Pneumatic radial tire having an excellent side-cut resistant property

A pneumatic radial tire having an excellent side-cut resistant property is disclosed. The radial tire comprises at least one extensible and compressible rubberized side portion reinforcing layer arranged at that area of a side portion of the tire which is inclusive of at least maximum cross-section position of the carcass and each containing a reinforcing element embedded therein and composed of helically formed filaments or at least 2 bundles each formed by merely assembling together the helically formed filaments without twisting at random. The helically formed filament is formed of a material having a tensile breaking strength of at least 140 kg/mm.sup.2. The reinforcing element has an elongation at tensile breaking strength which is at least 1.2 times larger than that of a metal cord of a radial carcass.

This invention relates to a pneumatic radial tire having an excellent 
side-cut resistant property such as a construction vehicle, for example, 
front-end loader, offhigher hauler, trucks, ralley racing vehicles, etc. 
which travel on road at least one part of which is inclusive of off-road 
area, and more particularly to an improved side portion reinforcing 
construction for pneumatic radial tires comprising a radial carcass 
containing carcass cords arranged along a radial plane of the tire or 
substantially in parallel therewith and a belt superimposed about the 
radial carcass and having a high rigidity in circumferential direction. 
Such kind of tire travels on a rough road which has not been completed as a 
running road and hence has an opportunity of being frequently subjected to 
cuts when the tire rides on sharp rock, mineral ore, metal piece or stub 
scattered on the road. When the pneumatic radial tire travels on such 
site, the cut caused by the ground contact surface is prevented by the 
presence of a thick tread rubber and belt layer having a rigidity, but an 
area of the tire extending from its shoulder portion to its side portion 
is substantially defenseless against the cut failure. 
In general, in the area of the pneumatic radial tire extending from its 
shoulder portion to its side portion are arranged only one or at most 
several carcass plies and a thin side wall rubber superimposed about these 
carcass plies. As a result, the cut resistance of such area becomes low. 
Particularly, a pneumatic radial tire comprising a carcass ply cord formed 
of a steel cord tends to produce rust by water penetrated through cracks 
produced by cuts and induces a premature brakage of the carcass ply. In 
addition, the cracks on the side are different from those on the ground 
contact surface and become open and grown into a large crack. As a result, 
even when such large crack is repaired, such repaired crack tends to be 
grown again, so that the repair becomes very difficult. As a result, the 
tire whose side portion is subjected to cut becomes useless waste tire. 
Many attempts have been made to overcome this problem, but hitherto none 
has led to fully satisfactory results. 
A first type tire which has heretofore been proposed to overcome this 
problem is provided at its area extending from a shoulder portion to a 
side portion with a rubber projection which functions to prevent the 
side-cut. This first type of tire can prevent the side portion from being 
damaged by rocks, etc. which are travelled over by the ground contact 
surface of the tire or which are pushed sidewardly from the ground contact 
surface of the tire. But, this first type tire can not prevent the side 
portion against rocks which are larger than the rubber projection or sharp 
end of the rocks raised upwardly when the ground contact surface rides on 
one side of the rocks. In addition, the presence of the thick projection 
extended from the shoulder portion to the side portion of the tire tends 
to raise the temperature at the belt end which is a weak point of the 
radial tire, thereby deteriorating the high speed durability inherent to 
the pneumatic radial tire. 
A second type tire which has also been proposed to overcome the above 
mentioned problem is provided on the inside of the carcass ply at the side 
portion with a thick rubber or a rubberized layer containing cords 
embedded therein. This second type tire only conservatively functions to 
decrease flexure of the side portion so as to make less a chance of 
producing the side-cut failure. The side-cut subjected to the tire is 
developed into a vital defect and hence any positive function of 
preventing the carcass ply at the side portion from being subjected to the 
side-cut could not be expected from this second type tire. 
A third type tire which has heretofore been proposed to overcome the above 
mentioned problem comprises a reinforcing cord arranged at the side wall 
so as to prevent the carcass ply from being subjected to the side-cut. 
This third type tire functions to prevent the carcass ply from being 
subjected to the side-cut to a certain extent. 
In the second type tire, the protective layer is formed of a textile cord 
having a small tensile breaking strength, so that the cut preventive 
effect is small. In the third type tire, the protective layer is arranged 
near the bead, so that the area of the tire which is extended from the 
shoulder portion to the side portion and which has many chances of being 
subjected to the cut is not protected. 
Under such circumstances, it is natural that skilled persons should imagine 
an idea of arranging a rubberized reinforcing layer containing steel cords 
embedded therein on overall surface of the side portion of the tire as the 
protective layer against the side-cut thereof. However, the side portion 
of the radial tire is subjected to the largest flexure, and as a result, 
when the tire is subjected to the load and the side portion thereof 
becomes deformed, the rubberized reinforcing layer containing the steel 
cords embedded therein and arranged at the side portion causes a large 
strain at the steel cord ends since the steel cord per se is inextensible, 
thereby inducing a separation failure of the steel cord ends and hence a 
breakage of the tire. 
An object of the invention, therefore, is to provide a pneumatic radial 
tire which can obviate the above described drawbacks which have been 
encountered with the conventional techniques and which can travel on 
off-road without a side-cut failure. 
A feature of the invention is the provision of a pneumatic radial tire 
having an excellent side-cut resistant property, comprising a radial 
carcass body composed of at least one rubberized ply layer each containing 
metal cords embedded therein and a belt superimposed about said radial 
carcass body and having a high rigidity, said tire comprising at least one 
extensible and compressible rubberized side portion reinforcing layer 
arranged at that area of a side portion of the tire which is inclusive of 
at least maximum cross-section position of the carcass and each containing 
a reinforcing element embedded therein and composed of helically formed 
filaments each formed of a material having a tensile breaking strength of 
at least 140 kg/mm.sup.2 or at least 2 bundles each formed by merely 
assembling together said helically formed filaments without twisting at 
random, said reinforcing elements each having an elongation at tensile 
breaking strength which is at least 1.2 times larger than that of said 
metal cord of the radial carcass. 
In preferred embodiments of the invention, the following conditions have to 
be satisfied. 
(1) The helically formed filament of the reinforcing element has a diameter 
.phi. of 0.1 mm to 1.0 mm, average diameter D of an outer contour 
projected on a plane perpendicular to the axial direction of one pitch of 
the filament and defined by 
##EQU1## 
of 2 .phi. to 20 .phi.. (2) The helically formed filament of the 
reinforcing element is formed of a steel wire. 
(3) The reinforcing element has a ratio .delta. of a space formed between 
the two adjacent reinforcing filaments to a pitch S in mm between the 
midlines of the reinforcing elements given by 
##EQU2## 
where d is an effective diameter in mm of the reinforcing element which 
is given by 
EQU 1.25.sqroot.N.times..phi. 
where N is the number of filaments for constituting the reinforcing 
element. 
(4) The rubber containing the reinforcing element embedded therein has a 
Shore A hardness of 50.degree. to 85.degree., 300% modulus of elasticity 
of 80 to 230 kg/cm.sup.2 and tensile breaking strength of 150 to 250 
kg/cm.sup.2. 
(5) The side portion reinforcing layer is arranged on the outside of the 
radial carcass. 
(6) The side portion reinforcing layer is independently arranged on each of 
two side portions of the tire. 
(7) The side portion reinforcing layer is continuously extended from one of 
the two side portions of the tire through the crown portion to the other 
side portion. 
(8) The reinforcing element of the side portion reinforcing layer located 
at the maximum width position of the carcass in a vertical center section 
through the rotational axis of the tire is inclined at 0.degree. to 
70.degree. with respect to a radial plane which is projected on and in 
parallel with said section. 
(9) The side portion reinforcing layer is composed of at least two layers 
whose reinforcing elements are crossed with each other. 
The side portion of the pneumatic tire is primarily subjected to the 
largest deformation and this deformation is particularly remarkable with 
respect to the pneumatic radial tire, so that it is very difficult to 
prevent the pneumatic radial tire for off-road vehicles from being 
subjected to the side-cut. 
As measures protecting the tire against the side-cut, it has been 
considered to apply a method of firmly reinforcing the side portion such 
that the cut can not be pierced therethrough and another method of 
considerably deforming the side portion when it is struck by rocks and 
stones, etc. and absorbing deformation energy thus reducing force 
subjected to the side portion. The former method, however, is not 
available at all. Because, if the side portion of the tire is reinforced 
to make its rigidity high, a deflection stiffness of the tire becomes 
large so as to eliminate the oscillation absorbing property required for 
the pneumatic tire, and as a result, a stress subjected to the bead 
portion or tread portion is increased, thereby inducing a premature 
failure of the tire. It is preferable, therefore, to apply the latter 
method of absorbing the deformation energy and prevent the side-cut.

In FIG. 1a is shown a graph illustrating a surface strain produced in a 
pneumatic radial tire for off-road vehicles having a size of 21.00 R35. In 
FIG. 1a, the surface strain in % is taken on ordinate and measurement 
positions in numbers 5, 10, 15 . . . in radial direction is taken on 
abscissa. 
In FIG. 1b is shown a graph illustrating a surface strain in % produced in 
the same tire as function of measurement positions in circumferential 
direction. 
As seen from FIGS. 1a and 1b, the side portion of the radial tire is 
significantly deformed. 
In the present invention, investigations have been made with respect to 
side portion reinforcing construction for permitting such large 
deformation and preventing the side-cut. 
The reinforcing element may be formed of materials such as rubber, shredded 
wires, textile cords represented by nylon cord, steel cord, etc. 
The problem which has been encountered with these materials when they are 
arranged at the area extending from the shoulder portion to the side 
portion will now be described. 
In the case of reinforcing the side portion of the tire without injuring 
its reflection stiffness, it is preferable to use a reinforcing element 
whose tensile and compression modulus of elasticities are small. That is, 
the reinforcing element is required to be easily extensible and 
compressible. 
In the above described materials, rubber is the most suitable for such 
object. Shredded wires, nylon cord and steel cord are contrary to the 
object in the order as mentioned above. 
As to the cut resistant force, it is preferable to use material having a 
large breaking strength. For this purpose, steel cord is most effective. 
Nylon cord, shredded wires and rubber are inferior in the cut resistant 
force in the order as mentioned above, this order being just opposite to 
the above mentioned order. 
A problem that occurs when the reinforcing element is different in material 
from adjacent portions will now be described. In the tread portion, even 
when the reinforcing element is arranged adjacent to portions whose 
properties are slightly different from those of the reinforcing element, 
an extremely large strain is not subjected to an interphase between the 
adjacent layers since the deformation of the tread portion is relatively 
small. As a result, separation does not occur. 
On the contrary, the deformation of the side portion is large as described 
above, so that if different elements are arranged adjacent with each other 
in the side portion, a large strain is produced at an interphase between 
the two adjacent members. There is a risk of this interphase as a nucleus 
being developed into a separation breakage of the tire. 
Judging from the above described point of view, the above mentioned 
materials for the reinforcing element have drawbacks and hence none has 
led to fully satisfactory results. That is, the rubber has an extremely 
small cut resistant force. The shredded wires are not only less in cut 
resistant force, but also liable to induce a premature separation failure 
and hence are not suitable. The nylon cords are extensible, so that they 
are well matched with the material of the adjacent portions, but are 
insufficient in the cut resistant force. 
The steel cords have an excellent cut resistant force, but they have 
extremely poor in extensible and compressive properties, so that they are 
not matched with the adjacent materials, thereby inducing separation at 
the cord ends. 
The inventors have noticed a helically formed filament described in U.S. 
Pat. No. 3,682,222 as a reinforcing element having a tensile breaking 
strength which is similar to that of the steel cord and an elongation at 
tensile breaking strength which is similar to that of rubber and nylon 
cord. Such helically formed filament has properties to be described later. 
The inventors have investigated the function and movement of the side 
portion reinforcing layer in greater detail in order to use the helically 
formed filament as the side portion reinforcing layer for the purpose of 
effectively protecting the pneumatic radial tire for off-road vehicles 
comprising the rubberized carcass ply containing the metal cords embedded 
therein against side cut. 
A neutral axis of deformation produced in the side portion when the 
rubberized carcass ply containing metal cords such as steel cords, etc. is 
subjected to load is present in the carcass ply since the carcass ply is 
inextensible and has a large tensile rigidity. 
As a result, when the side portion reinforcing layer is arranged on the 
outside of the carcass ply, the side portion reinforcing layer is 
subjected to deformation due to elongation. Thus, the reinforcing element 
of the side portion reinforcing layer is required to have an elongation 
which is larger than that of the carcass ply. The larger such elongation 
property of the side portion reinforcing layer must be made the more side 
portion reinforcing layer is distant apart from the outside of the carcass 
ply. 
On the one hand, when the tire side portion collides with rocks and stones, 
etc., the tire side portion becomes locally deformed inwardly. In this 
case, the property of the carcass ply causes the neutral axis of 
deformation to lie therein and the side portion reinforcing layer arranged 
on the outside thereof is subjected to compressive force. As a result, the 
reinforcing element of the side portion reinforcing layer is required to 
have also an excellent compressive deformation property. 
In addition, in the case of arranging the side portion reinforcing layer on 
the inside of the carcass ply, a reinforcing element having excellent 
extensible and compressive properties is also required. 
The above described considerations and experimental tests have yielded the 
result that the helically formed filament for the side portion reinforcing 
layer is required to have the following properties. 
The helically formed filament may be formed of material such as steel, 
metals having a high cut resistant property, glass or organic fibers. The 
material such as nylon, rayon and the like used usually as the tire cord 
and having a tensile breaking strength on the order of 80 kg/mm.sup.2 to 
110 kg/mm.sup.2 is substantially unsuitable as the cut resistant material. 
It has been found out that the cut resistant material aimed at the present 
invention may be of one having a tensile breaking strength of at least 140 
kg/mm.sup.2, preferably at least 170 kg/mm.sup.2 and at least 190 
kg/mm.sup.2 when the tire size is larger or the rigidity of the tire case 
cause the cut resistant property to give to the side portion reinforcing 
layer. 
The reinforcing element composed of helically formed filaments is required 
to have an elongation at tensile breaking strength which is at least 1.2 
times larger than that of the steel cord of the carcass ply. If the 
reinforcing element is separated from the carcass ply and arranged on the 
outside relative to, for example, a turn-up portion of the carcass ply, 
the reinforcing element is required to have an elongation at tensile 
breaking strength which is at least 1.5 times larger than that of the 
steel cord of the carcass ply. 
The configuration, construction and effect of the side portion reinforcing 
layer composed of the helically formed filaments will now be described in 
greater detail. In addition, the configuration and construction of the 
reinforcing element used for the present invention will be described. 
A permanently helically formed resilient filament is formed of material 
whose tensile breaking strength is high as described above and has a 
relatively small diameter of 0.1 mm to 1.0 mm, preferably 0.13 mm to 0.5 
mm. 2 to 50, preferably 3 to 30 of helically formed filaments are merely 
assembled together without twisting at random and without aligning the 
helically formed filaments and without twisting them together by means of 
exterior binding wires. 
In FIGS. 2a and 2b is shown a configuration of a helically formed filament. 
The ideal shape of an outer contour projected on a plane perpendicular to 
the axial direction of one pitch of the helically formed filament should 
be a true circle for the purpose of equalizing the stress subjected to it. 
However, it is very difficult in technique to obtain such true circle and 
a number of steps are obliged to be taken in order to incorporate such 
filament into the tire, so that it is further difficult to maintain such 
true circle in tire products. 
Experimental tests and considerations on practically allowable deviation 
from such true circle have yielded the result that if a ratio of a maximum 
diameter (Dmax) of the outer contour projected on a plane perpendicular to 
the axial direction of one pitch of the helically formed filament to a 
minimum diameter (Dmin) thereof at any position of the tire side portion 
lies within a range to be described later, the stress subjected to the 
filament becomes substantially uniformly distributed, and that hence the 
premature fatigue breakage is not induced. That is, in FIGS. 2a and 2b, 
##EQU3## 
is required to be 1 to 1.5. 
In addition, an average diameter D, that is, 
##EQU4## 
of the outer contour projected on a plane perpendicular to the axial 
direction of one pitch of the filament is required to be 2 .phi. to 20 
.phi., preferably 3 .phi. to 15 .phi., .phi. being the diameter of the 
helically formed filament. 
As an alternative method of obtaining a desirous elongation of filaments, 
each formed of material having a high tensile breaking strength, for 
example, high carbon steel and assembled together without twisting, it 
might be conceived to arrange undulate filaments in parallel with each 
other in one same plane. In this case, however, stress becomes 
concentrated into bent portions of the undulate filament in response to 
extension and compression in the lengthwise direction thereof. In 
addition, this stress is a bending stress to be concentrated into a part 
of the cross section of the filament, so that there frequently occurs the 
premature fatigue breakage at the bent portions of the filament. As a 
result, it has been found out that the measures described could not be 
used in practice in place of the above described helically formed 
filament. 
That is, in the present invention, the use of the helically formed filament 
ensures a necessary elongation. In this case, the stress produced in 
response to the extension or compression in the lengthwise direction of 
the helically formed filament is substantially uniformly distributed over 
any portion in the lengthwise direction thereof. In addition, the above 
mentioned stress is a torsional shearing stress which is liable to be 
easily distributed in a relatively uniform manner over the cross section 
of the filament, so that it is possible to completely prevent the fatigue 
breakage of the tire. 
As to the filament diameter .phi., in order to prevent the tire from being 
broken due to cord fatigue, it is preferable to make the filament diameter 
.phi. small. In addition, in view of improving the cut resistant property 
of the tire, the strong force per unit area of the same filament can be 
increased by working it, so that it is preferable to use a filament which 
is possibly small in diameter. But, the use of a filament whose diameter 
.phi. is smaller than 0.1 mm results in occurrence of cuts of the filament 
in non-allowable frequency in the step of shaping the helically formed 
filament and is not economical. 
On the contrary, if use is made of a filament whose diameter .phi. is 
larger than 1.0 mm, internal stress produced in the filament during the 
step of shaping the helically formed filament becomes excessively large. 
In addition, torsional shearing stress which occurs when extension or 
compression is subjected to the filament in its lengthwise direction is 
concentrated into the outer contour of the filament. As a result, the 
overall cross sectional area required for maintaining the strength which 
is sufficient to resist against the same exterior force becomes larger 
than that necessary for the thin filament, thereby requiring much amount 
of material. As a result the use of the filament having a diameter larger 
than 1.0 mm is not economical. 
As seen from the above, the diameter .phi. of the filament is required to 
lie within a range from 0.1 mm to 1.0 mm. 
The relation between the diameter .phi. of the filament and the average 
diameter D of the outer contour projected on a plane perpendicular to the 
axial direction of one pitch of the helically formed filament will now be 
described. If D is smaller than 2 .phi., the pitch of the helically formed 
filament is required to be excessively small for the purpose of obtaining 
the desired elongation. As a result, the cut of filament frequently occurs 
in non-allowable frequency in the same manner as in the case of using the 
filament whose diameter is excessively small. At the same time, the 
internal stress produced when the filament is helically formed becomes 
excessively large. 
Respective helically formed filaments are assembled together without 
twisting at random to form a cord-shaped reinforcing element which is then 
arranged in the tire. Each of respective helically formed filaments 
constituting each reinforcing element is arranged in the same element in 
zigzag. As a result, if D is larger than 20 .phi., the sectional area 
formed between the most protruded portions of two adjacent helically 
formed filaments becomes too small to maintain that distance therebetween 
which is required for maintaining the desired separation resistant 
property, and as a result, sufficiently large cut resistant property could 
not be obtained. On the contrary, if it is desired to obtain the 
sufficiently high cut resistant property, the above mentioned distance 
required between the two adjacent elements could not be obtained, so that 
a sufficiently high separation resistant property could not be obtained. 
In addition, in order to obtain the sufficiently high separation resistant 
property, not only the above mentioned distance required between the two 
adjacent helically formed filaments, but also the distance between the 
side rubber and the reinforcing element and the distance between the 
reinforcing element and the carcass in the case of one rubberized layer 
containing the reinforcing element are required to be kept within a 
certain range. In addition, in the case of at least two rubberized layers, 
the distance between the two adjacent reinforcing elements must also be 
kept within a certain range. Moreover, the last mentioned distance is 
required to be kept between the most protruded portions of the two 
adjacent reinforcing elements, so that it is necessary to use a thick 
rubberized layer containing the reinforcing elements embedded therein, 
thereby significantly impeding economy. As seen from the above, the 
average diameter D should be 2 .phi. to 20 .phi.. 
The pitch of the helically formed filament is suitably selected in 
association with modulus of elasticity of the filament, diameter .phi. of 
the filament and average diameter D of the outer contour of the helically 
formed filament for the purpose of obtaining an optimum elongation at 
tensile breaking strength and modulus of elasticity required for the use 
of the tire. 
The number of helically formed filaments adapted to be assembled together 
without twisting at random so as to provide a reinforcing element will now 
be described. If use is made of one helically formed filament, the 
diameter .phi. thereof becomes excessively large for the purpose of 
obtaining the required cut resistant property of the tire. As a result, 
the above mentioned problem is involved and at the same time the effect of 
improving reinforcing element-to-rubber bonding force will be decreased. 
On the contrary, if use is made of more than 50 helically formed 
filaments, the diameter of the outer contour projected on a plane 
perpendicular to the axial direction of one pitch of the reinforcing 
element becomes excessively large even though care is taken to make the 
average diameter D of the one helically formed filament small. As a 
result, the same problem occurs as in the case of making the average 
diameter D excessively large. As seen from the above, the number of 
helically formed filaments adapted to be assembled together without 
twisting at random to provide the reinforcing element is suitably selected 
into a range of 2 to 50, preferably, 3 to 30, by taking balance between 
the cut resistant property and other characteristics required for the use 
of the tires on the one hand and economy on the other hand into 
consideration. 
The relation between the force subjected to the reinforcing element 
constructed as above described according to the invention and to a 
conventional stranded steel cord on the one hand and elongations thereof 
on the other hand will now be described with reference to a practical 
example. 
In FIG. 3 is shown tensile test results with the force in kg/cord or 
kg/bundle taken on ordinate and with the elongation in % on abscissa. In 
FIG. 3, a dotted lines curve .alpha. shows a tensile test result yielded 
from a conventional steel cord having a strand construction of 1.times.5, 
filament diameter .phi. of 0.25 mm and cord diameter of 0.68 mm and full 
line curves .beta. and .gamma. show tensile test results yielded from 
reinforcing elements formed of helically formed steel filaments according 
to the invention. The tensile test result shown by the full line curve 
.beta. was yielded from a reinforcing element composed of a bundle of 5 
filaments according to the invention each having a filament diameter .phi. 
of 0.25 mm, average diameter D projected on a plane perpendicular to the 
axial direction of one pitch of the filament of 0.95 mm, 
##EQU5## 
and pitch of 10.5 mm. The tensile test result shown by the full line curve 
.gamma. was yielded from a reinforcing element composed of a bundle of 14 
filaments according to the invention each having a filament diameter .phi. 
of 0.175 mm, average diameter D projected on a plane perpendicular to the 
axial direction of one pitch of the filament of 1.1 mm, 
##EQU6## 
and pitch of 11 mm. In FIG. 3, a dotted lines curve .delta. shows a 
tensile test result yielded from a conventional nylon cord. 
As seen from FIG. 3, the reinforcing elements according to the invention 
provide an ideal relation between the force subjected to the reinforcing 
elements and the elongation thereof, which relation being usable for the 
side-cut protective layer for the pneumatic tire for off-road vehicles 
aimed at the present invention. 
As described above, the reinforcing element composed of helically formed 
filaments according to the invention is extremely deformable so as to 
reduce the amount of relative displacement between the rubber and the 
reinforcing element. As a result, it is possible to reduce separation 
failure to be induced at the ends of the reinforcing element. In addition, 
in the case of forming the helically formed filaments into bundles 14 as 
shown in FIG. 13, the filaments are not twisted together as in the case of 
the steel cords, but are merely assembled together without twisting at 
random. Thus, it is possible to sufficiently penetrate the rubber into gap 
formed between the filaments and mechanical bonding force thus produced 
can compensate for insufficient reinforcing rubber-to-filament chemical 
bonding force. 
The use of the reinforcing element composed of helically formed filaments 
according to the invention ensures a significant reduction of compression 
modulus of elasticity of the reinforcing element, so that the reinforcing 
element can absorb the compressive force instantaneously subjected 
thereto, thereby significantly decreasing occurrences of the cord breakage 
without breaking. 
The difference between the compression modulus of elasticity and 
compressive fatigue property of the reinforcing element according to the 
invention and those of the conventional stranded steel cord for tires will 
now be described with reference to practical examples. 
In FIG. 4 are shown compression test results. In FIG. 4, the compressive 
force in kg is taken on ordinate and the compressive strain in % is taken 
on abscissa. In this test, use was made of two test pieces, one of which 
being composed of a cylindrical rubber containing one conventional 
stranded steel cord embedded therein and the other being composed of a 
cylindrical rubber containing one bundle according to the invention 
embedded therein. 
In FIG. 4, a dotted lines curve .alpha. shows the relation between the 
compressive force in kg subjected to the conventional stranded steel cord 
having a strand construction of 1.times.5, filament diameter .phi. of 0.25 
mm and cord diameter of 0.68 mm and the compressive strain in % produced 
therein. A full line curve .beta. shows the relation between the 
compressive force in kg subjected to the reinforcing element composed of 5 
helically formed filaments according to the invention each having a 
diameter .phi. of 0.25 mm, average diameter D projected on a plane 
perpendicular to the axial direction of one pitch of the filament of 0.95 
mm, 
##EQU7## 
and pitch of 10.5 mm and the compressive strain in % produced therein. 
In FIG. 4, a dotted lines curve .epsilon. shows the same relation with 
respect to a test piece formed of rubber only. It is a matter of course 
that the rubber of all of these three test pieces is of the same rubber 
compound. 
As seen from FIG. 4, the compression modulus of elasticity of the 
reinforcing element according to the invention is extremely small, whose 
value being near to a value of the rubber specimen. 
In FIG. 5 is shown compressive fatigue test result. That is, retained 
tensile strength in % which is percentage of tensile strength after the 
fatigue test with that of a new tire is taken on ordinate and number of 
strains repeatedly occurred given in n is taken on abscissa. In the 
present test, use was made of two test pieces, one being composed of a 
rectangular rubber body containing a plurality of conventional stranded 
steel cords embedded therein and the other being composed of a rectangular 
rubber body containing a plurality of bundles according to the invention 
embedded therein, and these two test pieces were subjected to 5% repeating 
compressive strain. 
In FIG. 5, a dotted lines curve .alpha. shows retained tensile strength as 
a function of the number of strains repeatedly occurred for the 
conventional stranded steel cord having a strand construction of 
1.times.5, filament diameter .phi. of 0.25 mm and cord diameter of 0.68 mm 
and a full line curve .beta. shows a relation similar to the dotted lines 
curve .alpha. for the reinforcing element according to the invention 
composed of 5 helically formed steel filaments each having a filament 
diameter .phi. of 0.25 mm, average diameter D projected on a plane 
perpendicular to the axial direction of one pitch of the filament of 0.95 
mm, 
##EQU8## 
and pitch of 10.5 mm. As seen from FIG. 5, the retained tensile strength 
of the reinforcing force according to the invention is far superior to 
that of the conventional steel cord. 
The configuration, construction and effect of the side portion reinforcing 
layer containing the reinforcing element formed and constructed as above 
described will now be described. As coating rubber which constitutes the 
side portion reinforcing layer together with the reinforcing element 
according to the invention use may be made of a rubber compound having a 
Shore A hardness at room temperature of 45.degree. to 85.degree., 300% 
modulus of elasticity of 150 to 250 kg/cm.sup.2, and tensile breaking 
strength of 150 to 250 kg/cm.sup.2. It is preferable to change the 
physical property of the rubber in dependence with the position of the 
side portion reinforcing layer. Particularly, it is preferable to use a 
hard rubber as that rubber which is located near the carcass ply and a 
soft rubber as the rubber which is distant apart from the carcass ply for 
the purpose of obtaining a better effect of reinforcing the side portion 
of the tire against damage. 
Direction of arranging the reinforcing element in the side portion 
reinforcing layer may be selected in dependence with the physical property 
and location of the reinforcing element. The reinforcing element located 
at the maximum width position of the carcass in section is inclined at 
0.degree. to 70.degree. with respect to that radial plane of the tire 
which is projected on a vertical center section through the rotational 
axis of the tire. 
The use of an excessively large inclined angle has a great influence upon 
the tire displacement at the sacrifice of the elongation in the 
circumferential direction of the tire. Use may be made of one or at least 
two side portion reinforcing layers. In the latter case, it is preferable 
to extend the reinforcing elements associated with one of these layers in 
an opposite direction to the reinforcing elements associated with the 
other layer. 
The arrangement of the side portion reinforcing layer containing the 
reinforcing elements will now be described. The side portion reinforcing 
layer should be arranged so as to protect the maximum width position of 
the section of the carcass ply which tends to significantly project in the 
direction of the rotational axis of the tire when the tire is subjected to 
the load. The side portion reinforcing layer is normally extended from 
near the shoulder through the above described maximum width position to 
near the bead and to the near the tread. But, the side portion reinforcing 
layer may also be extended from near one of the beads through the crown 
portion to near the other bead, that is, may be made integral with the 
left and right side portion reinforcing layers. The side portion 
reinforcing layers may be disposed in the side wall such that these layers 
are made in contact with the carcass ply, that a thin rubber sheet is 
interposed between these layers and that these layers are separated from 
the carcass ply. Such arrangement of the side portion reinforcing layer is 
suitably adopted in dependence with the reinforcing element whose 
configuration and property are selected such that any desired effect can 
be attained. 
The rubber constituting the side portion reinforcing layer may change its 
rigidity in a stepwise manner. It is advisable to use a relatively hard 
rubber as rubber located near the reinforcing element and about this 
rubber is superimposed a soft rubber for the purpose of alleviating the 
stress and strain subjected to the side portion reinforcing layer. 
Alternatively, it is advisable to use a hard elastic rubber for the 
purpose of restraining the movement of the ends of the reinforcing element 
and preventing the separation thereof from the rubber. 
In addition, a rubberized layer containing cords composed of organic fiber 
such as nylon may preferably be superimposed about the side portion 
reinforcing layer. 
The use of the reinforcing element composed of the helically formed 
filaments or at least two bundles thereof ensures the following additional 
effect. The helically formed filaments consituting the reinforcing element 
are not twisted contrary to the steel cords and assembled together without 
twisting at random. As a result, a sufficient amount of rubber can be 
penetrated into gaps formed between the filaments of the bundles, so that 
insufficient chemical rubber-to-filament bonding force can sufficiently be 
compensated by the mechanical bodning force. 
As seen from the above, in the present invention, the rubber-to-filament 
bonding force is the sum of the chemical rubber-to-filament bonding force 
and the mechanical rubber-to-filament bonding force. The separation 
resistant property of the reinforcing element according to the invention, 
therefore, is far superior to that of the conventional steel cord. 
The maximum rubber-to-filament bonding force, however, is limited in the 
case of manufacturing the tire in an industrial mass production scale. In 
addition, the above mentioned kind of tire for off-road vehicles is 
subjected to excessively heavy load when the tire is used under severe 
conditions, and as a result, even though the reinforcing element composed 
of the helically formed filaments is used, there is a risk of the upper 
limit of the rubber-to-filament bonding force or the breaking strength of 
the rubber located between the two adjacent reinforcing elements being 
exceeded. Particularly, when the tire is used for a relatively long time 
and subjected to a number of strains repeatedly occurred, the rubber near 
the reinforcing elements or the rubber-to-filament bonding becomes 
minutely broken. Such minute breakage of the rubber is grown and developed 
to induce the separation failure of the tire. 
The inventors have foreseen that the tire for off-road vehicles subjected 
to heavy load when it is used under severe conditions is destined to often 
exceed an upper limit of the breaking strength of the tire even when the 
tire is designed to significantly increase its breaking strength. The 
inventors, therefore, have recognized that, even if the higher the 
rubber-to-reinforcing element bonding force and breaking strength of 
rubber near the reinforcing element, the better, it is more advantageous 
in commercial production that such breakage of rubber and bonding force is 
of ordinary value but also such breakage is prevented from being grown and 
developed than that both the bonding force and breaking strength is as 
high as possible. 
When the pneumatic tire for off-road vehicles is used for a relatively long 
time and hence the durability thereof is quite important, a ratio .delta. 
of a pitch between the two adjacent reinforcing elements each composed of 
the helically formed filaments to a pitch S in mm between the midlines of 
the reinforcing elements is given by 
##EQU9## 
where D is an average diameter projected on a plane perpendicular to the 
axial direction of one pitch of a helically formed filament in mm and d is 
an effective diameter of the reinforcing element in mm which is given by 
1.25.times..sqroot.N.times.filament diameter .phi., where N is the number 
of filaments for constituting the reinforcing element. 
It is preferable to arrange the reinforcing elements such that the number 
thereof per unit length of the reinforcing layer is relatively small, that 
is, .delta. is 0.11 to 0.78. 
Experimental tests have yielded the result that as the pitch S between the 
midline of the two adjacent reinforcing elements becomes smaller, the 
shearing force produced in the rubber surounding the reinforcing elements 
is increased, that if .delta. is smaller than the lower limit 0.11 
thereof, the shearing force is rapidly increased, that very small pitch S 
between the midlines of the two adjacent reinforcing elements causes the 
space formed therebetween to make extremely narrow thus rapidly growing 
the above mentioned initial breakage and hence inducing the separation 
failure of the tire, and that if .delta. exceeds its upper limit 0.78, the 
effect of improving the side-cut resistant property aimed at the present 
invention could not be attained. 
The pitch S between the midlines of the two adjacent elements is drived on 
the basis of the average number of reinforcing elements embedded in a 
length 100 mm of the reinforcing layer in a direction perpendicular to the 
axial direction of the reinforcing elements arranged in the maximum width 
position of the tire in the vertical center section through the rotational 
axis of the tire. 
The helically formed filament constituting the reinforcing element of the 
side portion reinforcing layer may be formed of wire materials having an 
excellent rubber-to-filament bonding property, for example, brass plated 
steel filament, glass fiber, aromatic polyamide having a high modulus of 
elasticity and the like. 
The invention will now be described in greater detail with reference to 
practical examples. 
EXAMPLE 1 
In FIG. 6 is shown a cross section of one-half of a pneumatic radial tire 
for off-road vehicles according to the invention, parts being shown in 
vertical center section through the rotational axis of the tire. The tire 
shown in FIG. 6 has a size of 18.00 R25 32 PR. 
A carcass ply 1 is composed of one rubberized carcass ply formed of a steel 
cord arranged along the above described section through the rotational 
axis of the tire and having a construction of (1.times.3).times.0.18 
mm+9.times.0.18 mm+(9.times.4).times.0.18 mm+0.1 mm. This steel cord has a 
tensile breaking strength of 310 kg/cord, elongation at breaking strength 
of 3% and the number of the steel cords at the crown center is 4.5 
cords/25 mm. 
The carcass ply is of a toroidal shape and wound about a pair of bead wires 
2 to form a turn-up portion 3 which is extended from a base line A toward 
the crown for 100 mm. In order to reinforce the bead portion, about the 
bead portion is superimposed a chipper 4 composed of a rubberized steel 
cord which is the same as that used for the carcass ply 1 and inclined at 
an angle of about 60.degree. with respect to the tire radial direction. 
In a triangular portion surrounded by the carcass ply 1 and the turn-up 
portion 4 wound around the bead wire 2 is arranged a bead filler 5 formed 
of a hard rubber. In a crown portion 6, between the carcass 1 and a tread 
7 are interposed 4 belts 8 each composed of a reinforcing ply. 
In a side portion 11, about the carcass ply 1 is superimposed a side 
portion reinforcing layer 12. Between the carcass ply 1 and the side 
portion reinforcing layer 12 is interposed a shock absorbing sheet 9 which 
is extended from a position distant apart from the base line A by 135 mm 
to a shoulder portion 10 and has a width of 275 mm and thickness of 1.0 
mm. The shock absorbing sheet 9 is formed of rubber having a Shore A 
hardness of 76.degree., breaking strength of 220 kg/cm.sup.2 and 300% 
modulus of elasticity of 200 kg/cm.sup.2 . 
The side portion reinforcing layer 12 is superimposed about the shock 
absorbing sheet 9 and extended from a position distant apart from the base 
line A to the shoulder portion 10. The side portion reinforcing layer 12 
has a width of 245 mm. The side portion reinforcing layer 12 is composed 
of a rubberized layer containing a reinforcing element formed of a bundle 
of 9 helically formed steel filaments. 
Each filament has a diameter .phi. of 0.25 mm, average diameter D projected 
on a plane perpendicular to the axial direction of one pitch of the 
filament of 2.07 mm, 
##EQU10## 
and pitch of 12 mm. 
The number of the reinforcing elements per 25 mm of the rubberized layer is 
6.5 elements/25 mm. The reinforcing elements are inclined at an angle of 
0.degree. with respect to the vertical center section through the 
rotational axis of the tire, that is, arranged along the radial plane. The 
reinforcing element has a tensile breaking strength of 117 kg/element and 
an elongation at breaking strength of 5.5%. 
The coating rubber containing the reinforcing elements embedded therein has 
a Shore A hardness of 76.degree., 300% modulus of elasticity of 200 
kg/cm.sup.2, and tensile breaking strength of 220 kg/cm.sup.2. The side 
portion reinforcing layer 12 is covered with a side wall rubber 13 having 
a shore A hardness of 54.degree., tensile breaking strength of 190 
kg/cm.sup.2 and 300% modulus of elasticity of 85 kg/cm.sup.2. That portion 
of the side wall rubber 13 which is located at the maximum width position 
B of the carcass ply of the tire has a thickness of 15 mm. 
The tire constructed as described in the present example 1 was used in mine 
site and compared with a pneumatic radial tire for off-road vehicles which 
is not provided with the side portion reinforcing layer 12 under the same 
service condition. Both the tire according to the present example 1 and 
the tire to be compared were used for a vehicle of Cat. 769B. The number 
of each of the respective tires tested was 50. 
Experimental tests have yielded the result that percentage of producing 
useless waste tires from the tire to be compared due to the side-cut 
penetration was 14% and the number of the useless waste tires was 7, while 
the similar percentage of the tire according to the invention was 4% and 
the similar number was 2. As seen from the above, the side-cut resistant 
property of the tire according to the invention is far superior to that of 
the tire to be compared. 
In addition, experimental tests have demonstrated that a ratio of the 
number of completely worn tires to be compared to the tested number 24 
thereof was 48%, that the similar ratio of the tire according to the 
invention was 56% and that the tire according to the invention had no bad 
influence upon the other properties of the tire. In addition, analytical 
tests have shown the result that, in the side portion reinforcing layer of 
the completely worn tire according to the invention, any separation could 
not be found out therein. 
Static load tests on longitudinal deflection and widthwise deflection of 
the tire according to the invention and the tire to be compared have 
yielded the result that, let both the longitudinal and widthwise 
deflection of the tire to be tested be 100, the longitudinal deflection of 
the tire according to the present example was 99 and the widthwise flexure 
was 95, these flexures being slightly smaller than those of the tire to be 
compared, and that these flexures had no influence upon the spring 
property of the tire as a whole. 
In FIG. 7 is shown test results of the side-cut resistant property of the 
tire shown in FIG. 6 as compared with those of two tires to be compared 
one of which is similar in construction to the tire shown in FIG. 6, but 
which is not provided with the side portion reinforcing layer and the 
other tire to be compared is similar in construction to the tire shown in 
FIG. 6, but the side portion reinforcing layer thereof is composed of a 
rubberized fabric containing steel cords embedded therein and having a 
strand construction of (7.times.3).times.0.175 mm+1.times.0.15 mm, 
elongation of 2.8% and tensile breaking strength of 116 kg/cord, number of 
cords of 6.5 cords/25 mm and cord angle of 90.degree. with respect to the 
tire circumferential direction. 
All of these tires were united with a standard rim of 13.00.times.25 and 
inflated by applying a standard internal pressure of 6.3 kg/cm.sup.3. The 
tires were remained as they were for about 24 hours. A tapered sharp 
cutter whose taper angle is approximately 15.degree. and blade width is 60 
mm was urged against the tires to be tested at room temperature with a 
speed of 50 mm/min. The side-cut resistant property of the tires to be 
tested was observed with respect to the breaking load as a function of the 
amount of axial displacement of the cutter into the tires. The cutter 
blade is inclined at an angle of 45.degree. with respect to the vertical 
center section through the rotational axis of the tire and urged against 
the maximum width position of the carcass line of the tire. The cutter 
blade is inclined because the tire is subjected to cut during rotation to 
produce a plenty of inclined cut defects. 
In FIG. 7, a full line curve A shows the test result of the tire according 
to the invention shown in FIG. 6. A dot-dash lines curve B shows the test 
result of one of the tires to be compared which is not provided with the 
side portion reinforcing layer. A dotted lines curve C shows the test 
result of the other tire to be tested which is provided with the 
rubberized fabric containing the conventional steel cords embedded 
therein. The cut resistant energy in kg.mm is represented by the area 
resulted from the multiplication together of the breaking load in kg and 
the displacement in mm. In FIG. 7, the breaking load in kg is taken on 
ordinate and the amount of displacement of the cutter in mm is taken on 
abscissa, so that the cut resistant energy is represented by the area of 
triangle formed between each of these curves A, B, C and the abscissa. 
As seen from FIG. 7, the cut resistant energy in kg.mm of the tire of the 
example 1 according to the invention shown by the full line curve A is 184 
kg.mm which is superior to 100 kg.mm and 147 kg.mm of the conventional 
tires to be compared shown by the dot-dash lines and dotted lines curves B 
and C, respectively. 
In FIG. 8 is shown a modified embodiment of the tire according to the 
invention. In the present embodiment, the side portion reinforcing layer 
12 shown in FIG. 6 is passed over the crown portion 6 toward another side 
portion (not shown). The present embodiment makes it possible to not only 
protect a shoulder portion against cuts, but also reinforce the belt 8. In 
addition, use may be made of only one side portion reinforcing layer 
instead of two side portion reinforcing layers shown in FIG. 6, thereby 
improving the manufacturing efficiency of the tire. 
In FIG. 9 is shown another modified embodiment of the tire according to the 
invention. In the present embodiment, the side portion reinforcing layer 
12 shown in FIG. 6 is composed of 2 rubberized layers 21A, 21B each 
containing a reinforcing element formed of a bundle of helically formed 
filaments embedded therein. The side portion reinforcing layer 21A is 
located near the carcass ply 1 and has a width of 245 mm which is made 
wider than a width of 215 mm of the side portion reinforcing layer 21B 
superimposed about the side portion reinforcing layer 21A. These 2 
rubberized layers 21A, 21B are symmetrically extended from a point of 
symmetry located at the maximum width position B of the tire. 
Each helically formed steel filament has a diameter .phi. of 0.175 mm, 
average diameter D projected on a plane perpendicular to the axial 
direction of one pitch of the filament of 0.95 mm, 
##EQU11## 
and pitch of 11 mm. 5 of these helically formed steel filaments are 
assembled together without twisting at random to form a bundle which is 
used as the reinforcing element. The number of the reinforcing elements 
per 25 mm of the rubberized layer is 5. The reinforcing element is 
inclined at 30.degree. with respect to the tire radial direction. The 
reinforcing element has a tensile breaking strength of 63 kg/element and 
an elongation at tensile breaking strength is 7.2%. The reinforcing 
elements in the first side portion reinforcing layer 21A are oppositely 
inclined to the reinforcing elements in the second side portion 
reinforcing layer 21B. 
The coating rubber containing the reinforcing element embedded therein has 
a Shore A hardness of 67.degree., 300% modulus of elasticity of 134 
kg/cm.sup.2, elongation at tensile breaking strength of 430% and tensile 
breaking strength of 250 kg/cm.sup.2. The use of the 2 side portion 
reinforcing layers 21A, 21B whose reinforcing elements are oppositely 
inclined with each other ensures a further improvement in the side-cut 
preventive effect. As a result, the rigidity of the side portion of the 
tire becomes increased. In addition, in order to prevent the stress from 
concentrating into the end of the reinforcing element, the reinforcing 
element whose elongation is large is surrounded by the soft coating 
rubber. 
In FIG. 10 is shown a further modified embodiment of the tire according to 
the invention which can further improve the side-cut preventive effect. In 
the present embodiment, the side portion reinforcing layer 12 shown in 
FIG. 6 is altered such that a side portion reinforcing layer 22 is distant 
apart from the carcass ply 1 and composed of 2 rubberized layers 22A, 22B 
each containing a bundle of helically formed filaments embedded therein. 
The side portion reinforcing layer 22A near the carcass ply 1 is extended 
upwardly from a point kept away 145 mm from the base line A and having a 
width of 230 mm. The side portion reinforcing layer 22B superimposed about 
the side portion reinforcing layer 22A is extended upwardly from a point 
kept away 130 mm from the base line A and having a width of 230 mm. 
Each helically formed steel filament has a diameter .phi. of 0.21 mm, 
average diameter D projected on a plane perpendicular to the axial 
direction of one pitch of the filament of 1.2 mm, 
##EQU12## 
and pitch of 8.8 mm. 5 of these helically formed steel filaments are 
assembled together without twisting at random to form a bundle which is 
used as the reinforcing element. The number of the reinforcing elements 
per 25 mm of the side portion reinforcing layer is 4.5. The reinforcing 
element is inclined at 45.degree. with respect to the tire radial 
direction. The reinforcing element has a tensile breaking strength of 63 
kg/bundle and an elongation at tensile breaking strength is 8.3%. The 
reinforcing elements in the first side portion reinforcing layer 22A are 
oppositely inclined to the reinforcing elements in the second side portion 
reinforcing element 22B. 
The coating rubber containing the reinforcing element embedded therein has 
a Shore A hardness of 67.degree., 300% modulus of elasticity of 134 
kg/cm.sup.2, elongation at tensile breaking strength of 430% and tensile 
breaking strength of 250 kg/cm.sup.2. 
Between the carcass ply 1 and the side portion reinforcing layers 22A, 22B 
is interposed a soft shock absorbing rubber pad 23. The pad 23 has a 
thickness of 11 mm at the maximum width point B of the carcass line. The 
pad 23 has a Shore A hardness of 58.degree., 300% modulus of elasticity of 
124 kg/cm.sup.2, tensile breaking strength of 274 kg/cm.sup.2 and 
elongation at tensile breaking strength of 484%. 
In the present embodiment, between the carcass line 1 and the side portion 
reinforcing layers 22A, 22B is interposed the soft rubber pad 23, so that 
the absorption of energy produced when the tire is deformed due to the 
penetration of rocks, etc. into the tire is improved, thereby further 
improving the side-cut protective effect of the tire. 
In FIG. 11 is shown a still further modified embodiment of the tire 
according to the invention. In the present embodiment, the turn-up portion 
3 of the carcass ply 1 formed of steel cords is extended upwardly beyond 
the maximum width position B of the carcass line and inside thereof is 
disposed a side portion reinforcing layer 12' composed of the reinforcing 
elements each formed of the bundle of helically formed steel filaments. 
In FIG. 12 is shown another modified embodiment of the tire according to 
the invention. In the present embodiment, the turn-up portion 3 of the 
carcass ply 1 formed of steel cords is extended upwardly beyond the 
maximum width position B of the carcass line and outside thereof is 
disposed a side portion reinforcing layer 12" composed of the reinforcing 
elements each formed of the bundle of helically formed steel filaments. 
The side portion reinforcing layer 12" functions to protect the turn-up 
portion 3 of the carcass ply 1. 
The above embodiments have been described with reference to the pneumatic 
tire for off-road vehicles, but the invention may also be applied to a 
tire for trucks, rally racing vehicles, etc. which are liable to be 
subjected to side-cuts.