JP2018192658A - Pneumatic bias tire, and method for manufacturing the same - Google Patents

Abstract

To improve blow resistance while exhibiting excellent grip performance and uneven wear resistance performance.SOLUTION: A method for manufacturing a pneumatic bias tire comprises a vulcanization process for vulcanizing a green tire 1N, including a carcass of bias structure, in a mold 20. The mold 20 has a contour shape 21 of a tread molding surface 2Scomposed of an inner mold arc part 21c having a curvature radius R1; and an outer mold arc part 21s connected to the inner mold arc part, and having a curvature radius R2smaller than the curvature radius R1. In the mold 20, a ratio BW/TWbetween a clip width BW and a width TWof a tread molding surface 2Ssatisfies 1.05-1.30. The young's modulus of a carcass cord 9 is 3000-10000 N/mm.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a pneumatic bias tire that is suitable as a tire for a racing cart and improves blow resistance while exhibiting excellent grip performance and uneven wear resistance, and a method for manufacturing the same.

  Pneumatic bias tires are frequently used as tires for racing carts. When manufacturing this type of tire, first, tire constituent members including a biased carcass are sequentially wound on a forming drum to form a cylindrical green tire. Next, the cylindrical raw tire is vulcanized while being expanded (shaped) in a toroid form in a mold.

  For this reason, in a pneumatic bias tire, the so-called low angle that causes the carcass cord tire equator in the crown region of the tread portion to be smaller than the carcass cord tire equator in the shoulder region due to the expansion. An angle is generated.

  As a result, the tire circumferential rigidity is smaller in the shoulder region than in the crown region. As a result, when the regular internal pressure is filled, the expansion of the shoulder region becomes large, and as shown in FIG. 4A, the crown region a tends to have a tread profile that is concave inward in the tire radial direction. Further, as shown in FIG. 4B, the contact surface shape f when a normal load is applied to the tire of the tread profile is extremely small in the contact length in the crown region a compared to the contact length in the shoulder region b. Become. As a result, the ground contact area is reduced, resulting in a decrease in grip performance and traction performance and a deterioration in wear resistance performance.

  Therefore, in a tire for a racing cart, in order to increase the ground contact area and improve the grip performance, it is desired to set a wide tread surface width (hereinafter sometimes referred to as “tread width”).

  However, when the clip width is kept as it is and the tread width is set to be large, a portion having a small curvature radius is generated in the sidewall portion in the case line of the tire in the mold. In this part, since the tension of the carcass cord is lowered, there arises a problem that the lateral rigidity of the tire is reduced and the steering stability is lowered.

  On the other hand, when both the clip width and the tread width are set large, the lateral rigidity of the tire can be ensured. However, since the clip width is increased, the tread portion is compressed in the tire axial direction when the rim is assembled. Therefore, the crown region tends to be concave, and the improvement in grip performance is not sufficiently achieved.

  The following Patent Document 1 proposes that the tire tread profile in the mold is formed by a convex crown arc having a curvature radius R1 and a convex shoulder arc having a curvature radius R2 larger than the curvature radius R1. ing.

  In this tread profile, the crown arc has a shape that protrudes outward in the tire radial direction as compared to the shoulder arc. Therefore, at the time of regular internal pressure filling, it is possible to suppress the crown region from becoming concave due to the protrusion, and it is possible to suppress a decrease in grip performance and traction performance and a deterioration in wear resistance performance.

  However, in the proposal, since the radius of curvature R1 is small, when a normal load is applied to a tire in a normal internal pressure state, a contact pressure distribution in which the contact pressure in the crown region becomes large is obtained. As a result, there is a problem that the temperature of the crown region rises locally during traveling and blow is likely to occur.

JP 2014-240171 A

  Then, this invention makes it a subject to provide the pneumatic bias tire which improves blow-proof performance, and its manufacturing method, exhibiting the outstanding grip performance and uneven wear-proof performance.

The first invention of the present application has two carcass plies in which the carcass extending from the tread portion to the bead portion through the sidewall portion is inclinedly arranged at an angle of 20 to 50 ° with respect to the tire equator, And the carcass ply is a method of manufacturing a pneumatic bias tire in which the direction of the inclination of the carcass cord is different from each other,
Including a vulcanization step of inflating and vulcanizing the raw tire containing the carcass in a mold,
In the mold, the contour shape of the tread molding surface that molds the contact surface of the tread portion is a mold arc portion having a radius of curvature R1 _K having an arc center at the tire equator, and a mold arc portion in the mold arc portion. contiguous and a convex arc shape made of a mold arcuate portion of the outer of the curvature radius R1 _K than the small radius of curvature R2 _K in the tire axial direction outer side,
The mold has a ratio BW / TW _K of 1.05 to 1.30 between the clip width BW and the width TW _K of the tread molding surface,
Moreover, the carcass cord has a Young's modulus of 3000 to 10000 N / mm ² .

In the method for manufacturing a pneumatic bias tire according to the present invention, a ratio R1 _K / R2 _K of the curvature radius R1 _K and the curvature radius R2 _K is preferably 2.5 to 7.0.

In the method for manufacturing a pneumatic bias tire according to the present invention, it is preferable that the curvature radius R1 _K is 200 to 1000 mm and the curvature radius R2 _K is 50 to 200 mm.

In the method of manufacturing the pneumatic bias tire according to the present invention, the width TW _K of the tread molding surface is preferably 100 to 120% of the rim width RW of the standard rim.

The second invention of the present application has two carcass plies in which the carcass extending from the tread portion to the bead portion through the sidewall portion is inclinedly arranged at an angle of 20 to 50 ° with respect to the tire equator, And the carcass ply is a pneumatic bias tire in which the direction of the inclination of the carcass cord is different from each other,
In a tire meridian cross section in a 5% internal pressure state in which a rim is assembled to a normal rim and 5% internal pressure is filled, the contour shape of the contact surface of the tread portion is a radius of curvature R1 _T having an arc center at the tire equator. A convex arc shape formed of an arc portion of the inner arc portion and an arc portion outside of the radius of curvature R2 _T which is continuous with the arc portion of the tire on the outer side in the tire axial direction and is smaller than the curvature radius R1 _T ,
Moreover, the carcass cord has a Young's modulus of 3000 to 10000 N / mm ² .

In the pneumatic bias tire according to the present invention, a ratio R1 _T / R2 _T of the curvature radius R1 _T and the curvature radius R2 _T is preferably 2.5 to 7.0.

In the pneumatic bias tire according to the present invention, it is preferable that the curvature radius R1 _T is 200 to 1000 mm and the curvature radius R2 _T is 50 to 200 mm.

In the pneumatic bias tire according to the present invention, the width TW _T of the ground surface of the tread portion is preferably 100 to 120% of the rim width RW of the standard rim.

The “landing surface” refers to a tire that is rim-assembled on a regular rim and filled with regular internal pressure, placed vertically on a flat plate at a camber angle of 0 degrees, and comes into contact with the flat plate when a normal load is applied. It means the surface to do. Further, the width TW _T of the ground plane means the maximum width in the tire axial direction of the ground plane.

  The “regular rim” is a rim determined for each tire in a standard system including a standard on which a tire is based. For example, a standard rim for JATMA, “Design Rim” for TRA, and ETRTO If there is, “Measuring Rim”. However, if the tire is for a racing cart, it shall be a rim prescribed by the Commission Internationale de Karting.

  The “regular internal pressure” is the air pressure defined by each standard for each tire in the standard system including the standard on which the tire is based. The maximum air pressure is specified for JATMA, and the table “TIRE LOAD LIMITS AT” for TRA. The maximum value described in “VARIOUS COLD INFLATION PRESSURES”. If ETRTO, “INFLATION PRESSURE”. However, if the tire is for a racing cart, the internal pressure specified by the International Cart Committee will be used.

  The “regular load” is a load determined by each standard for each tire in the standard system including the standard on which the tire is based. The maximum load capacity is specified for JATMA, and the table “TIRE LOAD LIMITS” is set for TRA. The maximum value described in "AT VARIOUS COLD INFLATION PRESSURES", or "LOAD CAPACITY" for ETRTO. However, if the tire is for a racing cart, the load specified by the International Cart Committee will be used.

  The “Young's modulus” of the carcass cord is a value measured according to a chemical fiber tire cord test method of JIS L1017.

In the first aspect of the invention, the contour of the tread molding surface of the mold, the curvature radius R1 _K of the mold arc portions of the inner, and larger than the radius of curvature R2 _K of the outer mold arcuate portion. Therefore, when the tire formed by this mold is filled with normal internal pressure, the crown region does not greatly protrude outward in the tire radial direction as compared with the shoulder region. As a result, it is possible to suppress the local rise in the temperature of the crown region during traveling, and it is possible to suppress the occurrence of blow.

Also in the mold, because it ensures the ratio BW / TW _K than 1.05 times, the width TW _K of the tread forming surface, can be set larger along with the clip width BW. Therefore, it is possible to suppress the occurrence of a portion having a small curvature radius in the case line of the tire in the mold while increasing the width of the contact surface, and the tire can be maintained in the lateral rigidity. On the contrary, when the clip width BW is increased, the carcass cord on the tire lumen side is deformed in the pulling direction when the rim is assembled, and the tension is increased, so that it can be expected to improve the lateral rigidity of the tire.

Here, when the radius of curvature R1 _K is larger than the radius of curvature R2 _K as described above, there is a disadvantage that the crown region tends to be a concave profile due to the low angle of the carcass cord. Further, when the clip width BW is increased, the tread portion is compressed in the tire axial direction when assembling the rim, which is disadvantageous in that the crown region tends to be concave.

However, in the present invention, the Young's modulus of the carcass cord is set to 3000 N / mm ² or higher, which is higher than the conventional one, and the ratio BW / TW _K is restricted to 1.30 or less. Therefore, when the normal internal pressure is filled, excessive expansion of the shoulder region can be suppressed by the high elasticity of the carcass cord, and the crown region can be prevented from having a concave profile. As a result, it is possible to exhibit excellent handling stability, grip performance, and uneven wear resistance.

In a second aspect, in the contour of the ground surface of the tire in the 5% pressure state, the curvature radius R1 _T of the arc portion of the inner, and larger than the radius of curvature R2 _T outside the arc portion. For this reason, when the tire is filled with the normal internal pressure, the crown region does not greatly protrude outward in the tire radial direction as compared with the shoulder region as in the tire of Patent Document 1. As a result, it is possible to suppress the local rise in the temperature of the crown region during traveling, and it is possible to suppress the occurrence of blow.

Further, when the radius of curvature R1 _T is larger than the radius of curvature R2 _T , there is a disadvantage that the crown region tends to have a concave profile when the tire is filled with normal internal pressure. However, the Young's modulus of the carcass cord is set to 3000 N / mm ² or higher, which is higher than before. Therefore, as in the first invention, when the regular internal pressure is filled, the shoulder region can be prevented from excessively expanding due to the high elasticity of the carcass cord, and the crown region can be prevented from having a concave profile, which is excellent. Grip performance and uneven wear resistance performance can be exhibited.

1 is a tire meridian cross-sectional view showing an embodiment of a pneumatic bias tire of the present invention. It is a development view of the carcass conceptually showing the arrangement state of the carcass cord. It is sectional drawing which shows a vulcanization process notionally. (A) is a tread profile of a conventional pneumatic bias tire in a normal internal pressure filling state, and (B) is a diagram showing a ground contact shape when a normal load is applied.

Hereinafter, embodiments of the present invention will be described in detail.
In FIG. 1, a pneumatic bias tire (hereinafter may be simply referred to as “tire”) 1 according to the present embodiment is assembled to a normal rim (not shown) and filled with an internal pressure of 5% of the normal internal pressure. In addition, a tire meridian cross section in the state of 5% internal pressure is shown. Unless otherwise specified, the dimensions and angles of the respective parts of the tire are values specified in the 5% internal pressure state.

  In this example, the case where the tire 1 is formed as a tire for a racing cart having an outer diameter of 350 mm or less is shown.

  As shown in FIG. 1, the tire 1 includes a carcass 6 having a bias structure that extends from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4. In this example, the carcass 6 includes folded portions 6b that are folded around the bead core 5 from the inner side to the outer side in the tire axial direction on both sides of the main body portion 6a straddling the bead cores 5 and 5.

  A bead apex rubber 8 having a triangular cross section extending from the bead core 5 to the outer side in the tire radial direction is disposed between the main body portion 6a and the folded portion 6b. The bead apex rubber 8 is made of a highly elastic rubber having a 100% modulus of about 10 to 15 MPa, for example, and reinforces the bead portion 4. The folded portion 6b terminates on the inner side in the tire radial direction from the outer end of the bead apex rubber 8.

  As conceptually shown in FIG. 2, the carcass 6 is formed of two carcass plies 6 </ b> A and 6 </ b> B in which a carcass cord 9 is inclined with respect to the tire equator C. The carcass plies 6A and 6B are stacked with the carcass cord 9 inclined in different directions.

  The angle α of the carcass cord 9 with respect to the tire equator C is 20 to 50 °. The tire 1 of the present embodiment is also vulcanized by expanding (shaping) a cylindrical raw tire into a toroidal shape in a mold 20 (shown in FIG. 3) in a vulcanization process, as in the conventional case. For this reason, due to the expansion (shaping), the angle αc of the carcass cord 9 in the crown region Yc of the tread portion 2 becomes lower than the angle αs of the carcass cord 9 in the shoulder region Ys. The angle difference αs−αc is about 10 to 30 °. The angles αc and αs are in the range of 20 to 50 °.

As the carcass cord 9, a highly elastic organic fiber cord having a Young's modulus of 3000 to 10000 N / mm ² is employed.

  As shown in FIG. 1, in the tire meridian section in the 5% internal pressure state, the contour shape 10 of the contact surface 2S of the tread portion 2 is the outer arc portion 10c that forms the crown region Yc and the outer portion that forms the shoulder region Ys. It forms a convex arc shape composed of the arc portion 10s.

Arc portion 10c of the inner consists arc curvature radius R1 _T having a circular arc centered on the tire equator C. The outer arcuate section 10s is made arc of small radius of curvature R2 _T than the radius of curvature R1 _T, connected to smoothly arcuate portion 10c of the inner.

The ratio R1 _T / R2 _T between the radius of curvature R1 _T and the radius of curvature R2 _T is preferably 2.5 to 7.0. The radius of curvature R1 _T is preferably 200 to 1000 mm, and the radius of curvature R2 _T is preferably 50 to 200 mm.

The width TW _T of the ground contact surface 2S is preferably 100 to 120% of the rim width RW of the regular rim.

  The tire 1 is manufactured by a tire manufacturing method including a vulcanization process conceptually shown in FIG. In the vulcanization step, the green tire 1N including the carcass is expanded in the mold 20 and vulcanized. The raw tire 1N can be formed by a method similar to the conventional method, and the vulcanization process can be performed by a method similar to the conventional method except for the mold 20 to be used.

The mold 20 includes a cavity surface K that molds the outer surface of the tire 1. The cavity surface K is formed a tread forming surface 2S _K for molding the contact surface 2S of the tread portion 2, a sidewall forming surface 3S _K for molding the outer surface of the sidewall portion 3, the outer surface of the bead portion 4 and a bead forming surface 4S _K.

Then, the contour 21 of the tread molding surface 2S _K includes a mold arc portion 21c of the curvature radius R1 _K having a circular arc centered on the tire equator C, and axially outward to the mold arc portion 21c of this It forms a convex arcuate consisting of an outer mold arc portion 21s of the radius of curvature R2 _K continuing smoothly. The inner arc portion 21c of the tire forms the inner arc portion 10c, and the outer mold arc portion 21s forms the outer arc portion 10s of the tire.

The radius of curvature R2 _K is smaller than the radius of curvature R1 _K, preferably, the ratio _R1 K / R2 _K is 2.5 to 7.0. The curvature radius R1 _K is preferably 200 to 1000 mm, and the curvature radius R2 _K is preferably 50 to 200 mm.

In Matakin type 20, and the clip width BW, the ratio BW / TW _K the width TW _K of the tread molding surface 2S _K is set to 1.05 to 1.30.

As described above, the curvature radius R1 _K of the mold arc portion 21c of the inner is greater than the radius of curvature R2 _K of the outer mold arcuate portion 21s. Therefore, in the tire 1 vulcanized by the mold 20, it is possible to suppress an excessive increase in the contact pressure of the crown region Yc when the normal internal pressure is filled and a normal load is applied. As a result, it is possible to suppress the occurrence of blow by the temperature locally rising in the crown region Yc during traveling.

In Matakin type 20, because it ensures the ratio BW / TW _K the width TW _K clip width BW and a tread molding surface more than 1.05 times, the width TW _K of the tread molding surface, with the clip width BW Can be set to large. Therefore, it is possible to suppress the occurrence of a portion having a small curvature radius in the case line of the tire 1 in the mold 20 while increasing the width of the ground contact surface 2S, and to maintain the lateral rigidity of the tire. On the contrary, when the clip width BW is increased, the carcass cord 9 on the tire lumen side is deformed in the pulling direction when the rim is assembled, and the tension is increased. Improvement of the tire lateral rigidity, in particular, the ratio BW / TW _K is easily triggered when more than 1.08 times. When the ratio BW / TW _K exceeds 1.15, particularly when it exceeds 1.20, the carcass cord of the folded portion 6b tends to be compressed and deformed when the rim is assembled. Therefore, the effect of improving the tire lateral rigidity gradually decreases.

Here, when the radius of curvature R1 _K is larger than the radius of curvature R2 _K as described above, there is a disadvantage that the crown region tends to be a concave profile due to the low angle of the carcass cord. Further, when the clip width BW is increased, the tread portion 2 is compressed in the tire axial direction when assembling the rim, so that there is a disadvantage that the crown region Yc tends to be concave.

However, in the present invention, the Young's modulus of the carcass cord 9 is set to 3000 N / mm ² or higher, which is higher than the conventional one, and the ratio BW / TWK is regulated to 1.30 or less. Therefore, excessive expansion of the shoulder region Ys during normal internal pressure filling can be suppressed by the high elasticity of the carcass cord, and the crown region Yc can be suppressed from having a concave profile. As a result, it is possible to exhibit excellent handling stability, grip performance, and uneven wear resistance.

If the Young's modulus is too high, the restraining force in the tire circumferential direction becomes strong, and the tire 1 cannot sufficiently expand during vulcanization. As a result, the finished shape of the tire may be defective. Upper limit of the Young's modulus from this point of view is at 10000 N / mm ² or less, preferably 8000 N / mm ² or less. Furthermore 6500N / mm ² or less, more 6000 N / mm ² or less. The lower limit of the Young's modulus, 5000N / mm ² or more, further 5500N / mm ² or more.

  By increasing the thickness of the carcass cord 9, excessive expansion suppression in the shoulder region Ys during normal internal pressure filling can be expected even when the Young's modulus is low. However, in this case, since the carcass cord 9 is thick, the envelope characteristics of the tire 1 are deteriorated, and the grip performance is deteriorated. Therefore, also from the viewpoint of ensuring the envelope characteristics, the carcass cord 9 having a high Young's modulus in the above range and having the cord diameter reduced to 1.0 mm or less is preferable.

  A cord having a high Young's modulus is inferior in compression fatigue resistance. Therefore, as shown in FIG. 1, it is preferable to secure a minimum thickness t of 0.6 mm or more from the carcass 6 to the outer surface of the buttress portion 12 in the buttress portion 12 of the tire that is likely to undergo compression deformation during traveling. The radius of curvature R of the arc on the outer surface of the buttress portion 12 is preferably 10 mm or more. Thereby, the compression deformation in the buttress part 12 can be reduced, and damage to the carcass cord 9 can be suppressed. The upper limit of the minimum thickness t is preferably 2.5 mm or less, and if it exceeds 2.5 mm, the rigidity of the buttress portion 12 is excessively increased and the steering stability tends to be adversely affected. Similarly, the upper limit of the radius of curvature R is preferably 35 mm or less, and if it exceeds 35 mm, the rigidity of the buttress portion 12 increases excessively and tends to adversely affect steering stability. From such a viewpoint, the lower limit of the minimum thickness t is more preferably 1.1 mm or more, and the upper limit is more preferably 2.0 mm or less. The lower limit of the radius of curvature R is more preferably 15 mm or more, and the upper limit is more preferably 30 mm or less.

Here, if the radius of curvature R1 _K of the inner mold arc portion 21c is less than 200 mm, the contact pressure in the crown region Yc becomes large. Therefore, the local temperature rise in the crown region Yc is not sufficiently suppressed, and the blow tends to occur. Further, there is a problem that uneven wear proceeds in the crown region Yc and the ground contact surface 2S cannot be used uniformly. In particular, when the radius of curvature R1 _K is 250 mm or more, the effect of improving uneven wear is great, and the entire ground contact surface 2S can be used uniformly.

On the other hand, if the radius of curvature R1 _K exceeds 1000 mm, the influence of the low angle of the carcass cord 9 increases, and it becomes impossible to sufficiently suppress the crown region Yc from becoming concave during normal internal pressure filling. From such a viewpoint, the lower limit value of the radius of curvature R1 _K is preferably 250 mm or more, and the upper limit value is preferably 800 mm or less.

The radius of curvature R2 _K of the mold arc portion 21s of Matasoto is below 50 mm, width of the ground plane 2S is narrowed, the grip performance is lowered. On the other hand, when the radius of curvature R2 _K exceeds 200 mm, the crown region Yc tends to have a concave profile during normal internal pressure filling. From this viewpoint, the lower limit value of the radius of curvature R2 _K is preferably at least 60 mm, the upper limit is preferably 150mm or less.

On the other hand, if the ratio R1 _K / R2 _{K of the} curvature radius is less than 2.5, the contact pressure of the crown region Yc becomes large, and the local temperature rise in the crown region Yc cannot be sufficiently suppressed, and the tendency of occurrence of blow It becomes. Further, there is a problem that uneven wear proceeds in the crown region Yc and the ground contact surface 2S cannot be used uniformly. In particular, uneven wear in the crown region Yc tends to occur when the ratio R1 _K / R2 _K is 3.0 or less. On the other hand, if the ratio R1 _K / R2 _K exceeds 7.0, the radius of curvature R1 _K becomes too large, and it becomes impossible to sufficiently suppress the crown region Yc from becoming concave during normal internal pressure filling. From such a viewpoint, the lower limit value of the ratio R1 _K / R2 _K is preferably 3.0 or more, more preferably 4.5 or more, and the upper limit value is preferably 6.5 or less, more preferably 5.5 or less.

If the ratio BW / TW _K of the clip width is below 1.05, the curvature radius in the sidewall molding surface 3S _K is a small a small arc portion occurs. Therefore, at the time of vulcanization, the tension of the carcass cord 9 is lowered at the small arc portion, and the lateral rigidity of the tire is lowered. Further, the carcass cord tends to be creased (folded) at the arc portion. On the other hand, if the ratio BW / TW _K exceeds 1.30, it becomes difficult to sufficiently prevent the crown region Yc from becoming concave even by adopting the carcass cord 9 having a high Young's modulus.

The width TW _K of the tread molding surface 2S _K is 100 to 120 percent of the rim width RW of the normal rim are preferred. When width TW _K falls below 100% of the rim width RW, width TW _T of ground plane 2S is narrowed, leading to reduction in grip performance. Conversely, if the width TW _K is larger than 120% of the rim width RW, because the clips width BW itself defined by the ratio BW / TW _K becomes wider, be prevented from crown region Yc is concave It becomes difficult. From this point of view, the lower limit of the width TW _K of the tread molding surface 2S _K is preferably at least 105% of the rim width RW, the upper limit is 115% or less.

Incidentally, as shown in FIG. 1, the contour shape 11 of the ground plane 2S of the tire 1 in a 5% internal pressure state, the rim varies slightly from the contour 21 of the tread molding surface 2S _K of the mold 20. However, the difference is small, and the preferable value of the curvature radius R1 _T , the preferable value of the curvature radius R2 _T , the preferable value of the ratio R1 _T / R2 _T , and the preferable value of the width TW _T of the contact surface 2S are the curvature in the mold 20. A preferable value of the radius R1 _K, a preferable value of the curvature radius R2 _K, a preferable value of the ratio R1 _K / R2 _{K, and} a preferable value of the width TW _K of the tread molding surface can be applied.

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

  A racing tire (size 10 × 4.50-5) for a racing cart having the structure shown in FIG. 1 was prototyped based on the specifications shown in Table 1. Each prototype tire was tested for grip performance, steering stability, blow resistance, and wear resistance.

In the test, the prototype tire was mounted on the front wheel of the racing cart under the following conditions, and the test course of one lap 734 (m) was run 10 laps. The grip performance and steering stability (turning performance) were evaluated by a five-point method based on the driver's sense. After running, the wear appearance of the tire was observed, and the wear resistance performance was evaluated by a five-point method. Further, the tire after running was disassembled, the degree of blow of the tread cross section was observed, and the blow resistance performance was evaluated by a five-point method. The larger the value, the better the performance.
・ Racing cart: 125cc 2-cycle four-wheel vehicle ・ Rim size: 4.75 inches ・ Internal pressure: 75kPa (front wheel)
-Road surface: DRY asphalt road A commercially available tire (size 11 x 7.10-5) is mounted on the rear wheel at an internal pressure of 75 kPa.

  As shown in Table 1, it was confirmed that the tires of the examples could improve the blow resistance while exhibiting excellent grip performance and uneven wear resistance.

DESCRIPTION OF SYMBOLS 1 Air-entry bias tire 1N Raw tire 2 Tread part 2S Grounding surface 2S _K tread molding surface 3 Idwall part 4 Bead part 6 Carcass 6A, 6B Carcass ply 9 Carcass cord 10 Arc part of arc part 10s in the contour shape 10c of the ground 20 Mold 21 Mold arc portion C of the mold arc portion 21c in the contour shape 21c of the tread molding surface C Tire equator

Claims (8)

The carcass from the tread portion through the sidewall portion to the bead portion has two carcass plies in which the carcass cord is inclined and arranged at an angle of 20 to 50 ° with respect to the tire equator, and the carcass ply is the carcass cord. A method of manufacturing a pneumatic bias tire stacked with different inclination directions of each other,
Including a vulcanization step of inflating and vulcanizing the raw tire containing the carcass in a mold,
In the mold, the contour shape of the tread molding surface that molds the contact surface of the tread portion is a mold arc portion having a radius of curvature R1 _K having an arc center at the tire equator, and a mold arc portion in the mold arc portion. contiguous and a convex arc shape made of a mold arcuate portion of the outer of the curvature radius R1 _K than the small radius of curvature R2 _K in the tire axial direction outer side,
The mold has a ratio BW / TW _K of 1.05 to 1.30 between the clip width BW and the width TW _K of the tread molding surface,
Moreover, the carcass cord is a method for producing a pneumatic bias tire having a Young's modulus of 3000 to 10000 N / mm ² . The ratio _R1 K / R2 _K of the radius of curvature R1 _K and the curvature radius R2 _K is a manufacturing method of claim 1 pneumatic bias tire according a 2.5 to 7.0 The method of manufacturing a pneumatic bias tire according to claim 1 or 2, wherein the curvature radius R1 _K is 200 to 1000 mm, and the curvature radius R2 _K is 50 to 200 mm. The width TW _K of the tread molding surface, method of manufacturing a pneumatic bias tire according to claim 1 which is 100 to 120% of the rim width RW of the standard rim. The carcass from the tread portion through the sidewall portion to the bead portion has two carcass plies in which the carcass cord is inclined and arranged at an angle of 20 to 50 ° with respect to the tire equator, and the carcass ply is the carcass cord. Pneumatic tires that are stacked with different inclination directions,
In a tire meridian cross section in a 5% internal pressure state in which a rim is assembled to a normal rim and 5% internal pressure is filled, the contour shape of the contact surface of the tread portion is a radius of curvature R1 _T having an arc center at the tire equator. A convex arc shape formed of an arc portion of the inner arc portion and an arc portion outside of the radius of curvature R2 _T which is continuous with the arc portion of the tire on the outer side in the tire axial direction and is smaller than the curvature radius R1 _T ,
Moreover, the carcass cord is a pneumatic bias tire having a Young's modulus of 3000 to 10000 N / mm ² . The ratio _R1 T / R2 _T and the radius of curvature R1 _T and the curvature radius R2 _T is pneumatic bias tire according to claim 5, wherein a 2.5 to 7.0. The pneumatic bias tire according to claim 5 or 6, wherein the curvature radius R1 _T is 200 to 1000 mm, and the curvature radius R2 _T is 50 to 200 mm. Width TW _T of the ground surface of the tread portion, pneumatic bias tire according to any one of claims 5-7 which is 100 to 120% of the rim width RW of the standard rim.

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