JPH04224402A - Heavy load radial tire - Google Patents

Abstract

PURPOSE:To decrease partial wear of the shoulder of a radial tire by setting the level difference between the tread equator and base point, which is equal to the distance in tire radial direction between a specific base point and the equator point, to a value meeting a specific equation related to a certain grounding half width. CONSTITUTION:The grounding half width SL is set which is equal to the distance in tire axial direction from the equator point T1 on the tread 2 surface to the grounding outer point T0 where the outer extreme point in tire axial direction of the grounding surface grounding when the normal load is applied to the tire 1 is located on the tread surface at the no-load time. The base point T2 is set which is apart by 0.2 times (0.2.SL) of the grounding half width SL from the grounding outer point T0 inward in the tire axial direction. The level difference Y1 between the tread equator and the base point equal to the distance in tire radial direction between the base point T2 and equator surface T1 is set relative to the grounding half width SL to the value to meet the following equation; Y1<=0,1060SL-4.32.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heavy-duty radial tire that can effectively suppress uneven wear in the shoulder portion of the tire.

0002

2. Description of the Related Art Pneumatic tires inevitably wear out as they run. Particularly in radial tires, which have been widely used in recent years, a belt layer made of high-tensile cords such as steel cords is placed on the outside of the carcass arranged in the radial direction, giving a large hoop effect, which allows the tread surface to contact the ground. Pressure distribution tends to be uneven, and uneven wear occurs in which the shoulder portion of the tire wears out earlier than the crown portion. On the other hand, for example, there is so-called heel-and-toe wear, which is sometimes seen especially in radial tires for passenger cars, and step-like wear in only the shoulder part, as shown in FIG. 7, which is seen in the tire for heavy loads such as trucks and buses according to the present invention. Abnormal wear such as stepped wear M may also occur.

[0003] Such uneven wear at the shoulder portion occurs because the tread surface has an almost arcuate cross section including the tire axis, so the circumferential length of the crown portion is smaller than the circumferential length of the shoulder portion. It is relatively long, so when the tread surface contacts the ground, the crown part forms the dragging side and the shoulder part forms the dragging side, for example, as shown in FIG. It is thought that this is caused by sliding friction that occurs between the protruding portion b and the road surface.

In particular, the stepped wear M is caused by the fact that when the tire is used for the front wheel on the non-drive side, wear of the ground contact end is accelerated by the attitude angle of the tire, and the stepped wear M It grows with the mileage of the tire and eventually spreads over the entire width of the outer rib, reducing the life of the tire.

Conventionally, this uneven wear and stepped wear can be prevented by increasing the radius of curvature of the tread surface and reducing the difference in circumferential length between the crown and shoulder parts, or by increasing the size of the blocks in the shoulder parts. Proposals have been made to increase the rigidity of the belt and further strengthen the rigidity of the belt layer, particularly in the shoulder area.

[0006]

[Problems to be Solved by the Invention] However, if the radius of curvature is simply increased carelessly and the difference in circumferential length is reduced, the ground pressure at the shoulder increases, which tends to cause heat generation in this area, and the belt ply in this area tends to increase. If anything, the durability is reduced, as the rubber tends to peel off at the edges.

As described above, uneven wear and heat generation, that is, durability, have antinomic characteristics. In addition, increasing the rigidity of the block and belt layer cannot sufficiently solve the above-mentioned wear problem, and excessively increasing the rigidity of the block and belt layer in the shoulder area tends to impede tire noise and ride comfort. Become.

The present inventors conducted various experiments to prevent uneven wear and stepped wear in the shoulder portions of heavy-duty radial tires, and as a result, they found a preferable range for the degree of curvature of the tread surface that can prevent uneven wear. Ta. In another embodiment, it has also been found that heat generation can be effectively reduced by setting the degree of curvature of the tread surface within a predetermined range. Furthermore, by setting the degree of curvature of the belt, which is a basic member, within a predetermined range, it is possible to reduce shear strain at the crown and shoulder portions of the belt, especially at the ends, and to control the movement of the tread rubber, thereby reducing the stepped wear M. They also discovered that it can be effectively prevented.

[0009] Accordingly, the first object of the present invention is to provide a heavy-duty radial tire that can effectively suppress the uneven wear that tends to occur in the shoulder portion.

0010

[Means for Solving the Problems] The present invention provides a carcass with a radial or semi-radial arrangement that goes from the tread part to the sidewall part and folds back at the bead core of the bead part, and a carcass that is arranged radially outside the carcass and inside the tread part. A belt layer consisting of at least three belt plies overlapping inside and outside using a belt cord tilted at an angle of 5 to 70 degrees with respect to the tire equator. In the standard state filled with internal pressure, from the equatorial point T1 on the tread surface, the outer end point in the tire axial direction of the contact surface that contacts the ground when a regular load is applied to the tire is the external point of contact that is located on the tread surface when no load is applied. T
0 of the ground contact half width SL, which is the distance in the tire axial direction from 0 to 0.
The tread equator-to-base height height Y1, which is the distance in the tire radial direction between the base point T2 that separates 2 times (0.2SL) from the ground contact point T0 inward in the tire axial direction and the equator point T1 is: This is a heavy-load radial tire that satisfies the following formula (2) for the ground contact width SL. Y1≦0.1060SL-4.32 ■

[0011]

[Operation] In the heavy-duty radial tire of the present invention, the degree of curvature of the tread is set in a standard state in which the tire is mounted on a regular rim and filled with a regular internal pressure. What is a regular rim? THE TIRE and RIM ASSO
CIATION INC. Year B issued by
OOK (commonly known as TRA) or THE EURO
PEANTYRE AND RIM TECHN
ST issued by ICAL ORGANIZATION
This is a standard rim specified by ANDARDS MANUAL (commonly known as ETRTO), and the normal internal pressure is TRA.
Alternatively, it is defined as the maximum air pressure of each tire in ETRTO. Note that the normal load means the maximum load.

Furthermore, in the heavy-duty radial tire of the present invention, the tread equator-to-base height Y1 satisfies the following equation (2) with respect to the ground contact half width SL. Y1≦0.1060SL-4.32
■

[0013] Here, the tread equator-to-base height height Y1 refers to the ground contact surface from the equator point T1 on the tread surface to which the tire contacts the ground when a normal load is applied, as shown by the dashed line in Fig. 1. 0.2 times (0.2
SL) is the distance in the tire radial direction between the base point T2, which is spaced inward in the tire axial direction from the off-ground contact point T0, and the equatorial point T1.

[0014] Here, in determining the base point T2,
The reason why the ground contact width SL is used instead of the tread width TW is because the ground contact point T, which is correlated to the outer end point c in the tire axial direction of the contact surface that actually contacts the ground, is determined in the actual vehicle test of the tire.
0 as the origin is related to the actual wear of the tread surface, and is located at a position that is 0.2 times the ground contact half width SL (0.2 SL) inwardly from the external contact point T0. This is because it has been found that the height of the base point T2 has a large effect on uneven wear and the like in the shoulder portion when making contact with the ground. Therefore, the tread equator-base point height Y1 is set as the distance in the radial direction between the base point T2 and the equator point T1.

FIG. 2 shows tires with various ground contact widths SL,
The uneven wear was measured after driving 50,000 km on a general paved road with 100% load capacity on a truck that matched the tire size.
The horizontal axis represents the height Y1 between the tread equator and the base point, and the vertical axis represents the height Y1.

In FIG. 2, the numbers attached to each mark are as follows:
The uneven wear rate w is, as shown in FIG. It is expressed by the ratio Sw/Cw to the crown wear amount Cw, which is the wear amount of the tread surface sandwiching the groove A2. index is 1
When it is 00, it means that the crown and shoulder parts are worn evenly, when it exceeds 100, the wear is accelerated on the shoulder part, and when it is less than 100, it shows that the wear is more uniform on the crown part than on the shoulder part. This means that wear is progressing. Note that the preferred range is 80 to 120, which is indicated by a white circle. A more preferable range of wear is 110 to 90. It has been found that within the above range, the desired wear life can almost be achieved.

The heavy-duty radial tire of the present invention satisfies the formula (2), so that it deforms smoothly and continuously in the tire radial direction from the crown portion to the shoulder portion upon contact with the ground, and further deforms between the crown portion and the shoulder portion upon contact with the ground. It is thought that uneven wear can be reduced by reducing the difference in the amount of deformation in the radial direction of the tire and suppressing the amount of deformation, which equalizes the ground pressure and reduces the amount of slippage between the shoulder and the road surface. .

As shown in FIG. 2, the uneven wear rate w is 12
In the range of 0 or less, there is a substantially linear correlation between the ground contact half width SL and the tread equator/base point height Y1, and the straight line X
It can be seen that it can be displayed as the following range. This range is
This is expressed by the above-mentioned formula (2), which is defined as claim 1 of the present invention.

[0019] The relationship of the above equation (2) is based on the tread width TW.
It has been found that this can be applied to heavy duty radial tires of 150 to 250 mm. Here, the tread width TW refers to the distance in the tire axial direction between the intersection points d of the extension lines of the tread surface and the buttress surface.

[0020] Next, according to the formula (■) above, the grounding half width SL
The ratio Y1/ of the standard tread height value S1, which is a value determined by each
FIG. 4 shows the results of measuring heat generation in the tread shoulder portion, with reference height ratio K1, which is S1, taken on the horizontal axis. In this test, the tires used in the test in FIG. 2 were measured using a rotating drum testing machine in a measurement room. Note that the load is the temperature value expressed as an index when a regular load is applied and the tire is rotated for 60 minutes at a speed equivalent to 80 km/h.

As is clear from FIG. 4, it has been found that when the reference height ratio K1 is smaller than 0.85, the temperature increases rapidly.

The fact that this reference height ratio K1 is smaller than 1 means that the tread equator-to-base point height Y1 is small compared to the reference tread height value S1, that is, the camber amount is reduced, and the tire tread is This means that the surface becomes flat. This is due to flattening, which increases the ground contact pressure at the shoulder area and rapidly increases the load bearing rate at the tire's thickest part, which increases heat generation.
It accelerates rubber deterioration, tends to cause rubber peeling at the belt ends, and has a negative impact on durability.

Therefore, as described in claim 2, the reference ratio K is set to 0.85 or more. That is, by combining with the above equation (2), the following equation (2) described in claim 2 is obtained. 0.0901SL-3.67≦Y1≦0.1060SL
-4.32 ■

Furthermore, in the test shown in FIG. 2, the present inventors found that stepped wear M occurred in the range below the reference tread height value S1 even if the uneven wear rate w was 120 or less. I noticed that there was something.

[0025] In order to investigate the cause of this, regarding tires,
The range in which the stepped wear occurs was considered in relation to the degree of curvature of the belt layer. As a result of organizing the data regarding the degree of curvature of this belt layer, the degree of curvature of the belt was found to be a belt base point B2 where a radius line passing through the base point T2 intersects with the outer surface of the second belt ply second from the carcass side.
and a belt equator-to-base point height Y2, which is a radial distance between the belt equator point B1 where the tire equatorial plane intersects the outer surface of the second belt ply, as one parameter, and the reference height The height Y between the belt equator and base point actually measured for each tire with the height ratio K1 as the vertical axis
2 and the belt reference height ratio K2, which is the ratio Y2/S1 of the reference tread height value S1, as shown in FIG. It was found that Moreover, this correlation formula is the following formula (■), where the height Y1 between the tread equator and the base point and the belt equator
It is given as a function of the sum Y1+Y2 with the base point height Y2. Y1+Y2≦1.85 (0.1060LS-4.32)
■

This means that even when the tread equator-to-base point height Y1 is less than the formula (2), that is, less than the standard tread height value S1 with respect to the tread surface, the belt equator-to-base point height Y2 When the curvature at the shoulder portion of the belt layer is excessive and the curvature at the shoulder portion of the belt layer is large, as shown in FIG. It is presumed that the movement of the rubber between the belt layer and the road surface (indicated by the arrow) increases, and the thickness of the rubber at the shoulder portion increases, making it easier for the stepped wear to occur.

By satisfying the equation (2), as shown in FIG. 6, it is possible to prevent the stepped wear and to further improve uniform wear.

Therefore, claim 3 of the present invention requires the above-mentioned formula (2). In this way, the tire of the present invention has:
Uneven wear can be reduced by using the formula. Further, as an example thereof, by satisfying the formula (2), heat generation in the shoulder portion can be prevented and the durability of the tire can be improved. As yet another embodiment, by satisfying the requirements of formula (2), a tire can be obtained that can more effectively prevent step wear.

Furthermore, in the heavy-duty radial tire of the present invention, in order to exhibit performance such as steering stability, rolling characteristics, and wear resistance, a belt layer is provided in the ground contact area that contacts the ground under normal load conditions. It is better to arrange Furthermore, at least three belt plies overlap in the ground contact area, and the intersecting belt cords exert a sufficient hoop effect.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. Figure 1 shows that a heavy-load radial tire 1 has a regular rim R.
This shows the standard condition in which the rim is assembled and filled with the normal internal pressure. As mentioned above, the regular rim R is the standard rim specified by TRA or ETRTO, and the regular internal pressure is the maximum air pressure of each tire in the TRA or ETRTO, and the regular load is the maximum load. Define as . The heavy-duty radial tire 1 has a tread portion 2, sidewall portions 3 extending radially inward from both ends of the tread portion, and bead portions 4 provided at both ends of the tread portion 2. It includes a carcass 6 that is folded back from the inside to the outside and is locked, and a belt layer 7 that is arranged on the outside of the carcass 6 in the radial direction.

In this embodiment, the carcass 6 is composed of one ply of radial structure with the carcass cord arranged at an angle of 90° with respect to the tire equatorial plane CO, and a steel cord is used as the carcass cord. There is. The carcass can also have a radial or semi-radial structure with carcass cords arranged at 60 to 90 degrees, and carcass cords can be made of steel cord, aramid, nylon,
It can be used by forming a plurality of plies of organic fiber cords such as rayon and polyester. Further, the carcass folds back the bead core 2, and the folded end 6A is interrupted above the bead core 5 and below the maximum width position of the tire. The bead portion 4 includes a reinforcing layer that prevents friction between the carcass 6 and the bead core 5 that move due to deformation due to tire contact with the ground, etc., and increases the rigidity of the bead portion, and a chafer (both not shown) to prevent rim slippage. ), other reinforcing layers 8 or the like may be provided to cover the folded portions of the carcass 6. Further, the tread portion 2 may be provided with a band layer (not shown) made of an organic fiber cord that covers the end portion of the belt layer 7 in the tire axial direction.

Further, the bead portion 4 is provided with a bead apex 10 made of a rubber material that tapers outward in the radial direction from the bead core 5 to improve lateral rigidity.

[0033] Also, the belt layer 7 is a carcass 6 in this example.
It has a four-layer structure consisting of a first belt ply 11, a second belt ply 12, a third belt ply 13, and a narrow fourth belt ply 14, which are arranged in order from the side toward the tread portion 2. , the ply width W2, which is the length between the outer edges of the second belt ply 12 in the tire axial direction, is larger than the ply width W1 of the first belt ply 11, and the ply width W2 of the third belt ply 13 is larger than the ply width W1 of the first belt ply 11. The width W3 is approximately the same as the ply width W1. That is, the second belt ply 12 has the maximum width of the four belt plies, and the belt-tread width ratio BW is the ratio of the belt maximum width BW, which is the ply width W2, and the tread width TW. /TW is 0.85
or more and 1.05 or less, the tread portion 6
almost its entire width is reinforced with a hoop effect. Note that when the belt-tread width ratio BW/TW is less than 085, the rigidity at the tread shoulder portion decreases, impairing running performance. Furthermore, when the belt-tread width ratio BW/TW exceeds 1.05, the belt end and the outer surface of the buttress portion of the tire are too close to each other, and external force from the buttress surface tends to cause a failure in which the belt end separates.

Furthermore, the belt cord is inclined at an angle of 5 to 70 degrees with respect to the tire equator CO, and in this embodiment,
The first belt ply 11 tilts its belt cord at an angle of 50 to 70 degrees with respect to the tire equator CO, and the second belt ply 12 tilts its belt cord in the same direction as the first belt cord and At an angle of inclination of 14 to 22 degrees with respect to the equatorial CO, also the third belt ply 13
The belt cord is arranged in the opposite direction to the second belt cord and at an inclination angle of 14 to 22 degrees with respect to the tire equator CO.

Therefore, in the belt layer 7, while the second and third belt cords intersect with each other, the first and second belt cords are inclined in the same direction. While the shear strain between the two belt plies 11 and 12 is alleviated, the belt cord angles of each ply 11 to 13 intersect to form a highly rigid triangular structure having a high restraining force across the ends of the belt layer. .

Also, the cord angle of the first belt ply 11 is the same as the cord angle of the carcass 7 and the cord angle of the second belt ply 12.
Since the cord angle is set midway between the cord angle and the cord angle, the difference in rigidity between the carcass 7 and the belt 9 is reduced and damage caused by peeling is prevented. Note that the fourth belt ply 14 is a ply 15 made of steel cord that is 45 to 10% narrower than the width of the third belt ply 13, and protects the first to third belt plies 11, 12, and 13 from external damage. .

Further, the first belt ply 11 is spaced apart from the carcass 6 on the outside in the tire axial direction, and the second belt ply 12 extends in the tire axial direction along the first belt ply, and the third belt ply 12 extends in the tire axial direction along the first belt ply. The belt ply 13 is spaced apart from the second belt ply 12 at its end, and a cushion rubber 15 extending in the tire axial direction is provided at each spaced apart portion.
, 16, the stress concentration at each ply end is alleviated and separation is prevented.

In addition to steel cords, a plurality of plies of organic fiber cords such as aramid, nylon, rayon, and polyester can be used as belt cords.

Furthermore, in the heavy-duty radial tire of the present invention, the tread equator-base point height Y1 satisfies the following formula (2) with respect to the ground contact half width SL. Y1≦0.1060SL-4.32
■

[0040]Here, the tread equator-to-base height height Y1 refers to the ground contact surface from the equator point T1 on the tread surface to the ground contact point when a normal load is applied to the tire, as shown by the dashed line in Fig. 1. 0.2 times (0.2
SL) is the distance in the tire radial direction between the base point T2, which is spaced inward in the tire axial direction from the off-ground contact point T0, and the equatorial point T1.

[0041] Thereby, as shown in Fig. 2, the uneven wear rate w can be kept in the range of 120 or less. In addition,
As shown in Fig. 3, the uneven wear rate w refers to the shoulder wear amount Sw, which is the amount of wear on the tread surfaces on both sides of the longitudinal groove A1 passing through the shoulder portion, and the wear amount on the tread surface sandwiching the longitudinal groove A2 on the equatorial point T1 side. The ratio Sw/C to the crown wear amount Cw
It is indicated by w. When the index is 100, it shows that the crown part and the shoulder part are worn evenly, when it exceeds 100, the wear accelerates at the shoulder part, and when it is less than 100, it shows that the wear is more uniform than the shoulder part. This means that the wear in the crown portion is progressing. The range with a more preferable wear pattern is 11
It is 0-90. In addition, this allows the tread surface to have an appropriate degree of curvature at the shoulder portion, so that it deforms smoothly and continuously in the tire radial direction from the crown portion to the shoulder portion upon contact with the ground. As a result of reducing the difference in the amount of deformation in the direction and suppressing the amount of deformation,
It is thought that the uneven wear can be reduced by equalizing the ground pressure and reducing the amount of slippage between the shoulder portion and the road surface.

[0042] Also, the height Y1 between the tread equator and the base point is
satisfies the expression. 0.0901SL-3.67≦Y1≦0.1060SL
-4.32 ■

[0043] As a result, heat generation in the tread shoulder portion is suppressed as shown in FIG. This formula (■) means to prevent the tread surface from becoming excessively flattened. This is because flattening increases the ground contact pressure at the shoulder area, and the load bearing rate at the thickest part of the tire increases rapidly, which increases heat generation.
It accelerates rubber deterioration, tends to cause rubber peeling at the belt ends, and has a negative impact on durability.

Furthermore, the following equation (2) is satisfied with respect to the tread equator-to-base point height Y1 and the belt equator-to-base point height Y2. Y1+Y2≦1.85 (0.1060LS-4.32)
■

[0045] Note that the height Y2 between the base points of the belt equator is
On the outer surface of the second belt ply second from the carcass side,
a belt base point B2 where a radius line passing through the base point T2 intersects;
It is the radial distance between the belt equatorial point B1 where the tire equatorial plane intersects the outer surface of the second belt ply. this is,
This study focuses on the fact that stepped wear M may occur even within the range of the equation (2), and by satisfying the equation (2), it is possible to prevent the stepped wear as shown in Fig. 6. Therefore, uniform wearability can be improved. The reason for this is that when the formula (■) is not satisfied, the height Y2 between the belt equator and the base point is excessive, and the curvature at the shoulder portion of the belt layer becomes large, as shown in FIG. Shearing strain is generated in the crown part and the shoulder part at the start part b (indicated by arrows in FIG. 6),
It is presumed that the increased movement of the rubber between the belt layer and the road surface and the increased rubber thickness at the shoulder portion tend to increase the stepped wear.

As described above, the tire of the present invention can reduce uneven wear according to formula (2). Further, as an example thereof, by satisfying the formula (2), heat generation in the shoulder portion can be prevented and the durability of the tire can be improved. As yet another embodiment, by satisfying the requirements of formula (2), a tire can be obtained that can more effectively prevent step wear.

[Specific Example] A tire with a tire size of 285/75R 24.5 having the tire structure shown in FIG. and the temperature rise in the tread shoulder area were measured. The results are listed in Table 3.

[0048]

[Table 1]

[0049]

[Table 2]

[0050]

[Table 3]

As shown in Table 1, the tires of the examples of the present invention have better results than the comparative examples in terms of uneven wear rate w, presence or absence of stepped wear, and temperature rise at the tread shoulder portion.

[0052] The temperature of the tread shoulder portion is as follows: Comparative Example Product 1
It is expressed as an index with 100, and the larger the number, the higher the heat generation.

The uneven wear rate w and stepped wear were measured after driving a truck on a general paved road with a 100% load and traveling 50,000 kilometers. The degree of temperature rise was measured using a rotating drum tester in the measurement chamber. Note that the load indicates the temperature when a regular load is applied and the tire is rotated for 60 minutes at a speed equivalent to 80 km/h.

[0054]

As described above, the heavy-duty radial tire of the present invention can prevent uneven wear in the shoulder portion.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of the present invention.

[Figure 2] Tread equator/base point height Y1 and ground contact half width S
It is a graph illustrating the relationship with L.

FIG. 3 is a plan view illustrating a pattern.

FIG. 4 is a graph illustrating the relationship between reference height ratio K1 and temperature.

FIG. 5 is a graph illustrating the relationship between the tread equator/base point height Y1 and the belt equator/base point height Y2.

FIG. 6 is a front view illustrating a ground contact shape.

FIG. 7 is a cross-sectional view illustrating stepped wear.

[Explanation of symbols]

2 Tread part 3 Sidewall section 4 Bead part 5 Bead core 6 Carcass 7 Belt layer

Claims (3)

[Claims] Claim 1: A carcass with a radial or semi-radial arrangement that extends from the tread part through the sidewall part and folds back at the bead core of the bead part, and a carcass arranged radially outside the carcass and inside the tread part and facing the tire equator. Te 5-7
It is equipped with a belt layer consisting of at least three belt plies overlapping inside and outside using a belt cord tilting in an angle range of 0 degrees, and in a standard state in which the rim is assembled to a regular rim and filled with a regular internal pressure, the tread surface equatorial point T
1, the ground contact half width SL, which is the distance in the tire axial direction from the tire axial outer end point of the tire contact patch that contacts the ground when a regular load is applied to the tire, to the ground contact outer point T0 located on the tread surface when no load is applied. The tread equator-to-base height is the distance in the tire radial direction between the base point T2 that separates 0.2 times (0.2SL) from the ground contact point T0 inward in the tire axial direction and the equator point T1. Y1 is a heavy-load radial tire that satisfies the following formula (2) for the ground contact width SL. Y1≦0.1060SL-4.32
■ 2. The heavy-duty radial tire according to claim 1, wherein the tread equator-to-base height Y1 satisfies the following formula (2). 0.0901SL-3.67≦Y1≦0.1060TW
-4.32 ■ 3. The second belt ply, which is the second belt ply from the carcass side, has a belt base point B2, where a radius line passing through the base point T2 intersects with the outer surface of the second belt ply, and a tire equatorial plane. The belt equator-base point height Y2, which is the radial distance between the belt equator point B1 that intersects with the outer surface of the second belt ply, is the sum (Y1+Y2) of the tread equator-base point height Y1, The heavy-duty radial tire according to claim 1 or 2, characterized in that it satisfies the following formula (2). Y1+Y2≦1.85 (0.1060SL-4.32)
■