Pneumatic tires

There is provided a pneumatic tire having slant main grooves extending from positions adjacent to a circumferential rib in a tread center zone toward each tread end in opposite directions to each other at a relatively small angle with respect to the circumferential direction of the tire. Each of the slant grooves extends at an angle of not more than 40.degree. to the circumferential direction of the tire, and slant auxiliary grooves are formed so as to extend at an angle of not less than 50.degree. with respect to the circumferential direction of the tire from the ends of the slant main grooves to the tread end in each of tread side zones, and further the negative ratio of the tread is maximized at the portion adjacent to the circumferential rib and tends to be decreased towards the tread ends. By means of this invention the wet property is enhanced and the pattern noise is reduced without adversely affecting the primary functions of the tire.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to pneumatic tires, and in particular to 
high-performance pneumatic tires which are capable of enhancing wet 
performance and reducing pattern noise compatibly without adversely 
affecting the primary properties of the tire. 
2. Description of the Prior Art 
In order to improve wet property and reduce pattern noise, for example, it 
is generally known to select a tread pattern having a combination of 
straight circumferential grooves and directional (uni-directional) slant 
grooves. In this case, it is effective to increase the negative ratio, 
which is the ratio of total groove area to the sum of total groove area 
and total land area. 
However, since a conventional pattern comprising a combination of straight 
circumferential grooves and slant grooves has large circumferential groove 
portions and small slant groove portions, problem exists in that the 
appropriate distribution of grooves across the tread in the widthwise 
direction of the tire is not obtained and hence drainage efficiency is not 
effectively enhanced. Further when the negative ratio is increased to 
enhance the wet property, the land area is small and the necessary land 
rigidity is not retained, resulting in other problems of decreasing 
resistance to wear and cornering property, in addition to degrading 
pattern noise. 
The present invention has been accomplished based on the realization that 
directional slant grooves having a small slant angle with respect to the 
circumferential direction of the tire is advantageous with respect to wet 
property, while when only these slant grooves are arranged, it is 
difficult to retain sufficient land rigidity resulting in degraded 
steering stability and the effect on reducing noise by pitch-variation is 
small because of the decreased number of pitches. 
The objects of the present invention are to provide a pneumatic tire having 
enhanced wet property and effectively reduced pattern noise without 
degrading primary functions such as steering stability and resistance to 
wear by selecting the position and angle of such slant grooves, combining 
other slant grooves having selected position, angle and width with these 
slant grooves, and defining the distribution of the negative ratio across 
the tread in the widthwise direction of the tread. 
SUMMARY OF THE INVENTION 
According to the invention, there is provided a pneumatic tire having a 
tread pattern comprising a circumferential rib extending continuously in 
the circumferential direction of the tire in a tread center zone, defined 
by having a width of the tread width divided into half and extending on 
both sides of the equatorial plane of the tire as the middle plane, and 
slant main grooves extending from positions adjacent to the 
circumferential rib toward each tread end in opposite directions to each 
other at a relatively small angle with respect to the circumferential 
direction of the tire, characterized in that each of said slant grooves 
extends at an angle of not more than 40.degree. with respect to the 
circumferential direction of the tire into a tread side zone defined 
between the tread center zone and the tread end, in that slant auxiliary 
grooves having relatively narrow width and extending at an angle of not 
less than 50.degree. with respect to the circumferential direction of the 
tire and opening to the tread end are formed in each tread side zone, and 
said slant auxiliary grooves extending at least in one tread side zone are 
connected with the ends or near end portions of the tread end sides of the 
slant main grooves reaching the tread side zone, and in that the negative 
ratio of the tread is maximized at the portion adjacent to said 
circumferential rib and tends to be decreased towards the tread ends. 
In this invention, the circumferential rib can be arranged in the center in 
the center zone or arranged to be at one side in the center zone. It is 
possible not only that the slant auxiliary grooves in only one tread side 
zone are connected with the ends or near end portions of the slant main 
grooves reaching the tread side zone but also that the slant auxiliary 
grooves in both of the tread side zones are connected with the slant main 
grooves. 
It is normal in high performance tires to provide directional slant grooves 
and to make the negative ratio of the entire tread 25-35% in order to 
obtain sufficient wet property, and such features can be applied to the 
tire according to present invention. 
Since in the tread contacting area water flows forward at an angle of 
0.degree.-20.degree. with respect to the circumferential direction of the 
tire near the equatorial plane of the tire, and forward at an angle of 
20.degree.-40.degree. near the border of the tread center zone and the 
tread side zone, and sideways at an angle of more than 40.degree. in the 
remaining portion of the tread side zone, the tire of the present 
invention is provided with excellent drainage property forward in the 
circumferential direction by forming slant main grooves extending at 
relatively small angle of not more than 40.degree. with respect to the 
circumferential direction of the tire and having sufficient groove volume 
in place of conventional circumferential straight grooves. 
Sufficient wet property during straight running is preferably obtained by 
providing at least one slant groove passing through the tread contacting 
print. 
Moreover, in order to ensure wet property during cornering and to reduce 
passing noise by making each frequency of air column resonance caused in 
each of the slant grooves different from one another, it is preferable to 
form slant auxiliary grooves, each of which has relatively narrow width, 
extending at a large angle of not less than 50.degree. with respect to the 
circumferential direction of the tire and connecting with the slant main 
grooves in at least one tread side zone, with shorter pitch than the 
length of contacting print. 
Further, since the slant main grooves here slantingly extend at a small 
angle with respect to the circumferential direction of the tire, the 
impulse of the land portion during tire rotation is small, and accordingly 
the slant main grooves do not produce an adverse effect on pattern noise. 
According to the observation that a water layer arises in the center zone 
of the tread, the negative ratio produced by the slant main grooves formed 
in the tread center zone and the side zone is made much larger than that 
of the entire tread resulting in ensuring enhanced wet drainage property, 
and the negative ratio is maximized at both the side portions adjacent to 
the circumferential rib and tends to be gradually decreased towards the 
tread end. 
It is preferable with respect to wet drainage property that the negative 
ratio of the edge portion in the tread center-side region which is defined 
as that where the slant main grooves exist and where the negative ratio is 
not less than 70% of the negative ratio of the whole tread, is made 50-80% 
of the maximum negative ratio of the portion adjacent to the 
circumferential rib. Moreover, it is preferable that the negative ratio of 
the tread end-side region outside the tread center-side region is made 
15-30% of the maximum negative ratio in order to ensure tread rigidity 
because the tread end-side region outside the tread center-side region 
contributes largely for steering stability rather than for drainage 
property. 
Furthermore, in the tread center-side region having width W.sub.0 and where 
the slant main grooves exist, it is preferable for retaining good wet 
property that the negative ratio owing to the slant main grooves is more 
than 80% of the negative ratio of the whole tread, and it is preferable 
for retaining steering stability near marginal cornering ability and 
reducing the pattern noise that the width W.sub.0 of the tread center-side 
region where the slant main grooves exist is not more than 85% of the 
tread width W. 
When the angle of the slant main grooves is more than 40.degree., it is 
difficult to ensure the compatibility of sufficient negative ratio and 
block rigidity; it is preferable to make this angle smoothly larger going 
from the equatorial plane of the tire toward the tread end in order to 
enhance wet drainage property and steering stability. 
Furthermore, when the angle of the slant auxiliary grooves is less than 
50.degree., it is difficult to ensure block rigidity by which sufficient 
steering stability is obtained. In this connection, in order to enhance 
steering stability it is preferable that this slant angle is substantially 
90.degree., whereby pattern noise can also be reduced in connection with 
the shape of the tread contacting print of the tire. 
In order to ensure steering stability during straight running and good 
response for handling, the circumferential rib continuously extending in 
the circumferential direction of the tire is arranged in the tread center 
zone. In addition , this circumferential rib contributes to reducing 
pattern noise effectively because of its continuity. 
Furthermore, in order to enhance particularly marginal cornering property 
among steering stability property, shoulder land rigidity is increased and 
tread contacting area is enlarged by making the negative ratio of the 
tread side zone small. 
When the circumferential rib is arranged in the center portion in the 
center zone, impact which occurs in the center portion during rotation and 
has a large effect on pattern noise is reduced, so that the noise is 
reduced more effectively. 
In the case of applying this circumferential rib to a high performance 
vehicle tire the width of which is wide in a front tire and narrow in a 
rear tire, the rigidity of the tread center portion during driving at 
small steering angle is enhanced because the circumferential rigidity of 
the tread center portion of the front tire, which has relatively narrow 
tread width, is enlarged. 
On the other hand, when this circumferential rib is arranged to be 
one-sided in the tread center zone, in a rear tire which has relatively 
wide tread width, stable cornering with enhanced rigidity is possible 
because the circumferential rib shifts to near the center portion in the 
shifted contacting print during cornering. 
Furthermore, when each of the slant auxiliary grooves in each of the tread 
side zones is connected with the slant main grooves, the ability to drain 
water sideways during cornering is enhanced, whereby resistance to 
hydro-planing during cornering is enhanced.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows a first embodiment of the tread pattern of a tire according to 
the invention. 
The basic structure of a pneumatic tire to which a tread pattern of the 
invention is applied is that a pair of sidewall portions and a crown 
portion connecting these sidewall portions to each other are reinforced 
with a radial carcass comprising a ply of cords wound around a bead core 
embedded in the bead portion along the inner edge of each sidewall, and a 
tread arranged along the crown portion is reinforced by a belt comprising 
a plurality of crossing layers of parallel arranged cords crossing at a 
small angle with respect to the circumferential direction around the crown 
portion. In FIG. 1, reference numeral 1 is the tread, 2 is a 
circumferential rib arranged on the equatorial plane and continuously 
extending in the circumferential direction of the tire, and 3 is slant 
main grooves. Further, numeral 4 shows a tread center zone defined by 
having a half width of the tread width and extending on both sides of the 
equatorial plane of the tire as the middle plane, and 5 are tread side 
zones defined between the tread center zone 4 and the tread ends. 
Slant main grooves 3 extending slantwise at an angle of not more than 
40.degree. in opposite directions to each other with respect to the 
circumferential direction are formed alternately from positions adjacent 
to the circumferential rib 2 in the center portion in the tread center 
zone 4 toward each tread end. Each of the slant main grooves 3 extends 
continuously to be convex toward the tread center in the tread center zone 
4 and be concave toward the tread center in the tread side zone 5, and 
ceases at the near tread center portion in the tread side zone 5. 
Further, in the tread side zone 5, slant auxiliary grooves 6 having a 
relatively narrower width than the slant main grooves 3 extend in the same 
direction as the slant main grooves 3 at an angle of not less than 
50.degree., at a relatively large angle of 50.degree.-80.degree. in this 
embodiment, and connect with the tread end-side ends 3a of the slant 
grooves 3, and intermediate grooves 7 extending in parallel with the slant 
auxiliary grooves 6 and connecting with intermediate portions of the slant 
main grooves 3 are formed so as to divide each intermediate portion 
between the slant auxiliary grooves 6. Here, an extended narrow portion 6a 
having a narrower width than the slant auxiliary groove 6 can be connected 
with the slant auxiliary groove 6 so as to reach another slant main groove 
3 inside the slant main groove 3 with which this slant auxiliary groove 6 
connects, and an extended narrow portion 7a having a narrower width than 
the intermediate groove 7 can be connected with the intermediate groove 7 
so as to cross the inner slant main groove 3 adjacent to the intermediate 
groove 7 and reach the tread center-side end 3b of the further inner slant 
main groove 3. 
With regard to the above description, it is preferable that the slant angle 
of the slant main grooves 3 is 5.degree.-20.degree.. When the slant main 
grooves 3 have a winding configuration as shown in FIG. 1, the average 
slant angle is measured by averaging the angle of each tangent at the 
point which equally divides the length of each of convex and concave curve 
lines positioned at each side of the inflection point. 
Each average width of each groove is narrower in the order of the slant 
main groove 3, the slant auxiliary groove 6, the intermediate groove 7, 
and each extended narrow portion 6a, 7a. Particularly, that of the slant 
main groove 3 is 2-5% of the tread width W, those of the slant auxiliary 
groove 6 and the intermediate groove 7 are each 20-50% of the maximum 
width of the slant main groove and have a lower limit of 2 mm to avoid 
closing when coming in contact with the road during rotating. Those of the 
narrow extended portions 6a, 7a are each 0.2-2 mm. 
Each average depth of the slant auxiliary grooves 6 and the intermediate 
grooves 7 is shallower than each average depth of the slant main grooves 
3, and each average depth of the extended narrow portions 6a, 7a is equal 
to or shallower than each average depth of the slant auxiliary grooves 6 
and intermediate grooves 7. 
In this tire in which the land portion is divided under above mentioned 
groove arrangement, the negative ratio of the entire tread is 25-35% and, 
as shown in the graph of FIG. 2, the negative ratio at each position in 
the widthwise direction across the tread is maximized at the portion 
adjacent to the circumferential rib 2 and tends to be decreased towards 
the tread ends. More preferably, the negative ratio of the edge portion in 
the tread center-side region, where the slant main grooves exist and the 
negative ratio is not less than 70% of the negative ratio of the entire 
tread and which has the width of, for example, 70-90% of the tread width, 
is made 50-80% of the maximum negative ratio, and further the negative 
ratio of the tread end-side region outside the tread center-side region is 
made 15-30% of the maximum negative ratio. 
A tire having the arrangement, as mentioned above, has both enhanced wet 
property and reduced pattern noise without degrading steering stability 
and other primary functions of the tire. 
Each of the narrow extended portions 6a, 7a has functions to enhance 
gripping the road surface and produce an edge effect on a slippery road 
such as a snow, ice or wet road. The intermediate grooves 7 produce twice 
as many pitches as the slant main grooves 3 in the tread shoulder portion 
in cooperation with the slant auxiliary grooves 6 resulting in greatly 
enhanced drainage property during cornering and effective reduction of 
pattern noise. 
This is especially effective when each average width of the slant auxiliary 
grooves 6 and the intermediate grooves 7 is 20-50% of the maximum width of 
the slant main grooves 3. 
FIG. 3 illustrate another embodiment of the tread pattern according to the 
invention. 
In this embodiment, the circumferential rib 2 is arranged on the right side 
in the tread center zone 4, in other words arranged to slightly to 
one-side toward the outer side of the tire viewing the tire mounted onto a 
vehicle. Intervals of slant main grooves 3 extending from positions 
adjacent to the circumferential rib are made relatively a little larger in 
the outer portion of the tire viewing the tire mounted onto the vehicle 
than in the inner portion. Each slant angle of the slant main grooves 3 
with respect to the circumferential direction of the tire is smaller in 
the outer portion than in the inner portion. 
In the inner portion of the tire, viewing the tire mounted onto the 
vehicle, both slant auxiliary grooves 6 connected with the tread end-side 
ends 3a of the slant main grooves 3 and intermediate grooves 7 connected 
with the intermediate portions of the slant main grooves 3 cease at the 
slant main grooves without having narrow extended portions. Further, each 
slant angle of the slant main grooves 3 is smaller near the tread 
center-side end 3b and its width is also smaller in this portion 3b, and 
narrow grooves 8 extending in the opposite direction with respect to the 
direction of the slant main grooves 3 from the end 3b are formed so as to 
extend toward the tread end. These narrow grooves 8 cross two slant main 
grooves 3 and cease by connecting with a third slant main groove 3 near 
the tread end-side end 3a. 
On the other hand, in the outer portion of the tire, the slant auxiliary 
grooves 6 are connected with the slant main grooves 3 near the tread 
end-side end 3a, and subsidiary slant grooves 9 are formed between the 
slant auxiliary grooves 6 and the intermediate grooves 7 so as to extend 
in parallel with the slant auxiliary grooves 6 and the intermediate 
grooves 7 and divide intermediate portions between these grooves equally, 
and each of subsidiary slant grooves 9 is opened to the tread end but 
ceases without connecting with the slant main grooves 3. Further, the 
slant angle and the width of the slant main grooves 3 are both made 
smaller near the tread center-side ends 3b of the slant main grooves 3 in 
the same way as i n the inner portion, and narrow grooves 8 extending in 
the opposite direction to the slant main grooves 3 are formed from the end 
3b, wherein the narrow grooves 8 cross one slant main groove 3 and cease 
by connecting with a second slant main groove 3 near the end 3a. 
Furthermore, subsidiary narrow grooves 10 are formed between adjacent 
slant main grooves 3 to extend in parallel with the narrow grooves 8, 
divide the intermediate portions between adjacent narrow grooves 8 equally 
and connect with both of the adjacent slant main grooves 3. 
In this embodiment, each average width of each groove is narrower in the 
order of the slant main groove 3, the group of the slant auxiliary groove 
6, the intermediate groove 7 and the subsidiary slant groove 9, and the 
group of the narrow groove 8 and the subsidiary narrow groove 10. In 
particular that of the slant main groove 3 is 2-5% of the tread width W; 
those of the slant auxiliary groove 6, the intermediate groove 7 and the 
subsidiary slant groove 9 are each 20-50% of the maximum width of the 
slant main groove 3 and have lower limit of 2 mm to avoid closing when 
coming in contact with the road during rotating; and those of the narrow 
groove 8 and the subsidiary narrow groove 10 are each 0.2-2 mm. 
Each average depth of the slant auxiliary grooves the intermediate grooves 
7 and the subsidiary grooves 9 is shallower than each average depth of the 
slant main grooves 3, and each average depth of the narrow grooves 8 and 
the subsidiary narrow grooves 10 is equal to or shallower than each 
average depth of the slant auxiliary grooves 6, intermediate grooves 7 and 
subsidiary slant grooves 9. 
Under such groove arrangement, as shown in the graph of FIG. 4, the 
negative ratio at each portion across the tread in the widthwise direction 
is maximized at the portion adjacent to the circumferential rib 2 and 
tends to be decreased towards the tread ends. 
The tire above mentioned with reference to FIGS. 3 and 4 has substantially 
the same effect as the tire of first embodiment of FIGS. 1 and 2 with 
regard to the wet property and the pattern noise based on the particular 
arrangement of the slant main grooves 3 and the slant auxiliary grooves 6, 
and the selection of the negative ratio of each point in the widthwise 
direction. 
In this embodiment, the narrow grooves 8 and the subsidiary narrow grooves 
10 both extending in the opposite direction to the direction of the slant 
main grooves 3 ensure the tread gripping ability and bring about the edge 
effect on a slippery road such as a wet road. 
Further, the subsidiary slant grooves 9, in cooperation with the slant 
auxiliary grooves 6 and the intermediate grooves 7, enhance the gripping 
ability without degrading the block rigidity in the shoulder portion, 
enhance the drainage property and the edge effect during cornering, and 
reduce pattern noise in the same way as the intermediate grooves 7 in the 
first embodiment. 
In the tire of this embodiment, the circumferential rib 2 can be arranged 
in the center portion in the tread center zone. 
Comparative Test 1 
A comparative test between tires of the invention and a conventional tire 
will be described with respect to the wet drainage property, the pattern 
noise and the steering stability on dry road. 
Test Tires 
The test tires have a size of 225/50 R16, a tread width of 200 mm and a 
tread contact length of 120 mm. 
Invention Tire 1 
This tire has a tread pattern as shown in FIG. 1, in which the negative 
ratio of the entire tread is 28%, the negative ratio at each portion in 
the widthwise direction is distributed as shown in FIG. 2, and the width, 
the depth and the angle with respect to the circumferential direction of 
the tire are shown in Table 1. 
TABLE 1 
______________________________________ 
Width (mm) 
Slant angle 
Depth (mm) 
______________________________________ 
Slant main groove 
6-8-5 10-20-10.degree. 
8 
Slant auxiliary 
4 70.degree. 6.5 
groove and inter- 
mediate groove 
Narrow extended 
2 60-70.degree. 
6.5 
portion 
______________________________________ 
Invention Tire 2 
This tire has an asymmetrical tread pattern as shown in FIG. 3, in which 
the negative ratio of the entire tread is 29%, the negative ratio at each 
portion in the widthwise direction is distributed as shown in FIG. 4, and 
the width, the depth and the angle with respect to the circumferential 
direction of the tire are shown in Table 2. 
TABLE 2 
______________________________________ 
Width Slant Depth 
(mm) angle (mm) 
______________________________________ 
Right slant main groove 
2-15-5 0-20-10.degree. 
8 
Left slant main groove 
2-13-10 0-25.degree. 
8 
Right slant auxiliary groove, 
4 75.degree. 
6.5 
intermediate groove and 
subsidiary slant groove 
Left slant auxiliary groove 
5 85.degree. 
6.5 
and subsidiary slant groove 
Right narrow groove and 
2 35.degree. 
6.5 
subsidiary narrow groove 
Left narrow groove 
2 40.degree. 
6.5 
______________________________________ 
Conventional Tire 
A tire as shown in FIG. 9. 
Test Method 
The test tire was inflated under an internal pressure of 2.3 kgf/cm.sup.2 
and mounted on a vehicle under loading with two passengers. The wet 
drainage property during straight running was evaluated by measuring a 
remaining area of the ground contacting area during passing on a wet road 
surface having a water depth of 5 mm at a speed of 80 km/hr and 90 km/hr. 
The wet drainage property during cornering was evaluated by measuring a 
marginal lateral gravity during passing on wet road having a water depth 
of 5 mm and a radius of 100 mm. 
The pattern noise was evaluated by feel inside the vehicle during drifting 
from 100 km/hr on a straight smooth road. 
The steering stability on dry road was evaluated by feeling during running 
on a dry circuit under various running modes. 
Test results 
The measured results are shown in Table 3, by an index value on the basis 
that the conventional tire is control. 
TABLE 3 
______________________________________ 
Conventional 
Invention 
Invention 
tire tire 1 tire 2 
______________________________________ 
Wet drainage 
100 125 120 
property during 
straight running 
Wet drainage 
100 120 115 
property during 
cornering 
Pattern noise 
100 105 105 
Steering stability 
100 100 105 
on dry road 
______________________________________ 
As seen from Table 3, the steering stability on dry road can be retained 
with high level, and enhancement of both the wet drainage property and 
reduction of the pattern noise can be effectively accomplished in each of 
the invention tires. 
FIG. 5 shows a further embodiment of the tread pattern according to the 
invention. 
In this embodiment, a circumferential rib 2 is arranged in the center 
portion in the tread center zone 4, and slant main grooves 3 extending 
slantwise at an angle of not more than 40.degree. in opposite directions 
to each other with respect to the circumferential direction are formed 
alternately from positions adjacent to the circumferential rib toward each 
tread end, and each of the slant main grooves 3 has narrower width near 
the tread end-side end 3a and the tread center-side end 3b than in the 
other portion. Here, in the tread center-side region having width W.sub.0 
and where the slant main grooves 3 exist, it is preferable for retaining 
good wet property that the negative ratio owing to the slant main grooves 
3 is more than 80% of the negative ratio of the entire tread, and it is 
preferable for retaining steering stability near marginal cornering 
ability and for reducing the pattern noise that the width W.sub.0 of the 
tread center-side region where the slant main grooves 3 exist is not more 
than 85% of the tread width W. 
The narrow width of the slant main grooves near the end 3a produces high 
block rigidity and enhances drainage effect by hastening the speed of 
water drainage, and the narrow width of the slant main grooves near the 
end 3b enlarge the area and the rigidity of the circumferential rib 2. 
Further, in the tread side zones 5, slant auxiliary grooves 6 connect with 
the tread end-side ends 3a of the slant grooves and extend curvedly with 
their convex upward as shown in the drawing from here to the tread end, 
and preferably the slant angle of these slant auxiliary grooves 6 is 
70.degree.-100.degree. with respect to the circumferential direction of 
the tire. Also, intermediate grooves 7 are formed so as to extend in 
parallel with the slant auxiliary grooves 6 and divide each intermediate 
portion between the slant auxiliary grooves 6, and these intermediate 
grooves 7 open to the tread end and cease without connecting to the slant 
main grooves 3 at the tread center-side. Here, it is preferable for 
effectively reducing the pattern noise, especially the pattern noise 
during cornering, and for retaining the wet drainage property during 
cornering, that each average width of the slant auxiliary grooves 6 and 
the intermediate grooves 7 is 20-50% of the maximum width of the slant 
main grooves. 
Furthermore, as mentioned with respect to FIG. 3, the slant angle of the 
slant main grooves 3 is made smaller near the tread center-side end 3b of 
the slant main grooves, and narrow grooves 11 are formed so as to extend 
in the opposite direction to the slant main grooves 3 from the ends 3b 
toward the tread end, wherein each of the narrow grooves 11 crosses two 
slant main grooves and ceases by connecting with a third slant main groove 
3 near the tread end-side end 3a. The narrow grooves 11 have slightly 
wider portions 11a to obtain large edge effect in the portions near the 
slant main grooves 3 and have narrower width in the remaining portions 
where the groove walls almost touch each other on contacting the road 
during the running of the loaded tire. Such narrow grooves 11 bring 
enhanced gripping road ability and edge effect to a slippery road. 
Moreover, since the narrow grooves 11 extend in the opposite direction to 
the slant main grooves 3, damage to the groove edge can be effectively 
prevented. 
Under above mentioned groove arrangement, as shown in the graph of FIG. 6, 
the negative ratio at each position across the tread in the widthwise 
direction is maximized at the portion adjacent to the circumferential rib 
2 and tends to be decreased towards the tread ends. 
In this tire also, as in each of the above mentioned embodiments, there is 
accomplished as enhancement of the wet property and a reduction of the 
pattern noise based on the position, the slant angle and the width of the 
slant main grooves 3 and the slant auxiliary grooves 6, and the negative 
ratio. 
FIG. 7 shows a yet further embodiment of the tread pattern according to the 
invention, in which a circumferential rib 2 is arranged on the left side 
in the tread center zone 4, in other words arranged to be one sided toward 
the inner side of the tire viewing the tire when mounted on a vehicle. The 
average slant angle of each of the slant main grooves 3 extending from 
each position adjacent to the circumferential rib 2 is made smaller in the 
inner portion of the tire viewing the tire mounted on the vehicle than in 
the outer portion, and the width is made a little larger and arranged 
pitches are made larger in the inner portion. 
Here, in the outer portion of the tire viewing the tire when mounted on a 
vehicle, slant auxiliary grooves 6, as mentioned with regard to FIG. 5, 
are formed so as to connect with the ends 3a of the slant main grooves 
having gradually decreased width toward the tread end, and intermediate 
grooves 7, as above mentioned, are formed without connecting with the 
slant main grooves 3. Further, narrow grooves 11, as mentioned with regard 
to FIG. 5, are formed from the ends 3b of the slant main grooves 3, 
wherein each of the narrow grooves 11 crosses three slant main grooves and 
ceases by connecting with a fourth slant main groove 3 near the end 3a. 
On the other hand, in the inner portion viewing the tire when mounted on a 
vehicle, narrow grooves 8, as mentioned with regard to FIG. 3, are formed 
so as to connect with the tread center-side ends 3b of the slant main 
grooves 3, wherein each of the narrow grooves 8 crosses two slant main 
grooves 3 and ceases at the end 3a of a third slant main groove 3. 
Further, subsidiary narrow grooves 10, as mentioned with regard to FIG. 3, 
are formed between two narrow grooves 8 to extend in parallel with the 
narrow grooves 8 and divide the intermediate portion between the narrow 
grooves 8 equally, and the tread end-side ends of the subsidiary narrow 
grooves 10 open to the intermediate portion of the slant main grooves 3 
and the tread center-side ends of the subsidiary narrow grooves 10 enter 
into the circumferential rib 2. 
In this inner portion, slant auxiliary grooves 6, intermediate grooves 7 
and subsidiary slant grooves 9 are formed substantially in parallel with 
one another and substantially at equal intervals, and one end of each of 
these grooves opens to the tread end and the other end ceases without 
connecting with the slant main grooves 3. In this connection, though the 
tread end-side ends 3a of the slant main grooves 3 cease without 
connecting with the slant auxiliary grooves 6, the slant main grooves 3 in 
the inner side go through the contact print from front to behind at a 
small slant angle during general running of a vehicle and bring about 
sufficiently effective drainage property. 
FIG. 8 shows the distribution of the negative ratio of the tire having this 
tread pattern, wherein the negative ratio at each position is also 
maximized at the portion adjacent to the circumferential rib 2 and also 
tends to be decreased towards the tread ends. 
Accordingly, this tire can bring about the same effect as each of the above 
mentioned embodiments. 
In this embodiment also, the circumferential rib 2 can be arranged in the 
center portion in the tread center zone 4. 
Also in these third and fourth embodiments, each average width of each 
groove is narrower in the order of the slant main groove 3, the group of 
the slant auxiliary groove 6, the intermediate groove 7 and the subsidiary 
slant groove 9, and the group of the narrow groove 11 and subsidiary 
narrow groove 10. In particular, the average width of the slant main 
groove 3 is 2-5% of the tread width W; the average widths of the slant 
auxiliary groove 6, the intermediate groove 7 and the subsidiary slant 
groove 9 are each 20-50% of the maximum width of the slant main groove and 
have a lower limit of 2 mm to avoid closing when coming into contact with 
the road during rotation; and the average widths of the narrow groove 11 
and subsidiary narrow groove 10 are each 0.2-2 mm. 
The average depths of each of the slant auxiliary grooves 6, the 
intermediate grooves 7 and the subsidiary slant grooves 9 are shallower 
than that of the slant main grooves 3, and those of the narrow grooves 11 
and the subsidiary narrow grooves 10 are equal to or shallower than those 
of the slant auxiliary grooves 6, intermediate grooves 7 and the 
subsidiary slant grooves 9. 
Comparative Test 2 
A comparative test between tires of the invention and a conventional tire 
will be described with respect to the wet drainage property, the pattern 
noise and the steering stability on dry road. 
Test Tires 
The test tires have a size of 225/50 R16, a tread width of 180 mm and a 
tread contact length of 120 mm. 
Invention Tire 1 
This tire has a tread pattern as shown in FIG. 5, in which the negative 
ratio of the whole tread is 29%, the width W.sub.0 of the region where the 
slant main grooves extend is 140 mm, the ratio of the negative ratio of 
slant main grooves to the negative ratio of the whole tread is 85% and 
further this tire has dimensions as shown in Table 4. 
TABLE 4 
______________________________________ 
Width (mm) 
Slant angle 
Depth (mm) 
______________________________________ 
Slant main groove 
3-11-5 0-25-40.degree. 
8 
Slant auxiliary 
4.5 90.degree. 6.5 
groove and (Contact end 
intermediate groove portion) 
Narrow groove 
1.0 35.degree. 6.5 
(Extended width 
(2.5) 
portion) 
______________________________________ 
The number of pitches in the tread shoulder portion is 56 per one circuit. 
Invention Tire 2 
This tire has a tread pattern as shown in FIG. 7, in which the negative 
ratio of the whole tread is 29%, the width W.sub.0 of the region where the 
slant main grooves extend is 145 mm, the ratio of the negative ratio of 
slant main grooves to the negative ratio of the whole tread is 83%, and 
further this tire has dimensions as shown in Table 5. 
TABLE 5 
______________________________________ 
Width (mm) 
Slant Angle 
Depth (mm) 
______________________________________ 
Right slant main 
3-11-5 0-20-25.degree. 
8 
groove 
Left slant main 
3-14-4 0-10-5.degree. 
8 
groove 
Slant auxiliary 
4.0 90.degree. 6.5 
groove and (Contact end 
intermediate groove portion) 
Subsidiary slant 
4.5 90.degree. 6.5 
groove (Contact end 
portion) 
Narrow groove 
1.0 40.degree. 6.5 
(2.5) 
Subsidiary narrow 
2.0 30.degree. 6.5 
groove 
______________________________________ 
The number of pitches in the left tread shoulder portion is 60 per one 
circuit. 
Conventional Tire 
A tire as shown in FIG. 9. 
Test Results 
The measured results of the wet drainage property respectively during 
straight running and during cornering, the pattern noise and the steering 
stability on dry road, measured by the same method as in the comparative 
test 1, are shown in Table 6 by index value. 
The index value is on the basis that the conventional tire is control, and 
the larger the index value, the better the results. 
TABLE 6 
______________________________________ 
Conventional 
Invention 
Invention 
tire tire 1 tire 2 
______________________________________ 
Wet drainage 
100 130 120 
property during 
straight running 
Wet drainage 
100 125 115 
property during 
cornering 
Pattern noise 
100 110 105 
Steering stability 
100 105 110 
on dry road 
______________________________________ 
According to this invention, as is apparent from the comparative tests, 
there is accomplished enhancement of the wet property and reduction of the 
pattern noise without degrading other primary properties by means of the 
structure and the formation of the slant main grooves and the slant 
auxiliary grooves and the negative ratio at each position in the widthwise 
direction. 
While the invention has been particularly shown and described with 
reference to certain preferred embodiments thereof, it will be understood 
by those skilled in the art that various changes and modifications may be 
made without departing from the spirit and scope of the invention.