JP5269326B2 - Motorcycle tires - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire for a motorcycle capable of improving its durability during high speed running while ensuring satisfactory grip performance when it runs straight by making distribution of losses at tangent of tread rubber constituting a tread part proper. <P>SOLUTION: This pneumatic tire for the motorcycle is provided with a pair of bead parts 1 having a buried bead core, a pair of side wall parts 2 extended onto an outer side in the radial direction of the tire from the bead parts 1, and the tread part 3 extended across and between both of the side wall parts 2. In this tread part 3, a central tread part region 5 including an equatorial plane 4 of the tire is constituted by two layers, namely, the cap rubber layer 6 positioned on an outer side in the radial direction of the tire and the base rubber layer 7 positioned on an inner side in the radial direction of the tire when viewed in a cross section in the direction of tire width. The loss at tangent of the rubber constituting the cap rubber layer 6 is within a scope of 1.5-3.2 times the loss at tangent of the rubber constituting the base rubber layer 7. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a pneumatic tire for a motorcycle including a pair of bead portions in which a bead core is embedded, a pair of sidewall portions extending outward in the tire radial direction from the bead portion, and a tread portion extending between both sidewall portions. In particular, the present invention relates to a pneumatic tire for a motorcycle for traveling at a high speed on a dry road surface, and in particular, to improve grip performance and high-speed durability when the pneumatic tire for a motorcycle travels straight.

  A pneumatic tire for a motorcycle has a grip performance (acceleration grip performance and deceleration grip performance during straight traveling and grip performance during cornering traveling) determined by the properties of the rubber constituting the tire and the groove shape of the tread portion. . Also, since racing tires require high grip performance, pneumatic tires for motorcycles with improved grip performance by reducing the rubber hardness and modulus of the entire tread and increasing the loss tangent are used. It has been. However, in such pneumatic tires for motorcycles, the grip performance is sufficiently ensured, but because it frequently travels at a high speed during straight traveling, the heat generation of the rubber cannot be sufficiently suppressed, resulting in the heat generation. The tread part may be damaged or the grip performance may be reduced.

  Therefore, for example, as described in Patent Documents 1 and 2, from the three tread portion regions of the central tread portion region including the tire equatorial plane and both shoulder tread portion regions located across the central tread portion region. The center tread area is made of rubber with a small loss tangent, and the shoulder tread area is made of rubber with a large loss tangent, ensuring straight grip while maintaining cornering performance. In some cases, pneumatic tires for motorcycles that suppress heat generation by rubber having a small loss tangent have been developed.

  In addition, as described in Patent Document 3, the tread portion includes a tread portion region including a central tread portion region including the tire equatorial plane and both shoulder tread portion regions located across the central tread portion region. The loss tangent of the rubber constituting the central tread area is smaller than the loss tangent of the rubber constituting the shoulder tread area, and the shoulder tread area is compared with the loss tangent when viewed in the tire radial direction. A base rubber layer composed of a small rubber and a cap rubber layer composed of a rubber with a loss tangent greater than that of the rubber constituting the base rubber layer are laminated to ensure grip performance during cornering For motorcycles that suppress heat generation of rubber not only in the central tread area but also in the shoulder tread area Pneumatic tire has been developed.

JP-A-60-94804 JP 2006-273240 A JP-A-8-72505

  However, the pneumatic tires described in Patent Documents 1 to 3 suppress excessive heat generation in the tread contact area during straight traveling by reducing the loss tangent of the tread portion in the tread contact area during straight traveling. Therefore, the damage of the tread due to heat generation can be sufficiently suppressed, but since the loss tangent in the tread contact area becomes too small, the temperature of the tread does not rise to a temperature range where favorable grip performance can be obtained. In addition, the grip performance may not be sufficiently ensured. As described above, it has been difficult to achieve both ensuring sufficient grip performance and ensuring durability by suppressing heat generation.

  Therefore, the object of the present invention is to optimize the distribution of loss tangent of the tread rubber constituting the tread portion, thereby ensuring the grip performance during straight traveling and improving the high-speed durability of the motorcycle. To provide tires.

In order to achieve the above object, a first aspect of the present invention includes a pair of bead portions in which a bead core is embedded, a pair of sidewall portions extending outward in the tire radial direction from the bead portion, and the both sidewall portions. The tread portion includes a cap rubber layer located on the outer side in the tire radial direction and a base rubber layer located on the inner side in the tire radial direction, with the tread portion including a tire equatorial plane in a cross section in the tire width direction. The loss tangent of the rubber constituting the cap rubber layer is the loss tangent of the rubber constituting the base rubber layer in at least one tread half region of the central tread region. in the range of 5 to 3.2 times, the tread portion is Ri Do different configuration of the tread portion between the half-frequency left and right bounded by the tire equatorial plane, the center tread An intermediate tread portion region located across the region, and a loss tangent of rubber constituting the intermediate tread portion region is larger than a loss tangent of rubber constituting the central tread region, and the intermediate tread portion region The loss tangent of the rubber constituting the base rubber layer is in the range of 1.5 times to 3.2 times greater than the loss tangent of the rubber constituting the base rubber layer, and only in one tread half region of the tread portion, The shoulder tread region is formed by laminating as a surface rubber layer located outside the intermediate tread region in the tire width direction and outside the intermediate tread region in the tire radial direction, and the shoulder tread region is loss tangent of the rubber constituting the said intermediate tread pneumatic tire for a motorcycle, wherein the greater than the loss tangent of the rubber constituting the region It is. Such pneumatic tires for motorcycles have an optimized distribution of loss tangent of the rubber that constitutes the tread part. The rubber temperature in the contact area is in a temperature range that can ensure favorable acceleration grip performance and deceleration grip performance, while effectively preventing the failure of the tread part, so high-speed durability and grip when traveling straight ahead The performance can be sufficiently improved. The “loss tangent” here is a loss tangent (tan δ) represented by a ratio of a loss elastic modulus and a dynamic elastic modulus. The loss tangent is a temperature of 100 ° C. using a spectrometer manufactured by Ueshima Seisakusho. The measurement was performed under the conditions of an initial elongation of 6%, an excitation strain of 4%, and a frequency of 52 Hz .
Furthermore, the loss tangent of the rubber constituting the cap rubber layer is in the range of 1.5 to 3.2 times the loss tangent of the rubber constituting the base rubber layer only in the one tread half region. Is preferred.
In addition, the second aspect of the present invention includes a pair of bead portions in which a bead core is embedded, a pair of sidewall portions extending outward in the tire radial direction from the bead portion, and a tread portion extending between both sidewall portions. The tread portion includes, in the tire width direction cross section, the central tread portion region including the tire equatorial plane, which is composed of two layers, a cap rubber layer located on the tire radial direction outer side and a base rubber layer located on the tire radial inner side. The loss tangent of the rubber constituting the cap rubber layer is in the range of 1.5 to 3.2 times the loss tangent of the rubber constituting the base rubber layer, and sandwiches the central tread portion region. And the loss tangent of the rubber constituting the intermediate tread region is larger than the loss tangent of the rubber constituting the central tread region, and The loss tangent of the rubber constituting the intermediate tread region is in the range of 1.5 to 3.2 times the loss tangent of the rubber constituting the base rubber layer, and the tire width direction of the intermediate tread region It has a shoulder tread portion region that is laminated as a surface rubber layer that is located on the outer side and on the outer side in the tire radial direction of the intermediate tread portion region, and the loss tangent of the rubber that constitutes the shoulder tread portion region is A pneumatic tire for a motorcycle characterized by being larger than a loss tangent of rubber constituting the intermediate tread portion region .

  The width of the base rubber layer in the tire width direction is preferably less than 0.5 times the tread width. The “tread width” here refers to a distance measured along the periphery of the tread portion in the cross section in the tire width direction.

  Furthermore, it is preferable that the thickness of the cap rubber layer is in the range of 50 to 350% of the thickness of the base rubber layer.

  In addition, the width of the central tread region is in the range of 0.15 to 0.35 times the tread width, and the sum of the widths of the two intermediate tread regions is 0.25 to 0.80 times the tread width. It is preferable that the sum of the widths of the two shoulder tread portion regions be in the range of 0.05 to 0.40 times the tread width. Here, the “width of the tread portion region” refers to a distance measured along the periphery of the tread portion region in the cross section in the tire width direction.

  According to the present invention, by optimizing the distribution of loss tangent of the tread rubber constituting the tread portion, it is possible to provide a pneumatic tire for a motorcycle with improved grip performance and high-speed durability when traveling straight ahead. It becomes possible.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a tire width direction sectional view of a typical motorcycle pneumatic tire (hereinafter referred to as “tire”) according to the present invention, and FIG. 2 is a perspective view of the tire width direction section of the tire shown in FIG. 3 to 8 are sectional views in the tire width direction of other tires according to the present invention.

  The tire shown in FIGS. 1 and 2 includes a pair of bead portions 1 in which bead cores are embedded, a pair of sidewall portions 2 extending from the bead portion 1 outward in the tire radial direction, and a tread extending between both sidewall portions 2. Part 3 is provided. The tread portion 3 includes, in the tire width direction cross section, a central tread portion region 5 including the tire equatorial plane 4 of a cap rubber layer 6 positioned on the outer side in the tire radial direction and a base rubber layer 7 positioned on the inner side in the tire radial direction. It consists of two layers. Further, the loss tangent of the rubber constituting the cap rubber layer 6 is in the range of 1.5 to 3.2 times the loss tangent of the rubber constituting the base rubber layer 7. Such a tire has a large loss tangent at the portion that contacts the road surface when traveling straight, and a small loss tangent at the portion that does not contact the road surface. The tread portion 3 is prevented from being damaged due to excessive heat generation, and the rubber temperature in the road contact area is a temperature range where the grip performance can be effectively exhibited. The grip performance can be sufficiently improved. At this time, when the loss tangent of the rubber constituting the cap rubber layer 6 is less than 1.5 times the loss tangent of the rubber constituting the base rubber layer 7, the rubber in the road contact area does not sufficiently generate heat. Although it is possible to prevent the tread portion 3 from being destroyed due to heat generation, the rubber temperature in the road contact area does not rise to a temperature range where the grip performance is effectively exhibited, and the grip performance is not sufficiently ensured. On the other hand, when the loss tangent of the rubber constituting the cap rubber layer 6 exceeds 3.2 times the loss tangent of the rubber constituting the base rubber layer 7, the heat generated by the rubber in the road contact area becomes excessive, resulting in heat generation. The resulting tread portion 3 is destroyed, and the rubber temperature in the road contact area exceeds the temperature range in which the grip performance is effectively exhibited, so that the grip performance is not sufficiently ensured. Note that the loss tangent is defined under the condition of 100 ° C. because the rubber temperature of the tread portion 3 becomes as high as 80 to 100 ° C. when the tire for high speed running used in a race runs at high speed. It is.

  The width in the tire width direction of the base rubber layer 7 is preferably less than 0.5 times the tread width, and more preferably less than 0.4 times. This is because when the width of the base rubber layer 7 in the tire width direction is 0.5 times or more of the tread width, the range in which the base rubber layer is disposed becomes too narrow. In addition, the heat generated in the road surface area cannot be sufficiently suppressed, and the tread part may be damaged due to excessive heat generation of the rubber. Also, the rubber temperature in the road surface area is effective for grip performance. This is because the grip performance may not be sufficiently ensured because the temperature range that is exhibited in the above is exceeded.

  Furthermore, the thickness of the cap rubber layer 6 is preferably in the range of 50 to 350% of the thickness of the base rubber layer 7, and more preferably in the range of 100 to 300%. This is because, when the thickness of the cap rubber layer 6 exceeds 350% of the thickness of the base rubber layer 7, the ratio of the rubber layer composed of rubber having a small loss tangent is too low, and when traveling at high speed. Since the rubber temperature in the road contact area cannot be sufficiently suppressed, a failure of the tread portion 3 due to the heat generation of the rubber may occur, and the rubber temperature in the road contact area effectively exhibits the grip performance. If the temperature of the cap rubber layer 6 is less than 50% of the thickness of the base rubber layer 7, there is a possibility that the grip performance is not sufficiently secured. Since the ratio of the rubber layer composed of small tangent rubber becomes too high and the rubber temperature does not rise sufficiently when traveling at high speed, the rubber temperature in the road contact area effectively demonstrates the grip performance. Without reaching to a temperature range which can Rukoto, there is a possibility that the grip performance is not sufficiently ensured.

  Furthermore, as shown in FIG. 3, the tread portion 3 is composed of a central tread portion region 5 and a shoulder tread portion region 8 located across the central tread portion region 5, and a loss tangent of rubber constituting the cap rubber layer 6. Is larger than the loss tangent of the rubber constituting the shoulder tread portion region 8, and the loss tangent of the rubber constituting the shoulder tread portion region 8 is 1.5 times the loss tangent of the rubber constituting the base rubber layer 7. It is preferably within a range of 3.2 times or less, more preferably within a range of 1.7 to 3.0 times. This is because when the loss tangent of the rubber constituting the shoulder tread portion region 8 is 1.5 times or less than the loss tangent of the rubber constituting the base rubber layer 7, the loss of the rubber constituting the shoulder tread portion region 8 is reduced. Since the tangent becomes too small, the heat generation of rubber in the road interview area during cornering running is suppressed, and the rubber temperature in the road interview area during cornering running does not rise to the temperature range where the grip performance is effectively exhibited. There is a possibility that sufficient grip performance during traveling may not be ensured. On the other hand, the loss tangent of rubber constituting the shoulder tread region 8 is 3.2 times the loss tangent of rubber constituting the base rubber layer 7. In the case of exceeding, the loss tangent of the rubber constituting the shoulder tread portion region 8 becomes too large, and the road contact area during cornering traveling The rubber in the tire may generate excessive heat, which may cause destruction of the shoulder tread portion region 8 due to the heat generation, and the rubber temperature in the road contact area during cornering traveling can effectively exert grip performance. This is because the temperature range may be exceeded and the grip performance during cornering traveling may not be sufficiently ensured.

  In addition, as shown in FIG. 4, the tread portion 3 is sandwiched between a central tread portion region 5, two shoulder tread portion regions 8 including the tread grounding end, and the central tread portion region 5 and the shoulder tread portion region 8. The loss tangent of the rubber constituting the intermediate tread portion region 9 is in a range larger than 1.5 times the loss tangent of rubber constituting the base rubber layer 7 and not more than 3.2 times. Preferably, it exists in the range of 1.7 to 3.0 times. Because, when the loss tangent of the rubber constituting the intermediate tread portion region 9 is 1.5 times or less than the loss tangent of the rubber constituting the base rubber layer 7, the loss of the rubber constituting the intermediate tread portion region 9 is Since the tangent is too small, heat generation of rubber in the road surface area during cornering is suppressed, and the rubber temperature does not rise to a temperature range where the grip performance is effectively exhibited, and sufficient grip performance during cornering is secured. On the other hand, if the loss tangent of the rubber constituting the intermediate tread portion region 9 exceeds 3.2 times the loss tangent of the rubber constituting the base rubber layer 7, the intermediate tread portion Since the loss tangent of the rubber composing the region 9 becomes too large, the rubber in the road surface contact area during cornering travels excessively generates heat, and the intermediate tread region caused by the heat generation 9 may cause damage, and the rubber temperature in the road contact area during cornering will exceed the rubber temperature to the extent that the grip performance is effectively exhibited, and the grip performance during cornering will be sufficient. There is a possibility that it cannot be secured.

  In addition, the width of the central tread portion region 5 is preferably in the range of 0.15 to 0.35 times the tread width, and more preferably in the range of 0.20 to 0.30 times. The sum of the widths of the two intermediate tread portion regions 9 is preferably in the range of 0.25 to 0.80 times the tread width, and more preferably in the range of 0.35 to 0.70 times. . Furthermore, the sum of the widths of the two shoulder tread region 8 is preferably in the range of 0.05 to 0.40 times the tread width, more preferably in the range of 0.08 to 0.30 times. . This is because, when they are out of the respective ranges, the balance between the high-speed durability and the grip performance during straight traveling and the grip performance during cornering traveling is biased, and the traveling performance may be deteriorated.

  The above description shows only a part of the embodiment of the present invention, and these configurations can be combined alternately or various changes can be made without departing from the gist of the present invention. For example, as shown in FIG. 5, the tread portion 3 is sandwiched between the left and right intermediate tread portion regions 9 made of rubber having a relatively large loss tangent, and the intermediate tread portion region 9. A central tread portion region 5 made of rubber having a loss tangent smaller than that of the constituting rubber is provided. The central tread portion region 5 is composed of a cap rubber layer 6 and a base rubber layer 7, and an intermediate tread. It is also possible to laminate the shoulder tread portion region 8 as the surface rubber layer 10 on the outer side in the tire radial direction of the intermediate tread portion region 9 on the outer side in the tire width direction of the portion region 9. The surface rubber layer 10 is made of rubber having a loss tangent greater than that of the rubber constituting the intermediate tread portion region 9. Similar to the tire shown in FIG. 3 in which the tread portion 3 is divided into five tread portion regions, such a tire ensures grip performance when cornering and sufficiently secures high-speed durability and grip performance when traveling straight. The Further, since the loss tangent of the intermediate tread portion region 9 where the surface rubber layer 10 is laminated is large, excessive heat generation can be suppressed as a whole of the tread portion 3, and the durability of the tire is improved. Further, as shown in FIG. 6, the surface rubber layer 10 can be disposed only in one tread half region (right half region in the illustrated example) of the tread portion 3. Further, as shown in FIG. 7, the shoulder tread portion region 8 can be disposed only in one tread half region (right half region in the illustrated example) of the tread portion 3. Further, as shown in FIG. 8, the tread portion is made of rubber having different loss tangents in the left and right tread halves, and is smaller than the loss tangent of rubber constituting the tread halves inside the tread half area in the tire radial direction. It is possible to dispose a base rubber layer 7 made of rubber. The tires shown in FIGS. 6 to 8 can suppress excessive heat generation by a base rubber layer made of rubber having a small loss tangent, and can sufficiently ensure high-speed durability and grip performance during straight running. Since the left and right tread halves have different configurations, the grip performance characteristics during cornering run differ between the left and right tread halves. For example, the desired cornering depends on the direction, distance or banking angle on the race course. This can be applied when the grip performance during running differs between the left and right tires. Of course, the structure of the tread portion is different from each other, and the characteristics of the grip performance during cornering traveling are also different.

Next, tires were prototyped and running performance was evaluated, which will be described below.

As shown in FIG. 4, the tires 1 and 2 have tread portions in five tread portion regions including a central tread portion region, a shoulder tread portion region, and an intermediate tread portion region formed by laminating a base rubber layer and a cap rubber layer. The width of the base rubber layer in the tire width direction is 0.38 times the tread width, the thickness of the cap rubber layer is 160% of the thickness of the base rubber layer, and the rubber constituting the base rubber layer This is a pneumatic slick tire for a motorcycle with a tire size of 190 / 650R16.5, in which the loss tangent of the tire is 0.3 and no groove is provided in the tread portion, and has the specifications shown in Table 1. In addition, the numerical value of the loss tangent shown in Table 1 represents the loss tangent in the other tread region as a relative value when the loss tangent of the base rubber layer in the central tread region of the tires 1 and 2 is 100. is there.

  For comparison, the following conventional tires 1 and 2 were also prototyped. The conventional tire 1 has the configuration shown in FIG. 9 and the specifications shown in Table 1. Further, the conventional tire 2 has the configuration shown in FIG. 10 and the specifications shown in Table 1.

  Each of these test tires is attached to a rim of size MT6.25 × 16.5 to form a tire wheel, and is mounted on a 1000 cc class racing vehicle used for the test. Air pressure: 220 kPa (relative pressure), tire load load 2 0.0 kN was applied, and high speed durability when traveling on a dry road surface and acceleration grip performance and deceleration grip performance during straight traveling were evaluated. The acceleration grip performance is evaluated comprehensively for both the rider's feeling evaluation during acceleration running and the slip rate of the rear tire measured by the measuring instrument in the actual vehicle test. Both rider's feeling evaluation when traveling and the slip rate of the rear tire measured by a measuring instrument were comprehensively evaluated. In addition, the high-speed durability during straight running is set to the heat generation temperature condition of the tire when straight running at high speed on the racing course, the durability drum test is performed indoors, and the running speed at which tread baldness and cracks occur is set. Evaluated by verification.

  In addition, the numerical value of evaluation of various tests is evaluated as a full scale of 10 points, and the evaluation result is shown in Table 2.

As is apparent from the results in Table 2, the tires 1 and 2 have the same high speed durability as the conventional tire 1, but the acceleration grip performance and the deceleration grip performance are improved. In addition, the tires 1 and 2 have the same level of acceleration grip performance and deceleration grip performance as compared with the conventional tire 2, but the high-speed durability is improved. That is, in tires 1 and 2 , all of high-speed durability, acceleration grip performance, and deceleration grip performance that were difficult to achieve with conventional tires were improved.

  As is clear from the above, by this invention, the distribution of loss tangent of the tread rubber constituting the tread portion is optimized to improve the grip performance and high-speed durability when traveling straight ahead. It has become possible to provide tires containing tires.

It is a tire width direction sectional view of a tire. It is a one part perspective view of the tire width direction cross section of the tire shown in FIG. It is a tire width direction sectional view of other tires . It is a tire width direction sectional view of other tires . FIG. 5 is a sectional view in the tire width direction of another typical tire according to the present invention. FIG. 5 is a sectional view in the tire width direction of another typical tire according to the present invention. FIG. 5 is a sectional view in the tire width direction of another typical tire according to the present invention. FIG. 5 is a sectional view in the tire width direction of another typical tire according to the present invention. It is a tire width direction sectional view of a conventional example tire. It is a tire width direction sectional view of a conventional example tire.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Bead part 2 Side wall part 3 Tread part 4 Tire equatorial plane 5 Center tread part area | region 6 Cap rubber layer 7 Base rubber layer 8 Shoulder tread part area | region 9 Middle tread part area | region 10 Surface rubber layer

Claims (6)

A pair of bead portions in which a bead core is embedded, a pair of sidewall portions extending outward in the tire radial direction from the bead portion, and a tread portion extending between both sidewall portions;
The tread portion has a cross section in the tire width direction, and the central tread portion region including the tire equatorial plane is composed of two layers, a cap rubber layer located on the outer side in the tire radial direction and a base rubber layer located on the inner side in the tire radial direction. The loss tangent of the rubber constituting the cap rubber layer is 1.5 to 3.2 times the loss tangent of the rubber constituting the base rubber layer in at least one tread half region of the central tread portion region. In the range of
The tread portion is Ri Do different configuration of the tread portion between the half-frequency left and right bounded by the tire equatorial plane,
Having an intermediate tread portion region located across the central tread portion region;
The loss tangent of rubber constituting the intermediate tread region is larger than the loss tangent of rubber constituting the central tread region, and the loss tangent of rubber constituting the intermediate tread region constitutes the base rubber layer. In the range of more than 1.5 times the loss tangent of the rubber
Only in one tread half region of the tread portion, the shoulder is formed by laminating as a surface rubber layer located outside the intermediate tread portion region in the tire width direction and outside the intermediate tread portion region in the tire radial direction. Having a tread area,
A pneumatic tire for a motorcycle , wherein a loss tangent of rubber constituting the shoulder tread portion region is larger than a loss tangent of rubber constituting the intermediate tread portion region . The loss tangent of the rubber constituting the cap rubber layer is in a range of 1.5 to 3.2 times the loss tangent of the rubber constituting the base rubber layer only in the one tread half region. The pneumatic tire for motorcycles described in 1. A pair of bead portions in which a bead core is embedded, a pair of sidewall portions extending outward in the tire radial direction from the bead portion, and a tread portion extending between both sidewall portions;
The tread portion has a cross section in the tire width direction, and the central tread portion region including the tire equatorial plane is composed of two layers, a cap rubber layer located on the outer side in the tire radial direction and a base rubber layer located on the inner side in the tire radial direction. The loss tangent of the rubber constituting the cap rubber layer is in the range of 1.5 to 3.2 times the loss tangent of the rubber constituting the base rubber layer,
Having an intermediate tread portion region located across the central tread portion region;
The loss tangent of rubber constituting the intermediate tread region is larger than the loss tangent of rubber constituting the central tread region, and the loss tangent of rubber constituting the intermediate tread region constitutes the base rubber layer. In the range of more than 1.5 times the loss tangent of the rubber
A shoulder tread region formed by laminating as a surface rubber layer located on the outer side in the tire width direction of the intermediate tread region and on the outer side in the tire radial direction of the intermediate tread region;
A pneumatic tire for a motorcycle , wherein a loss tangent of rubber constituting the shoulder tread portion region is larger than a loss tangent of rubber constituting the intermediate tread portion region . The pneumatic tire for a motorcycle according to any one of claims 1 to 3, wherein a width of the base rubber layer in a tire width direction is less than 0.5 times a tread width . The pneumatic tire for a motorcycle according to any one of claims 1 to 4, wherein a thickness of the cap rubber layer is in a range of 50 to 350% of a thickness of the base rubber layer . The width of the central tread portion region is in the range of 0.15 to 0.35 times the tread width, and the sum of the widths of the two intermediate tread portion regions is in the range of 0.25 to 0.80 times the tread width. The pneumatic tire for a motorcycle according to claim 3, wherein a sum of widths of the two shoulder tread portion regions is in a range of 0.05 to 0.40 times a tread width .

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