Motorcycle tires

Abstract

To provide a tire for a motorcycle, which maintains wear resistance performance exhibited during straight running, and furthermore has improved grip performance exhibited during cornering.SOLUTION: A tire for a motorcycle including a tread portion 2 is provided. The tread portion 2 includes a base rubber layer 10, and a cap rubber layer 11 arranged outside in a tire radial direction, of the base rubber layer 10 and constituting a grounding surface of the tread portion 2. The cap rubber layer 11 includes a crown cap portion 12 arranged at a center portion in a tire axial direction and a pair of shoulder cap portions 13 arranged at both sides in the tire axial direction, of the crown cap portion 12. A loss tangent tanδc at 0°C of the crown cap portion 12, loss tangents tanδs at 0°C of the shoulder cap portions 13 and a loss tangent tanδb at 0°C of the base rubber layer 10 satisfy the following formula (1): tanδc<tanδs≤tanδb (1).SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a tire for a motorcycle. [Background technology]

[0002] Conventionally, various motorcycle tires with improved tread rubber have been proposed. For example, the following Patent Document 1 proposes a motorcycle pneumatic tire that can exhibit excellent durability and steering stability by using a rubber composition in which the amount of oil component is greater in the shoulder rubber layer of the tread rubber than in the base rubber layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-76002 A Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, as motorcycles have become more sophisticated, there has been a demand for motorcycle tires with excellent grip performance during cornering. However, improving the grip performance of motorcycle tires can sometimes result in a loss of wear resistance during straight-ahead driving.

[0005] The present invention has been devised in view of the above-mentioned circumstances, and has as its main object to provide a motorcycle tire which maintains wear resistance during straight-line driving while improving grip performance during cornering. [Means for solving the problem]

[0006] The present invention is a motorcycle tire including a tread portion, the tread portion including a base rubber layer, and a cap rubber layer arranged radially outward of the base rubber layer and constituting the contact surface of the tread portion, the cap rubber layer including a crown cap portion arranged in the center of the tire axial direction, and a pair of shoulder cap portions arranged on both sides of the crown cap portion in the tire axial direction, and a loss tangent tan δc of the crown cap portion at 0°C, a loss tangent tan δs of the shoulder cap portion at 0°C, and a loss tangent tan δb of the base rubber layer at 0°C satisfy the following formula (1). tan δc <tanδs≦tanδb …(1)

[0007] In the motorcycle tire of the present invention, it is preferable that the thickness of the base rubber layer on the radially inner side of the shoulder cap portion is greater than the thickness of the base rubber layer on the radially inner side of the crown cap portion.

[0008] In the motorcycle tire of the present invention, it is preferable that the thickness of the base rubber layer continuously increases from an axial center portion of the tire toward both axial outer sides.

[0009] In the motorcycle tire of the present invention, it is preferable that the JIS-A hardness of the shoulder cap portion is in the range of -2 degrees to +5 degrees with respect to the JIS-A hardness of the crown cap portion.

[0010] In the motorcycle tire of the present invention, the maximum axial width of the ground contact surface of the crown cap portion is desirably 20% to 60% of the maximum axial width of the ground contact surface of the tread portion.

[0011] In the motorcycle tire of the present invention, it is preferable that the thickness of the base rubber layer on the radially inner side of the crown cap portion is 10% to 40% of the total thickness of the tread rubber constituting the tread portion.

[0012] In the motorcycle tire of the present invention, it is preferable that a plurality of grooves are provided in the ground contact surface of the tread portion, and the depth of each of the plurality of grooves is smaller than the thickness of the cap rubber layer. Effect of the Invention

[0013] By adopting the above-mentioned configuration, the motorcycle tire of the present invention can improve grip performance during cornering while maintaining wear resistance during straight running. [Brief description of the drawings]

[0014] [Figure 1] 1 is a cross-sectional view showing one embodiment of a motorcycle tire of the present invention. [Diagram 2] FIG. 2 is an enlarged view of the tread portion of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a tire meridian cross-sectional view including the tire rotation axis of a motorcycle tire 1 (hereinafter, sometimes simply referred to as "tire") according to this embodiment in a normal state. The tire 1 according to this embodiment is a tire for the rear wheel of a motorcycle suitable for on-road sports driving. However, the tire of the present invention is not limited to this embodiment.

[0016] "Normal condition" means, in the case of a pneumatic tire for which various standards are established, that the tire is mounted on a normal rim, inflated to the normal internal pressure, and no load is applied. In the case of a tire for which various standards are not established, the normal condition means a standard use condition according to the intended use of the tire, and a condition in which no load is applied. In this specification, unless otherwise specified, the dimensions of each part of the tire are values ​​measured in the normal condition.

[0017] A "genuine rim" is a rim that is defined for each tire by the standard system that includes the standard on which the tire is based. For example, in the case of JATMA, it is called a "standard rim," in the case of TRA, it is called a "Design Rim," and in the case of ETRTO, it is called a "Measuring Rim."

[0018] "Normal internal pressure" is the air pressure set for each tire by each standard in the standard system on which the tire is based. In the case of JATMA, it is the "maximum air pressure." In the case of TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES." In the case of ETRTO, it is the "INFLATION PRESSURE."

[0019] As shown in Fig. 1, a tire 1 of this embodiment includes a tread portion 2, a pair of sidewall portions 3, and a pair of bead portions 4. The sidewall portions 3 are continuous with both sides of the tread portion 2 in the tire axial direction. The bead portions 4 are continuous with the sidewall portions 3 on the inner side in the tire radial direction. In the tread portion 2, the contact surface between one tread end Te and the other tread end Te is curved in an arc shape that is convex outward in the tire radial direction so that a sufficient contact area can be obtained even during cornering with a large camber angle.

[0020] The tire 1 of this embodiment includes a carcass 6 that extends from one bead portion 4 through one sidewall portion 3, the tread portion 2, the other sidewall portion 3, and then to the other bead portion 4.

[0021] The carcass 6 includes, for example, a carcass ply 6A including a plurality of carcass cords. The carcass 6 of this embodiment is configured, for example, with two carcass plies 6A. The carcass ply 6A includes a main body portion 6a and a turn-up portion 6b. The main body portion 6a extends from the tread portion 2 through the sidewall portions 3 on both sides to the bead cores 5 of the bead portions 4 on both sides. The turn-up portions 6b are connected to the main body portion 6a and are turned up around the bead cores 5 from the inside to the outside in the tire axial direction.

[0022] The tread portion 2 is provided with, for example, a belt layer 7. The belt layer 7 includes, for example, a belt ply including a plurality of belt cords inclined at an angle of 10 to 45 degrees with respect to the tire circumferential direction. The belt layer 7 in this embodiment is configured with one belt ply, but may be configured with a plurality of belt plies superposed. Such a belt layer 7 can effectively reinforce the tread portion 2.

[0023] Fig. 2 shows an enlarged view of the tread portion 2. As shown in Fig. 2, the tread portion 2 includes a tread rubber 2G arranged on the outer side in the tire radial direction of the carcass 6 and the belt layer 7. The tread rubber 2G of the tread portion 2 includes a base rubber layer 10 and a cap rubber layer 11 arranged on the outer side in the tire radial direction of the base rubber layer 10 and constituting the contact surface of the tread portion 2.

[0024] The cap rubber layer 11 includes a crown cap portion 12 disposed at the center in the tire axial direction, and a pair of shoulder cap portions 13 disposed on both sides of the crown cap portion 12 in the tire axial direction.

[0025] In the present invention, the loss tangent tan δc of the crown cap portion 12 at 0° C., the loss tangent tan δs of the shoulder cap portion 13 at 0° C., and the loss tangent tan δb of the base rubber layer 10 at 0° C. satisfy the following formula (1). tan δc <tanδs≦tanδb …(1)

[0026] In this specification, the "loss tangent tan δ" is a value measured in accordance with the provisions of JIS-K6394 under the following conditions using a "viscoelasticity spectrometer" manufactured by Iwamoto Seisakusho Co., Ltd. Initial distortion: 10% Amplitude: ±1% Frequency: 10Hz Deformation mode: Tensile Measurement temperature: 0℃

[0027] By adopting the above-mentioned configuration, the present invention can improve grip performance during cornering while maintaining wear resistance during straight driving. The following mechanism is presumed to be the reason for this.

[0028] In the present invention, since the loss tangent tanδs of the shoulder cap portion 13 is larger than the loss tangent tanδc of the crown cap portion 12, the crown cap portion 12 that comes into contact with the ground during straight running has a relatively low heat generation property and can maintain its wear resistance. On the other hand, the shoulder cap portion 13 that comes into contact with the ground during cornering generates moderate heat due to the deformation of the tread rubber 2G and can exhibit excellent grip performance during cornering.

[0029] In addition, in the present invention, the loss tangent tanδb of the base rubber layer 10 is set to be equal to or greater than the loss tangent tanδs of the shoulder cap portion 13, so that high heat generation can be expected in the base rubber layer 10. As a result, during straight running when the crown cap portion 12 touches the ground or during cornering at a relatively small camber angle, the amount of deformation of the tread rubber 2G is small, so that the base rubber layer 10 generates little heat and the wear resistance during straight running is maintained. During cornering when the shoulder cap portion 13 touches the ground, the amount of deformation of the tread rubber 2G is large, so that the base rubber layer 10 generates moderate heat and the grip force of the shoulder cap portion 13 can be further increased. In the present invention, it is believed that such a mechanism can improve grip performance during cornering while maintaining wear resistance during straight running.

[0030] A more detailed configuration of this embodiment will be described below. Each configuration described below shows a specific aspect of this embodiment. Therefore, it goes without saying that the present invention can achieve the above-mentioned effects even if it does not have the configuration described below. In addition, even if any one of the configurations described below is applied alone to the tire of the present invention having the above-mentioned characteristics, an improvement in performance according to each configuration can be expected. Furthermore, when some of the configurations described below are applied in combination, a composite improvement in performance according to each configuration can be expected.

[0031] In this embodiment, the loss tangent tan δc (hereinafter may be simply referred to as "tan δc") of the crown cap portion 12, the loss tangent tan δs (hereinafter may be simply referred to as "tan δs") of the shoulder cap portion 13, and the loss tangent tan δb (hereinafter may be simply referred to as "tan δb") of the base rubber layer 10 are each, for example, 0.20 to 1.60. More specifically, tan δc is, for example, 0.20 to 0.90, and preferably 0.70 to 0.90. tan δs is, for example, 0.80 to 1.40, and preferably 0.90 to 1.10. tan δb is, for example, 0.80 to 1.60, and preferably 1.00 to 1.20.

[0032] Also, tan δs is, for example, 105% to 140% of tan δc, and preferably 105% to 120%. Tan δb is preferably larger than tan δs. Tan δb is more preferably 100% to 140% of tan δs, and further preferably 105% to 120%. This makes it possible to suppress damage such as peeling of each rubber layer while achieving the above-mentioned effects.

[0033] The JIS-A hardness of the shoulder cap portion 13 is desirably in the range of -2 degrees to +5 degrees with respect to the JIS-A hardness of the crown cap portion 12. This improves the transient characteristic of the response when leaning the vehicle body while achieving the above-mentioned effects, and also suppresses uneven wear at the boundary between the crown cap portion 12 and the shoulder cap portion 13.

[0034] In this specification, JIS-A hardness means the hardness of rubber at 25° C. measured with a durometer type A based on JIS-K6253.

[0035] Similarly, the JIS-A hardness of the base rubber layer 10 is desirably in the range of -2 degrees to +5 degrees with respect to the JIS-A hardness of the shoulder cap portion 13. This makes it possible to suppress peeling between the base rubber layer 10 and the shoulder cap portion 13 during cornering.

[0036] The rubber layer having the above-mentioned characteristics can be obtained by appropriately combining known materials used in the production of rubber.

[0037] The thickness of the base rubber layer 10 on the radially inner side of the shoulder cap portion 13 is desirably greater than the thickness of the base rubber layer 10 on the radially inner side of the crown cap portion 12. Such a base rubber layer 10 can reliably improve grip performance during cornering while maintaining wear resistance during straight driving.

[0038] In a more desirable embodiment, the thickness of the base rubber layer 10 increases continuously from the axial center toward both axial outer sides of the tire, thereby improving the transient characteristics of the response when the vehicle body is leaned over.

[0039] The thickness t2 of the base rubber layer 10 at the center position of the contact patch of the shoulder cap portion 13 (the center position in the longitudinal direction of the contact patch in the tire cross section) is desirably 1.5 times or more, more desirably 1.8 times or more, and desirably 2.5 times or less, more desirably 2.2 times or less, of the thickness t1 of the base rubber layer 10 on the tire equator C. This improves abrasion resistance during straight driving and grip performance during cornering in a well-balanced manner.

[0040] On the radially inner side of the crown cap portion 12, the thickness of the base rubber layer 10 is preferably 10% or more, and more preferably 10% to 40%, of the total thickness (thickness from the ground contact surface to the outer surface of the belt layer) of the tread rubber 2G constituting the tread portion 2. Also, on the radially inner side of the crown cap portion 12, the minimum thickness of the base rubber layer 10 (in this embodiment, the thickness t1 ) is 10% to 20% of the total thickness of the tread rubber 2G. This ensures that the wear resistance of the crown cap portion 12 is maintained.

[0041] The maximum width W2 in the tire axial direction of the ground contact surface of the crown cap portion 12 is 20% to 60%, and preferably 20% to 40%, of the maximum width W1 (shown in FIG. 1) in the tire axial direction of the ground contact surface of the tread portion 2. This reliably maintains wear resistance during straight running and cornering at a relatively small camber angle.

[0042] The tread rubber 2G of this embodiment is composed of only the above-mentioned base rubber layer 10 and cap rubber layer 11, and no other rubber members are arranged. This ensures the above-mentioned effects. However, the present invention is not limited to this embodiment.

[0043] A plurality of grooves 15 may be provided on the ground contact surface of the tread portion 2. In this case, it is preferable that the depth of each of the plurality of grooves 15 is smaller than the thickness of the cap rubber layer 11. In other words, it is preferable that the base rubber layer 10 is not exposed on the inner surface of the groove 15. As a result, even if the wear of the tread portion 2 progresses, the base rubber layer is not exposed, and excellent wear resistance and driving stability are continuously exhibited.

[0044] Although the motorcycle tire according to one embodiment of the present invention has been described in detail above, the present invention is not limited to the above-mentioned specific embodiment and can be modified and carried out in various aspects. EXAMPLES

[0045] A motorcycle tire (rear tire) of size 180 / 55R17 having the basic structure of FIG. 1 was manufactured based on the specifications in Tables 1 and 2. In addition, a tire in which the crown rubber was made of a single rubber was manufactured as a comparative example. The comparative tire has substantially the same structure as the tire of the example, except for the above-mentioned points. Each test tire was tested for wear resistance during straight running, grip performance during straight running, grip performance during cornering, and steering stability. The common specifications and test methods of each test tire are as follows. Rim size: MT5.50 Tire pressure: 250kPa Test vehicle: Displacement 1000cc

[0046] <Wear resistance when driving straight> The test tire was driven 10,000 km on a general road, and the thickness of the remaining rubber in the center of the tread was measured. The results are expressed as an index with the rubber thickness of the comparative example being 100, and the larger the value, the thicker the rubber is and the more excellent the wear resistance is.

[0047] <Grip performance when driving straight ahead, grip performance when cornering, and handling stability> The test tires were driven on a circuit and the driver's senses evaluated the grip performance during straight driving, grip performance during cornering, and handling stability. Each result was scored based on the comparative example being 100, with the higher the score, the better the result. The test results are shown in Tables 1-2.

[0048] [Table 1]

[0049] [Table 2]

[0050] As a result of the test, it was confirmed that the tire of the embodiment has improved grip performance during cornering while maintaining wear resistance during straight running. It was also confirmed that the tire of the embodiment exhibits excellent driving stability. [Explanation of symbols]

[0051] 2 Tread section 10 Base rubber layer 11 Cap rubber layer 12 Crown cap part 13 Shoulder cap section

Claims

1. A motorcycle tire including a tread portion, The tread portion includes a base rubber layer and a cap rubber layer that is disposed radially outward of the base rubber layer and that constitutes a contact surface of the tread portion, The cap rubber layer includes a crown cap portion disposed at a center portion in an axial direction of the tire, and a pair of shoulder cap portions disposed on both sides of the crown cap portion in an axial direction of the tire, a loss tangent tan δc of the crown cap portion at 0° C., a loss tangent tan δs of the shoulder cap portion at 0° C., and a loss tangent tan δb of the base rubber layer at 0° C. satisfy the following formula (1): The tan δc is 0.70 to 0.90, The tan δs is 0.90 to 1.

10. Tires for motorcycles. tanδc<tanδs≦tanδb…(1)

2. The motorcycle tire according to claim 1 , wherein a thickness of the base rubber layer on a radially inner side of the shoulder cap portion is greater than a thickness of the base rubber layer on a radially inner side of the crown cap portion.

3. 3. The motorcycle tire according to claim 1, wherein the base rubber layer has a thickness that increases continuously from an axial center portion toward both axial outer portions of the tire.

4. 4. The motorcycle tire according to claim 1, wherein the JIS-A hardness of the shoulder cap portion is in the range of -2 degrees to +5 degrees with respect to the JIS-A hardness of the crown cap portion.

5. 5. The motorcycle tire according to claim 1, wherein a maximum width in the tire axial direction of the ground contact surface of the crown cap portion is 20% to 60% of a maximum width in the tire axial direction of the ground contact surface of the tread portion.

6. 6. The motorcycle tire according to claim 1, wherein a thickness of the base rubber layer on an inner side in the tire radial direction of the crown cap portion is 10% to 40% of a total thickness of a tread rubber constituting the tread portion.

7. A plurality of grooves are provided on the ground contact surface of the tread portion, The motorcycle tire according to claim 1 , wherein a depth of each of the plurality of grooves is smaller than a thickness of the cap rubber layer.

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