JP2013199266A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire 20 in which improvement in ground contact following property is achieved.SOLUTION: In a tire 20, an arc located outside among a plurality of arcs for forming the profile of a tread surface 40 of a tread 22 is made a reference arc, and a position where a straight line in contact with both the arc of a shoulder 38 of the tread 22, and the arc of a side wall 24 cross the extended line of the reference arc is made a first reference position. An axial direction length from an equator face is 70% of a half of an axial direction length of the tread surface 40. When the position of the tread surface 40 is made a second reference position, the ratio of a height to the first reference position to a length to the first reference position is 0.05 or more and 0.15 or less. The ratio of a height to the second reference position to the length to the second reference position is 0.015 or more and 0.040 or less.

Description

  The present invention relates to a pneumatic tire. More particularly, the present invention relates to a pneumatic tire mounted on a competition vehicle.

  FIG. 5 is a cross-sectional view showing a part of a conventional pneumatic tire 2. The tire 2 is attached to a racing cart as a competition vehicle. In FIG. 5, the alternate long and short dash line CL represents the equator plane. The shape of the tire 2 is symmetric with respect to the equator plane.

  The tire 2 includes a tread 4, a sidewall 6, a bead 8, a carcass 10, and a belt 12. The tread 4 has a shape protruding outward in the radial direction. The sidewall 6 extends substantially inward in the radial direction from the end of the tread 4. The bead 8 includes a core 14 and an apex 16 that extends radially outward from the core 14. The carcass 10 includes two plies 18. Each of the plies 18 is folded around the core 14 from the inner side toward the outer side in the axial direction. The belt 12 is laminated with the carcass 10. The belt 12 reinforces the carcass 10.

  The tread 4 is in contact with the road surface during traveling. The profile of the tread 4 affects the shape of the ground plane. Various studies have been made on this profile from the viewpoint of optimizing the shape of the ground plane. An example of this study is disclosed in Japanese Patent Publication No. 08-005065.

  The ply 18 includes a large number of carcass cords arranged in parallel. The absolute value of the angle formed by each carcass cord with respect to the equator plane is usually 75 ° to 90 °. The tire 2 having the carcass 10 made of such a ply 18 is referred to as a radial tire.

Japanese Patent Publication No. 08-005065

  The belt 12 is located on the inner side in the radial direction of the tread 4. The belt 12 includes a number of belt cords arranged in parallel. The belt 12 has high rigidity. The belt 12 can contribute to traction and wear resistance. However, on the other hand, the belt 12 influences the ground following ability. In the tire 2, when the center of gravity on the ground contact surface moves, the ground contact width greatly varies. The fluctuation of the contact width causes a decrease in grip force. The tire 2 is inferior in handling stability.

  From the viewpoint of traction, a reinforcing member may be added to the side wall 6 portion of the tire 2. The addition of the reinforcing member reduces the amount of bending of the side wall 6 portion. A small deflection affects the ground following ability. In the tire 2, when the center of gravity on the ground contact surface moves, the ground contact width greatly varies. The fluctuation of the contact width causes a decrease in grip force. The tire 2 is inferior in handling stability.

  An object of the present invention is to provide a pneumatic tire in which improvement in contact following property is achieved.

The pneumatic tire according to the present invention includes a tread that is in contact with a road surface during traveling, a pair of sidewalls that extend substantially inward in the radial direction from the end of the tread, and each of which is positioned substantially radially inward of the sidewalls. A pair of beads, a carcass having a bias structure extending between the one bead and the other bead along the inside of the tread and the sidewall, and the carcass stacked on the inner side in the radial direction of the tread. Belt. The tread includes a main body whose outer surface forms a tread surface, and a pair of shoulders that are positioned on the outer side in the axial direction of the main body. The profile of the tread surface is formed by a plurality of arcs. Each arc is in contact with the adjacent arc. The radius of curvature of each arc is smaller than the radius of curvature of the arc on the inner side in the axial direction. The profile of the outer surface of the shoulder is formed by an arc. The profile of the outer surface of the sidewall is formed by an arc. Of the plurality of arcs forming the profile of the tread surface, an arc located outside in the axial direction is set as a reference arc, and a virtual straight line in contact with both the shoulder arc and the side wall arc is an extension of the reference arc. A position on the tread surface where the position intersecting the line is the first reference position, and the axial length of the tire from the equator plane is 70% of the half of the axial length of the tread surface. Is the second reference position,
A ratio of a radial height from the equator of the tire to the first reference position to an axial length from the equator plane of the tire to the first reference position is 0.05 to 0.15. The ratio of the radial height from the tire equator to the second reference position to the axial length from the tire equator plane to the second reference position is 0.015 or more and 0.040 or less.

  Preferably, in the pneumatic tire, the arc of the shoulder is in contact with the reference arc. The radius of curvature of the shoulder arc is smaller than the radius of curvature of the reference arc.

  Preferably, in this pneumatic tire, the carcass includes a first ply and a second ply. Each of the first ply and the second ply includes a large number of carcass cords arranged in parallel. Each of these carcass cords is inclined with respect to the equator plane. The absolute value of the inclination angle of the carcass cord is 40 ° or more and 60 ° or less.

  Preferably, in this pneumatic tire, the belt includes a plurality of belt cords arranged in parallel. Each of these belt cords is inclined with respect to the equator plane. The absolute value of the inclination angle of the belt cord is 15 ° or more and 30 ° or less.

  Preferably, in the pneumatic tire, when the arc that contacts the straight line that defines the outer diameter of the tire is the first arc among the plurality of arcs that form the profile of the tread surface, The ratio of the radius of curvature of the arc to the axial length of the tread surface is 4.0 or more and 11.0 or less.

  Preferably, in the pneumatic tire, an arc located outside the first arc in the axial direction and out of contact with the first arc among the plurality of arcs forming the profile of the tread surface is a second arc. Then, the ratio of the curvature radius of the first arc to the curvature radius of the second arc is 3.0 or more and 17.0 or less.

  Preferably, in this pneumatic tire, a ratio of an axial length from the equator plane to the contact point between the first arc and the second arc with respect to an axial length from the equator plane to the second reference position. Is 0.9 or more and 1.4 or less.

  Preferably, in this pneumatic tire, the absolute value of the angle formed by the virtual line with respect to the radial direction is not less than 30 ° and not more than 50 °.

  In the pneumatic tire according to the present invention, the ratio of the radial height from the equator to the first reference position to the axial length from the equator plane to the first reference position, and from the equator to the second reference position. The ratio of the radial height to the axial length from the equatorial plane to the second reference position is appropriately adjusted. The outer surface of the tire tread has an optimum profile. In this tire, even if the center of gravity moves on the contact surface, the variation in the contact width is small. This tire is excellent in contact following ability. In addition, the carcass of the bias structure contributes to traction, and the belt laminated on the carcass can contribute to wear resistance. ADVANTAGE OF THE INVENTION According to this invention, the pneumatic tire in which the improvement in the ground following ability was achieved without impairing traction and abrasion resistance can be obtained.

FIG. 1 is a cross-sectional view showing a part of a pneumatic tire according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view showing a part of the tire of FIG. FIG. 3 is a plan view showing a part of the carcass of the tire of FIG. FIG. 4 is a plan view showing a part of the belt of the tire of FIG. FIG. 5 is a cross-sectional view showing a part of a conventional tire.

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

  FIG. 1 shows a pneumatic tire 20. In FIG. 1, the vertical direction is the radial direction of the tire 20, the horizontal direction is the axial direction of the tire 20, and the direction perpendicular to the paper surface is the circumferential direction of the tire 20. In FIG. 1, an alternate long and short dash line CL represents the equator plane of the tire 20. The shape of the tire 20 is symmetric with respect to the equator plane except for the tread pattern.

  The flatness ratio of the tire 20 is not less than 30% and not more than 50%. The tire 20 is a pneumatic tire for a competition vehicle. The tire 20 is attached to a racing cart as a competition vehicle.

  The tire 20 includes a tread 22, a sidewall 24, a bead 26, a carcass 28, a belt 30, an inner liner 32, and a chafer 34. The tire 20 is a tubeless type.

  The tread 22 has a shape protruding outward in the radial direction. The tread 22 contacts the road surface during traveling. The tread 22 is made of a crosslinked rubber having excellent wear resistance, heat resistance, and grip properties. As is apparent from FIG. 1, the tread 22 has no groove. The tire 20 is a slick tire. A groove may be cut in the tread 22 to form a tread pattern.

  The tread 22 of the tire 20 includes a main body 36 and a pair of shoulders 38. The main body 36 extends outward in the axial direction from the equator plane. The tire 20 is grounded in the main body 36. The outer surface of the main body 36 forms a tread surface 40. Each shoulder 38 is located outside the main body 36 in the axial direction. The shoulder 38 rarely contacts the road surface. In the figure, the symbol PE indicates the intersection of the tread surface 40 and the equator plane. In the present application, this intersection PE is called the equator. A solid line LB represents a straight line passing through the equator PE and extending in the axial direction. The straight line LB is a straight line that defines the outer diameter of the tire 20. The symbol TE represents the boundary between the main body 36 and the shoulder 38 on the outer surface of the tread 22. This boundary TE is also an end of the tread surface 40. In addition, when a groove exists on the equator plane in the tread 22 in which the groove is engraved, the equator PE is represented by the intersection of the virtual tread surface and the equator plane obtained as if there is no groove.

  The sidewall 24 extends substantially inward in the radial direction from the end of the tread 22. The outer surface of the sidewall 24 forms the side surface of the tire 20. The sidewall 24 is made of a crosslinked rubber having excellent cut resistance and weather resistance. The sidewall 24 prevents the carcass 28 from being damaged. In the tire 20, the sidewall 24 is integral with the tread 22. Accordingly, the material of the sidewall 24 is the same as that of the tread 22. The sidewall 24 may be made of a material different from the material of the tread 22.

  The bead 26 is located substantially inward of the sidewall 24 in the radial direction. The bead 26 includes a core 42 and an apex 44 that extends radially outward from the core 42. The core 42 has a ring shape and includes a wound non-stretchable wire. A typical material for the wire is steel. The apex 44 is tapered outward in the radial direction. The apex 44 is made of a highly hard crosslinked rubber.

  The carcass 28 includes a first ply 46a and a second ply 46b. The first ply 46 a and the second ply 46 b are bridged between the beads 26 on both sides, and extend along the tread 22 and the sidewall 24. The first ply 46a is folded around the core 42 from the inner side to the outer side in the axial direction. By this folding, a main portion 48a and a folding portion 50a are formed in the first ply 46a. The second ply 46b is folded around the core 42 from the inner side to the outer side in the axial direction. By this folding, a main portion 48b and a folding portion 50b are formed in the second ply 46b. The end of the folded portion 50a of the first ply 46a is located outside the end of the folded portion 50b of the second ply 46b in the radial direction. In the tire 20, the carcass 28 may be formed from three plies 46. When the carcass 28 is formed from a single ply 46, the rigidity of the tire 20 is too low to obtain sufficient performance. When the carcass 28 is formed from four plies 46, the rigidity of the tire 20 becomes excessive and sufficient performance cannot be obtained.

  As shown in FIG. 2, each of the first ply 46 a and the second ply 46 b includes a large number of carcass cords 52 and a topping rubber 54 arranged in parallel. In the tire 20, the carcass cord 52 is made of an organic fiber. Examples of preferable organic fibers include nylon fibers, polyethylene terephthalate fibers, polyethylene naphthalate fibers, aramid fibers, and polyketone fibers. In the tire 20, the carcass cord 52 of the first ply 46a is equivalent to the carcass cord 52 of the second ply 46b. As the carcass cord 52 of the first ply 46a, a cord made of a material different from the material of the carcass cord 52 of the second ply 46b may be used.

  As shown in FIG. 3, in the first ply 46a, the carcass cord 52 is inclined with respect to the equator plane. In the second ply 46b, the carcass cord 52 is inclined with respect to the equator plane. The inclination direction of the carcass cord 52 of the first ply 46a with respect to the equator plane is opposite to the inclination direction of the carcass cord 52 of the second ply 46b with respect to the equator plane. The carcass 28 of the tire 20 has a bias structure. The carcass 28 can contribute to improvement of traction.

  In FIG. 3, a solid line L1 represents the extending direction of the carcass cord 52 of the first ply 46a. The angle α represents an angle formed by the solid line L1 with respect to the equator plane. This angle α is an inclination angle formed by the carcass cord 52 of the first ply 46a with respect to the equator plane. A solid line L2 represents the extending direction of the carcass cord 52 of the second ply 46b. An angle β represents an angle formed by the solid line L2 with respect to the equator plane. This angle β is an inclination angle formed by the carcass cord 52 of the second ply 46b with respect to the equator plane.

  In the tire 20, from the viewpoint of improving traction, the absolute value of the inclination angle α is preferably 40 ° or more, and preferably 60 ° or less. The absolute value of the inclination angle β is preferably 40 ° or more, and preferably 60 ° or less.

  As shown in FIG. 1, the belt 30 is located radially inward of the tread 22. The belt 30 is laminated with the carcass 28. The belt 30 reinforces the carcass 28. The belt 30 includes an inner layer 56a and an outer layer 56b. As apparent from FIG. 1, the width of the inner layer 56a is slightly larger than the width of the outer layer 56b in the axial direction. The axial width of the belt 30 is preferably 0.7 times or more the maximum width of the tire 20. The belt 30 may be composed of one layer 56. If the belt 30 is composed of three or more layers 56, the rigidity of the tire 20 becomes excessive and sufficient performance cannot be obtained.

  As shown in FIG. 2, each of the inner layer 56 a and the outer layer 56 b includes a plurality of belt cords 58 and a topping rubber 60 that are arranged in parallel. In the tire 20, a cord made of an organic fiber or a cord made of steel is used for the belt cord 58. Examples of the organic fiber include nylon fiber, polyethylene terephthalate fiber, polyethylene naphthalate fiber, aramid fiber, and polyketone fiber. In the tire 20, the belt cord 58 of the inner layer 56a is equivalent to the belt cord 58 of the outer layer 56b. As the belt cord 58 of the inner layer 56a, a cord made of a material different from the material of the belt cord 58 of the outer layer 56b may be used.

  As shown in FIG. 4, in the inner layer 56a, the belt cord 58 is inclined with respect to the equator plane. In the outer layer 56b, the belt cord 58 is inclined with respect to the equator plane. The inclination direction of the inner layer 56a with respect to the equator plane of the belt cord 58 is opposite to the inclination direction of the outer layer 56b with respect to the equator plane of the belt cord 58. The belt 30 can contribute to the rigidity of the tread 22 portion of the tire 20. The belt 30 can contribute to improvement of wear resistance.

  In FIG. 4, the solid line L3 represents the extending direction of the belt cord 58 of the inner layer 56a. The angle γ represents an angle formed by the solid line L3 with respect to the equator plane. This angle γ is an inclination angle formed by the belt cord 58 of the inner layer 56a with respect to the equator plane. A solid line L4 represents the extending direction of the belt cord 58 of the outer layer 56b. An angle δ represents an angle formed by the solid line L4 with respect to the equator plane. This angle δ is an inclination angle formed by the belt cord 58 of the outer layer 56b with respect to the equator plane.

  In the tire 20, from the viewpoint of wear resistance, the absolute value of the inclination angle γ is preferably 15 ° or more, and more preferably 30 ° or less. The absolute value of the inclination angle δ is preferably 15 ° or more, and preferably 30 ° or less.

  As shown in FIG. 1, the inner liner 32 is located inside the carcass 28. The inner liner 32 forms the inner surface of the tire 20. The inner liner 32 is made of a crosslinked rubber. For the inner liner 32, rubber having excellent air shielding properties is used. A typical base rubber of the inner liner 32 is butyl rubber or halogenated butyl rubber. The inner liner 32 holds the internal pressure of the tire 20.

  The chafer 34 is located in the vicinity of the bead 26. When the tire 20 is assembled into the rim, the chafer 34 comes into contact with the rim. By this contact, the vicinity of the bead 26 is protected. In this embodiment, the chafer 34 is made of a cloth and a rubber impregnated in the cloth. The chafer 34 may be made of a crosslinked rubber.

  In the tire 20, the profile of the tread surface 40 is formed by a plurality of arcs. As shown in FIG. 1, the tread surface 40 of the tire 20 includes an arc having a radius of curvature R1 (hereinafter referred to as a first arc), a pair of arcs having a radius of curvature R2 (hereinafter referred to as a second arc), and a pair of curvatures. It is formed by an arc having a radius R3 (hereinafter referred to as a third arc). Each second arc is located outside the first arc in the axial direction. Each third arc is located further axially outside the second arc.

  In the tire 20, among the plurality of arcs forming the profile of the tread surface 40, the third arc is located outside in the axial direction. In the present application, the third arc is a reference arc.

  The first arc is in contact with a straight line LB that defines the outer diameter of the tire 20 at the equator PE. The second arc is adjacent to the first arc. The first arc is in contact with the second arc. The third arc is adjacent to the second arc. The second arc is in contact with the third arc. In the tire 20, each of the plurality of arcs forming the profile of the tread surface 40 is in contact with the arc adjacent thereto.

  The first arc is located inside the second arc in the axial direction. The radius of curvature R2 of the second arc is smaller than the radius of curvature R1 of the first arc. The second arc is located inside the third arc in the axial direction. The radius of curvature R3 of the third arc is smaller than the radius of curvature R2 of the second arc. In the tire 20, the radius of curvature of each of the plurality of arcs forming the profile of the tread surface 40 is smaller than the radius of curvature of the arc on the inner side in the axial direction.

  In the tire 20, the profile of the tread surface 40 is formed by a plurality of arcs, and each arc is in contact with an arc adjacent to the arc, and the radius of curvature of each arc is the radius of curvature of the arc on the inner side in the axial direction. Smaller than. The tread surface 40 is in sufficient contact with the road surface. The shape of the ground contact surface obtained by the tread surface 40 is appropriate. The tread surface 40 can contribute to steering stability.

  As shown in FIG. 1, the profile of the outer surface of the shoulder 38 that forms a part of the tread 22 is formed by an arc having a radius of curvature Rs (hereinafter referred to as a shoulder arc). The shoulder arc is adjacent to the aforementioned third arc. In the tire 20, the shoulder arc is in contact with the third arc at the boundary TE. The third arc is located on the inner side in the axial direction than the shoulder arc. In the tire 20, the curvature radius Rs of the shoulder arc is smaller than the curvature radius R3 of the third arc.

  Here, if the curvature radius Rs of the shoulder arc is larger than the curvature radius R3 of the third arc, the thickness of the tread 22 from the shoulder 38 to the buttress becomes excessive. In this case, the contact pressure at the shoulder 38 increases, and uneven wear occurs in the tire 20. As described above, in the tire 20, the shoulder arc is in contact with the third arc, and the curvature radius Rs of the shoulder arc is smaller than the curvature radius R3 of the third arc. In the tire 20, the occurrence of uneven wear is prevented.

  As shown in FIG. 1, in the tire 20, the profile of the outer surface of the sidewall 24 is formed by an arc having a radius of curvature Rw (hereinafter referred to as a sidewall arc). In the tire 20, the sidewall arc is adjacent to the shoulder arc described above. This sidewall arc is not in contact with the shoulder arc.

  When the tread 22 comes into contact with the road surface, the sidewall 24 bends. In the tire 20, the profile of the outer surface of the sidewall 24 is formed by an arc, so that the load is dispersed throughout the sidewall 24. Since the sidewall 24 bends appropriately, the tread surface 40 sufficiently contacts the road surface. The sidewalls 24 can contribute to steering stability.

  In FIG. 1, a solid line LC represents a straight line that touches both the shoulder arc and the side wall arc. In the present application, the solid line LC is also referred to as a virtual straight line. Reference numeral P1 represents a position where the straight line LC has a tolerance with an extension line of the reference arc (third arc). In the present application, this position P1 is referred to as a first reference position. A double-headed arrow X1 represents the axial length from the equator plane to the first reference position P1. A double-headed arrow Y1 represents the height in the radial direction from the equator PE to the first reference position P1.

  In the tire 20, the ratio of the height Y1 to the length X1 is 0.05 or more and 0.15 or less. By setting this ratio to 0.15 or less, a ground plane having a sufficient axial length is formed. The grip force of the tire 20 is large. By setting this ratio to 0.05 or more, fluctuations in the distance from the road surface to the tread surface 40 can be suppressed. In the tire 20, even when the center of gravity moves on the ground contact surface, the variation in the ground contact width is small. The tire 20 is excellent in ground followability. In the tire 20, the grip force is properly maintained even during high-speed turning. Since the slip in the ground plane is suppressed, the wear resistance is improved. With this tire, the lap time is stable.

  In FIG. 1, a double-headed arrow TW / 2 represents the axial length from the equator plane to the boundary TE. This length TW / 2 is half the axial length of the tread surface 40. Reference symbol P2 represents a position on the tread surface 40 where the axial length from the equator plane is 70% of the length TW / 2. In the present application, this position P2 is referred to as a second reference position. A double-headed arrow X2 represents the axial length from the equator plane to the second reference position P2. A double-headed arrow Y2 represents the height in the radial direction from the equator PE to the second reference position P2.

  In the tire 20, the ratio of the height Y2 to the length X2 is 0.015 or more and 0.040 or less. By setting this ratio to 0.040 or less, the tread surface 40 is sufficiently in contact with the road surface even during turning. In the tire 20, the influence of the profile of the tread surface 40 on the grip force during turning is suppressed. By setting this ratio to 0.015 or more, fluctuations in the distance from the road surface to the tread surface 40 can be suppressed. In the tire 20, even when the center of gravity moves on the ground contact surface, the variation in the ground contact width is small. The tire 20 is excellent in ground followability. In the tire 20, the grip force is properly maintained even during high-speed turning. Since the slip in the ground plane is suppressed, the wear resistance is improved. With this tire, the lap time is stable.

  As described above, the first arc is in contact with the straight line LB that defines the outer diameter of the tire 20 at the equator PE. In the tire 20, the ratio of the curvature radius R1 of the first arc to the axial length of the tread surface is appropriately adjusted. In the tire 20, even if the center of gravity moves on the contact surface, the increase in contact pressure in the intermediate portion between the equator portion of the tread 22 and the shoulder 38 portion is effectively suppressed. Since a sufficient ground contact area is ensured, the tire 20 is excellent in ground tracking ability. In the tire 20, the grip force is properly maintained even during high-speed turning. Since the slip in the ground plane is suppressed, the wear resistance is improved. With this tire, the lap time is stable. From this viewpoint, the ratio of the radius of curvature R1 of the first arc to the axial length of the tread surface is preferably 4.0 or more, and preferably 11.0 or less.

  As described above, the second arc of the tire 20 is an arc located outside the first arc in the axial direction and out of contact with the first arc among the plurality of arcs forming the profile of the tread surface 40. . In the tire 20, the ratio of the curvature radius R1 of the first arc to the curvature radius R2 of the second arc is appropriately adjusted. In the tire 20, even if the center of gravity moves on the contact surface, the increase in contact pressure in the intermediate portion between the equator portion of the tread 22 and the shoulder 38 portion is effectively suppressed. Since a sufficient ground contact area is ensured, the tire 20 is excellent in ground tracking ability. In the tire 20, the grip force is properly maintained even during high-speed turning. Since the slip in the ground plane is suppressed, the wear resistance is improved. With this tire, the lap time is stable. From this viewpoint, the ratio of the radius of curvature R1 of the first arc to the radius of curvature R2 of the second arc is preferably 3.0 or more, and preferably 17.0 or less. This ratio is more preferably 5.3 or more from the viewpoint of easy profile construction.

  In FIG. 1, the code | symbol P3 represents the contact of a 1st circular arc and a 2nd circular arc. A double-headed arrow X3 represents the axial length from the equator plane to the contact point P3. In FIG. 1, the angle θ represents an angle formed by the virtual straight line (straight line LC) with respect to the radial direction.

  In the tire 20, the ratio of the length X3 to the length X2 is appropriately adjusted. In the tire 20, even if the center of gravity moves on the contact surface, the increase in contact pressure in the intermediate portion between the equator portion of the tread 22 and the shoulder 38 portion is effectively suppressed. Since a sufficient ground contact area is ensured, the tire 20 is excellent in ground tracking ability. In the tire 20, the grip force is properly maintained even during high-speed turning. Since the slip in the ground plane is suppressed, the wear resistance is improved. With this tire, the lap time is stable. From this viewpoint, the ratio of the length X3 to the length X2 is preferably 0.9 or more, and preferably 1.4 or less.

  In the tire 20, the absolute value of the angle θ is appropriately adjusted. In the tire 20, fluctuations in the distance from the road surface to the tread surface 40 are suppressed. In the tire 20, even when the center of gravity moves on the ground contact surface, the variation in the ground contact width is small. Since a sufficient ground contact area is ensured, the tire 20 is excellent in ground tracking ability. In the tire 20, the grip force is properly maintained even during high-speed turning. From this viewpoint, the absolute value is preferably 30 ° or more, and preferably 50 ° or less.

  Thus, the outer surface of the tread 22 of the tire 20 has an optimal profile. In particular, in the tire 20, improvement in contact following property during high-speed turning is achieved. In the tire 20, a grip force is sufficiently ensured. The tire 20 is excellent in handling stability. In addition, in the tire 20, the carcass 28 of the bias concept contributes to traction, and the belt 30 laminated on the carcass 28 can contribute to wear resistance. According to the present invention, it is possible to obtain the pneumatic tire 20 in which improvement in contact with ground contact is achieved without impairing traction and wear resistance. The tire 20 can contribute to shortening the lap time.

  In the present invention, the size and angle of each member of the tire 20 are measured in a state where the tire 20 is incorporated in a regular rim and the tire 20 is filled with air so as to have a regular internal pressure. During the measurement, no load is applied to the tire 20. In the present specification, the normal rim means a rim defined in a standard on which the tire 20 depends. “Standard rim” in the JATMA standard, “Design Rim” in the TRA standard, and “Measuring Rim” in the ETRTO standard are regular rims. In the present specification, the normal internal pressure means an internal pressure defined in a standard on which the tire 20 depends. “Maximum air pressure” in JATMA standard, “maximum value” published in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in TRA standard, and “INFLATION PRESSURE” in ETRTO standard are normal internal pressures. In the case of the passenger car tire 20, the dimensions and angles are measured in a state where the internal pressure is 180 kPa.

  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.

[Experiment A]
[Example 1]
A pneumatic tire of Example 1 having the basic configuration shown in FIG. 1 and having the specifications shown in Table 1 below was obtained. The tire size is 11 × 7.10-5. The carcass includes a first ply and a second ply. For each of the first ply and the second ply, a cord made of polyethylene terephthalate fiber (described as polyester in the table) was used as a carcass cord. The fineness of this cord was 1620 dtex. The density of the carcass cord was 45 ends / 5 cm. The inclination angle α of the carcass cord in the first ply was 45 ° (degrees). The inclination angle β of the carcass cord in the second ply was −45 °. The belt consists of an inner layer and an outer layer. For each of the inner layer and the outer layer, a cord made of aramid fibers (described as aramid in the table) was used as a belt cord. The fineness of this cord was 1110 dtex. The density of the belt cord was 40 ends / 5 cm. The inclination angle γ of the belt cord in the inner layer was set to 30 ° (degrees). The inclination angle δ of the belt cord in the outer layer was −30 °.

  In the profile of the tread surface, the ratio (Y1 / X1) of the radial height Y1 from the equator to the first reference position P1 to the axial length X1 from the equator surface to the first reference position P1 is 0.077. It was said. The ratio (Y2 / X2) of the radial height Y2 from the equator to the second reference position P2 to the axial length X2 from the equator plane to the second reference position P2 was 0.029.

[Example 2-7 and Comparative Example 2]
Tires of Examples 2-7 and Comparative Example 2 were obtained in the same manner as Example 1 except that the height Y1 was changed and the ratio (Y1 / X1) was changed as shown in Tables 1 and 2 below.

[Examples 8-10 and Comparative Example 3]
Tires of Examples 8-10 and Comparative Example 3 were obtained in the same manner as Example 1 except that the height Y2 was changed and the ratio (Y2 / X2) was changed as shown in Table 3 below.

[Comparative Example 1]
A tire of Comparative Example 1 was obtained in the same manner as in Example 1 except that the ratio (Y1 / X1) and ratio (Y2 / X2) were changed as shown in Table 1 below by changing the height Y1 and the height Y2. .

[Examples 11-15]
Tires of Examples 11-15 were obtained in the same manner as in Example 1 except that the inclination angle α and the inclination angle β were as shown in Table 4 below.

[Example 16-20]
Tires of Examples 16-20 were obtained in the same manner as in Example 1 except that the inclination angle γ and the inclination angle δ were as shown in Table 5 below.

[Real car running test]
The prototype tire was mounted on a racing cart with a displacement of 125 cc. The internal pressure of this tire was 75 kPa. The size of the rim is 8 × 5.0. With this racing cart, I drove the circuit course and measured the lap time. This result is shown in Tables 1 to 5 below.

  As shown in Tables 1 to 5, the tire of the example has a higher evaluation than the tire of the comparative example. From this evaluation result, the superiority of the present invention is clear.

[Experiment B]
[Example 26]
A pneumatic tire of Example 26 having the basic configuration shown in FIG. 1 and having the specifications shown in Table 7 below was obtained. The tire size is 11 × 7.10-5. The carcass includes a first ply and a second ply. For each of the first ply and the second ply, a cord made of polyethylene terephthalate fiber was used as a carcass cord. The fineness of this cord was 1620 dtex. The density of the carcass cord was 45 ends / 5 cm. The inclination angle α of the carcass cord in the first ply was 45 °. The inclination angle β of the carcass cord in the second ply was −45 °. The belt consists of an inner layer and an outer layer. For each of the inner layer and the outer layer, a cord made of aramid fibers was used as a belt cord. The fineness of this cord was 1110 dtex. The density of the belt cord was 40 ends / 5 cm. The inclination angle γ of the belt cord in the inner layer was 30 °. The inclination angle δ of the belt cord in the outer layer was −30 °.

  The axial length X1 from the equator plane to the first reference position P1 was 88 mm. The radial height Y1 from the equator to the first reference position P1 was 5.8 mm. Therefore, the ratio (Y1 / X1) of the height Y1 to the length X1 was 0.066. The axial length X2 from the equator plane to the second reference position P2 was 58 mm. The radial height Y2 from the equator to the second reference position P2 was 1.3 mm. Therefore, the ratio (Y2 / X2) of the height Y2 to the length X2 was 0.023. Half of the axial length TW of the tread surface was 83 mm. At the equator, the radius of curvature R1 of the first arc in contact with the straight line LB defining the outer diameter of the tire was 1260 mm. The curvature radius R2 of the second arc located outside the first arc and in contact with the first arc was 95 mm. The axial length X3 from the equator plane to the contact point P3 between the first arc and the second arc was 65 mm. The ratio of the radius of curvature R1 to the length TW (R1 / TW) was 7.6. The ratio (R1 / R2) of the curvature radius R1 to the curvature radius R2 was 13.3. The ratio (X3 / X2) of the length X3 to the length X2 was 1.1. The angle θ formed by the virtual straight line LS in contact with both the shoulder arc and the sidewall arc with respect to the radial direction was set to 43 °.

[Examples 21-25 and 27]
Adjusting the length X1, height Y1, length X2, height Y2, length (TW / 2), radius of curvature R1, radius of curvature R2, and length X3, ratio (Y1 / X1), ratio (Y2 / X2), ratio (R1 / TW), ratio (R1 / R2), ratio (X3 / X2) and angle θ are the same as in Example 26 except that Tables 6 and 7 below are used. 21-25 and 27 tires were obtained. In addition, although the construction of a profile in which the ratio (R1 / R2) is smaller than 5.3 was examined, in this experiment B, such a profile could not be constructed.

[Real car running test]
The prototype tire was mounted on a racing cart with a displacement of 125 cc. The internal pressure of this tire was 75 kPa. The size of the rim is 8 × 5.0. With this racing cart, I drove the circuit course and measured the lap time. This result is shown in Tables 6 to 7 below.

  As shown in Tables 6 to 7, the tire of the example has a higher evaluation than the tire of the comparative example. From this evaluation result, the superiority of the present invention is clear.

  The tire configuration described above can be applied to various tires.

2, 20 ... Tire 4, 22 ... Tread 6, 24 ... Sidewall 8, 26 ... Bead 10, 28 ... Carcass 12, 30 ... Belt 18, 46a, 46b, 46 ... Ply 36 ... Main body 38 ... Shoulder 40 ... Tread surface 52 ... Carcass cord 58 ... Belt cord

Claims (8)

A tread that is in contact with the road surface during traveling, a pair of sidewalls each extending substantially inward in the radial direction from an end of the tread, a pair of beads each positioned substantially inward of the sidewall in the radial direction, the tread and A biased carcass bridged between one bead and the other bead along the inside of the sidewall, and a belt laminated with the carcass on the radially inner side of the tread,
This tread is composed of a main body whose outer surface forms a tread surface, and a pair of shoulders each positioned on the outer side in the axial direction of the main body.
The tread surface profile is formed by a plurality of arcs,
Each arc touches the adjacent arc,
The radius of curvature of each arc is smaller than the radius of curvature of the arc on the inner side in the axial direction,
The profile of the outer surface of the shoulder is formed by an arc,
The profile of the outer surface of the sidewall is formed by an arc,
Of the plurality of arcs forming the profile of the tread surface, an arc located outside in the axial direction is set as a reference arc, and a virtual straight line in contact with both the shoulder arc and the side wall arc is an extension of the reference arc. A position on the tread surface where the position intersecting the line is the first reference position, and the axial length of the tire from the equator plane is 70% of the half of the axial length of the tread surface. Is the second reference position,
The ratio of the radial height from the equator of the tire to the first reference position to the axial length from the equator plane of the tire to the first reference position is from 0.05 to 0.15,
A ratio of a radial height from the equator of the tire to the second reference position to an axial length from the equator plane of the tire to the second reference position is 0.015 or more and 0.040 or less. Pneumatic tire. The shoulder arc is in contact with the reference arc,
2. The pneumatic tire according to claim 1, wherein a radius of curvature of the arc of the shoulder is smaller than a radius of curvature of the reference arc. The carcass includes a first ply and a second ply,
Each of the first ply and the second ply includes a plurality of carcass cords arranged in parallel,
Each of these carcass cords is inclined with respect to the equator plane,
The pneumatic tire according to claim 1 or 2, wherein an absolute value of an inclination angle of the carcass cord is 40 ° or more and 60 ° or less. The belt includes a number of parallel belt cords,
Each of these belt cords is inclined with respect to the equatorial plane,
The pneumatic tire according to any one of claims 1 to 3, wherein an absolute value of an inclination angle of the belt cord is 15 ° or more and 30 ° or less. Among the plurality of arcs forming the profile of the tread surface, when the arc that contacts the straight line defining the outer diameter of the tire is the first arc at the equator,
The pneumatic tire according to any one of claims 1 to 4, wherein a ratio of a curvature radius of the first arc to an axial length of the tread surface is 4.0 or more and 11.0 or less. Among the plurality of arcs forming the profile of the tread surface, when the arc located outside the first arc and in contact with the first arc is a second arc,
The pneumatic tire according to claim 5, wherein a ratio of a curvature radius of the first arc to a curvature radius of the second arc is 3.0 or more and 17.0 or less.   The ratio of the axial length from the equator plane to the contact point between the first arc and the second arc to the axial length from the equator plane to the second reference position is 0.9 or more and 1.4 or less. The pneumatic tire according to claim 6, wherein   The pneumatic tire according to any one of claims 1 to 7, wherein an absolute value of an angle formed by the imaginary straight line with respect to a radial direction is 30 ° or more and 50 ° or less.

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