JP2017121751A - Manufacturing method of motor cycle tire for irregular ground - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a motor cycle tire for irregular ground suppressing generation of crack of a side wall and excellent in rotation performance and operational stability.SOLUTION: A manufacturing method has a preliminary molding process for providing a roll cover by preliminary molding and a vulcanization process for injecting the roll cover to a mold 28 and compressing and heating the same. The mold 28 satisfies the following relational expressions, where Rc is a curvature radius in a center region of a tread cavity surface 34, Rs is a curvature radius in a shoulder region, Wt is width in an axis direction of the tread cavity surface 34, Ht is height defining tire height and He is height in a radial direction of the tread cavity surface 34 in a cross section vertical to a circumferential direction of the mold 28. 0.7≤Rc/Rs≤0.9. 0.7≤Ht/Wt≤0.8. 0.40≤He/Ht≤0.45.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method of manufacturing a tire suitable for a motorcycle that travels on rough terrain such as a forest or a wilderness.

  In rough terrain, rocks, gaps, and undulations are scattered. In rough terrain, the road surface is full of undulations. A motorcycle traveling on rough terrain repeats jumping and landing. In motorcycle tires running on rough terrain, landing impacts are absorbed by flexible sidewalls. When landing, a large load is applied to the tire. Tires traveling on rough terrain repeatedly undergo large deformations compared to those traveling on paved road surfaces. Severe use on rough terrain can cause the tire to crack. Damage to the sidewall may occur.

  In Japanese Patent Laid-Open No. 2008-247193, a split position between a tread segment of a mold and a side plate is formed at a predetermined position of a side portion of a tire. Thereby, the tire which improved the crack resistance of the side part is disclosed. In the tire disclosed in Japanese Patent Application Laid-Open No. 2012-139898, a built-up portion that allows shoulder blocks to be continuous is formed. In the tire mold, the split position between the tread segment and the side plate is set between the apex of the built-up portion and the base point of the shoulder block. Thus, a tire in which the occurrence of side wall cracks is suppressed is disclosed.

JP 2008-247193 A JP2012-139898A

  However, even in these tires, cracks have occurred in the sidewalls due to long-term use under severe conditions. From the viewpoint of suppressing the occurrence of side wall cracks, further tire improvements are required.

  An object of the present invention is to provide a method for manufacturing a motorcycle tire for rough terrain, in which the occurrence of cracks in the sidewall is suppressed and the traction performance and the turning performance are excellent.

The method for manufacturing a motorcycle tire for rough terrain according to the present invention includes a preforming step in which a raw cover is obtained by preforming, and a vulcanization step in which the raw cover is put into a mold and pressurized and heated. .
The mold used in this vulcanization step includes a tread segment having a tread cavity surface that forms a tread surface, and a side plate having a sidewall cavity surface that forms an axial outer surface of the sidewall.
The tread cavity surface forms a tread surface composed of an outer peripheral surface of each independent block.
In a cross section perpendicular to the circumferential direction, the radius of curvature in the center region of the tread cavity surface is Rc, the radius of curvature in the shoulder region of the tread cavity surface is Rs, and the axial width of the tread cavity surface is Wt, thereby determining the tire height. When the height is Ht and the radial height of the tread cavity surface is He, the following relational expression is satisfied.
0.7 ≦ Rc / Rs ≦ 0.9
0.7 ≦ Ht / Wt ≦ 0.8
0.40 ≦ He / Ht ≦ 0.45

  Preferably, in the tire manufacturing method, the raw cover that is put into the mold in the vulcanization step is positioned on the tread member that is vulcanized to form the tread, and on the radially inner side of the tread member. A band member is provided that forms a band by being vulcanized. The band member includes a cord extending in the circumferential direction and a rubber member constituting a topping rubber. This cord is made of steel and polyamide fibers (aramid fibers).

  Preferably, in this tire manufacturing method, the height Hb of the mold for determining the height of the block is 8 mm or more and 19 mm or less.

Preferably, in this tire manufacturing method, the ratio Hd / Ht between the radial height Hd and the height Ht of the split position between the tread segment and the side plate satisfies the following relational expression.
0.3 ≦ Hd / Ht ≦ 0.4

The metal mold | die which concerns on this invention is used for the vulcanization process of the motorcycle tire for rough terrain. The mold includes a tread segment including a tread cavity surface that forms a tread surface, and a side plate including a sidewall cavity surface that forms an axial outer surface of the sidewall.
The tread cavity surface forms a tread surface composed of an outer peripheral surface of each independent block. In a cross section perpendicular to the circumferential direction, the radius of curvature in the center region of the tread cavity surface is Rc, the radius of curvature in the shoulder region of the tread cavity surface is Rs, and the axial width of the tread cavity surface is Wt, thereby determining the tire height. When the height is Ht and the radial height of the tread cavity surface is He, this mold satisfies the following relational expression.
0.7 ≦ Rc / Rs ≦ 0.9
0.7 ≦ Ht / Wt ≦ 0.8
0.40 ≦ He / Ht ≦ 0.45

  In the motorcycle tire for rough terrain according to the production method of the present invention, occurrence of cracks in the sidewall is suppressed. This tire is excellent in traction performance and turning performance.

FIG. 1 is a cross-sectional view illustrating a part of a motorcycle tire for rough terrain manufactured by a manufacturing method according to an embodiment of the present invention. FIG. 2 is an explanatory view showing a part of a mold used in the vulcanizing process of the tire of FIG.

  Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

  FIG. 1 is a cross-sectional view illustrating a part of a motorcycle tire 2 for rough terrain according to an embodiment of the present invention. In FIG. 1, the vertical direction is the radial direction of the tire 2, the horizontal direction is the axial direction of the tire 2, and the direction perpendicular to the paper surface is the circumferential direction of the tire 2. A one-dot chain line CL represents the equator plane of the tire 2. A straight line BL indicates a bead base line of the tire 2. The shape of the tire 2 is substantially symmetric with respect to the equator plane CL.

  The tire 2 includes a tread 4, a sidewall 6, a bead 8, a carcass 10, and a band 12. The tire 2 is a pneumatic tire. The tire 2 is a tube type. The tire 2 is used for, for example, an off-road type two-wheeled vehicle. The tire 2 is attached to a motorcycle that runs on rough terrain. The tire 2 may be a tubeless type.

  The tread 4 is made of a crosslinked rubber having excellent wear resistance. The tread 4 has a shape protruding outward in the radial direction. The tread 4 has a large number of blocks 14 standing substantially outward in the radial direction. A groove 18 is formed between one block 14 and another block 14. In the tire 20, adjacent blocks 14 are separated by the groove 18 in the axial direction and the circumferential direction. The blocks 14 are independent in the axial direction and the circumferential direction.

  Point E in FIG. 1 indicates a tread edge. Point B indicates the root of the block 14 located on the outermost side in the axial direction. In the tire 2, the outer surface of the block 14 of the tread 4 forms a tread surface 16. The outer end in the axial direction of the tread surface 16 is a tread edge E. The tread surface 16 contacts the road surface.

  The sidewall 6 extends substantially inward in the radial direction from the axial end of the tread 4. The sidewall 6 is made of a crosslinked rubber. The sidewall 6 absorbs an impact from the road surface by bending. Further, the sidewall 6 prevents the carcass 10 from being damaged.

  The bead 8 is located substantially inward of the sidewall 6 in the radial direction. The bead 8 includes a core 20 and an apex 22 that extends radially outward from the core 20. The core 20 has a ring shape. The core 20 includes a plurality of non-stretchable wires. A typical material for the wire is steel. The apex 22 is tapered outward in the radial direction. The apex 22 is made of a highly hard crosslinked rubber.

  The carcass 10 is spanned between the beads 8 on both sides, and is along the inside of the tread 4 and the sidewall 6. The carcass 10 includes a carcass ply 24. The carcass ply 24 is folded around the core 20 from the inner side to the outer side in the axial direction. By this folding, the carcass ply 24 is formed with a main portion 24a and a pair of folded portions 24b. The main portion 24 a extends from the equator plane toward each bead 26. The folded portion 24b extends continuously outward in the radial direction continuously to the main portion 24a. The folded portion 24b is stacked on the main portion 24a. The carcass ply 24 can contribute to improvement of the rigidity of the tire 2.

  Although not shown, the carcass ply 24 includes a large number of cords arranged in parallel and a topping rubber. Preferably, the absolute value of the angle formed by each cord with respect to the equator plane is 45 ° or more. The tire 2 having an absolute value of 45 ° or more has excellent steering stability. From this viewpoint, the absolute value of a more preferable angle is 65 ° or more and 90 ° or less. The carcass 10 having an absolute value of 65 ° or more and 90 ° or less has a radial structure. The cord is usually made of organic fibers. Examples of preferable organic fibers include polyester fibers, nylon fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers. The carcass 10 may include a plurality of carcass plies 24. A carcass 10 having a bias structure may be employed.

  The band 12 is located on the inner side in the radial direction of the tread 22. Although not shown, the band 12 includes a band cord spirally wound along a substantially circumferential direction. This band 12 has a jointless structure. The angle formed by the band cord with respect to the equator plane is preferably 5 ° or less, more preferably 2 ° or less. The carcass 10 is restrained by this band cord. The band 12 contributes to improvement in rigidity in the circumferential direction and the radial direction of the tread 4. This band 12 contributes to the improvement of the traction performance of the tire 2. The tire 2 provided with the band 12 exhibits excellent steering stability when traveling at high speed.

  For example, steel is used for the band cord. For the band cord, organic fibers such as polyamide fiber (aramid fiber), nylon fiber, polyester fiber, rayon fiber, polyethylene naphthalate fiber may be used.

  Projections 26 are formed on the sidewalls 6. The protrusion 26 is integrated with the sidewall 6. The protrusion 26 protrudes outward in the axial direction. The protrusion 26 extends in the circumferential direction. The protrusion 26 is formed in a ring shape continuously on the axial outer surface 6a of the sidewall in the circumferential direction. A point P in FIG. 1 indicates the tip of the protrusion 26. This tip P is the outer end of the projection 26 in the axial direction.

  The tire 2 may include a belt. The belt is stacked on the radially outer side of the carcass 10. The belt reinforces the carcass 10. This belt contributes to improving the rigidity of the tread 4. The belt is composed of a large number of belt cords arranged in parallel and a topping rubber. The absolute value of the angle formed by each belt cord with respect to the equator plane is usually 10 ° to 35 °. A preferred material for the belt cord is steel. Organic fibers may be used for the belt cord. The tire 2 may include a plurality of belts.

  A two-dot chain line TF in FIG. 1 indicates a curve passing through the tread surface 16 in the cross section in FIG. A two-dot chain line TB indicates a curve passing through the groove bottom. This curve TB is a curve passing through the tread surface formed when the block 14 is removed. 1 indicates the radius of curvature of the tread surface 16 (the radius of curvature of the curve TF) in the center region. An arrow RS indicates the radius of curvature of the tread surface 16 (the radius of curvature of the curve TF) in the shoulder region. The tread 4 is composed of a center region straddling the equator plane and a pair of shoulder regions located on the outer side in the axial direction of the center region. This curve TF is formed from a curvature radius RC and a curvature radius RS. In the tread surface 16, the radius of curvature RC of the center region is smaller than the radius of curvature RS of the shoulder region. A double arrow WT indicates a tread width. The tread width WT is measured as a distance from one tread edge E in the axial direction to the other tread edge E (not shown). A double arrow WC indicates the width of the center region of the tread surface 16. The tread width WT and the width WC are measured as linear distances in the axial direction in the cross section shown in FIG. For example, the ratio of the center region width WC to the tread width WT (WC / WT) is not less than 0.10 and not more than 0.40.

  A double arrow HT in FIG. 1 indicates the height of the tire 2. The height HT is measured as a radial distance from the bead base line BL to the intersection of the equatorial plane CL and the curve TF. A double-headed arrow HE indicates the height of the tread surface 16. The height HE is measured as a radial distance from the tread edge E to the intersection of the equatorial plane CL and the curve TF. A double-headed arrow HD indicates the height of the protrusion 26. This height HD is measured as a radial distance from the bead base line BL to the tip P of the protrusion 26. The heights HT, HE and HD are measured as radial distances in the radial direction in the cross section shown in FIG.

  The base B of the block 14 is specified as an intersection of the curve TB passing through the groove bottom and the axial outer surface of the tire 2. In the tire 2, the base B is also an intersection of the arc of the outer surface 6 a of the sidewall 6 and the arc of the axial outer wall surface 14 a of the block 14 shown in FIG. 1.

  The manufacturing method of the tire 2 includes a preforming step and a vulcanizing step. In the preforming step, a plurality of members constituting the tread 4, the sidewall 6, the bead 8, and the like are combined to obtain an unvulcanized raw cover. Although not shown, the raw cover includes a band member that is vulcanized to form the band 12. The band member includes a cord extending in a substantially circumferential direction and a rubber member that is vulcanized to form a topping rubber.

  FIG. 2 shows a part of the mold 28 used in the vulcanization process. In the vulcanization step, the raw cover is put into the mold 28 and vulcanized and molded at a predetermined pressure and temperature. By this vulcanization molding, the tire 2 is obtained.

  The mold 28 includes a plurality of tread segments 30 and a pair of side plates 32. In FIG. 2, the shape of the tire 2 that is vulcanized and molded by the mold 28 is indicated by hatching. The mold 28 includes a plurality of arc-shaped tread segments 30. By arranging the plurality of tread segments 30 in the circumferential direction, a tread cavity surface 34 that makes one round in the circumferential direction is formed. The plurality of tread segments 30 include a tread cavity surface 34 and a joint surface 36. The side plate 32 includes a sidewall cavity surface 38 and a bonding surface 40.

  Although not shown, the tread segment 30 moves outward in the radial direction, the pair of side plates 32 moves outward in the axial direction, and the mold 28 is in an open state. The raw cover is put into the mold 28 in the opened state.

  After the raw cover is inserted, the pair of side plates 32 moves inward in the axial direction. The tread segment 30 moves radially inward. The joint surface 36 of the tread segment 30 and the joint surface 40 of the side plate 32 abut. The mold 28 shifts from the open state to the closed state in FIG.

  Although not shown, the swollen bladder presses the raw cover against the tread segment 30 and the side plate 32 from the inside. The raw cover is vulcanized at a predetermined pressure and temperature. The tread cavity surface 34 mainly forms the tread surface 16, the block 14, and the groove 18 of the tire 2. The tread cavity surface 34 forms a portion of the outer surface 6 a of the sidewall 6 that is radially outward from the protrusion 26. The sidewall cavity surface 38 forms a radially inner portion of the outer surface 6 a of the sidewall 6 of the tire 2 from the protrusion 26. The tire 2 is obtained by vulcanizing the raw cover. With the mold 28 opened, the tire 2 is taken out from the mold 28.

  A dashed-dotted line CLv in FIG. 2 indicates a virtual equator plane of the tire 2. A solid line BLv indicates a virtual bead base line of the tire 2. The equatorial plane CLv and the bead base line BLv are determined as positions corresponding to the equatorial plane CL and the bead base line BL of the tire 2. In the mold 28, the tread segment 30 and the side plate 32 are substantially symmetrical with respect to the virtual equatorial plane CLv.

  A two-dot chain line Tf in FIG. 2 indicates a curve passing through a portion of the tread cavity surface 34 that forms the tread surface 16 of the tire 2. An alternate long and two short dashes line Tb indicates a curve passing through a portion forming the groove bottom of the groove 18 of the tire 2. An arrow Rc indicates the radius of curvature of the curve Tf in the center region. An arrow Rs indicates the radius of curvature of the curve Tf in the shoulder region. The curve Tf, the curve Tb, the curvature radius Rc, and the curvature radius Rs of the mold 28 form a curve TF, a curve TB, a curvature radius RC, and a curvature radius RS of the tire 2.

  A point e in FIG. 2 indicates an axial end of a portion of the tread cavity surface 34 that forms the tread surface 16 of the tire 2. This point e corresponds to the tread edge E of the tire 2. The point b is a point corresponding to the base point B of the block 14 of the tire 2. In this mold 28, this point b is specified as an intersection of the curve Tb and the portion of the tread cavity surface 34 that forms the axial outer wall surface 14a of the block 14 and the sidewall axial outer surface 6a. . It may be obtained as an intersection of an arc that forms the outer surface 6 a of the sidewall 6 and an arc that forms the axially outer wall surface 14 a of the block 14.

  A point p in FIG. 2 corresponds to the tip P of the protrusion 26 of the tire 2. This point p is located on the line where the joining surface 36 of the tread segment 30 and the joining surface 40 of the side plate 32 abut. This point p indicates the split position of the mold 28.

  A double arrow Wt in FIG. 2 indicates an axial width from one point e in the axial direction to the other point e. This width Wt corresponds to the tread width WT of the tire 2. A double-headed arrow Wc indicates the width of the tread cavity surface 34 that forms the center region of the tire 2. This width Wc corresponds to the width WC of the center region of the tire 2. The width Wt and the width Wc are measured as a linear distance in the axial direction.

  A double arrow Ht in FIG. 2 indicates a height corresponding to the height HT of the tire 2. This height Ht is measured as the radial distance from the virtual bead base line BLv to the intersection of the virtual equatorial plane CLv and the curve Tf. A double-headed arrow He indicates a height corresponding to the height HE of the tread surface 16 of the tire 2. This height He is measured as the distance in the radial direction from the point e to the intersection of the virtual equatorial plane CLv and the curve TF. This height He indicates the radial height of the tread cavity surface. A double arrow Hd indicates the height of the split position of the mold 28. This height Hd corresponds to the height HD of the tire 2. The height Hd is measured as a radial distance from the virtual bead base line BLv to the point p. The heights Ht, He and Hd are measured as linear distances in the radial direction in the cross section shown in FIG.

  In the mold 28, the radius of curvature Rc in the center region is smaller than the radius of curvature in the shoulder region. Thereby, the tire 2 vulcanized and molded by the mold 28 has a larger ratio HE / HT between the height HT and the height HE of the tread surface 16 than the conventional tire. By increasing the ratio HE / HT, the radial deformation of the tire 2 is dispersed in the tread 4 as compared with the conventional tire. The strain concentration on the sidewall 6 is alleviated. The tire 2 has improved sidewall crack resistance.

  In the tire 2, since the cord of the band 12 extends substantially in the circumferential direction, the movement of the block 14 in the circumferential direction is suppressed. The band 12 contributes to improvement of the traction performance of the tire 2. Furthermore, the improvement in rigidity contributes to the improvement in traction performance. From the viewpoint of obtaining high rigidity, this cord is preferably made of steel or polyamide fiber (aramid fiber).

  When the tire 2 travels straight on a flat road, the center region of the tread surface 16 is grounded. At this time, the shoulder region is not grounded. The radius of curvature Rc of the mold 28 is, for example, not less than 65 mm and not more than 85 mm. By making the curvature radius Rc of the mold 28 smaller than the curvature radius Rs, the ground contact width in the axial direction of the tread surface 16 is reduced. Since the ground contact width in the axial direction is small, the contact length in the circumferential direction of the tread surface 16 is relatively long. By increasing the contact length, the traction performance by the band 12 is further improved. From this viewpoint, the radius of curvature Rc of the mold 28 is set to be 0.9 times or less of the radius of curvature Rs.

  On the other hand, increasing the radius of curvature Rc of the mold 28 increases the ground contact width in the axial direction of the tread surface 16. By increasing the ground contact width in the axial direction to some extent, the traction performance of the tire 2 is easily secured. From this point of view, the radius of curvature Rc of the mold 28 is 0.7 times or more of the radius of curvature Rs.

  When the tread width WT increases with respect to the height HT of the tire 2, the height of the sidewall 6 decreases. If the tread width WT becomes too large, distortion is locally increased in the sidewall 6. From the viewpoint of alleviating local distortion at the sidewall 6, the height Ht of the mold 28 is set to 0.7 times or more of the width Wt.

  On the other hand, when the tread width WT becomes smaller than the height HT of the tire 2, the height of the tread 4 becomes smaller. If the height of the tread 4 becomes too small, the distortion is locally increased in the tread 4. From the viewpoint of suppressing this local distortion, the height Ht of the mold 28 is set to 0.8 times or less of the width Wt.

  In the tire 2, since the radius of curvature Rc is smaller than the radius of curvature Rs, even if the width Wt is relatively small, it is easy to obtain a deep limit inclination in turning. Thereby, even if the height Ht of the mold 28 is 0.7 times or more and 0.8 times or less of the width Wt, high turning performance is easily obtained.

  By increasing the height HE of the tread surface 16, a deeper limit inclination can be obtained in turning. Thereby, high turning performance can be obtained. From this viewpoint, the height He of the mold 28 is set to 0.40 times or more of the height Ht.

  On the other hand, local distortion of the sidewall 6 can be reduced by reducing the height HE of the tread surface 16 of the tire 2. From this viewpoint, the height He of the mold 28 is set to 0.45 times or less of the height Ht.

  The split position p of the mold 28 is located radially inward from the point b corresponding to the base point B of the block 14. Thereby, in the tire 2, the protrusions 26 are positioned on the sidewalls 6 in the radial direction.

  In the tire 2, a protrusion 26 is formed at a split position of the mold 28. By forming the projections 28, the rigidity of the sidewalls 6 is improved. The local deformation of the sidewall 6 can be alleviated by positioning the protrusion 26 at a position where the distortion is most likely to be large in the sidewall 6. Thereby, the occurrence of cracks in the sidewall can be suppressed. From this viewpoint, it is preferable that the height Hd of the split position of the mold 28 is set to 0.3 times or more of the height Ht. From the same viewpoint, the height Hd is preferably set to 0.4 times or less of the height Ht.

  In the tire 2, on a smooth road surface, the tread surface 16 of the block 14 is mainly in contact with the road surface. On the soft ground, a part of the tire 2 is buried and this block 14 scratches mud. The block 14 can contribute to the traction force of the tire 2. The height HB of the block 14 is determined based on the height Hb of the mold 28. From the viewpoint of the traction force of the tire 2, the height Hb of the mold 28 is preferably 8 mm or more. On the other hand, the tire 2 with the low block 14 is excellent in the rigidity and durability of the block 14. From this viewpoint, the height Hb is preferably 19 mm or less.

  Hereinafter, the effects of the present invention will be clarified by examples. However, the present invention should not be construed in a limited manner based on the description of the examples.

[Example 1]
A tire having the structure shown in FIG. 1 was obtained. This tire was vulcanized with the mold shown in FIG. The tire size is “120 / 80-19”. The ratio Rc / Rs between the radius of curvature Rc of the center region of the tread cavity surface of the mold and the radius of curvature of the shoulder region Rs was as shown in Table 1. Table 1 shows the ratio Ht / Wt between the axial width Wt of the mold tread cavity surface and the mold height Ht corresponding to the tire height HT. Table 1 shows a ratio He / Ht between the height Ht and the radial height He of the tread cavity surface. Table 1 shows the ratio Hd / Ht between the height Ht and the radial height Hd of the split position between the tread segment and the side plate.

[Example 2-3 and Comparative Example 1-2]
The ratio Rc / Rs, the ratio He / Ht, and the ratio Hd / Ht were set as shown in Table 1. Otherwise, a tire was obtained using a mold similar to that of Example 1.

[Example 4-6 and Comparative Example 3-4]
The ratio Ht / Wt, ratio He / Ht, and ratio Hd / Ht were set as shown in Table 2. Table 2 shows the presence or absence of protrusions at the split position of the mold. Otherwise, a tire was obtained using a mold similar to that of Example 1.

[Example 7-10]
The ratio Hd / Ht was set as shown in Table 3. Table 3 shows the radial positional relationship between the split position of the mold and the point b corresponding to the base point B of the shoulder block of the tire. Table 3 shows the presence or absence of the protrusion at the split position. Otherwise, a tire was obtained using a mold similar to that of Example 1.

[Examples 11-12]
Table 4 shows the radial positional relationship between the split position of the mold and the point b shown in FIG. Table 4 shows the presence or absence of the protrusion at the split position. Otherwise, a tire was obtained using a mold similar to that of Example 1.

[Comparative Example 6]
A mold made of a two-piece mold was prepared. The heights Ht, He, width Wt, radii of curvature Rc and Rs of this mold were in the relationship shown in Table 4. Attempts have been made to vulcanize tires using this mold. A low cover for radial tires was prepared. This tire (low cover) has a small shape change before and after vulcanization molding. In the two-piece mold, the tread portion of the raw cover interfered with the tread cavity surface of the mold. It was difficult to put the raw cover into the mold. For this reason, no tire was prototyped with this mold.

[Crack durability]
Tires were incorporated into regular rims. This tire was mounted on a 450cc motocross bike. This motocross bike was driven on the motocross course. This motocross course was a dry road surface, and was a circuit course of about 2 minutes per round. The presence or absence of cracks in the sidewall was confirmed every 15 laps of this motocross course. The durability of the crack was evaluated based on the running time until the occurrence of this crack was confirmed. The results are shown in Tables 1 to 4. This evaluation result is a perfect score, and the larger the value, the better.

[Traction performance and turning performance]
The motocross bike used for the evaluation of crack durability was run on the motocross course, and the professional riders were made to evaluate the traction performance and turning performance. The evaluation results are shown in Tables 1 to 4. In this evaluation, the greater the number, the better.

[Mold strength]
Together with the tire evaluation, the strength of the mold used was evaluated. The mold strength was evaluated based on ease of deformation and breakage. The evaluation results are shown in Tables 1 to 4. This evaluation result is a perfect score, and the larger the value, the better.

  As shown in Tables 1 to 4, the tires of the examples have higher evaluation than the tires of the comparative examples. From this evaluation result, the superiority of the present invention is clear.

  The pneumatic tire described above can be widely applied as a motorcycle tire for rough terrain. This tire is particularly suitable for motorcycle tires for rough terrain.

2 ... tyre 4 ... tread 6 ... side wall 8 ... bead 10 ... carcass 12 ... band 14 ... block 16 ... tread surface 18 ... groove 20 ... -Core 22 ... Apex 24 ... Carcass ply 26 ... Projection 28 ... Mold 30 ... Tread segment 32 ... Side plate 34 ... Tread cavity surface 36, 40 ... Bonding surface 38 ... Side wall cavity surface

Claims (5)

A preforming step in which a raw cover is obtained by preforming, and a vulcanizing step in which the raw cover is put into a mold and pressurized and heated,
The mold used in this vulcanization process includes a tread segment including a tread cavity surface that forms a tread surface, and a side plate including a sidewall cavity surface that forms an axial outer surface of the sidewall,
This tread cavity surface forms a tread surface consisting of the outer peripheral surface of each independent block,
In a cross section perpendicular to the circumferential direction, the radius of curvature in the center region of the tread cavity surface is Rc, the radius of curvature in the shoulder region of the tread cavity surface is Rs, and the axial width of the tread cavity surface is Wt, thereby determining the tire height. A method for manufacturing a motorcycle tire for rough terrain satisfying the following relational expression when the height is Ht and the radial height of the tread cavity surface is He.
0.7 ≦ Rc / Rs ≦ 0.9
0.7 ≦ Ht / Wt ≦ 0.8
0.40 ≦ He / Ht ≦ 0.45 The raw cover put into the mold in the vulcanization process,
A tread member that is vulcanized to form a tread;
It is located inside the tread member in the radial direction and includes a band member that is vulcanized to form a band.
The band member is composed of a cord extending in the circumferential direction and a rubber member constituting a topping rubber,
The tire manufacturing method according to claim 1, wherein the cord is made of steel or polyamide fiber (aramid fiber).   The method for manufacturing a tire according to claim 1 or 2, wherein a height Hb of a mold for determining a height of the block is 8 mm or more and 19 mm or less. The tire manufacturing method according to any one of claims 1 to 3, wherein a ratio Hd / Ht between a radial height Hd and a height Ht at a split position between the tread segment and the side plate satisfies the following relational expression.
0.3 ≦ Hd / Ht ≦ 0.4 A tread segment having a tread cavity surface forming a tread surface;
A side plate having a sidewall cavity surface that forms an axial outer surface of the sidewall,
This tread cavity surface forms a tread surface consisting of the outer peripheral surface of each independent block,
In a cross section perpendicular to the circumferential direction, the radius of curvature in the center region of the tread cavity surface is Rc, the radius of curvature in the shoulder region of the tread cavity surface is Rs, and the axial width of the tread cavity surface is Wt, thereby determining the tire height. A mold used in a vulcanization process of a motorcycle tire for rough terrain satisfying the following relational expression when the height is Ht and the radial height He of the tread cavity surface is set.
0.7 ≦ Rc / Rs ≦ 0.9
0.7 ≦ Ht / Wt ≦ 0.8
0.40 ≦ He / Ht ≦ 0.45

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