JP2012111438A - Tire for heavy load - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve partial wear resistance performance and wet grip performance.SOLUTION: A plurality of horizontal thin grooves are provided to an inner land section in a circumferential direction disposed on both sides of a tire equator C. The horizontal thin groove forms an S-like shape including an outer circular arc groove section at the tread end side of a curvature radius R1 having a circular arc center i1 more on one side in a tire circumferential direction from the horizontal thin groove, and an inner circular arc groove section at the tire equator side of a curvature radius R2 including a circular arc center i2 at the other side in the tire circumferential direction. The curvature radius R2 is 10 to 40 mm, and the curvature radius R1 is not larger than the curvature radius R2, and a difference (R2-R1) between the curvature radius R1 and the curvature R2 is 5 mm or less. Moreover, the center angle α of the outer circular arc groove section, and the center angle β of the inner circular arc groove section is 45 to 90 degrees.

Description

  The present invention relates to a heavy duty tire with improved uneven wear resistance and wet grip performance.

  As a heavy-duty tire used for trucks, buses, etc. with improved uneven wear resistance and wet grip performance, the following Patent Document 1 has been proposed.

  In the proposed tire, as shown in FIG. 8, the circumferential land portions di and di in the tread portion b are arranged on both sides of the tire equator C by a plurality of longitudinal main grooves a extending in the tire circumferential direction. Are divided into a plurality of circumferential land portions d, and the inner circumferential land portion di is formed with a narrow groove elongating the circumferential land portion di or a transverse narrow groove e made of siping. The lateral narrow groove e is formed from an inner lateral groove e1 inside the tire axial direction, an outer lateral groove e2 outside the tire axial direction, and a central lateral groove e3 connecting between the inner lateral groove e1 and the tire axial direction line. The inclination angle α of the inner lateral groove e1, the inclination angle β of the outer lateral groove e2, and the inclination angle γ of the central lateral groove e3 are in the range of 0 ° ≦ β <α <60 ° ≦ γ.

  However, in the proposed tire, the lateral narrow groove e is formed in a bent line shape composed of three linear lateral groove portions e1, e2, and e3, so that the inclination angles α, β, and γ are optimized. No further improvement is desired, for example, the water flow during drainage is not smooth and the wet grip performance is insufficient.

JP 2005-289122 A

  Therefore, in the present invention, the lateral narrow groove has a substantially S shape having an arc groove portion outside the curvature radius R1 and an arc groove portion inside the curvature radius R2, and the curvature radii R1, R2 and the inside and outside arc groove portions. An object of the present invention is to provide a heavy-duty tire with improved uneven wear resistance and wet grip performance based on the regulation of the center angle.

In order to solve the above-mentioned problem, the invention of claim 1 of the present application provides a plurality of longitudinal main grooves extending in the tire circumferential direction in the tread portion so that the tread portion is arranged on both sides of the tire equator. A plurality of circumferential land portions including a plurality of circumferential land portions, and a plurality of pieces crossing between a land portion side edge on a tread end side of the inner circumferential land portion and a land portion side edge on a tire equator side. A heavy duty tire provided with a lateral narrow groove,
The lateral narrow groove has an arc center i1 on one side in the tire circumferential direction than the lateral narrow groove, and an arc groove portion outside the radius of curvature R1 extending in an arc shape from the land portion side edge on the tread end side; A substantially S-shape having an arc center i2 on the other side in the tire circumferential direction from the lateral narrow groove and an arc groove portion having a radius of curvature R2 extending in an arc shape from a land side edge on the tire equator side. With eggplant,
The curvature radius R2 is 10 to 40 mm, the curvature radius R1 is not more than the curvature radius R2, and the difference (R2−R1) from the curvature radius R2 is not more than 5 mm.
Moreover, the center angle α around the arc center i1 between both ends of the outer arc groove is 45 to 90 degrees, and the center angle β around the arc center i2 between both ends of the inner arc groove is 45 to 90 degrees. It is characterized by being.

  According to a second aspect of the present invention, the lateral narrow groove has a linear joint groove portion that contacts and joins the inner arc groove portion and the outer arc groove portion, and a tire axial length Lm of the joint groove portion. Is characterized by being 40% or less of the tire axial direction length L0 of the lateral narrow groove.

  According to a third aspect of the present invention, the lateral narrow groove includes a lower groove portion extending from the groove bottom and an upper groove portion extending from the lower groove portion to the tread surface, and the groove width Wa of the lower groove portion is set to 0.3 to 1. The groove width Wb of the upper groove portion is set to be larger than the groove width Wa and 50% or less of the groove width W0 of the longitudinal main groove.

  According to a fourth aspect of the present invention, the horizontal narrow groove has a groove depth h in the range of 10 to 80% of the groove depth H0 of the vertical main groove, and the groove depth hb of the upper groove portion is the groove. It is characterized by being 10 to 50% of the depth h.

  According to a fifth aspect of the present invention, the inner circumferential land portion extends in a zigzag shape in the tire circumferential direction, and the outer end on the tread end side of the lateral narrow groove is the tread end of the inner circumferential land portion. The distance K is arranged in the tire circumferential direction with a distance K from the protruding corner end on the side, and the distance K is 25 to 75 of the tire circumferential direction distance Lj between the protruding corner end and the entering corner end on the tread end side. %.

  In the present invention, as described above, a plurality of lateral narrow grooves are provided in the circumferential land portions disposed on both sides of the tire equator. The lateral narrow groove has an arc groove portion outside the radius of curvature R1 extending in an arc shape from the land portion side edge on the tread end side, and an arc groove portion within the curvature radius R2 extending in an arc shape from the land portion side edge on the tire equator side. Are formed in a substantially S-shape.

  Thus, since the said horizontal fine groove makes a smooth substantially S-shaped curve, the flow of the water which passes along a horizontal fine groove becomes smooth at the time of drainage, and can improve wet grip performance. On the other hand, since the lateral narrow groove is substantially S-shaped, the groove wall surfaces of the lateral narrow groove are mutually restrained, and the tire axial rigidity of the inner circumferential land portion is suppressed in order to suppress misalignment in the tire axial direction. Highly secure. Further, since the lateral narrow groove is a narrow groove, the positional deviation in the tire circumferential direction can be restricted, and the tire circumferential rigidity of the inner circumferential land portion is ensured to be high. Therefore, the amount of slip with the road surface can be suppressed, and uneven wear resistance can be improved.

  In particular, the above-described effects can be exhibited by setting 10 mm ≦ R2 ≦ 40 mm, R1 ≦ R2, and 0 ≦ (R2−R1) ≦ 5 mm. That is, when the difference in radius of curvature (R2-R1) exceeds 5 mm, the difference in rigidity between the rigidity on the tread end side and the rigidity on the tire equator side in the inner circumferential land portion becomes large. Due to this, uneven wear occurs.

  Further, when the radius of curvature R2 is out of the range of 10 mm ≦ R2 ≦ 40 mm, the restraining force between the groove wall surfaces of the lateral narrow grooves is reduced, so that the rigidity of the inner circumferential land portion is not sufficiently ensured. Uneven wear tends to occur. Also, since the contact pressure on the tire equator side is higher than that on the tread end side, when R1> R2, it is easier for water to enter from the tire equator side into the lateral narrow groove than R1 ≦ R2. And the ease of water removal to the tread end side is deteriorated, and the wet grip performance is lowered.

  When the center angle α of the outer arc groove and the center angle β of the inner arc groove are less than 45 degrees, the restraining force between the groove wall surfaces of the lateral narrow grooves is reduced, and the rigidity of the inner circumferential land portion is reduced. Not enough is ensured, and uneven wear tends to occur. On the other hand, when the central angles α and β exceed 90 degrees, the amount of meandering of the S-shaped transverse grooves increases, so that the water passing through the transverse grooves does not flow smoothly and the wet grip performance is deteriorated.

It is an expanded view which shows an example of the tread pattern of the tire for heavy loads of this invention. It is a top view which expands and illustrates an inner circumferential direction land part. It is a top view which expands and illustrates a horizontal fine groove further. (A), (B) is sectional drawing orthogonal to the length direction of a horizontal fine groove and a vertical main groove. It is a perspective view which expands and shows a notch part. (A)-(E) are the conceptual diagrams which show the horizontal fine groove of the comparative example of Table 1. FIG. (A)-(D) are the conceptual diagrams which show the horizontal narrow groove of the comparative example of Table 1. FIG. It is a top view which illustrates the tread pattern of the conventional tire.

Hereinafter, embodiments of the present invention will be described in detail.
In FIG. 1, the heavy load tire 1 of the present embodiment includes a plurality of longitudinal main grooves 3 extending in the tire circumferential direction in the tread portion 2, whereby the tread portions 2 are arranged on both sides of the tire equator C. Are divided into a plurality of circumferential land portions 4 including a circumferential land portion 4i.

  In this example, three vertical main grooves 3 are formed, which are a central vertical main groove 3i extending on the tire equator C and a pair of outer vertical main grooves 3o arranged on both outer sides thereof. The portion 2 includes the inner circumferential land portion 4i between the central vertical main groove 3i and the outer vertical main groove 3o, and the outer circumferential land between the outer vertical main groove 3o and the tread end Te. It is divided into part 4o.

  Each of the longitudinal main grooves 3i, 3o is a zigzag groove extending in a zigzag shape in the tire circumferential direction in this example, thereby enhancing traction while ensuring high-speed running performance. The longitudinal main grooves 3i, 3o are formed so that the circumferential pitch of the zigzag is the same and in phase with each other, so that the inner circumferential land portion 4i has a substantially constant width and has a zigzag shape. It extends continuously in the tire circumferential direction. The groove width W0 and the groove depth H0 (shown in FIG. 4B) of the longitudinal main grooves 3i and 3o are approximately the same as the groove width and depth of the longitudinal main groove of the conventional heavy duty tire. For example, a range of 8 to 15 mm for the groove width W0 and a range of 16 to 26 mm for the groove depth H0 can be preferably used. The groove width W0 means a groove width on the tread surface 2S measured in a direction perpendicular to the groove length direction, and the groove depth H0 is a depth from the tread surface 2S to the groove bottom (deepest part). Means.

  Next, the inner circumferential land portion 4i includes a plurality of lateral surfaces that cross between the tread end side land portion side edge Et and the tire equator side land portion side edge Ec of the inner circumferential land portion 4i. A narrow groove 5 is provided, thereby dividing the inner circumferential land portion 4i into a plurality of block-like portions 6 arranged in the tire circumferential direction.

  As shown in FIGS. 2 and 3, the lateral narrow groove 5 has a groove width center line having an arc center i1 on one side in the tire circumferential direction from the lateral narrow groove 5 and the tread end Te side. An arcuate groove portion 9t outside the radius of curvature R1 extending in an arc shape from the land portion side edge Et, and an arc center i2 on the other side in the tire circumferential direction from the lateral narrow groove 5, and the land on the tire equator C side. It is formed in a substantially S shape having an arc groove portion 9c having a radius of curvature R2 extending in an arc shape from the part side edge Ec.

  At this time, the radius of curvature R2 is 10 to 40 mm, and the radius of curvature R1 is not more than the radius of curvature R2 and the difference (R2−R1) from the radius of curvature R2 is not more than 5 mm. The lateral narrow groove 5 has a center angle α around the arc center i1 between both ends of the outer arc groove portion 9t in the range of 45 to 90 degrees, and the arc center between both ends of the inner arc groove portion 9c. The central angle β around i2 is in the range of 45 to 90 degrees.

  As the horizontal narrow groove 5, in this example, a case is shown in which the inner arc groove portion 9c and the outer arc groove portion 9t are in contact with each other and have a linear joint groove portion 9m that connects between them. The length Lm of the joint groove portion 9m in the tire axial direction is preferably 40% or less of the tire axial direction length L0 of the lateral narrow groove 5.

  In the circumferential land portion 4i having the above-described configuration, since the horizontal narrow groove 5 forms a smooth substantially S-shaped curve, the flow of water through the horizontal narrow groove 5 can be smoothed during drainage. And wet grip performance can be improved. On the other hand, since the said horizontal narrow groove 5 makes a substantially S shape, the groove wall surfaces of this horizontal narrow groove 5 mutually mesh and restrain, and it can suppress the position shift of a tire axial direction. That is, high rigidity in the tire axial direction of the inner circumferential land portion 4i can be ensured. Further, since the lateral narrow groove 5 is a narrow groove, the positional deviation in the tire circumferential direction is limited, and the tire circumferential rigidity of the inner circumferential land portion 4i is ensured high. As a result, the rigidity of the inner circumferential land portion 4i is enhanced as a whole, and the amount of slippage with the road surface can be suppressed to improve uneven wear resistance.

  Further, when the horizontal narrow groove 5 has the joint groove portion 9m, the inner and outer arc groove portions 9c and 9t can be connected more smoothly, and the water flow can be further smoothed to improve the wet grip performance.

  When the difference in radius of curvature (R2-R1) exceeds 5 mm, there is a large difference in rigidity between the region on the tread end Te side and the region on the tire equator C side in the inner circumferential land portion 4i. Thus, uneven wear due to this rigidity difference tends to occur. When the radius of curvature R2 exceeds 40 mm, the S-shaped curve of the lateral narrow groove 5 becomes gentle, so that the restraining force between the groove wall surfaces becomes weak, and the tire shaft of the inner circumferential land portion 4i becomes weaker. The directional rigidity is reduced. On the other hand, when the radius of curvature R2 is less than 10 mm, the ratio of the inner and outer arc groove portions 9c and 9t becomes too small, and similarly, the tire axial rigidity of the inner circumferential land portion 4i is lowered. In either case, the uneven wear resistance cannot be sufficiently improved.

  Further, since the contact pressure on the tire equator C side is higher than that on the tread end Te side, when R1> R2, the tire equator C side enters the lateral narrow groove 5 as compared with the case of R1 ≦ R2. The ease of entering water becomes worse, and the ease of water removal toward the tread end Te becomes worse. Therefore, wet grip performance is reduced. Further, when the center angle α of the outer arc groove portion 9t and the center angle β of the inner arc groove portion 9c are less than 45 degrees, the S-shaped curve of the horizontal narrow groove 5 becomes gentle. The force becomes weak, leading to a decrease in the rigidity in the tire axial direction of the inner circumferential land portion 4i, and uneven wear tends to occur. On the other hand, when the center angles α and β exceed 90 degrees, the amount of S-shaped meandering of the lateral narrow groove 5 increases, so that water does not flow smoothly and the wet grip performance is deteriorated.

  If the tire axial direction length Lm of the joint groove portion 9m exceeds 40% of the tire axial direction length L0 of the lateral narrow groove 5, the ratio of the inner and outer circular groove portions 9c, 9t becomes too small, and the inner circumferential portion This causes a decrease in the rigidity of the directional land portion 4i, which is disadvantageous in improving uneven wear resistance.

  Here, as shown in FIG. 4A, the lateral narrow groove 5 includes a narrow groove (including siping) having a groove width W of 0.5 mm or more and 50% or less of the groove width W0 of the longitudinal main groove 3. ). When the groove width W is less than 0.5 mm, the drainage is insufficient. Conversely, when the groove width W exceeds 50% of the groove width W0, the restraint force between the groove wall surfaces is not exhibited, and the block-shaped portion is heeled. Uneven wear such as & toe wear occurs. Further, the groove depth h of the horizontal narrow groove 5 is preferably in the range of 10 to 80% of the groove depth H0 of the vertical main groove 3. If the groove depth h is less than 10% of the groove depth H0 of the vertical main groove 3, the effect of the horizontal narrow groove 5 is reduced. Conversely, if it exceeds 80%, the rigidity of the end of the horizontal narrow groove 5 is small. This tends to cause damage such as rubber chipping.

  In particular, in this example, a preferable case is shown in which the lateral narrow groove 5 has a stepped groove shape including a lower groove portion 5a extending from the groove bottom and an upper groove portion 5b extending from the lower groove portion 5a to the tread surface 2S. The groove width Wa of the lower groove portion 5a is in the range of 0.3 to 1.5 mm, and the groove width Wb of the upper groove portion 5b is larger than the groove width Wa and 50% or less of the groove width W0 of the vertical main groove 3. Is formed. The groove depth h of the horizontal narrow groove 5 is in the range of 10 to 80% of the groove depth H0 of the longitudinal main groove 3, and the groove depth hb of the upper groove portion 5b is set to the groove depth h. 10 to 50%. In this case, since the narrow lower groove portion 5a can exert a high restraining force between the groove wall surfaces, the rigidity of the inner circumferential land portion 4i can be increased and the uneven wear resistance can be improved. On the other hand, with the wide upper groove portion 5b, the groove volume can be secured and the drainage can be improved. If the groove depth hb is less than 10% of the groove depth h, the drainage is disadvantageous. Conversely, if it exceeds 50% of the groove depth h, the uneven wear resistance is disadvantageous. If the groove width Wb of the upper groove portion 5b exceeds 50% of the groove width W0, the rigidity is reduced, which causes disadvantages in uneven wear resistance and block chipping. If the groove width Wa exceeds 1.5 mm, the effect of improving the uneven wear resistance by the lower groove portion 5a cannot be obtained, and if it is less than 0.3 mm, the drainage is disadvantageous.

  Next, as shown in FIG. 2, in the lateral narrow groove 5, the inner end 5e2 on the tire equator C side is located at the exit corner end Jc1 on the tire equator C side of the inner circumferential land portion 4i. On the other hand, the outer end 5e1 on the tread end Te side is arranged at a distance K in the tire circumferential direction from the protruding corner end Jt1 on the tread end Te side of the inner circumferential land portion 4i. At this time, the distance K is preferably 25 to 75% of the tire circumferential direction distance Lj between the protruding corner end Jt1 and the entering corner end Jt2 on the tread end Te side.

  This is because the contact pressure on the tread end Te side is lower than that on the tire equator C side. Therefore, when the outer end 5e1 of the lateral narrow groove 5 is positioned near the protruding corner end Jt1 on the tread end Te side. The rigidity in the vicinity of the outer end 5e1 is lowered, which can be a starting point for uneven wear. In particular, when the distance K is less than 25% of the distance Lj, the outer end 5e1 is likely to have a rubber chip. Also, when the distance K exceeds 75% of the distance Lj, the outer end 5e1 becomes too close to the corner end Jt2, and similarly, the rigidity in the vicinity of the outer end 5e1 is lowered, and the origin of uneven wear and Rubber chipping tends to occur at the outer end 5e1.

  Further, in this example, as shown in FIG. 5, the inner circumferential land portion 4i is connected to each intersecting portion Q where the transverse narrow groove 5 and the longitudinal main groove 3 intersect with each other from the tread surface 2S. A notch 12 is provided by a notch 12 having a triangular slope 12 </ b> S extending below the crossing line q between the horizontal narrow groove 5 and the vertical main groove 3. Since the notch 12 makes the edge of the intersecting portion Q an obtuse angle, the notched portion 12 is useful for preventing the rubber missing at the intersecting portion Q. In addition, the cutout portion 12 inevitably cuts out the protruding corner end Jc1 on the tire equator C side of the inner circumferential land portion 4i and removes a portion having low rigidity. An effect of suppressing uneven wear starting from the protruding corner end Jc1 can also be achieved. The depth h12 of the notch portion 12 is preferably larger than the groove depth hb of the upper groove portion 5b.

  Next, the outer circumferential land portion 4o is a continuous rib that does not have the lateral narrow groove 5, and in this example, the cutout portion 12 is formed at the protruding corner end Jo1 on the tire equator C side. The same notch 13 is formed.

  In addition, a hollow groove 14 in the form of a narrow lag groove having a substantially trapezoidal shape in a plan view is provided in the tread end Te of the outer circumferential land portion 4o. The hollow groove 14 is formed at a position facing the protruding corner end Jo1, and alleviates a change in rigidity of the outer circumferential land portion 4o due to zigzag. Thereby, the occurrence of uneven wear in the outer circumferential land portion 4o is prevented.

  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.

In order to confirm the effects of the present invention, a heavy duty tire (tire size 315/315) having the tread pattern shown in FIG. 1 as a basic pattern and the lateral narrow groove formed in the circumferential land portion in the inside changed according to the specifications shown in Table 2. 80R22.5) was prototyped. Each sample tire was tested for wet grip performance, uneven wear resistance, and block chipping resistance, and the results are shown in Table 1.
6 (A) to 6 (E) and FIGS. 7 (A) to 7 (D) show the groove width center lines of the lateral narrow grooves in the comparative example.

  As a conventional example, as shown in FIG. 8, a prototype with a bent line shape in which a lateral narrow groove is formed by three linear lateral groove portions e1, e2, e3 was manufactured. The angles α, β, and γ with respect to the tire axial direction lines of the lateral groove portions e1, e2, and e3 are as follows. α = 19.0 degrees, β = 8.5 degrees, γ = 51.0 degrees.

The specifications are substantially the same except those described in the specifications of Table 2, and only the lateral narrow grooves are made different.
The groove width W0 of the longitudinal main groove 18.6mm,
Groove depth H0 of vertical main groove 17.3mm,
The groove depth h of the horizontal narrow groove-12.9 mm,
(Ratio h / H0) --0.73,

The test conditions are as follows.
(1) Wet grip performance:
Tires are mounted on all wheels of a vehicle (domestic truck 2D car) under the conditions of rim (9.00) and internal pressure (830 kPa), and the speed is adjusted to a course with a puddle on a circular asphalt road surface with a radius of 30 m. The vehicle entered while gradually increasing, and the lateral acceleration (lateral G) was measured, evaluated at an average lateral G at a speed of 70 to 90 km / h, and the result was indexed.

(2) Uneven wear resistance performance:
After the tires of Example 1 were mounted on all the wheels of the vehicle under the conditions of the rim (9.00) and the internal pressure (830 kPa), after traveling 30,000 km at a rate of 80% on the highway and 20% on the general road The wear-like body of the tire of Example 1 mounted on the steering wheel side was used as an evaluation standard. Then, a vehicle equipped with the tire of Example 1 on the drive wheel side and the test tire on the steering wheel side traveled 30,000 km at a rate of 80% on the highway and 20% on the general road, respectively. Then, the wear state of the test tire on the side of the steered wheel after traveling was compared with the evaluation standard, and evaluated with an index with the evaluation standard (Example 1) being 100. The larger the number, the better.

(3) Block chipping resistance:
With the rim (9.00) and internal pressure (830 kPa), the tires of Example 1 were mounted on all the wheels of the vehicle, and the tires were intentionally idled by climbing on a rough road and mounted on the drive wheels. The block missing state of the tire of Example 1 was used as an evaluation criterion. Then, the vehicle equipped with the tire of Example 1 on the steered wheel side and the test tire on the drive wheel side is climbed up the rough road and the tire is intentionally idled, and the test tire block on the drive wheel side is missing. The state was indexed by “number of chips × depth” and evaluated by an index with the evaluation criterion (Example 1) being 100. The larger the number, the better.

  As shown in the table, it can be confirmed that the tires of the examples can improve the wet grip performance without deteriorating the uneven wear resistance performance and the block chipping resistance performance.

DESCRIPTION OF SYMBOLS 1 Heavy load tire 2S Tread surface 2 Tread part 3 Longitudinal main groove 4 Circumferential land part 5 in the circumferential land part 4i Horizontal narrow groove 5a Lower groove part 5b Upper groove part 5e1 Outer end 5e2 Inner end 9c Arc groove part 9m Joint groove part 9t Outer arc groove Jt1 Outgoing corner end Jt2 Incoming corner end

Claims (5)

By providing a plurality of longitudinal main grooves extending in the tire circumferential direction in the tread portion, the tread portion is divided into a plurality of circumferential land portions including a circumferential land portion disposed on both sides of the tire equator. And the heavy load tire provided with a plurality of lateral narrow grooves that cross between the land portion side edge on the tread end side of the circumferential land portion and the land portion side edge on the tire equator side,
The lateral narrow groove has an arc center i1 on one side in the tire circumferential direction than the lateral narrow groove, and an arc groove portion outside the radius of curvature R1 extending in an arc shape from the land portion side edge on the tread end side; A substantially S-shape having an arc center i2 on the other side in the tire circumferential direction from the lateral narrow groove and an arc groove portion having a radius of curvature R2 extending in an arc shape from a land side edge on the tire equator side. With eggplant,
The curvature radius R2 is 10 to 40 mm, the curvature radius R1 is not more than the curvature radius R2, and the difference (R2−R1) from the curvature radius R2 is not more than 5 mm.
Moreover, the center angle α around the arc center i1 between both ends of the outer arc groove is 45 to 90 degrees, and the center angle β around the arc center i2 between both ends of the inner arc groove is 45 to 90 degrees. A heavy duty tire characterized by that.   The lateral narrow groove has a linear joint groove portion that contacts and joins the inner arc groove portion and the outer arc groove portion, and the tire axial length Lm of the joint groove portion is the tire of the lateral narrow groove. The heavy duty tire according to claim 1, wherein the tire is 40% or less of the axial length L0.   The lateral narrow groove includes a lower groove portion extending from the groove bottom and an upper groove portion extending from the lower groove portion to the tread surface, and the groove width Wa of the lower groove portion is in the range of 0.3 to 1.5 mm, and the upper groove portion. The heavy duty tire according to claim 1 or 2, wherein the groove width Wb is set to be larger than the groove width Wa and not more than 50% of the groove width W0 of the longitudinal main groove.   The horizontal narrow groove has a groove depth h in the range of 10 to 80% of the groove depth H0 of the vertical main groove, and the groove depth hb of the upper groove portion is 10 to 50% of the groove depth h. The heavy duty tire according to claim 3, wherein the tire is a heavy duty tire.   The inner circumferential land portion extends in a zigzag manner in the tire circumferential direction, and the outer end on the tread end side of the lateral narrow groove extends from the corner of the inner circumferential land portion on the tread end side. The distance K is arranged at a distance in the direction, and the distance K is 25 to 75% of the tire circumferential direction distance Lj between the protruding corner end and the entering corner end on the tread end side. The heavy duty tire according to any one of 1 to 4.

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