Motorcycle tires

Abstract

To provide a motorcycle tire capable of improving robustness with respect to engagement with a rim and operation stability.SOLUTION: A motorcycle tire includes a pair of bead parts 4. The pair of bead parts 4 is provided with bead cores 5 and bead bottom surfaces 11 respectively. In the motorcycle tire, the following formula (1) is satisfied so that a distance in a tire axis direction between outer surfaces in a tire axial direction of the pair of bead parts 4 matches a rim width of a regular rim R in a non-rim assembly state holding the pair of bead parts 4: 0.99≤Dc / (Dr+2T)≤1.00 ...(1) Here, "Dc" is an inner diameter of the bead core 5 at a central position in the tire axial direction of the bead core 5; "Dr" is a rim diameter of the regular rim R; and "T" is a distance in a tire radial direction from an inner surface of the bead core 5 at the central position to the bead bottom surface 11.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a tire for a motorcycle.

Background Art

[0002] In Patent Document 1 below, a tire for a motorcycle has been proposed in which the angle of the bead bottom surface of the bead portion with respect to the tire axis direction is specified, thereby improving the fitting property with the rim and the handling stability in a balanced manner.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] A tire for a motorcycle is mounted on a rim defined by standards, but the rim diameter varies within an inevitable tolerance range. The variation in the rim diameter affects the fitting property with the tire for a motorcycle and the handling stability of the tire for a motorcycle, but it is desirable to minimize such an influence. That is, there is a demand for a tire for a motorcycle that is highly robust and hardly affected by external factors such as the tolerance of the rim diameter.

[0005] The present disclosure has been devised in view of the above actual situation, and the main object thereof is to provide a tire for a motorcycle that can improve the robustness with respect to the fitting property with the rim and the handling stability.

Means for Solving the Problems

[0006] This disclosure relates to a motorcycle tire including a pair of bead portions, each of which comprises a bead core and a bead bottom surface located radially inward from the bead core, and satisfies the following equation (1) in a non-rim-assembled state in which the pair of bead portions are held such that the distance between the outer surfaces of the pair of bead portions in the tire axial direction matches the rim width of a normal rim. 0.99≦Dc / (Dr+2T)≦1.00 …(1) Here, "Dc" is the inner diameter of the bead core at its center position in the tire axial direction, "Dr" is the rim diameter of the regular rim, and "T" is the radial distance from the inner surface of the bead core to the bottom surface of the bead at the center position. [Effects of the Invention]

[0007] By adopting the above configuration, the motorcycle tire of this disclosure can improve robustness with respect to rim fitment and handling stability. [Brief explanation of the drawing]

[0008] [Figure 1] This is a cross-sectional view showing one embodiment of a motorcycle tire according to the present disclosure. [Figure 2] This is a magnified view of the bead portion in Figure 1. [Figure 3] This is an enlarged view showing the outline of the bead portion in Figure 2. [Modes for carrying out the invention]

[0009] Hereinafter, one embodiment of the present disclosure will be described with reference to the drawings. Figure 1 is a meridian cross-sectional view of the motorcycle tire 1 of this embodiment (hereinafter sometimes simply referred to as "tire") including the tire rotation axis in the normally mounted rim state. The tire 1 of this embodiment is a rear tire for a motorcycle suitable for on-road sports riding. However, the tire of this disclosure is not limited to this embodiment.

[0010] "Standard rim mounting condition" means a state in which the tire is mounted on a standard rim R and adjusted to the standard internal pressure.

[0011] "Regular Rim R" refers to the rim specified for each tire within the standard system that the tire is based on. For example, it is the "Standard Rim" for JATMA, the "Design Rim" for TRA, and the "Measuring Rim" for ETRTO.

[0012] "Regular internal pressure" refers to the air pressure specified for each tire by each standard within the tire standard system, including the standard on which the tire is based. For JATMA, it is the "maximum air pressure," for TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES," and for ETRTO, it is the "INFLATION PRESSURE."

[0013] As shown in Figure 1, the 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 connected to both sides of the tread portion 2 in the tire axial direction. The bead portions 4 are connected to the radially inward side of the sidewall portions 3. The tread portion 2 has a contact surface 2s between one tread end Te and the other tread end Te that is convex outward in the tire radial direction and curved in an arc shape, so that sufficient contact area can be obtained even when turning with a large camber angle. A bead core 5 is embedded in the bead portion 4.

[0014] The tread edge Te corresponds to the edge of the contact surface 2s of the tread portion 2, and contacts the road surface when turning at the maximum camber angle.

[0015] 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 the other bead portion 4.

[0016] The carcass 6 includes, for example, a carcass ply 6A containing multiple carcass cords. In this embodiment, the carcass 6 is composed of a single carcass ply 6A, but it may also consist of multiple carcass plies stacked on top of each other. The carcass ply 6A includes a main body portion 6a and a folded portion 6b. The main body portion 6a extends from the tread portion 2 through the sidewall portions 3 on both sides to the bead core 5 of the bead portions 4 on both sides. The folded portion 6b is connected to the main body portion 6a and is folded around the bead core 5 from the inside to the outside in the tire axial direction.

[0017] The tread portion 2 is provided with, for example, a belt layer 7 and a band layer 8. The belt layer 7 includes, for example, a belt ply containing multiple belt cords inclined at an angle of 10 to 45° with respect to the circumferential direction of the tire. In this embodiment, the belt layer 7 is composed of a single belt ply, but multiple belt plies may be stacked on top of each other. The band layer 8 includes, for example, a jointless band ply in which band cords are spirally wound at an angle of 5° or less with respect to the circumferential direction of the tire. Such belt layer 7 and band layer 8 can effectively reinforce the tread portion 2.

[0018] Figure 2 shows an enlarged view of the bead portion 4. As shown in Figure 2, each pair of bead portions 4 comprises a bead core 5, a bead outer surface 12 which is the surface that is outward from the bead core 5 in the tire axial direction, a bead bottom surface 11 which is located inward from the bead core 5 in the tire radial direction, and an arc-shaped bead heel surface 13 which connects the bead outer surface 12 and the bead bottom surface 11. The bead outer surface 12, the bead bottom surface 11 and the bead heel surface 13 are in contact with the normal rim R (shown in Figure 1) when the tire is mounted on the normal rim.

[0019] In this disclosure, the following equation (1) is satisfied in a non-rim-assembled state in which a pair of bead portions 4 are held such that the distance L1 between the outer surfaces of the pair of bead portions 4 in the tire axial direction matches the rim width W1 of the regular rim (shown in Figure 1). In this specification, unless otherwise specified, the dimensions of each part of the tire are values ​​measured in the non-rim-assembled state. 0.99≦Dc / (Dr+2T)≦1.00 …(1)

[0020] Here, "Dc" is the inner diameter of the bead core 5 at the center position of the bead core 5 in the tire axial direction. Also, as shown in FIG. 1, "Dr" is the rim diameter of the standard rim R, and is measured at the bead base line BL which is the rim diameter position determined by the standard. Further, as shown in FIG. 2, "T" is the distance in the tire radial direction from the inner surface 5a of the bead core 5 to the bead bottom surface 11 at the center position. The rim width W1 is defined by the standard. The distance L1 is preferably measured, for example, at the center positions of the pair of bead cores 5 in the tire radial direction.

[0021] When the inner diameter Dc of the bead core 5 varies slightly depending on the measurement position, it is desirable to adopt, for example, the average value of the values measured at a plurality of different positions as the inner diameter Dc. The average value is preferably obtained from at least two inner diameter values measured at positions shifted by 90° in the tire circumferential direction. The average value is preferably obtained based on the inner diameters measured at as many positions as possible. Similarly, it is desirable to adopt a similar average value for the distance T.

[0022] By adopting the above configuration, the tire 1 of the present disclosure can improve the robustness of the fitting property with the rim and the handling stability. The mechanism is as follows.

[0023] "Dr + 2T" in the above formula (1) is obtained by adding twice the distance T from the inner surface 5a of the bead core 5 to the bead bottom surface 11 to the rim diameter Dr of the standard rim, and corresponds to the substantial outer diameter of the portion where the bead core 5 is fitted. That is, in the present disclosure, the inner diameter Dc of the bead core 5 and the substantial outer diameter of the portion where the bead core 5 is fitted are accurately defined by formula (1). As a result, even when the rim diameter of the rim on which the tire 1 is mounted is smaller or larger than the design value, or when there is a large variation in the rim diameter dimension depending on the measurement position, excessive deterioration is unlikely to occur in terms of the fitting property of the rim and the handling stability. Therefore, the tire 1 of the present disclosure can improve the robustness with respect to the fitting property with the rim and the handling stability.

[0024] In this specification, rim fitment refers to the ease of mounting the tire to the rim. Therefore, the smaller the internal tire pressure when the bead portion 4 of the tire 1 crosses the rim hump, the better the rim fitment. On the other hand, handling stability refers to the stability when a two-wheeled vehicle equipped with the tire is driven, and the greater the fitting force of the tire 1 acting on the rim, the greater the handling stability tends to be. In other words, rim fitment and handling stability are performance characteristics that tend to be inversely related. With the above-described configuration, the tire 1 of this disclosure can be expected to improve both of these inversely related performance characteristics, rim fitment and handling stability.

[0025] The configuration of this embodiment will be described in more detail below. Note that each configuration described below represents a specific aspect of this embodiment. Therefore, it goes without saying that this disclosure can achieve the above-described effects even without the configurations described below. Furthermore, even if any one of the configurations described below is applied individually to a tire of this disclosure having the above-described features, an improvement in performance corresponding to each configuration can be expected. Moreover, if several of the configurations described below are applied in combination, a combined improvement in performance corresponding to each configuration can be expected.

[0026] The bead core 5 of this embodiment has a rectangular cross-sectional shape in the tire cross-section, enclosed by inner surface 5a and outer surface 5b in the tire radial direction, and first side surface 5c and second side surface 5d in the tire axial direction. However, the corner portions where these surfaces meet are curved in an arc shape. Also, the first side surface 5c is located further outward in the tire axial direction than the second side surface 5d. The inner surface 5a and outer surface 5b each extend along the tire axial direction. The first side surface 5c and the second side surface 5d each extend along the tire radial direction. The angular difference between the first side surface 5c and the second side surface 5d is, for example, 10° or less, and preferably 5° or less. In a more desirable embodiment, the first side surface 5c and the second side surface 5d extend substantially parallel to each other. Such a bead core 5 helps to reliably suppress the collapse of the bead portion 4 and improve steering stability.

[0027] In the non-rim-mounted state described above, the diameter Dv at the intersection of a virtual first straight line 16 extending outward in the tire axial direction from the bead bottom surface 11 and a virtual second straight line 17 extending inward in the tire radial direction from the bead outer surface 12 is preferably 99.2% to 99.6% of the rim diameter Dr of the regular rim (shown in Figure 1), and more preferably 99.3% to 99.5%. This optimizes the inner diameter of the bead portion 4, improving rim slippage prevention performance and handling stability while maintaining fit with the rim.

[0028] The first straight line 16 corresponds to a tangent line passing through the end of the bead bottom surface 11 on the bead heel surface 13 side, and the second straight line 17 corresponds to a tangent line passing through the end of the bead outer surface 12 on the bead heel surface 13 side. The bead heel surface 13 is a curved surface that is convex in the diagonal direction of the bead portion 4 (the direction outward in the tire axial direction and inward in the tire circumferential direction), and in this embodiment it is configured as an arc-shaped curved surface having a single radius of curvature. Furthermore, the diameter Dv corresponds to the diameter of a virtual circle formed when the intersection points 18 of the first straight line 16 and the second straight line 17 are gathered over the entire circumference of the tire.

[0029] In a preferred embodiment, the angle θ3 between the first straight line 16 and the second straight line 17 is, for example, 90 to 110°, and preferably 95 to 105°.

[0030] Figure 3 shows an enlarged view showing only the outline of the bead portion 4. As shown in Figure 3, the bead bottom surface 11 includes a first bottom surface 21 inclined with respect to the tire axis, and a second bottom surface 22 that is connected to the inner side of the first bottom surface 21 in the tire axis and extends at a larger angle with respect to the tire axis than the first bottom surface 21. The bead bottom surface 11, including the first bottom surface 21 and the second bottom surface 22, improves the rim fitment and rim slippage prevention performance in a balanced manner.

[0031] In the tire cross-section in the non-rim-mounted state described above, the first bottom surface 21 of this embodiment extends in a straight line. The angle θ1 of the first bottom surface 21 with respect to the tire axis is, for example, 15° or less, preferably 10° or less, and more preferably 7° or less. Specifically, the angle θ1 of the first bottom surface 21 is 3 to 7°. In a more desirable embodiment, the angle between the first bottom surface 21 and the inner surface 5a of the bead core 5 (shown in Figure 2) is 0 to 10°. In this embodiment, the angle of the first bottom surface 21 coincides with the angle of the first straight line 16 with respect to the tire axis.

[0032] In the tire cross-section in the non-rim-mounted state described above, the second bottom surface 22 of this embodiment extends in a straight line. The angle θ2 of the second bottom surface 22 with respect to the tire axis is, for example, 30° or less, and preferably 24° or less. Specifically, the angle θ2 of the second bottom surface 22 is 18 to 24°. Such a second bottom surface 22 can improve rim slippage prevention performance while maintaining rim fitability.

[0033] As shown in Figure 2, in order to improve the rim fit and rim slippage prevention performance in a balanced manner, the angle θ4 (shown in Figure 2) between the first bottom surface 21 and the second bottom surface 22 is preferably 150° or more, and more preferably 160°. That's all. The angle is preferably 175° or less, and more preferably 170° or less.

[0034] The angle θ4 between the first bottom surface 21 and the second bottom surface 22 is greater than the angle θ3 between the first straight line 16 and the second straight line 17. The difference between angle θ3 and angle θ4 is, for example, 60 to 80°, preferably 65 to 75°. This balances and improves the pressure on the outer surface 12 of the bead acting on the rim and the pressure on the second bottom surface 22 acting on the rim, resulting in excellent handling stability.

[0035] In the cross-section of the tire, the boundary 25 between the first bottom surface 21 and the second bottom surface 22 is located, for example, within a region where the bead core 5 is virtually extended inward in the tire radial direction. Furthermore, it is desirable that the boundary 25 is located inward in the tire axial direction from the center position of the bead core 5 in the tire axial direction. The distance in the tire axial direction between the boundary 25 and the center position of the bead core 5 is, for example, 25% to 35% of the width of the bead core 5 in the tire axial direction. This allows the second bottom surface 22 to adhere firmly to the rim, improving the durability of the bead portion 4.

[0036] The aforementioned distance T is, for example, 20% to 40% of the tire circumferential width of the bead core 5, preferably 25% to 35%. This improves both the fit with the rim and handling stability in a balanced manner.

[0037] The outer surface 12 of the bead includes a portion that extends linearly from the end on the bead heel surface 13 side in the tire cross-section. This portion has an angle difference of 5° or less with respect to, for example, the first side surface 5c of the bead core 5.

[0038] At the radial position of the bead core 5 at the center of the tire in the tire's radial direction, it is desirable that the rubber thickness of the bead core 5 on the outer side in the tire's axial direction is 3.0 mm or less. This makes it easier for the bead portion 4 to overcome the hump, further improving the fit to the rim.

[0039] As shown in Figure 3, in the cross-section of the bead portion 4, the radius of curvature r1 of the bead heel surface 13 is preferably 2.5 to 4.0 mm. Such a bead heel surface 13 can effectively balance rim fitment and rim slippage prevention performance.

[0040] Although one embodiment of a motorcycle tire according to the present disclosure has been described in detail above, the present disclosure is not limited to the specific embodiment described above and can be implemented in various modified forms. [Examples]

[0041] A motorcycle tire (rear wheel tire) of size 190 / 55ZR17 having the basic structure shown in Figure 1 was manufactured based on the specifications in Tables 1 and 2. As a comparative example, a tire with Dc / (Dr+2T) outside the scope of this disclosure was also prototyped. Except for the matters described above, the comparative tire had substantially the same configuration as the example tire. The fit with the rim, handling stability, rim slippage prevention performance, and robustness of the fit with the rim and handling stability were tested for each test tire. The common specifications and test methods for each test tire are as follows. Rim size: MT6.00 Tire pressure: 250kPa Test vehicle: 1000cc engine displacement

[0042] <Fitting compatibility with the rim> The maximum internal pressure at which the tire bead crosses the rim hump during tire pressure inflation when mounting the tire to the rim was measured. The result is the reciprocal of the maximum internal pressure and is shown as an index with the comparative example set to 100. A larger value indicates a lower maximum internal pressure and better fit with the rim.

[0043] <Rim slip prevention performance> In accordance with JIS-D4230, a load was applied laterally to the bead portion of a tire mounted on a rim but without internal pressure filling, and the resistance force was measured when the bead portion detached from the rim. The results are shown as an index with the resistance force of Comparative Example 1 set to 100, and a higher value indicates better rim slippage prevention performance.

[0044] <Handling Stability> The handling stability of test vehicles equipped with test tires was evaluated subjectively by the drivers during track driving. The results are scored with the comparative example set to 100, and a higher number indicates better handling stability.

[0045] <Robustness of rim engagement and handling stability> The fitting force of the bead to the rim (in this embodiment, the Hoffman fitting force, in units of "kN") was measured using a bead expansion force testing machine (a testing machine manufactured by Hoffman GmbH), and the robustness of the fit with the rim and the handling stability were evaluated based on the measured value. The specific evaluation method is as follows. (1) A test tire was mounted on a test fixture that could be set to any rim diameter, and the fitting force was measured when the rim diameter of the fixture was 0.3 mm larger than the rim diameter of the regular rim (hereinafter referred to as the first measurement value), and when the rim diameter of the fixture was 0.3 mm smaller than the rim diameter of the regular rim (hereinafter referred to as the second measurement value). (2) The first and second measured values ​​were plotted on a coordinate system with the rim diameter on the horizontal axis and the fitting force on the vertical axis, and the slope of the line connecting these two points was measured. (3) The robustness was evaluated by the slope of the straight line measured in (2) above. The result is an index where the reciprocal of the slope of the straight line for the comparative example is set to 100. The larger this value, the smaller the change in fitting force due to differences in rim diameter, and the better the robustness. The test results are shown in Tables 1 and 2.

[0046] [Table 1]

[0047] [Table 2]

[0048] The test results confirmed that the tire in the embodiment exhibited improved robustness in terms of rim fitment and handling stability. Furthermore, it was confirmed that the tire in the embodiment showed a well-balanced improvement in rim fitment, rim slippage prevention performance, and handling stability.

[0049] [Note] This disclosure includes the following aspects.

[0050] [Disclosure 1] A motorcycle tire including a pair of bead portions, Each of the pair of bead portions comprises a bead core and a bead bottom surface located inward from the bead core in the tire radial direction. In a non-rim-assembled state where the pair of bead portions are held together such that the distance between the outer surfaces of the pair of bead portions in the tire axial direction matches the rim width of the regular rim, the following equation (1) is satisfied. Motorcycle tires. 0.99≦Dc / (Dr+2T)≦1.00 …(1) Here, "Dc" is the inner diameter of the bead core at its center position in the tire axial direction, "Dr" is the rim diameter of the regular rim, and "T" is the radial distance from the inner surface of the bead core to the bottom surface of the bead at the center position. [Disclosure 2] In the aforementioned non-rim assembled state, The diameter Dv at the intersection of a hypothetical first straight line extending outward in the tire axial direction from the bottom surface of the bead and a hypothetical second straight line extending inward in the tire radial direction from the outer surface of the bead, which is the outer surface of the bead portion in the tire axial direction, is 99.2% to 99.6% of the rim diameter Dr of the regular rim, as described in Disclosure 1. For motorcycles tire. [Disclosure 3] The pair of bead portions include an arc-shaped bead heel surface connecting the outer surface of the bead, which is the outer surface in the tire axial direction, and the bottom surface of the bead. In the cross-section of the bead portion, the radius of curvature of the bead heel surface is 2.5 to 4.0 mm, as described in Disclosure 1. For motorcycles tire. [Disclosure 4] The motorcycle tire according to Disclosure 1, wherein the bead bottom surface includes a first bottom surface and a second bottom surface that is connected to the tire axially inward side of the first bottom surface and extends at a larger angle with respect to the tire axial direction than the first bottom surface. [Disclosure 5] The motorcycle tire according to disclosure 4, wherein the angle of the first bottom surface with respect to the tire axis is 7° or less. [Disclosure 6] The motorcycle tire according to disclosure 4 or 5, wherein the angle of the second bottom surface with respect to the tire axis is 24° or less. [Explanation of Symbols]

[0051] 4. Bead section 5 Bead core 11. Bead bottom R Regular Rim DC: Inner diameter of the bead core at the center position in the tire axial direction. Dr. Regular rim diameter T: The distance in the radial direction of the tire from the inner surface of the bead core to the bottom surface of the bead at the center position of the bead core.

Claims

1. A motorcycle tire including a pair of bead portions, Each of the pair of bead portions comprises a bead core and a bead bottom surface located inward from the bead core in the tire radial direction. In a non-rim-assembled state where the pair of bead portions are held together such that the distance between the outer surfaces of the pair of bead portions in the tire axial direction matches the rim width of the regular rim, the following equation (1) is satisfied: The bead bottom surface includes a first bottom surface and a second bottom surface that is connected to the inner side of the first bottom surface in the tire axial direction and extends at a larger angle with respect to the tire axial direction than the first bottom surface. The angle of the first bottom surface with respect to the tire axis is 7° or less. The angle of the second bottom surface with respect to the tire axis is 24° or less. Motorcycle tires. 0.99≦Dc / (Dr+2T)≦1.00…(1) Here, "Dc" is the inner diameter of the bead core at its center position in the tire axial direction, "Dr" is the rim diameter of the regular rim, and "T" is the radial distance from the inner surface of the bead core to the bottom surface of the bead at the center position.

2. In the aforementioned non-rim assembled state, The motorcycle tire according to claim 1, wherein the diameter Dv at the intersection of a hypothetical first straight line extending outward in the tire axial direction from the bottom surface of the bead and a hypothetical second straight line extending inward in the tire radial direction from the outer surface of the bead, which is the outer surface of the bead portion in the tire axial direction, is 99.2% to 99.6% of the rim diameter Dr of the regular rim.

3. The pair of bead portions include an arc-shaped bead heel surface connecting the outer surface of the bead, which is the outer surface in the tire axial direction, and the bottom surface of the bead. The motorcycle tire according to claim 1, wherein the radius of curvature of the bead heel surface in the cross-section of the bead portion is 2.5 to 4.0 mm.

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