JPH0669762B2 - Heavy duty pneumatic tire with low rolling resistance and excellent side durability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) Regarding heavy-duty pneumatic radial tires with low rolling resistance, the side wall lower part accompanied by the improvement of the carcass radial surface profile at the time of normal internal pressure filling aiming at the reduction of rolling resistance The purpose of this invention is to propose a pneumatic tire for heavy loads, which is more useful mainly as a wheel for trucks, buses, etc., by achieving the conformation of the outer contour shape of the lower part of the sidewall, which helps to appropriately avoid the deterioration of weather resistance in the parts. is there.

(Prior Art) In order to reduce the rolling resistance of a heavy duty pneumatic tire, it is necessary to use a rubber composition that increases the repulsion elastic modulus (Resilience) so that the internal friction of the tread rubber, which has the largest contribution, is reduced. In addition, the rubber compound with reduced internal friction is applied to the sidewall rubber, and the proportion of the groove area of other patterns is increased to suppress the minute slip during rolling, in the same manner as described above for the characteristics of the tread rubber. To reduce rolling resistance,
It was thought once, but the effect was limited in all cases.

Therefore, the inventors have taken measures to reduce rolling resistance of heavy-duty pneumatic tires that have deviated from the conventional idea described above. The details of the finding that a wide reduction in rolling resistance can be advantageously achieved without sacrificing wet performance and the like have been disclosed.

Of this disclosure, the following points are particularly important:

First of all, the shear deformation in the upper part of the sidewall near the buttress is small under the load when the tire is rolling due to a load, but it significantly increases when it enters or leaves the ground contact surface. It goes without saying that this shear deformation has an inverse relationship with bending deformation, but the shear deformation decreases as the bending deformation increases.

Therefore, since the upper part of the sidewall is also a relatively thin part, even if the bending deformation in the vicinity of the load is slightly increased, if the shear deformation which is disadvantageous for energy consumption can be reduced, the energy consumption as a whole can be reduced. This is advantageous in expecting reduction of

Next, under the natural equilibrium shape that has been the basis of conventional tire design, the lower sidewall portion, where the contribution of bending deformation to the rolling resistance is large, is repeated on the surface along with the bending deformation of the tire during rolling. It is also advantageous to transfer the resulting compressive strain in the radial direction into a shear deformation that has a smaller effect on rolling resistance.

In the radiation surface profile designed to reduce rolling resistance based on the above idea, under the specific deformation at the time of the internal pressure air filling and the specific carcass pass line passing through it,
Rather, the tension distribution of the carcass that leads to bending deformation in the upper part of the sidewall and conversely to shear deformation in the lower part of the sidewall is introduced. However, when observing the movement of the points on the surface of the sidewall lower area due to the above deformation at the time of filling the internal pressure air, it is said that it was heading outward in the radial direction under the conventional natural equilibrium shape carcass pass line. On the contrary, it moves inward in the radial direction, and this inward movement in the radial direction causes a strong radial compression force on the surface of the tire.

The reason for this will be described below. As described in JP-A-60-61305, since the carcass has a metal cord embedded therein and is non-extendable, the peripheries of the carcass pass line in the sidewall are substantially equal in length before and after the internal pressure filling, In addition, when the carcass is deformed by filling with internal pressure, the carcass is deformed to a large extent in the lower region of the sidewall, with a large radius of curvature. The component that goes outward in the radial direction is canceled by the deformation that increases the radius of curvature. Therefore, all the points on the carcass line in the above area are displaced inward in the radial direction. With the deformation of the carcass, the sidewall surface is compressed inward in the radial direction.

When this is combined with the compression input due to rolling under load, a large compressive force is applied, and when the lower curvature of the sidewall of the tire is large, it is converted to out-of-plane shear and cracks on the surface occur and the weather resistance of the case And became a practical problem.

As a general measure against this, the improvement of the rubber quality and the covering of the surface with a rubber having good weather resistance were all stopped, and the essential solution from the above-mentioned input surface could not be expected.

(Problems to be Solved by the Invention) A lower side wall region accompanying the application of the special radiation surface profile of the carcass pass line disclosed in JP-A-60-61305, which is useful for reducing rolling resistance. It is an object of the present invention to provide an effective means for fundamentally solving the deterioration of the weather resistance of the side portion.

(Structure of the Invention) The present invention is provided with a carcass consisting of at least one layer of metal ply cords substantially in a radial arrangement and a breaker consisting of at least two layers of metal cords as main reinforcement, and for a heavy load including a hard stiffener in a bead portion. In the process of assembling the pneumatic tire to the rim and filling the air to the normal internal pressure, the radial surface profile of the carcass is closer to the shoulder than the maximum width position from 5% of the normal internal pressure to the completion of the filling. In the upper area, the deformation is very small compared to the maximum width position and it does not deform substantially, on the other hand, in the vicinity of the maximum width position, it bulges more than in the upper area and is closer to the bead than the maximum width position. In the lower area of the tire, the car car in the tire mounting posture is continuously deformed so as to generate a larger protrusion than the bulge in the vicinity of the maximum width position. For each pass line, the tangent line at the maximum width position of the carcass pass line parallel to the line segment (BC) connecting the intersection points (B) and (C) defined below and the above line segment circumscribing at the point (E) ( When the natural equilibrium shape of the carcass is approximated by a virtual reference arc having ▲ ▼) as a string, the distance from the intersection (C) to the tangent and the contact (F) to reach the contact (F) , With a curvature larger than that of the reference arc, deviated to the outside of the reference arc, extending across the reference arc radially inside the contact (F), and further extending from the contact (F) to the intersection (B) On the contrary, the carcass deviated from the natural equilibrium shape by having an inflection point (V) in the middle between the contact point (F) and the intersection point (B) while being separated from the reference arc to the inside by the contrary. Low rolling resistance with a radiation surface profile In a heavy-duty pneumatic tire, in the lower portion of the sidewall that is continuous with the above bead portion, the portion of the tire cross-section height (SH) that covers the range of 20 to 45% has the curvature of the tire cross-section outer contour curve within the tire radial direction. 6x10 ^-3 at an intermediate height of 32.5% of the tire cross-sectional height (SH), which gradually decreases from the outside to the outside.
Low rolling resistance with excellent side durability, which is characterized by having a radial cross-sectional profile of the outer surface of the sidewall, which has a curvature l / ρ of mm ⁻¹ or less and which is a curve approximate to a cubic curve. Is a heavy duty pneumatic tire.

(Note) Intersection point (B); Regarding a heavy-duty tire in which a rim is assembled and filled with air to a normal internal pressure, a rim parallel to the rotation axis passing through a point at which 1/2 of the nominal diameter of the rim is separated from the rotation axis of the tire. An intersection point (C) at which a straight line parallel to the above-mentioned axis of rotation, which is separated from the radial line (1) outwardly in the radial direction of the tire by a distance corresponding to 15% of the sectional height (SH) of the tire, intersects with the carcass pass line; Similarly, a perpendicular line passing through the intersection point (B) perpendicular to the straight line intersects with the carcass pass line on the outer side in the tire radial direction from the intersection point (B).
Consisting of at least one layer of metal ply cord so that it can withstand the high internal pressure filling required to support the heavy loads acting on tire wheels for traveling trucks, buses, etc. as already mentioned This is a type of application of a tire that is commonly used in the industry as a category of use of a tire having a carcass and a breaker composed of at least two layers of metal cords as main reinforcement. In addition, the normal internal pressure with respect to the air pressure filled through the rim assembly is
It is also customary to refer to the maximum air pressure corresponding to the maximum load that is determined according to the size and ply rating of the tire. Furthermore, for this rim assembly, it is possible to use a rim specified for each tire size by the tire standard, for example, the JATMA standard by the Tire Standards Committee, and it is not necessary to specify this, the point is that the rim assembly The carcass radiation surface profile, which has the above-described specific deformation in the process of filling air to the normal internal pressure and whose deviation from the natural equilibrium shape is specified as described above, is provided with the radiation cross-sectional profile of the specific sidewall outer surface. It goes without saying that all possible rims fit.

Now, referring to FIG. 1, according to the present invention, a carcass consisting of at least one layer of metal ply cords in a radial arrangement and a breaker consisting of at least two layers of metal cords are provided as main reinforcements, and a heavy load including a hard stiffener at a bead portion. For heavy duty pneumatic tires, rim this
A radial cross section in a state of being filled with air up to a normal internal pressure is shown. Here, illustration of a conventional reinforcing element of this type of tire is omitted, and the right half is also omitted because it is symmetrical.

In the figure, 1 is a carcass pass line in the above state, 2
Is a reference arc for defining the pass line 1, and 3 is
A curve representing a natural equilibrium shape of a carcass approximated by the reference arc 2, 4 is a tire bead portion, 5 is a sidewall portion, 6 is a buttress portion, 7 is a tread crown portion, and Reference numeral 8 is a cross-sectional contour of the inner surface of the rim in which the above tire is assembled.

As is apparent from FIG. 1, the reference arc 2 that approximates the natural equilibrium shape of the carcass passes through the intersection points B and C and the contact point E defined as described above, and therefore its radius R'is determined, and the carcass pass line 1 The reference arc 2 between the intersection B and the contact F
The ratio of the radius of curvature R of the portion having a larger curvature to R'is preferably in the range of 0.70 to 0.80 among 0.65 to 0.85, and the arc intersects the reference arc 2 at the contact point F. The part from the contact point F to the intersection point B, which is separated from the inside to the inside, has a single inflection point V and is preferably separated from the reference arc by 3 to 8 mm. Sho 60-
This is as disclosed in Japanese Patent No. 61305.

(Working) With respect to the range of R / R ', if the value exceeds 0.85 and is too large, the effect of reducing the shear deformation in the upper part of the side wall and improving the rolling resistance is sufficiently obtained as will be shown later in Examples. On the other hand, if it is less than 0.65, it corresponds to the upper region of the carcass' radiation surface profile closer to the shoulder than the maximum width position, but excessively bending deformation occurs in the buttress 6 which is relatively thick and the sidewall The rolling resistance improving effect, which is obtained by reducing the shear deformation in the upper part, is canceled out and the win is achieved.

Next, regarding the bending deformation of the lower part of the sidewall, considering the energy consumption due to it, it can be generally expressed as the following equation.

Energy consumption = A ・ E ・ tanδ ・ (ΔC) ²・ S ...
(1) where A: appropriate constant E: elastic coefficient of the lower part of the sidewall ΔC: curvature change of the lower part of the sidewall due to bending deformation S: length of the lower part of the sidewall measured from the maximum width position of the carcass radiation surface profile Therefore, it is clear that if E, tan δ and S are equivalent, the energy consumption is proportional to (ΔC) ² .

Therefore, the change in the curvature of the outer contour curve of the tire section under the sidewall when a load is applied to an actual tire is important in the following point.

That is, as shown in FIG. 2, when a normal load is applied to the tire, the deformation in which the curvature of the lower portion of the sidewall is reversed, that is, the outwardly convex curvature radius R ₁ before the load deformation, It means that after the deformation, the deformation occurs such that it is outwardly inverted like a concave radius of curvature R ₂ .

Here, the curvature change (ΔC) ² in the lower region of the sidewall in the equation (1) can be expressed by the following equation.

Here, when the tire is assembled on the rim and filled with the normal internal pressure, if the lower region of the sidewall already has an inverse R, the curvature change (ΔC ′) ² is Therefore, it is obviously smaller than (ΔC) ² according to the above formula (2), and the energy consumption according to the formula (1) can be reduced in proportion thereto.

From this point of view, it is effective to give an inverted R shape to the sidewall lower region under normal internal pressure filling, but considering that bending deformation occurs mainly at the carcass that bears the internal filling pressure, It is necessary to reverse the curvature of the carcass itself.

Regarding the extent to which the curvature of this carcass is reversed, the carcass pass line 1 shown in FIG. And of the reference arc 2 It can be represented by the value of f which is the maximum distance between and, and as a proper range, f is 3 to 8 mm, as already mentioned.
It is preferably 4 to 7 mm.

In the lower part of the sidewall, a carcass (not shown) is wound around the bead core outward in the radial direction, and a bead part is solidified by filling a stiffener between the winding part and the carcass. , Out of Carcass Pass Line 1 Is the reference arc 2 that approximates the natural equilibrium shape Occupy the inside of.

Here, when f is less than 3 mm, the effect of reducing energy consumption cannot be fully exerted by the principle shown in the above formulas (1) to (3), and when f exceeds 8 mm, when filling with internal pressure. The tension of the carcass in the lower portion of the side wall becomes too high, which adversely affects the durability, and also deteriorates the mating with the rim.

The fact that the heavy-duty pneumatic tire according to the present invention has a radial surface profile that deviates from the natural equilibrium shape can be easily distinguished from the external appearance by observing the change in the carcass radial surface profile during the filling of the tire internal pressure.

That is, regarding the change from when the tire is assembled to the rim and the internal pressure is filled to 5% of the normal internal pressure to when the internal pressure is filled to the normal internal pressure, in the case of a so-called natural equilibrium radial surface profile, 1000R20 size is shown in Fig. 3. In the case of the carcass radiation surface profile deformed according to the present invention, as shown in FIG. The amount of protrusion deformation in the lower region is much larger than that in the width position, and a slight amount of protrusion deformation occurs in the region above the maximum width position, but it does not substantially deform.

In FIGS. 3 and 4, the solid line and the broken line show the shape of the tire outer surface before and after the overhanging deformation, which are modeled with gypsum, respectively.

It goes without saying that the difference in the deformation pattern of the carcass radiation surface profile due to this internal pressure filling affects the tension distribution of the carcass. In the case of the tire according to the present invention, the carcass tension is high near the bead portion where the amount of deformation is large and the apparent rigidity is also large, but the amount of deformation is relatively small from the upper side of the sidewall to the buttress portion, so the carcass is relatively Has a low tension and a low apparent rigidity.

First, in the case where a slip angle is added to the tire, a lateral force acts on the tire at this time, which causes lateral deformation, but in the case of the tire of the present invention,
Since the carcass tension near the bead portion is high and the apparent rigidity is large, the rigidity against lateral deformation is also large, and high cornering power and particularly good stability are exhibited when the slip angle is large.

This kind of improvement is exhibited even when the road surface is dry, that is, on a dry road surface, and also when the road surface is wet, that is, on a wet road surface.For example, the running time required to run the slalom on the same path on the wet road surface at the same distance. The difference can be clearly understood.

However, the portion below the maximum width of the tire cross section in the lower portion of the sidewall extends to the bead portion, and the outer surface of the sidewall has the following disadvantage in terms of weather resistance of the side portion due to the influence of the cross-sectional profile of the carcass line.

That is, when the lower portion of the sidewall described above with reference to FIG. 4 is deformed to the extent of being extruded due to air pressure filling, the point on the outer surface of the lower portion of the sidewall moves inward in the radial direction, and Will have ingredients. This is because the compression input applied to the sidewall part is combined with the compression input applied during rolling compared to the case of the natural equilibrium shape in which the sidewall part protrudes substantially uniformly when the internal pressure is filled and the sidewall part has no component in the compression direction. It will be bigger.

As shown in FIG. 5 (a), the outer surface S of the lower portion of the sidewall is
Receives repeated compression input as the tire deforms from the solid line to the broken line during load rolling. When there is an inclination in the direction of the compression input as shown in FIG. 5 (b), the surface S is converted into a shift in the vertical direction (out-of-plane shear) as shown in FIG. 5 (c).
That is, if the curvature of the outer contour curve in the lower portion of the sidewall is large, the vertical deviation that occurs there is large.

Deterioration of the rubber due to the action of ozone (O ₃ ) is promoted on the surface of the rubber subjected to such a force, and a crack-like flaw is generated, which is one factor that deteriorates the case durability.

Regarding this disadvantage, as shown in Fig. 1 again, a portion extending from 20 to 45% of the tire cross-section height SH connected from a bead portion having a large curvature (a portion below 20% of the tire cross-section height SH) Regarding P, the curvature of the outer contour curve Q of the tire cross section gradually decreases from the inner side to the outer side in the tire radial direction, and becomes 6 × 10 ⁻³ mm at an intermediate height of 32.5% of the tire section height SH. Avoiding the disadvantage of converting the radial compression input to out-of-plane shear by having a radial cross-section profile of the sidewall outer surface that has a curvature l / ρ less than ^-1 and is composed of a curve approximate to a cubic curve It can be done.

Regarding the tire cross-section outer contour curve Q having the above curvature l / ρ, when there is an annular projection or the like locally protruding on the outer surface of the sidewall, it is formed by a cubic curve that smoothly connects the remaining areas excluding this. I shall.

Curvature l / ρ at an intermediate height of 32.5% of the tire section height SH
When it is larger than 6 × 10 ⁻³ mm ⁻¹ , the effect of improving the weather resistance cannot be effectively achieved.

(Embodiment) In the present invention, as shown in FIG. 6, a ply which becomes a rubber coating of metal ply cords arranged substantially in a radial plane of a tire is provided around a bead core 11 with a hard and soft stiffener 12,1.
A carcass 13 of at least one layer extended by rolling out 2'to extend outward in the radial direction of the tire, and the carcass 13 around the carcass 13 and arranged to intersect each other at a relatively small angle with respect to the center line of the tire. At least two layers of breakers 14 that are made of rubber coated steel cord are provided as body reinforcements that work in cooperation with each other, and the side wall 15 has rubber on both sides of the carcass 13 and the tread portion 16 has rubber on the outer periphery of the belt 14. An example of the arranged tires for trucks and buses is shown.

This tire has a carcass pass line in the tire mounting posture with the carcass radial surface profile changed as described above when the tire is assembled with the rim and filled with the normal internal pressure as described in detail above. It has a carcass radiation surface profile that deviates from the natural equilibrium shape.

Here, 17 is a rim, and 18 is a lower part of the sidewall part 15.

In this example, the stiffener is a combination structure of hard rubber 12 and soft rubber 12 ', and its volume ratio is hard: soft = 1: (1.0 to 2.0).
Preferably (1.3-1.7) is acceptable, and Shore A
Hard stiffener 12 is 80 to 95 °, soft stiffener 1
2'is 50 to 75 °, and the difference in Shore A hardness between the two is 20 to 3
It is preferably 0 °.

Here, the outer contour curve of the tire cross section of the sidewall lower part 18 is approximated by a cubic curve as shown in the figure, and in a portion P covering 20 to 45% of the tire cross section height (SH), from the inside in the radial direction of the tire. It has a curvature that decreases gradually outwards, especially at an intermediate height of 32.5% of the tire section height (SH)
ρ is set to 6 × 10 ⁻³ mm ⁻¹ or less.

As shown in Fig. 6, the tire size is 1000R20, and the carcass 13 has a steel cord arranged at 90 ° to the tire equator. 1 ply (cord twist structure 1x3 + 9 + 15)
X 0.17 mm) as a breaker 14 with steel cords arranged at a cord angle of 67 ° -18 ° -18 ° -18 ° with respect to the tire equator with four layers intersecting two layers and three layers (cord twisting) Structure 1 x 3 x 0.20 mm + 6 x 0.38 mm), the stiffener is a hard stiffener 12 Vol: soft stiffener 12 '
The configuration is common in that the hardness of the hard stiffener 12 is 90 ° and the hardness of the soft stiffener 12 ′ is 65 ° at Vol = 40: 60, but the radiation surface profiles of the carcass lines are as shown in Table 1 below. Four different types of test tires, each 700T in size
The rim was assembled on 20 rims, filled with various internal pressures, and the following tests were conducted.

(1) Rolling resistance test results Test method: Press the tire against a drum with a diameter of 1707 mm Table 2
It is calculated by measuring the tangential force acting on the contact surface during rotational driving by accelerating to various predetermined speeds shown in FIG.

The test load was set to the normal load at the time of 7.25 kg / cm ² normal internal pressure filling, but the effect on the rolling resistance due to the increase / decrease in the filling air pressure was also investigated and the results were also shown.

(2) Maneuverability test results (3) Wet performance test Concrete road surface (Skid No.SN indicating the roughness of the road surface)
= 35) and the wet performance on an asphalt road surface (SN = 50 of the same), the tire C of the present invention was indistinguishable from the comparative tire A, and the tire of the present invention did not deteriorate in wet performance.

(4) Weather resistance test For tires A and C, the tire cross-section height (SH) is 20 to 45.
When the curvature at the intermediate height of 32.5% of the tire section height SH is compared as the average value of the curvature of the tire section outer contour curve Q of the portion P over the range of%, the comparative tire A has l / ρ of 10 × 10.
^-3 mm ^-1 , whereas the curvature of the tire C of the present invention is 3.0 x 10 ^-3 mm ^-1 , 4.4 x 10 ^-3 mm ^-1 , 5.9 x 10.
As a result of comparing the average depth of ozone cracks (during 50,000 km run) by a drum running test under UV irradiation instead of ^-3 mm ^-1 , the results shown in Fig. 7 were obtained. The above tire C
The outer contour curve Q of the tire cross section in (3) was a profile approximate to the following cubic curve.

y = 1 × 10 ⁻³ × x ³ + 6.530 × 10 ⁻³ x ² −1.296x + 5
9.87 y = 4 × 10 ⁻³ × x ³ −0.3214 × x ² + 10.21x −68.45 y = 6.5 × 10 ⁻³ × x ³ −0.5948 × x ² + 19.81x−175.5
In the cubic curve of 1 or more, the x-axis is the rim diameter line (1), and the y-axis is the rim width which is a straight line orthogonal to the rim diameter line (1).

Here, the weather resistance of the comparative tire A is shown as an index, and for the tire under test C, l / ρ is 10 × 10 ⁻³ mm for reference.
Contrary to the deterioration of 77 when set to ^-1 , according to the present invention
All three types having l / ρ of 6 × 10 ⁻³ mm ⁻¹ or less have a remarkable improvement in weather resistance as the above index is about 170.

The amount of protrusion of these tires C due to internal pressure filling is, for example, about 10 mm at an intermediate height of 32.5% of the tire sectional height SH, and the curvature at the intermediate height is approximately tripled by the internal pressure filling. . The mold of the tire C was designed to have a mold surface that was substantially the same as the profile before the internal pressure filling.

(Effects of the Invention) According to the present invention, the rolling resistance of the heavy duty pneumatic tire can be controlled without deteriorating the steering performance and the wet performance.
It can be reduced particularly advantageously, and the weather resistance of the side portion does not deteriorate.

[Brief description of drawings]

FIG. 1 is an explanatory view of a relationship between a radial surface profile (solid line) of a tire and a reference arc (broken line) according to the present invention, and FIG. 2 is an explanatory view of deformation behavior when a normal load is applied to the tire, FIG. FIG. 4 is an explanatory view of deformation behavior of a tire having a natural equilibrium profile due to internal pressure filling, FIG. 4 is an explanatory view of deformation behavior of a tire having a carcass radial surface profile of the present invention due to internal pressure filling, and FIG. 5 is a sidewall lower portion. 6 is a cross-sectional view of a test tire, and FIG. 7 is a graph showing a weather resistance test result. 1 …… Carcass pass line 2 …… Standard arc 3 …… Natural equilibrium shape 4 …… Bead part 5 …… Sidewall part 6 …… Butless 7 …… Tread crown part 11 …… Bead core 12,12 ′ …… Staffner 13 …… Carcass, 14 …… Breaker 15 …… Sidewall 17 …… Rim 18 …… Lower sidewall

Claims (1)

[Claims] 1. A heavy-duty pneumatic tire including a carcass consisting of at least one layer of metal ply cords substantially in a radial arrangement and a breaker consisting of at least two layers of metal cords as main reinforcement, and including a hard stiffener at a bead portion. In the process of assembling the tires on the rim and filling air to the regular internal pressure, the radial surface profile of the carcass above the maximum width position is closer to the shoulder than 5% of the regular internal pressure to completion of filling. In the case of the maximum width position, the deformation is very small and it does not substantially deform.On the other hand, in the vicinity of the maximum width position, it bulges more than in the upper region and below the bead part from the maximum width position. In the region, a carcass path dry in the tire mounting posture, which is continuously deformed so as to generate a larger protrusion than the bulge in the vicinity of the maximum width position. The tangent line at the maximum width position of the carcass pass line parallel to the line segment (BC) connecting the intersection points (B) and (C) defined below and the above line segment (BC) circumscribing at the point (E) When the natural equilibrium shape of the carcass is approximated by an imaginary reference arc having a chord as a string, the above-mentioned reference is provided between the intersection (C) and the tangent (F) to the contact (F). With a curvature larger than that of the arc, it is biased to the outside of the reference arc, extends across the reference arc radially inward of the contact (F), and further extends from the contact (F) to the intersection (B). In contrast, the carcass radiating surface deviated from the natural equilibrium shape by having an inflection point (V) between the contact point (F) and the intersection point (B), which is conversely spaced inward from the reference arc. Empty for heavy loads with low rolling resistance that has a profile In the filled tire, the curvature of the tire cross-section outer contour curve is from the inner side to the outer side in the tire radial direction of the portion of the sidewall lower part that is continuous with the bead portion over the range of 20 to 45% of the tire cross-section height (SH). 6x10 ^-3 at the mid height of 32.5% of the tire cross-sectional height (SH)
Low rolling resistance with excellent side durability, which is characterized by having a radial cross-sectional profile of the outer surface of the sidewall, which has a curvature l / ρ of mm ⁻¹ or less and which is a curve approximate to a cubic curve. Pneumatic tires for heavy loads. (Note) Intersection point (B); Regarding a heavy-duty tire in which a rim is assembled and filled with air to a normal internal pressure, a rim parallel to the rotation axis passing through a point at which 1/2 of the nominal diameter of the rim is separated from the rotation axis of the tire. An intersection point (C) at which a straight line parallel to the above-mentioned axis of rotation, which is separated from the radial line (1) outwardly in the radial direction of the tire by a distance corresponding to 15% of the sectional height (SH) of the tire, intersects with the carcass pass line; Similarly, a perpendicular line passing through the intersection (B) orthogonal to the straight line intersects with the carcass pass line outside the intersection (B) in the radial direction of the tire.