures good running 
performance over snow- or ice-covered road surfaces without requiring 
studs on the tread surface. 
The use of spiked tires with studs embedded in the tread has been popular 
on automobiles running on snow- or ice-covered road surfaces. However, in 
recent years an increasing number of local governments are banning the use 
of spiked tires because they cause the problem of wearing the surface of 
bare pavement with the protruding end of studs. 
Under the circumstances, the use of studless tires which assure an 
improvement in the running performance over snow- or ice-covered road 
surfaces without providing studs on the tread surface is increasing. With 
such studless tires, their running performance on snow- or ice-covered 
road surfaces is improved by providing the tread with a block pattern 
consisting of a plurality of blocks, with a plurality of sipes being 
provided in each block. 
However, the performance requirements for tires to possess include starting 
and accelerating performance, braking performance, cornering performance 
and hill climbing performance and it is necessary that a good balance be 
attained between these performance characteristics. With conventional 
studless tires, however, emphasis is placed on improvements in the braking 
performance on snow- or ice-covered road surfaces and they cannot be said 
to be completely satisfactory in other aspects such as cornering 
performance. 
Furthermore, the conventional studless tires have had the problem that 
their running performance on highways in a bare condition is rather poor. 
To insure better grip on snow and ice surfaces, the studless tires have 
ends of the tread formed in square shoulders but this causes unsteady 
running, or "wandering", in the ruts worn in wheel tracks. 
Still a further problem with studless tires which are specially designed to 
maintain low temperatures is that they adopt tread rubber formulations 
having the tendency to provide lower grip on bare pavement. A vehicle with 
such tires installed on wheels will experience increased understeer when 
it corners. 
With the recent increase in the number of local governments that ban the 
use of spiked tires, there is a growing need for the development of 
studless tires having better running performance on highways in a bare 
condition. 
An object, therefore, of the present invention is to provide a studless 
tire that is improved in running performance, particularly cornering 
performance, on snow- or ice-covered road surfaces. 
Another object of the present invention is to provide a studless tire that 
is improved in running performance not only on snow- or ice-covered road 
surfaces but also on highways in a bare condition. 
SUMMARY OF THE INVENTION 
The above-stated object of the invention can be attained by a studless tire 
with a tread pattern comprising blocks that are defined by longitudinal 
and transverse grooves and having at least one row of blocks that extends 
in the peripheral direction of the tire. The peripheral rows of blocks are 
such that at least one sub-block is provided within one pitch of the tread 
pattern outside an adjacent block in the tire's rotating axle. And the 
sub-block is separated from the block by a sub-groove less deep than the 
longitudinal and transverse grooves and has the longer side in the 
peripheral direction and the shorter side in the direction of the rotating 
axle. 
Furthermore, in the studless tire according to the invention, any two 
sub-blocks that are formed on opposite sides of the center line through 
the area of contact with the ground and which are spaced by equal 
distances from the center line alternate in the peripheral direction. 
Still further, the ratio of the land area L to the sea area S is set to lie 
within the range L/S=(0.5-0.65)/(0.5-0.35). 
Still further, the studless tire further satisfies the following 
conditions: 
EQU m/M=0.025-0.050 
EQU a/c=0.055-0.15 
EQU d/D=0.40-0.80 
EQU 0.2&lt;e/T&lt;0.8 
where M is the in-pitch land area within one pitch of the tread pattern; m 
is the surface area of one sub-block; a is the width of a sub-block; c is 
the length of the sub-block; D is the depth of a longitudinal or a 
transverse groove; d is the depth of a sub-groove; e is the distance from 
the center line through the area of contact with the ground to a 
sub-block; and T is one half the width of the area of the tread in contact 
with the ground. 
The other object of the invention can be attained by a studless tire whose 
tread has blocks that are defined by longitudinal and transverse grooves, 
wherein recesses are formed in the buttress portion which extends radially 
inward from the tread end of shoulder blocks arranged in each shoulder 
portion and that, with the tire being installed on a normal rim and 
inflated, .beta./.alpha.=0.05-0.15 and .gamma./ .delta.=0.1-0.3, in which 
the letter .alpha. represents the area of the triangle defined by the 
vertical line extending radially from the tread end of a tire section as 
taken along a plane including the tire's rotating axle, the slope line of 
the buttress portion and by the straight line parallel to the rotating 
axle at distance A, which is a quarter of the tire's height H, from the 
straight line drawn parallel to the rotating axle from the outer 
peripheral edge of the tire, letter .beta. represents the cross-sectional 
area of each of the recesses, letter .gamma. represents the area of the 
opening in each of the recesses, and letter .delta. represents the area of 
the buttress portion, and that the angle .theta. the vertical line 
extending radially from the tread end forms with the slope line of each 
buttress portion is set to lie within the range from 10 to 40 degrees. 
The sub-blocks provided in the invention contribute not only to improve the 
running performance of the tire on snow- or ice-covered road surfaces but 
also to increase the lateral rigidity of the tread pattern by a sufficient 
amount to prevent skidding and increase the cornering limit speed while, 
at the same time, those sub-blocks insure that the vehicle, if it skids, 
can be easily corrected in attitude, thereby enhancing its 
maneuverability. 
Without any sub-blocks in one pitch of the tread pattern, only insufficient 
anti-skid effect is provided by the portion of one pitch and the anti-skid 
effect achieved in the peripheral direction of the tire becomes so uneven 
that the stability of a vehicle running on snow- or ice-covered road 
surfaces is affected adversely. 
If L/S is smaller than 0.5/0.5 (=1), the land area L is excessively small 
and, hence, the blocks are so small that their rigidity decreases, thereby 
reducing the grip force on the road surface. If L/S is greater than 
0.65/0.35 (=65/35), the sea area S is excessively small and, hence, the 
grooves are too narrow to form adequate amount of snow ridges during 
running on the snow surface, whereby the force of friction between the 
tire and the road surface decreases so much as to deteriorate its running 
performance on the snow surface. 
If m/M is smaller than 0.025, the individual inner or outer sub-blocks are 
so small that their lateral rigidity is insufficient to achieve the 
intended improvement in maneuverability. 
If m/M is greater than 0.050, the individual inner or outer sub-blocks are 
so large that they will deform in only small amounts, thereby producing 
reduced anti-skid effect. 
If a/c is smaller than 0.055, the sub-blocks are so narrow that their 
rigidity becomes insufficient. If a/c is greater than 0.15, the sub-blocks 
will deform in only small amounts, thereby achieving reduced anti-skid 
effect. 
If d/D is smaller than 0.40, the sub-grooves are so shallow that they 
achieve only small effect as grooves. If d/D is greater than 0.80, the 
sub-grooves are so deep that the rigidity of the sub-blocks will decrease. 
The recesses provided in the buttress portions of the shoulder blocks 
reduce the rigidity of the latter and absorb the impact that develops when 
the tread ends in square shoulders contact ruts, thereby contributing to 
prevent "wandering". 
In addition, the lateral force that is applied to the shoulder portion on 
the outer side of each front wheel on a cornering vehicle is effectively 
absorbed to prevent the skidding of front wheels while suppressing the 
occurrence of understeer. 
The values of .beta./.alpha. and .gamma./.delta. preferably lie within the 
ranges from 0.05 to 0.15 and from 0.1 to 0.3, respectively. If the lower 
limits of the respective ranges are not reached, the intended effects of 
the invention are not achieved. If the higher limits are exceeded, not 
only is the grip force reduced but also an additional problem such as the 
trapping of air occurs during tire manufacture.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiments of the invention are described below with reference to the 
accompanying drawings. 
As shown in FIGS. 1 and 2, a tread 1 has in the equatorial plane a center 
longitudinal groove 2 that extends in the peripheral direction of the 
tire. An intermediate longitudinal groove 3 and an outer longitudinal 
groove 4 are provided on either side of the center longitudinal groove 2. 
Transverse grooves 5 are provided in such a way that they extend from one 
tread end 1a to the other tread end 1a in the width direction of the tire. 
The center longitudinal groove 2, intermediate longitudinal grooves 3 and 
transverse grooves 5 define inner blocks 6; the intermediate longitudinal 
grooves 3, outer longitudinal grooves 4 and transverse grooves 5 define 
outer blocks 7; and the outer longitudinal grooves 4, tread ends 1a and 
transverse grooves 5 define shoulder blocks 8. 
It should be noted that the intermediate longitudinal grooves 3 do not lie 
in one line in the peripheral direction but are staggered in the width 
direction; hence, at the crossings of the intermediate longitudinal 
grooves 3 and transverse grooves 5, the edges of inner blocks 6 and outer 
blocks 7 are not positioned in straight lines in the peripheral direction 
but are offset from each other, whereby enhanced edge bite into the snow 
or ice surface is provided to insure better grip performance. 
Each inner block 6 has sipes 9 provided in such a way that their opposite 
ends communicate with the center longitudinal groove 2 and the 
intermediate longitudinal groove 3; each outer block 7 has sipes 10 
provided in such a way that their opposite ends communicate with the 
intermediate longitudinal groove 3 and the outer longitudinal groove 4; 
each shoulder block 8 has sipes 11 provided in such a way that their 
opposite ends communicate with the outer longitudinal groove 4 and the 
tread end 1a. The number of sipes to be provided in each block is 
typically three to five (four in the embodiment under consideration) and 
no other sipes or cuts need be provided. 
These sipes increase the area of contact between the block and snow or ice 
surfaces to provide better grip on snow- or ice-covered road surfaces. 
Further, they produce a snow or ice plowing effect to provide better 
traction on snow- or ice-covered road surfaces. In addition, communicating 
the sipes with the longitudinal grooves contributes a marked improvement 
in these effects of the sipes. 
If each of the blocks 6, 7 and 8 has less than three sipes, the rigidity of 
the blocks is too high to improve the running performance on snow- or 
ice-covered road surfaces. If the number of sipes exceeds five, the 
rigidity of the blocks drops so much as to adversely affect the 
maneuverability of the tire, particularly on dry roads. 
To secure these effects more positively, it is desired that the sipes 
extend over distances longer than the blocks in the axial direction. In 
the embodiment under consideration, this is achieved by forming a wavy 
pattern in the central portion of each sipe. 
Every other block in each peripheral row of inner blocks 6 (or outer blocks 
7) is provided with an anti-skid inner sub-block 12 (or outer sub-block 
13) outward in the direction of the tire's rotating axle, as spaced by a 
sub-groove 6a (or 7a) that is formed to be less deep than grooves 2, 3, 4 
and 5 (see FIG. 4). The inner sub-block 12 (or outer sub-block 13) has the 
longer side in the peripheral direction and the shorter side in the 
direction of the rotating axle. Each inner sub-block 12 is offset from 
adjacent outer sub-block 13 in the peripheral direction by a distance 
corresponding to one block. 
It should be particularly mentioned that as regards the peripheral rows of 
inner blocks 6 provided on opposite sides of the center line OL through 
the area of contact with the ground, the inner sub-blocks 12 spaced by 
equal distances from the center line OL alternate in the peripheral 
direction. Similarly, as regards the peripheral row of outer blocks 7 
provided on both sides of the center line OL through the ground contact 
area, the outer sub-blocks 13 spaced by equal distances from the center 
line OL alternate in the peripheral direction. 
These inner sub-blocks 12 and outer sub-blocks 13 contribute not only to 
improve the running performance of the tire on snow- or ice-covered road 
surfaces but also to increase the lateral rigidity of the tread pattern by 
a sufficient amount to prevent skidding and increase the cornering limit 
speed while, at the same time, those sub-blocks insure that the vehicle, 
if it skids, can be easily corrected in attitude, thereby enhancing its 
maneuverability. 
The tread end 1a of each shoulder block 8 is connected to a buttress 
portion 14 which extends to either side portion 15 of the tire, and 
recesses 16 are provided in the buttress portion 14. The recesses 16 lower 
the rigidity of shoulder blocks 8 so as to prevent not only "wandering" 
during running on the pavement of highways in a bare condition but also 
understeer when the vehicle corners. 
It is recommended that in the ground contact area between the tread end 1a 
on one side and the tread end 1a on the other side, the ratio of the land 
area L, which is the total sum of the surface areas of all blocks 6, 7, 8, 
12 and 13 on the entire circumference of the tire, to the sea area S which 
is the total sum of the areas of the openings in all grooves 2, 3, 4, 5, 
6a and 7a, should be in the range L/S=(0.5-0.65)/(0.5-0.35), provided that 
the total area of contact with the ground is expressed by L+S=1. 
If L/S is smaller than 0.5/0.5=1, the land area L is excessively small and, 
hence, the blocks are so small that their rigidity decreases, thereby 
reducing the grip force on the road surface. If L/S is greater than 
0.65/0.35 (=65/35), the sea area S is excessively small and, hence, the 
grooves are too narrow to form adequate amounts of snow ridges during 
running on the snow surface, whereby the force of friction between the 
tire and the road surface decreases so much as to deteriorate its running 
performance on the snow surface. 
It is also recommended that if the in-pitch land area which is the sum of 
the surface areas of blocks 6, 7, 8, 12 and 13 within one pitch of the 
tread pattern is expressed by M and the surface area of one inner 
sub-block 12 or one outer sub-block 13 by m, the ratio of m to M should be 
set to lie within the range m/M=0.025-0.050. 
If m/M is smaller than 0.025, either the inner sub-blocks 12 or the outer 
sub-blocks 13 are so small that their lateral rigidity is insufficient to 
insure the intended improvement in maneuverability. 
If m/M is greater than 0.050, the inner sub-blocks 12 or the outer 
sub-blocks 13 are so large that they will deform in only small amounts, 
thereby producing reduced anti-skid effect. 
It is also desirable that the ratio of the width a of each of inner 
sub-block 12 and outer sub-block 13 to its length c be set within the 
range a/c=0.055-0.15. If a/c is smaller than 0.055, sub-blocks 12 and 13 
are so narrow that their rigidity is insufficient. If a/c is greater than 
0.15, both sub-blocks 12 and 13 will deform in only small amounts, 
producing reduced anti-skid effect. 
A further recommendation is that d/D range from 0.40 to 0.80, with D 
representing the depth of each of the grooves 2, 3, 4 and 5, and d 
representing the depth of each of the sub-grooves 6a and 7a. If d/D is 
smaller than 0.40, the sub-grooves 6a and 7a are too shallow to work 
effectively as grooves. If d/D is greater than 0.80, the sub-grooves 6a 
and 7a are so deep that the rigidity of inner sub-blocks 12 and outer 
sub-blocks 13 will decrease. 
It is essential for the purposes of the present invention that at least one 
inner sub-block 12 and at least one outer sub-block 13 be provided within 
one pitch of the tread pattern. 
Without any sub-blocks within one pitch of the tread pattern whether they 
are inner sub-blocks 12 or outer sub-blocks 13, only insufficient 
anti-skid effect is provided by the portion of one pitch and the anti-skid 
effect achieved in the peripheral direction of the tire becomes so uneven 
that the stability of a vehicle running on snow- or ice-covered road 
surfaces is affected adversely. 
It is also advisable in the present invention that if the distance from the 
center line OL through the ground contacting area of the tread 1 to the 
ridgeline of inner sub-block 12 closer to the center of the ground contact 
area is expressed by e.sub.1 whereas the distance from the center line OL 
to the ridgeline of outer sub-block 13 closer to the center of the ground 
contact area is expressed by e.sub.2, the inner sub-blocks 12 and the 
outer sub-blocks 13 should be provided in a region that satisfies the 
condition 0.2&lt;e/T&lt;0.8, where e stands for e.sub.1 or e.sub.2 and T is one 
half the width of the ground contact area which is equal to the distance 
between tread ends 1a on opposite sides of the tire. 
If e/T is equal to or smaller than 0.2, the inner sub-blocks 6 decrease in 
width in the direction of the tire's rotating axle and their rigidity will 
also decrease to cause adverse effects on tire performance characteristics 
such as traction performance and the stability of running on snow- or 
ice-covered road surfaces. 
If e/T is equal to or greater than 0.8, the shoulder blocks 8 decrease in 
width in the direction of the tire's rotating axle and their rigidity will 
also decrease, again adversely affecting tire performance characteristics 
such as traction performance and the stability of running on snow- or 
ice-covered road surfaces. 
Invention tire sample (Example 1; see FIG. 4), three comparative tire 
samples (Comparative Examples 1 to 3) that had sub-blocks but which were 
structurally outside the scope of the invention in one or more aspects, 
and one other comparative tire sample (Comparative Example 4) having a 
prior art structure were tested for their performance. The test results, 
as well as the specifications of the respective tire samples are shown in 
Tables 1 and 2. 
The tire of Comparative Example 1 (see FIG. 4) was outside the scope of the 
invention only in terms of d/D (=0.34&lt;0.40, the lower limit of the range 
specified by the invention). 
The tire of Comparative Example 2 (see FIG. 5) was outside the scope of the 
invention in terms of m/M (=0.0145&lt;0.025, the lower limit of the range 
specified by the invention) and a/c (0.050&lt;0.055, the lower limit of the 
range specified by the invention). 
The tire of Comparative Example 3 (see FIG. 6) was also outside the scope 
of the invention in terms of m/M (=0.058&gt;0.050, the upper limit of the 
range specified by the invention) and a/c (=0.200&gt;0.15, the upper limit of 
the range specified by the invention). 
The tire of Comparative Example 4 (see FIG. 7) had a conventional tread 
pattern absent inner and outer sub-blocks. 
As for the running performance data given by indices in Tables 1 and 2, the 
criteria are the data in Comparative Example 4 and the higher the indices, 
the better the performance. 
TABLE 1 
______________________________________ 
Comparative 
Comparative 
Example 1 
Example 1 Example 2 
______________________________________ 
L/S 0.58/0.42 0.58/0.42 0.56/0.44 
m/M 0.029 0.029 0.0145 
a/c 0.100 0.100 0.050 
d/D 0.588 0.34 0.588 
No. of sub-blocks 
2 2 2 
within one pitch 
(e/T) e.sub.1 /T 
0.27 0.27 0.29 
e.sub.2 /T 0.62 0.62 0.64 
(Performance on the 
ice) 
Index of cornering 
105 102 102 
performance 
Index of slalom 
106 102 101 
time 
(Performance on the 
snow) 
Time to pass 98.09 101.34 102.22 
handling track 
(seconds) 
Speed of cornering 
32.6 31.2 31.1 
at R = 35 m (km/h) 
Rating for 7 6 6 
stability during 
lane change 
Controllability 
8 7 6 
after skidding 
______________________________________ 
TABLE 2 
______________________________________ 
Comparative 
Comparative 
Example 3 
Example 4 
______________________________________ 
L/S 0.60/0.40 0.55/0.45 
m/M 0.058 -- 
a/c 0.200 -- 
d/D 0.588 -- 
No. of sub-blocks within 
2 -- 
one pitch 
(e/T) e.sub.1 /T 0.25 -- 
e.sub.2 /T 0.60 -- 
(Performance on the ice) 
Index of cornering 
101 100 
performance 
Index of slalom time 
103 100 
(Performance on the snow) 
Time to pass handling 
101.87 103.40 
track (seconds) 
Speed of cornering at 
30.9 29.3 
R = 35 m (km/h) 
Rating for stability 
7 5 
during lane change 
Controllability after 
5 5 
skidding 
______________________________________ 
As one can see from Tables 1 and 2, the provision of sub-blocks according 
to claim 1 contributed improvements in tire's performance on both the ice 
and the snow; it should particularly be noted that by providing sub-blocks 
that satisfied the requirements according to the present invention, the 
performance on the ice and the snow, especially cornering performance, 
could be further improved. 
Having the structural features described herein, the studless tire of the 
invention has the following advantages. 
The provision of sub-blocks contributes not only to improve the running 
performance of the tire on snow- or ice-covered road surfaces but also to 
increase the lateral rigidity of the tread pattern by a sufficient amount 
to prevent skidding and increase the cornering limit speed while, at the 
same time, those sub-blocks insure that the vehicle, if it skids, can be 
easily corrected in attitude, thereby enhancing its maneuverability. 
Without any sub-blocks in one pitch of the tread pattern, only insufficient 
anti-skid effect is provided by the portion of one pitch and the anti-skid 
effect achieved in the peripheral direction of the tire becomes so uneven 
that the stability of a vehicle running on snow- or ice-covered road 
surfaces is affected adversely. 
If L/S is smaller than 0.5/0.5 (=1), the land area L is excessively small 
and, hence, the blocks are so small that their rigidity decreases, thereby 
reducing the grip force on snow- or ice-covered road surfaces. If L/S is 
greater than 0.65/0.35 (65/35), the sea area S is excessively small and, 
hence, the grooves are too narrow to form adequate amounts of snow ridges 
during running on the snow surface, whereby the force of friction between 
the tire and the road surface decreases so much as to deteriorate its 
running performance on the snow surface. 
If m/M is smaller than 0.025, the individual inner or outer sub-blocks are 
so small that their lateral rigidity is insufficient to achieve the 
intended improvement in maneuverability on snow- or ice-covered road 
surfaces. 
If m/M is greater than 0.050, the individual inner or outer sub-blocks are 
so large that they will deform in only small amounts, thereby producing 
reduced anti-skid effect on snow- or ice-covered road surfaces. 
If a/c is smaller than 0.055, the sub-blocks are so narrow that their 
rigidity becomes insufficient. If a/c is greater than 0.15, the sub-blocks 
will deform in only small amounts, thereby achieving reduced anti-skid 
effect on snow- or ice-covered road surfaces. 
If d/D is smaller than 0.40, the sub-grooves are so shallow that they 
achieve only small effect as grooves. If d/D is greater than 0.80, the 
sub-grooves are so deep that the rigidity of the sub-blocks will decrease. 
Another embodiment of the invention are described below with reference to 
the accompanying drawings. 
In a studless tire as shown in FIGS. 1 and 2, the tread end 1a of each 
shoulder block 8 is connected to a buttress portion 14 which extends to 
either side portion 15 of the tire, and recesses 16 are provided in the 
buttress portion 14 (see FIGS. 3 and 8). 
As shown in FIG. 9, the angle .theta. of the vertical line VL extending 
radially from the tread end 1a of an inflated tire forms with the slope 
line SL of the buttress portion 14 is set to range from 10 to 40 degrees 
(.theta.=32.degree. in the embodiment under consideration). 
Consider triangle S that is formed by the vertical line VL, the slope line 
SL, and straight line HL that is parallel to the rotating axle of the tire 
at distance A (A=H/4) from the straight line drawn parallel to the 
rotating axle from the outer peripheral edge of tire OL, with H being the 
height of tire as defined by the distance from the baseline BL (the 
reference plane of the rim) to OL. Also consider the cross section s 
(triangular in the embodiment) of each recess 16 in the buttress portion 
14 as taken along a plane including the rotating axle. If the areas of 
triangle S and cross section s are written as .alpha. and .beta., 
respectively, it is necessary that .beta./.alpha. range from 0.05 to 0.15 
(.beta./.alpha.=0.13 in the embodiment). 
The recesses 16 lower the rigidity of shoulder blocks 8 so as to prevent 
"wandering" and understeer. 
If .beta./.alpha. is smaller than 0.05, the recesses 16 are too small to 
achieve the intended effects; if .beta./.alpha. is greater than 0.15, not 
only the grip force decreases but also problems such as the trapping of 
air occur during tire manufacture. 
Let assume the area of the opening in each recess 16 to be written as 
.gamma. (see FIG. 2); also assume that the area of the shoulder block 8 
that is surrounded by the slope line of the buttress surface 17 (including 
the area of the opening in recess 16) has area .delta.. According to the 
invention, .gamma./.delta. is specified to range from 0.1 to 0.3 
(.gamma./.delta.=0.21 in the embodiment), and the angle .theta. the 
vertical line extending radially from the tread side end forms with the 
slope line of the buttress portion is set to range from 10 to 40 degrees. 
These conditions are necessary to provide better running characteristics on 
highways in a bare condition such as cornering performance and stability 
during running in ruts. If .gamma./.delta. is smaller than 0.1, recesses 
16 are too small to achieve the intended effects; if .gamma./.delta. is 
greater than 0.3, not only the grip force decreases but also problems such 
as the trapping of air occur during tire manufacture. 
Tire samples were constructed in accordance with the present invention and 
tested for their performance in comparison with a conventional tire. The 
test results are shown in Tables 3 and 4. 
First invention tire sample (Example 2) did not have any sipes in the 
blocks in the direction of the tire's rotating axle and the recesses 16 in 
the buttress portions 14 had a triangular cross section (see FIG. 10A). 
Second invention tire sample (Example 3) did not have any sipes in the 
blocks in the direction of the tire's rotating axle and the recesses 16 
had a rectangular cross section (see FIG. 10B). 
Third invention tire sample (Example 4) had sipes in the blocks in the 
direction of the tire's rotating axle and the recesses 16 had a triangular 
cross section (see the embodiment described in preceding paragraphs). 
Fourth invention tire sample (Example 5) had sipes in the blocks in the 
direction of the tire's rotating axle and the recesses 16 had a triangular 
cross section (see FIG. 10C). 
Fifth invention tire sample (Example 6) had sipes in the blocks in the 
direction of the tire's rotating axle and the recesses 16 had a 
rectangular cross section (see FIG. 10D). 
The conventional tire as a comparative sample (Comparative Example 5) had 
sipes in the blocks in the tire's rotating axle but the buttress portions 
14 did not have any recesses (see FIG. 10E). 
TABLE 3 
______________________________________ 
Example 2 
Example 3 Example 4 
______________________________________ 
.beta./.alpha. 0.078 0.18 0.13 
.gamma./.delta. 
0.17 0.17 0.21 
.theta. 17.degree. 
17.degree. 
32.degree. 
Performance on highways 
in bare condition 
(stability during 
7 7 7 
straight run) 
(stability during lane 
8 6 7 
change) 
(cornering perform- 
7 6 8 
ance) 
Handling track running 
63.21 67.01 62.54 
time 
Running along ruts 
(in ruts) 8 7 8 
(escape from ruts) 
7 6 8 
Performance on the snow 
or ice surface 
(braking on snow) 
102 102 103 
(braking on ice) 
104 101 100 
(cornering on ice; 
105 102 100 
R = 25 m) 
______________________________________ 
TABLE 4 
______________________________________ 
Compara- 
tive 
Example 5 
Example 6 Example 5 
______________________________________ 
.beta./.alpha. 0.13 0.042 -- 
.gamma./.delta. 
0.34 0.21 -- 
.theta. 32.degree. 
32.degree. 
32.degree. 
Performance on highways 
in bare condition 
(stability during 
7 6 6 
straight run) 
(stability during lane 
6 6 5 
change) 
(cornering perform- 
6 6 5 
ance) 
Handling track running 
65.89 67.01 68.70 
time 
Running along ruts 
(in ruts) 7 7 6 
(escape from ruts) 
7 6 6 
Performance on the snow 
or ice surface 
(braking on snow) 
102 100 100 
(braking on ice) 
101 101 100 
(cornering on ice; 
102 100 100 
R = 25 m) 
______________________________________ 
As one can see from Tables 3 and 4, the invention tire samples had better 
performance on highways in a bare condition than the comparative sample 
without deterioration in the running performance on snow- or ice-covered 
road surfaces. 
Having the structural features described herein, the studless tire of the 
invention has the following advantages. 
The recesses provided in the buttress portions of the shoulder blocks 
reduce the rigidity of the latter and absorb the impact that develops when 
the tread ends in square shoulders contact ruts, thereby contributing to 
prevent "wandering". 
In addition, the lateral force that is applied to the shoulder portion on 
the outer side of each front wheel on a cornering vehicle is effectively 
absorbed to prevent the skidding of front wheels while suppressing the 
occurrence of understeer.