JP4312141B2 - Heavy duty radial tire - Google Patents

Description

  The present invention relates to a heavy-duty radial tire that is particularly suitable as a drive wheel of a heavy-duty vehicle and that can suppress block chipping while ensuring necessary traction.

  Heavy-duty radial tires mounted on heavy vehicles such as trucks and buses require long-distance travel on normal roads and sometimes on snowy roads, especially on construction sites. Trucks that carry earth and sand and materials sometimes have to travel in a muddy area. At this time, traction is particularly important for tires attached to the drive shaft.

  Therefore, in this type of tire, as shown in Patent Document 1, in order to secure grip force in shallow snow roads and muddy areas, a block pattern of 5 to 6 rows is usually adopted and the block occupying the entire surface of the tread surface is used. Traction performance is improved by increasing the number of blocks in the land ratio, which is the ratio of the surface area, in the range of 55 to 75%.

No. 2003-118320

  However, this conversely causes a decrease in block rigidity, which causes a problem that block breakage is likely to occur. In the past, the block rigidity of each block, especially the circumferential rigidity, was regulated based on, for example, load capacity, etc., and the design was developed so that it would not become a predetermined value or less. It may also occur when it seems to be secured.

  As a result of research conducted by the inventor, this block chip greatly affects the shape of the contact surface, and in particular, the shorter the contact length, in other words, the greater the force acting on the block row having a smaller number of blocks in the contact surface. For this reason, it has been clarified that even when the block rigidity is high, chipping of the block is likely to occur.

  The present invention is based on the restriction of block row rigidity, which is the product of the number of blocks in the ground plane in each block row and the block stiffness, and more reliable blockage while ensuring necessary traction. It aims at providing the radial tire for heavy loads which can be suppressed.

In order to achieve the above object, according to the invention of claim 1 of the present application, a block is juxtaposed in the circumferential direction in the tread portion by providing a longitudinal main groove extending in the tire circumferential direction and a lateral groove extending in an intersecting direction. A heavy-duty radial tire in which a block pattern consisting of six to six block rows is formed, and a land ratio that is a ratio of the surface area of the block to the entire surface of the tread surface is 55 to 75%.
Each block is divided into two block pieces in the circumferential direction by a horizontal narrow groove extending in the width direction,
The number N of grounding blocks for each block row in the ground contact surface that is grounded in the normal load state in which the rim is assembled to the normal rim and filled with the normal internal pressure and the normal load M is loaded, and the circumferential direction of the block for each block row Value obtained by dividing each block row rigidity RG by the normal load M (unit kN), where the product of the stiffness (unit N / mm) G is the block row rigidity RG (= N × G) of each block row P (= RG / M) is in the range of 10.0 to 16.0 ,
In addition, the tread rubber forming the tread portion is characterized in that the breaking energy (T × E / 2) obtained by dividing the product of the tensile strength T and the elongation E upon cutting by 2 is 6000 to 8500 J.

According to a second aspect of the present invention, the longitudinal main groove is composed of an inner longitudinal main groove passing through both sides of the tire equator and an outer longitudinal main groove on both sides thereof. A block row in the middle between the main grooves, a block row between the inner vertical main groove and the outer vertical main groove, and an outer block row between the outer vertical main groove and the tread edge. While forming 5 block rows,
The block width Wm in the tire axial direction of the inner block row has a ratio Wm / Wi of 0.95 to 1.05 with respect to the block width Wi in the tire axial direction of the central block row, and the outer block row. The block width Wo in the tire axial direction is characterized in that the ratio Wo / Wi to the block width Wi is 1.00 to 1.65.

  In the invention of claim 3, the groove depth of the inner vertical main groove is Dgi, the groove depth of the outer vertical main groove is Dgo, the groove depth of the horizontal groove arranged in the central block row is Dyi, When the groove depth of the horizontal groove arranged in the inner block row is Dym and the groove depth of the horizontal groove arranged in the outer block row is Dyo, the following relationship is satisfied. Dyi / Dgi ≧ Dym / Dgi ≧ Dyo / Dgo

In the invention of claim 4, the vertical main groove comprises a central vertical main groove passing through the tire equator, a vertical main groove on both sides thereof, and a vertical main groove on both sides of the vertical main groove. The block pattern includes a block row between the central vertical main groove and the middle vertical main groove, a block row between the middle vertical main groove and the outer vertical main groove, and the outer While forming 6 block rows consisting of the outer block row between the vertical main groove and the tread edge,
The block width Wm in the tire axial direction of the inner block row has a ratio Wm / Wi of 0.95 to 1.15 with the block width Wi in the tire axial direction of the inner block row, and the outer block row. The block width Wo in the tire axial direction is characterized in that the ratio Wo / Wi to the block width Wi is 1.00 to 1.45.

In the invention of claim 5, the depth of the central vertical main groove is Dgi, the depth of the central vertical main groove is Dgm, the depth of the outer vertical main groove is Dgo, and the inner block row When the groove depth of the horizontal groove arranged in the inner block row is Dyi, the groove depth of the horizontal groove arranged in the inner block row is Dym, and the groove depth of the horizontal groove arranged in the outer block row is Dyo, the following: It is characterized by satisfying the relationship.
Dyi / Dgi ≧ Dym / Dgm ≧ Dyo / Dgo

  In the invention of claim 6, the block pattern is characterized in that the total number n of blocks in each block row is 40 to 56.

  The “regular rim” is a rim determined for each tire in the standard system including the standard on which the tire is based, for example, a standard rim for JATMA, “Design Rim” for TRA, or ETRTO means "Measuring Rim". The “regular internal pressure” is the air pressure specified by the tire for each tire. The maximum air pressure in the case of JATMA, the maximum value described in the table “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in the case of TRA, If it is ETRTO, it means "INFLATION PRESSURE". The “regular load” is the load specified by the standard for each tire. The maximum load capacity shown in the table “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” is the maximum load capacity for JATMA and TRA for TRA. In the case of ETRTO, it means a load obtained by multiplying "LOAD CAPACITY" by 0.88.

  Since the present invention is configured as described above, block missing can be more reliably suppressed while ensuring necessary traction.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing a case where a heavy-duty radial tire 1 (hereinafter referred to as a tire 1) of the present invention is a truck / bus tire.

  In FIG. 1, a tire 1 includes a carcass 26 that extends from a tread portion 22 through a sidewall portion 23 to a bead core 25 of a bead portion 24, and a belt layer 27 that is disposed inside the tread portion 22 and outside the carcass 26. With.

  The carcass 26 includes one or more, in this example, one carcass ply, in which steel carcass cords are arranged at an angle of 70 to 90 ° with respect to the tire circumferential direction. The carcass ply includes a series of ply folding portions 26b that are folded back and locked inward and outward around the bead core 25 on both sides of the ply main body portion 26a straddling the bead cores 25 and 25.

  The belt layer 27 is composed of 3 to 4 belt plies using a steel belt cord. In this example, the innermost first belt ply 27A in which the belt cord is inclined at a cord angle of, for example, about 60 ± 10 ° with respect to the tire circumferential direction, and the belt cords 10 to 40 with respect to the tire circumferential direction. The case where it consists of the 2nd-4th belt plies 27B-27D inclined by the angle is illustrated. The belt cords of the belt plies 27A and 27B are inclined in the same direction with respect to the tire circumferential direction, and the belt cords of the belt plies 27C and 27D are inclined in the opposite direction to the belt plies 27A and 27B, thereby forming a truss structure. The belt rigidity is improved.

  In the tire 1 of the first embodiment, as shown in FIGS. 2 and 3, the tread portion 22 is provided with a longitudinal main groove 3 extending in the tire circumferential direction and a transverse groove 4 in a direction intersecting with the longitudinal main groove 3. A block pattern composed of five block rows 6 in which the blocks B are juxtaposed in the circumferential direction is formed in the portion 22.

  Specifically, the longitudinal main groove 3 is composed of an inner longitudinal main groove 3i passing through both sides of the tire equator C and an outer longitudinal main groove 3o on both sides thereof. The block pattern includes a central block row 6i composed of blocks Bi divided between the inner vertical main grooves 3i and 3i by inner horizontal grooves 4i, and the inner vertical main grooves 3i and the outer vertical main grooves 3o. An inner block row 6m made up of blocks Bm divided by an inner horizontal groove 4m, and an outer block row made up of blocks Bo divided by the outer horizontal grooves 4o between the outer longitudinal main groove 3o and the tread edge Te. 6o.

  Here, the longitudinal main groove 3 has a groove width Wg (referred to as the width in the shortest direction on the tread surface, hereinafter the same) continuous in the tire circumferential direction of 3 mm or more, preferably 5 mm or more, as enlarged in FIG. The groove depth Dg (shown in FIG. 4) is preferably 9 mm or more, and more preferably 15 mm or more from the viewpoint of traction. In this example, the case where each vertical main groove 3 is a straight groove is illustrated, but a part or all of the vertical main grooves 3 may be zigzag grooves. The groove depth refers to the depth in the normal direction with respect to the virtual tread surface at the groove width center.

  The horizontal groove 4 has a groove width Wy of 3 mm or more, more preferably 5 mm or more, like the vertical main groove 3. In this example, as the lateral groove 4, the inner ends of the straight portions y1 and y1 on both sides extending from both ends of the lateral groove to the vicinity of the center of the lateral groove at an angle α of 30 ° or less with respect to the tire axial direction are maintained at substantially the same width. A substantially Z-shaped one joined by a bent portion y2 that is bent in a shape is illustrated. This enhances traction and lateral slip resistance. The angle α between the lateral groove 4i and the lateral groove 4m is inclined in different directions, thereby balancing the lateral force generated in the tire axial direction.

  Each block Bi to Bo is formed with a transverse narrow groove 10 extending in the width direction, and is divided into two block pieces 11a and 11b in the circumferential direction, thereby reducing the initial circumferential rigidity of each block Bi to Bo. And traction performance is improved. The lateral narrow groove 10 has a groove width Ws of less than 3 mm and is narrower than the lateral groove 4, and siping with the groove width Ws substantially zero is also included in the lateral narrow groove 10. Further, the groove depth of the lateral narrow groove 10 is, for example, about 2 to 4 mm, which is shallower than any of the longitudinal main groove 3 and the lateral groove 4, and preferably the groove depth Dy of the lateral groove 4 in the same block row. It is set to 35% or less, and further 10% or more. Although not shown, siping can be arranged on the bottom of the lateral narrow groove 10 to reduce the rigidity.

  At this time, in order to achieve a good balance between traction performance and steering stability on a good road, the total number n of blocks in each block row 6i to 6o is in the range of 40 to 56, and blocks occupying the entire surface of the tread surface. The land ratio, which is the ratio of the surface area of B, is in the range of 55 to 75%. If the total number n of blocks is less than 40, the traction performance cannot be sufficiently exhibited. Conversely, if the number exceeds 56, the block rigidity becomes insufficient and the steering stability is lowered. On the other hand, if the land ratio is less than 55%, the actual ground contact area is too small, resulting in a decrease in performance on ice and steering stability. Conversely, if the land ratio exceeds 75%, the traction performance is degraded.

  And in this embodiment, in order to suppress the block missing in each block row 6i-6o, it regulates as follows.

Specifically, first, the tread surface is grounded to a flat surface in a normal load load state in which the tire 1 is assembled on a normal rim and filled with a normal internal pressure and a normal load M is applied. On the ground contact surface 20 (shown in FIG. 5) at this time, the number of ground blocks Ni, Nm, No to which the blocks Bi, Bm, Bo are grounded is obtained for each block row. In the case of a block pattern tire, in order to reduce pattern noise, for example, the circumferential length of the block in the block row and the interval (width of the lateral groove) may be changed in the block row. In such a case, in each block row, the total number of blocks in the block row is n, the tire circumferential length of the circumferential line passing through the width center of the block row is TL, and the contact length at the width center of the block row on the ground contact surface 20 When the thickness is FL, the number N of ground blocks in each block row is approximated by the following expression.
N = n × (FL / TL)

  Next, the circumferential rigidity (unit N / mm) Gi, Gm, Go of each block Bi, Bm, Bo is obtained. As shown schematically in FIG. 6, the circumferential rigidity G is obtained by applying a circumferential force Kx to the block surface BS, and the movement amount X when the block surface BS moves in the circumferential direction and the circumferential force Kx. It can be determined as the ratio Kx / X. At this time, for example, a circumferential force Kx is applied via a metal plate or the like fixed to the block surface BS with an adhesive or the like so that a vertical load does not act on the block B. The circumferential rigidity G may be obtained by computer analysis based on information such as the block shape size, the siping shape size, and the Young's modulus of the rubber of the block. When the circumferential rigidity G of the block B changes in the block row, the average of the circumferential stiffnesses of all the blocks B in the block row is used as the circumferential rigidity G of the block B in the block row. .

Then, the product of the number of ground blocks Ni, Nm, No and the circumferential rigidity Gi, Gm, Go is the block row rigidity RGi (= Ni × Gi) of the central block row 6i, and the block row 6m in the middle, respectively. Block row stiffness RGm (= Nm × Gm) and block row stiffness RGo (= No × Go) of the outer block row 6o, and the block row stiffnesses RGi, RGm, RGo are divided by the normal load M (unit kN). The value Pi (= RGi / M), the value Pm (= RGm / M), and Po (= RGo / M) are restricted to the range of 10.0 to 16.0, respectively.

  This is because block chipping is greatly affected by the ground contact length FL of the ground contact surface 20, and the shorter the ground contact length FL, the greater the force acting on each block, resulting in greater deformation and damage such as block chipping. This is because it occurs. Therefore, by using the block row stiffness RG, which is the product of the number N of grounding blocks and the circumferential stiffness G, as a parameter, it is possible to more accurately grasp the occurrence of block chipping.

Here, if the value Pi (= RGi / M), value Pm (= RGm / M), Po (= RGo / M) is less than 10.0 , the block row rigidity RGi, RGm, RGo becomes insufficient, and the block Block defects are likely to occur in Bi, Bm, and Bo. On the other hand, when the values Pi, Pm, Po exceed 16.0, the block row rigidity RGi, RGm, RGo is excessive, and therefore the increase in the total number of blocks n, the increase in the groove depth Dy of the lateral groove 4, etc. This means that there is still enough room for improvement, and it is possible to further improve the performance on snow and ice, in other words, the current performance on snow and ice is insufficient. Therefore, the value Pi, Pm, Po is the upper limit value of that is to 15.0 or less favorable preferable.

  Further, such values Pi, Pm, and Po can be obtained by adjusting the block width W of the block B in the tire axial direction, the groove depth Dg of the longitudinal main groove 3, the groove depth Dy of the lateral groove 4, and the like. can do. However, at this time, in order to achieve both of partial wear, stone biting, drainage, and the like and the block chipping, the block width Wi of the central block row 6i and the block of the middle block row 6m as shown in FIG. The ratio Wm / Wi to the width Wm is 0.95 to 1.05, and the ratio Wo / Wi between the block width Wi and the block width Wo of the outer block row 6o is 1.00 to 1.65. Is preferred. When the block width W is not constant, an average value of the maximum value and the minimum value of the block width W is adopted.

  When the ratio Wm / Wi is less than 0.95, uneven wear (particularly punching wear) occurs because the rigidity of the middle block row 6m is lower than the rigidity of the central block row 6i. Conversely, if the ratio Wm / Wi exceeds 1.05, uneven wear (particularly center wear) occurs because the rigidity of the central block row 6i is lower than the rigidity of the middle block row 6m.

  On the other hand, if the ratio Wo / Wi is less than 1.00, uneven wear (especially shoulder wear / shoulder wear) occurs due to the lower rigidity of the outer block row 6o, and conversely the ratio Wo / Wi. However, if it exceeds 1.65, uneven wear (particularly center wear and punching wear) occurs because the rigidity of the outer block row 6o is high.

As shown in FIG. 4, the horizontal groove 4 has a groove depth Dy set equal to or smaller than the groove depth Dg of the longitudinal main groove 3 intersecting the horizontal groove 4, and in this example, in particular, the horizontal groove 4 The case where the groove depth ratio Dy / Dg is set to be equal to or greater than the groove depth ratio Dy / Dg of the lateral grooves 4 adjacent on the outer side in the tire axial direction is illustrated. In this ratio Dy / Dg, when the groove depth Dg differs between the left and right vertical main grooves 3 intersecting the lateral grooves 4, the groove depth Dg of the vertical main grooves 3 intersecting on the inner side in the tire axial direction is adopted. That is, the groove depth of the inner vertical main groove 3i is Dgi, the groove depth of the outer vertical main groove 3o is Dgo, the groove depth of the inner horizontal groove 4i is Dyi, and the groove depth of the inner horizontal groove 4m is Dym. When the groove depth of the outer lateral groove 4o is Dyo, the following equation (1) is satisfied, and more preferably, the following equation (1A) is satisfied.
Dyi / Dgi ≧ Dym / Dgi ≧ Dyo / Dgo ----- (1)
Dyi / Dgi> Dym / Dgi> Dyo / Dgo ----- (1A)

  This is because in shallow snow roads and muddy areas, the tire equator side sinks deeper into the road, so the degree of contribution to traction is higher in the lateral groove 4 on the tire equator side. Therefore, the groove depth Dy of the lateral groove 4 is set to Dyi ≧ Dym ≧ Dyo, preferably Dyi> Dym> Dyo, and satisfying the expression (1), preferably the expression (1A) in the ratio Dy / Dg, Traction can be improved.

  In particular, from the viewpoint of traction, as shown in FIG. 4, the gradually increasing portion 12 in which the groove depths Dym and Dyo gradually increase toward the inner side in the tire axial direction in the inner and outer lateral grooves 4 m and 4 o It is preferable to form it in a region of 50% or more, preferably 70% or more. In this example, the inner lateral groove 4m is formed only by the gradually increasing portion 12. Further, the outer lateral groove 4o has a gradually increasing portion 12 having a minimum groove depth in the vicinity of the tread edge Te, and abruptly from the minimum groove depth position to the outer side in the tire axial direction of the minimum groove depth position. The groove depth is increased, and a portion 13 opening at the buttress surface is extended. Thus, when the groove depth Dy changes in the groove, the average value of the maximum value and the minimum value is defined as the groove depth Dyi, Dym, Dyo.

  When the tire 1 travels on a good road, on the tread edge Te side, due to the difference in the tire radius, the tire 1 is more slippery with the road surface than the tire equator side, and tends to be unevenly worn. Therefore, when satisfying the formula (1) or the formula (1A), the lateral groove 4 disposed on the outer side in the tire axial direction is set to have the groove width Wy of the lateral groove 4 in order to suppress uneven wear such as shoulder wear. It is preferable to form it as wide as possible.

Also in order to prevent the block chipping, a tread rubber constituting the tread portion 22, the breaking energy is divided by the 2 the product (T × E / 2) of the rubber tensile strength T and the elongation at break E is 6000J It is made of rubber that does not break easily. However, rubber with increased rupture energy tends to be inferior in rubber elasticity and trauma resistance, so the upper limit of rupture energy is 8500 J or less from the viewpoint of handling stability and trauma resistance . The above-mentioned “rubber tensile strength T” and “elongation at break E” are values measured in accordance with “Tensile test method for vulcanized rubber” of JIS K6251.

  Next, FIGS. 7 and 8 illustrate the tire of the second embodiment in which the block pattern is composed of six block rows 6. In the present embodiment, the longitudinal main groove 3 includes a central longitudinal main groove 3i passing through the tire equator C, a longitudinal main groove 3m in both sides thereof, and an outer longitudinal main groove 3o disposed on both sides thereof. Consists of. As a result, the tread portion 22 has an inner block row 6i composed of blocks Bi divided by the inner transverse groove 4i between the central longitudinal main groove 3i and the inner longitudinal main groove 3m, and the inner longitudinal main groove 3m. An inner block row 6m composed of blocks Bm divided between the outer vertical main groove 3o and the outer vertical main groove 3o by an inner horizontal groove 4m, and an outer horizontal groove 4o between the outer vertical main groove 3o and the tread edge Te. An outer block row 6o composed of the blocks Bo is formed.

  Each of the blocks Bi to Bo is divided into two block pieces 11a and 11b in the circumferential direction from the transverse narrow groove 10 extending in the width direction, and is equally divided in this example. At this time, the land ratio of the block pattern is 55 to 75%, and the total number n of blocks in each block row is in the range of 40 to 56.

Then, in order to suppress block missing in each of the block rows 6i to 6o, the block row rigidity RGi (= Ni × Gi) of the inner block row 6i and the block row rigidity of the inner block row 6m, as in the first embodiment. RGm (= Nm × Gm), a value Pi (= RGi / M) obtained by dividing the block row rigidity RGo (= No × Go) of the outer block row 6o by the normal load M, a value Pm (= RGm / M), Po (= RGo / M) is regulated to the range of 10.0 to 16.0, respectively.

  In the second embodiment, the block width Wi of the inner block row 6i and the blocks of the inner block row 6m are used in order to achieve both the partial wear, stone biting, drainage and the like and the block chipping. The ratio Wm / Wi to the width Wm is 0.95 to 1.15, and the ratio Wo / Wi between the block width Wi and the block width Wo of the outer block row 6o is 1.00 to 1.45. This is preferable for the same reason as in the first embodiment. In addition, when the block width W changes, the average value is taken.

Further, as shown in FIG. 8, the depth of the central vertical main groove 3i is Dgi, the depth of the inner vertical main groove 3m is Dgm, the depth of the outer vertical main groove 3o is Dgo, and the inner horizontal groove When the groove depth of 4i is Dyi, the groove depth of the inner lateral groove 4m is Dym, and the groove depth of the outer lateral groove 4o is Dyo, the following expression (2) and further the following expression (2A) are satisfied. Is preferred.
Dyi / Dgi ≧ Dym / Dgm ≧ Dyo / Dgo ----- (2)
Dyi / Dgi> Dym / Dgm> Dyo / Dgo ----- (2A)

  Thereby, like the case of the said 1st Embodiment, traction property can be improved. At this time, from the viewpoint of traction, it is preferable to provide the gradually increasing portion 12 in each of the lateral grooves 4i, 4m, 4o, and from the viewpoint of suppressing uneven wear, the groove width Wy of the lateral grooves 4 is arranged on the outer side in the tire axial direction. It is preferable that the lateral groove 4 is formed wider.

  As mentioned above, although especially preferable embodiment of this invention was explained in full detail, this invention is not limited to embodiment of illustration, It can deform | transform and implement in a various aspect.

  A heavy-duty radial tire with a tire size of 315 / 80R22.5 according to the first embodiment, which is based on the tread pattern shown in FIG. 2 and has the specifications shown in Table 1, and the tread pattern shown in FIG. While preparing a prototype of a heavy-duty radial tire having a tire size of 315 / 80R22.5 according to the second embodiment having the specifications shown, the resistance to block chipping of each sample tire was evaluated.

(1) Block chip resistance:
A sample tire is left in advance at an ambient temperature of 80 ° C. for 8 days to deteriorate the tread rubber, and then mounted on the front wheel of the truck under the rim (9.00 × 22.5) and internal pressure (825 kPa). . Then, using a general brake tester testing machine used at a car inspection site or the like, the truck is placed in a locked state on the front wheel on the drum of the testing machine having an uneven surface, and the drum is rotated at a speed of 5 km / h. Rotate at speed for 20 seconds. And the presence or absence of the block defect was determined visually.

It is sectional drawing which shows one Example of the radial tire for heavy loads of this invention. It is an expanded view which shows the tread pattern of 1st Embodiment. It is an enlarged view of a part of the tread pattern. It is sectional drawing which shows the groove depth of a horizontal groove with the groove depth of a vertical main groove. It is a diagram which shows a ground plane. It is a diagram explaining the circumferential direction rigidity of a block. It is an expanded view which shows the tread pattern of 2nd Embodiment. It is sectional drawing which shows the groove depth of a horizontal groove with the groove depth of a vertical main groove.

Explanation of symbols

3, 3i, 3m, 3o Vertical main groove 4, 4i, 4m, 4o Horizontal groove 6, 6i, 6m, 6o Block row 10 Horizontal narrow groove 11a, 11b Block piece 20 Grounding surface 22 Tread portion B, Bi, Bm, Bo block

Claims (6)

By providing a longitudinal main groove extending in the tire circumferential direction and a transverse groove in a direction intersecting with the longitudinal main groove, a block pattern consisting of 5 to 6 block rows in which the blocks are juxtaposed in the circumferential direction is formed on the tread portion, and the tread A radial tire for heavy loads having a land ratio of 55 to 75%, which is a ratio of the surface area of the block to the entire surface,
Each block is divided into two block pieces in the circumferential direction by a horizontal narrow groove extending in the width direction,
The number N of grounding blocks for each block row in the ground contact surface that is grounded in the normal load state in which the rim is assembled to the normal rim and filled with the normal internal pressure and the normal load M is loaded, and the circumferential direction of the block for each block row Value obtained by dividing each block row rigidity RG by the normal load M (unit kN), where the product of the stiffness (unit N / mm) G is the block row rigidity RG (= N × G) of each block row P (= RG / M) is in the range of 10.0 to 16.0 ,
Moreover, the tread rubber forming the tread portion has a breaking energy (T × E / 2) obtained by dividing the product of the tensile strength T and the elongation at break E by 2 (T × E / 2) of 6000 to 8500J. tire. The longitudinal main groove is composed of an inner longitudinal main groove passing through both sides of the tire equator and an outer longitudinal main groove on both sides thereof, so that the block pattern is a central block row between the inner longitudinal main grooves. And forming a block row of 5 blocks comprising a block row between the inner vertical main groove and the outer vertical main groove and an outer block row between the outer vertical main groove and the tread edge. ,
The block width Wm in the tire axial direction of the inner block row has a ratio Wm / Wi of 0.95 to 1.05 with respect to the block width Wi in the tire axial direction of the central block row, and the outer block row. The radial tire for heavy loads according to claim 1, wherein the block width Wo in the tire axial direction has a ratio Wo / Wi to the block width Wi of 1.00 to 1.65. The groove depth of the inner vertical main groove is Dgi, the groove depth of the outer vertical main groove is Dgo, the groove depth of the horizontal groove arranged in the central block row is Dyi, and the inner block row is arranged in the inner block row. The radial tire for heavy loads according to claim 2, wherein the following relationship is satisfied, where Dym is the groove depth of the lateral groove and Dyo is the groove depth of the lateral groove arranged in the outer block row.
Dyi / Dgi ≧ Dym / Dgi ≧ Dyo / Dgo The vertical main groove is composed of a central vertical main groove passing through the tire equator, a vertical main groove in both sides thereof, and an outer vertical main groove on both sides thereof. An inner block row between the main groove and the inner vertical main groove, an inner block row between the inner vertical main groove and the outer vertical main groove, and the outer vertical main groove and the tread edge. While forming 6 block rows consisting of outer block rows in between,
The block width Wm in the tire axial direction of the inner block row has a ratio Wm / Wi of 0.95 to 1.15 with the block width Wi in the tire axial direction of the inner block row, and the outer block row. The radial tire for heavy loads according to claim 1, wherein the block width Wo in the tire axial direction has a ratio Wo / Wi to the block width Wi of 1.00 to 1.45. The groove depth of the central vertical main groove is Dgi, the groove depth of the inner vertical main groove is Dgm, the groove depth of the outer vertical main groove is Dgo, and the groove depth of the horizontal groove arranged in the inner block row The following relationship is satisfied, where Dyi is the depth, Dym is the groove depth of the horizontal groove arranged in the inner block row, and Dyo is the groove depth of the horizontal groove arranged in the outer block row. The radial tire for heavy loads according to claim 4.
Dyi / Dgi ≧ Dym / Dgm ≧ Dyo / Dgo   The radial tire for heavy loads according to any one of claims 1 to 5, wherein the block pattern has a total number n of blocks of 40 to 56 in each block row.

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