tire

Abstract

The present invention provides a tire (2) capable of achieving improved braking performance without a substantial increase in rolling resistance. The tire (2) comprises a tread (4), a pair of sidewalls (6), a pair of beads (10), and a carcass (12). The bead (10) comprises a core (30) and an apex (32). The ratio (A / H) of the height A of the apex (32) to the cross-sectional height H is not less than 5% and not more than 15%. In a meridian cross-section of the tire (2) under standard conditions, the profile of the side surface S including the maximum width position (PW) comprises two arcs connected at the maximum width position (PW), the arc radially located inside the maximum width position (PW) of the two arcs being the first arc and the arc radially located outside the maximum width position being the second arc, and the ratio (R1 / R2) of the radius R1 of the first arc to the radius R2 of the second arc being not less than 70% and not more than 91%.

Description

Technical Field

[0001] The present invention relates to a tire. Background Art

[0002] For example, Patent Document 1 below describes adjusting the profile from the tread shoulder to the sidewall, i.e., the side profile, to control tire performance such as durability, rolling resistance, and ride comfort. In order to control tire performance, in addition to adjusting the physical properties and arrangement of the tire's components, the tire profile is sometimes also adjusted.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2017-121899 Summary of the Invention

[0006] Problems to be solved by the invention

[0007] Environmental concerns have led to the search for tires with low rolling resistance. Using low-heat-generating rubber for the tread reduces rolling resistance. However, using low-heat-generating rubber for the tread reduces the tire's coefficient of friction. This reduces braking performance. Increasing the tire's coefficient of friction to improve braking performance increases rolling resistance.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a tire capable of achieving improved braking performance without a significant increase in rolling resistance.

[0009] Solutions to Problems

[0010] A tire according to one embodiment of the present invention comprises a tread that contacts a road surface, a pair of sidewalls connected to one end of the tread and radially inwardly located on the tread, a pair of beads radially inwardly located on the sidewalls, and a carcass located inwardly of the tread and the pair of sidewalls. The beads comprise a core and an apex rubber radially located outwardly of the core. The ratio of the apex rubber height to the cross-sectional height is 5% to 15%. When the tire is assembled on a standard rim and the internal pressure is adjusted to 250 kPa, and the tire is unloaded, the profile of the side surface including the maximum width position in a meridian cross section includes two arcs that meet at the maximum width position. Of the two arcs, the arc radially inwardly located on the maximum width position is a first arc, and the arc radially outwardly located on the maximum width position is a second arc. Furthermore, the ratio of the radius of the first arc to the radius of the second arc is 70% to 91%.

[0011] Preferably, in the tire, a radius of the first arc is not less than 50 mm and not more than 65 mm.

[0012] Preferably, in this tire, the carcass includes a carcass ply. The carcass ply includes a ply body extending between one bead and the other bead, and a pair of turnbacks connected to the ply body and folded back axially from the inside toward the outside around the bead. The ratio of the radial distance from the bead base line to one end of the turnback to the radial distance from the bead base line to the maximum width position is not less than 48% and not more than 68%.

[0013] Preferably, in this tire, the tread is engraved with a plurality of circumferential grooves to form a plurality of land portions. Among the plurality of land portions, the land portion located axially outward is a shoulder land portion, and the land portion located inward of the shoulder land portion is a middle land portion. The outer surface of the middle land portion has an outwardly curved profile. The maximum height of the outer surface is not less than 0.05 mm and not more than 0.15 mm.

[0014] Preferably, in this tire, the middle land portion is engraved with a transverse sipe extending substantially in the axial direction, and edges of the transverse sipe are chamfered.

[0015] Preferably, in this tire, the shoulder land portion is engraved with transverse grooves and transverse sipes extending substantially in the axial direction, and edges of the transverse grooves and transverse sipes are chamfered.

[0016] Effects of the Invention

[0017] According to the present invention, it is possible to obtain a tire capable of achieving improved braking performance without a significant increase in rolling resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a cross-sectional view showing a portion of a tire according to one embodiment of the present invention.

[0019] Figure 2 It is a cross-sectional view showing the bead portion of the tire.

[0020] Figure 3 A developed view showing the outer surface of the tread.

[0021] Figure 4 A cross-sectional view showing a portion of the tread.

[0022] Figure 5 For the Figure 3 Cross-sectional view of line aa.

[0023] Figure 6 For the Figure 3 Cross-sectional view of line bb. DETAILED DESCRIPTION

[0024] Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

[0025] In this disclosure, the state in which a tire is assembled to a standard rim and its internal pressure is adjusted to the standard internal pressure, and the tire is unloaded, is referred to as the standard state. The state in which a tire is assembled to a standard rim and its internal pressure is adjusted to 250 kPa, and the tire is unloaded, is referred to as the standard state.

[0026] Unless otherwise specified in this disclosure, the dimensions and angles of various tire components are measured under standard conditions. Dimensions and angles of various tire components in a meridian cross-section that cannot be measured with the tire assembled on a standard rim can be measured by aligning the distance between the left and right beads in the cross-section of the tire, obtained by cutting the tire along a plane including the axis of rotation, with the distance between the beads aligned with the distance between the beads of a tire assembled on a standard rim.

[0027] Standard rims are defined by the tire's specifications. Examples include the "standard rim" under the JATMA standard, the "design rim" under the TRA standard, and the "measuring rim" under the ETRTO standard.

[0028] Standard internal pressure refers to the internal pressure specified in the tire's standards. These include the "Maximum Air Pressure" in the JATMA standard, the "Maximum Pressure" listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "INFLATION PRESSURE" in the ETRTO standard.

[0029] Standard load refers to the load specified in the tire's standards. The standard loads include the "maximum load capacity" in the JATMA standard, the "maximum value" listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard.

[0030] In this disclosure, the tire's tread is the portion of the tire that contacts the road surface. The bead is the portion of the tire that engages the wheel rim. The sidewalls are the portions of the tire that span between the tread and bead. A tire includes a tread, a pair of bead portions, and a pair of sidewalls.

[0031] The rim includes a bead seat and a flange. When the tire is assembled on the rim, the inner peripheral surface of the bead portion is placed on the bead seat, and the outer surface of the bead portion contacts the flange.

[0032] In the present disclosure, the loss tangent (also referred to as tanδ) of the element composed of cross-linked rubber among the elements constituting the tire at a temperature of 30°C is measured in accordance with the provisions of JIS K6394 using a viscoelastic spectrometer ("VES" manufactured by Iwamoto Seisakusho Co., Ltd.) under the following conditions.

[0033] Initial strain = 10%

[0034] Dynamic strain = 2%

[0035] Frequency = 10 Hz

[0036] Deformation Mode = Stretch

[0037] In this measurement, a test piece is sampled from the tire. If a test piece cannot be sampled from the tire, a test piece can be sampled from a sheet of cross-linked rubber (hereinafter also referred to as a rubber bead seat) obtained by pressurizing and heating the rubber composition forming the element to be measured at 170°C for 12 minutes.

[0038] In this disclosure, the hardness of a tire-constituting element composed of crosslinked rubber is measured using a Type A durometer at 23°C in accordance with JIS K6253. If tire hardness cannot be measured, a test piece composed of crosslinked rubber obtained by pressurizing and heating a rubber composition to be measured at 170°C for 12 minutes may be used.

[0039] Figure 1 1 is a diagram showing a portion of a tire 2 according to an embodiment of the present invention. The tire 2 is a tire for a passenger car. Figure 1 In the embodiment, the tire 2 is assembled to the rim R. The rim R is a standard rim. The interior of the tire 2 is filled with air, and the internal pressure of the tire 2 is adjusted. Figure 1 The tire 2 is shown in a standard condition.

[0040] The tire 2 assembled to the rim R is also referred to as a tire-rim assembly. The tire-rim assembly includes the rim R and the tire 2 assembled to the rim R.

[0041] Figure 1 1 shows a portion of a cross section (hereinafter also referred to as a meridian cross section) of the tire 2 along a plane including the rotation axis (not shown) of the tire 2 . Figure 1 In the figure, the left and right directions are the axial directions of the tire 2, and the up and down directions are the radial directions of the tire 2. Figure 1The direction of the paper is the circumferential direction of the tire 2. Figure 1 In FIG. 2 , a dashed line CL indicates the equatorial plane CL of the tire 2 .

[0042] exist Figure 1 In FIG, a solid line BBL extending in the axial direction is a bead base line BBL. The bead base line BBL is a line that defines the rim diameter of the rim R (see JATMA, etc.).

[0043] exist Figure 1 In the figure, the position indicated by the symbol PW is the axial outer end of the tire 2. When the outer surface is decorated with patterns, text, or other decorations, the outer end PW is specifically designated based on the hypothetical outer surface obtained by assuming no decoration. The axial distance from one outer end PW to the other outer end PW is the maximum width of the tire 2, that is, the cross-sectional width (see JATMA, etc.). The outer end PW is the position where the tire 2 exhibits its maximum width (hereinafter referred to as the maximum width position). The maximum width position PW is specifically designated for the tire 2 in its standard state.

[0044] The tire 2 includes a tread 4 , a pair of sidewalls 6 , a pair of clinchers 8 , a pair of beads 10 , a carcass 12 , a belt 14 , a reinforcing layer 16 , a pair of scuff layers 18 , and an inner liner 20 .

[0045] The outer surface of the tread 4 is in contact with the road surface. The tread 4 is engraved with grooves 22. This constitutes a tread pattern.

[0046] The grooves 22 constituting the tread pattern of the tire 2 include circumferential grooves 24 extending continuously in the circumferential direction. In the tire 2, a plurality of circumferential grooves 24 arranged in parallel in the axial direction are engraved on the tread 4. Figure 1 In the tire 2 shown, three circumferential grooves 24 are engraved in the tread 4. Among the three circumferential grooves 24, the circumferential groove 24 located axially outward is a shoulder circumferential groove 24s. The circumferential groove 24 located axially inward of the shoulder circumferential groove 24s is an intermediate circumferential groove 24m. In this tire 2, the intermediate circumferential groove 24m is located on the equatorial plane CL.

[0047] In the tire 2 , the arrangement, depth, and width of the circumferential grooves 24 engraved on the tread 4 are not particularly limited. Common arrangements, depths, and widths of the circumferential grooves 24 of the tire 2 can be applied to the tread 4 .

[0048] Figure 1 , the position indicated by symbol PC is the equator of the tire 2. The equator PC is the intersection of the outer surface of the tread 4 and the equatorial plane CL. In this tire 2, since the middle circumferential groove 24m is located on the equatorial plane CL, the equator PC is specified based on a virtual outer surface obtained by assuming that the middle circumferential groove 24m does not exist.

[0049] Figure 1In the diagram, the length indicated by symbol H is the cross-sectional height of the tire 2 (see JATMA, etc.). Cross-sectional height H is the radial distance from the bead base line BBL to the equator PC. Cross-sectional height H is measured for the tire 2 in a standard state.

[0050] The tread 4 includes a base layer 26 and an overlay layer 28. The base layer 26 covers the belt layer 14 and the reinforcing layer 16. The base layer 26 is made of a low-heat-generating crosslinked rubber. In the tire 2, the loss tangent of the base layer 26 at 30°C is 0.11 or less.

[0051] The cover layer 28 is radially located outside the base layer 26. The cover layer 28 covers the entire base layer 26. The outer surface of the cover layer 28 corresponds to the outer surface of the tread 4. The cover layer 28 is composed of a cross-linked rubber designed for wear resistance and grip performance. The loss tangent of the cover layer 28 is greater than that of the base layer 26. To help reduce rolling resistance, the loss tangent of the cover layer 28 is preferably 0.30 or less, and more preferably 0.20 or less.

[0052] Each sidewall 6 is connected to one end of the tread 4. The sidewall 6 is located radially inside the tread 4. The sidewall 6 extends from one end of the tread 4 toward the clinch 8 along the carcass 12. The sidewall 6 is made of a cross-linked rubber that is cut-resistant.

[0053] Each clinch 8 is located radially inward of the sidewall 6. The clinch 8 is in contact with the flange G of the rim R. The clinch 8 is made of a cross-linked rubber in consideration of wear resistance.

[0054] Each bead 10 is located axially inside the clinch portion 8. The bead 10 is located radially inside the sidewall 6. The bead 10 includes a core 30 and an apex 32. Although not shown, the core 30 includes a metal wire made of steel.

[0055] The apex 32 is radially outside the core 30. The apex 32 tapers outward. The apex 32 is made of highly rigid cross-linked rubber. The hardness of the apex 32 is between 80 and 98 degrees. Figure 1 , the position indicated by symbol PA is the radially outer end (hereinafter also referred to as the front end) of the apex 32 .

[0056] The carcass 12 is located inside the tread 4, the pair of sidewalls 6, and the pair of clinch portions 8. The carcass 12 is spanned between one bead 10 and the other bead 10. The carcass 12 has a radial structure.

[0057] The carcass 12 includes at least one carcass ply 34. From the viewpoint of reducing rolling resistance, it is preferable that the carcass 12 be composed of one carcass ply 34.

[0058] The carcass 12 of the tire 2 is composed of a single carcass ply 34. The carcass ply 34 includes a ply main body 34a that spans between one bead 10 and the other bead 10, and a pair of folded portions 34b connected to the ply main body 34a and folded axially outward around each bead 10. One end of the folded portion 34b is radially inward of the maximum width position PW. One end of the folded portion 34b is located between the ply main body 34a and the sidewall 6. The folded portion 34b is joined to the ply main body 34a in the region from the front end PA of the apex 32 to one end of the folded portion 34b.

[0059] Although not shown, the carcass ply 34 includes a plurality of carcass cords arranged in parallel. Each carcass cord intersects the equatorial plane CL. The carcass cords are made of organic fibers. Examples of organic fibers include nylon fibers, rayon fibers, polyester fibers, and aramid fibers.

[0060] The belt layer 14 is located radially inward of the tread 4. The belt layer 14 is laminated radially from the outside to the carcass 12. In the tire 2, the axial width of the belt layer 14 is 65% to 85% of the cross-sectional width.

[0061] The belt layer 14 is composed of at least two layers 36 laminated in the radial direction. The belt layer 14 of the tire 2 is composed of two layers 36 laminated in the radial direction. Of the two layers 36, the layer 36 located on the inner side is the inner layer 36a, and the layer 36 located on the outer side is the outer layer 36b. Figure 1 As shown, the width of the inner layer 36a is wider than that of the outer layer 36b. The length from one end of the outer layer 36b to one end of the inner layer 36a is 3 mm to 10 mm.

[0062] Although not shown, the inner layer 36a and the outer layer 36b each include a plurality of parallel belt cords. Each belt cord is inclined with respect to the equatorial plane CL. The belt cords are made of steel wire.

[0063] The reinforcing layer 16 is radially positioned between the tread 4 and the belt 14. The reinforcing layer 16 is laminated to the belt 14 on the inner side of the tread 4. The reinforcing layer 16 covers the entire belt 14. The reinforcing layer 16 is wider than the belt 14. The length from one end of the belt 14 to one end of the reinforcing layer 16 is 3 mm to 7 mm.

[0064] Although not shown, the reinforcement layer 16 includes a helically wound reinforcement cord. The reinforcement cord extends substantially in the circumferential direction. Specifically, the angle formed by the reinforcement cord with respect to the circumferential direction is 5° or less. The reinforcement layer 16 has a seamless structure. In this tire 2, a cord composed of organic fibers is used as the reinforcement cord. Examples of the organic fiber include nylon fiber, rayon fiber, polyester fiber, and aramid fiber.

[0065] The reinforcement layer 16 of the tire 2 includes a whole reinforcement layer 16F and a pair of edge reinforcement layers 16E. The whole reinforcement layer 16F has two ends opposite to each other across the equatorial plane CL. One end of the whole reinforcement layer 16F is located axially outside one end of the belt layer 14. The whole reinforcement layer 16F covers the entire belt layer 14 from the outside in the radial direction. A pair of edge reinforcement layers 16E are arranged axially separated across the equatorial plane CL. The edge reinforcement layer 16E is laminated to the whole reinforcement layer 16F. The edge reinforcement layer 16E covers one end of the whole reinforcement layer 16F from the outside in the radial direction. The reinforcement layer 16 can be composed of either a whole reinforcement layer 16F or a pair of edge reinforcement layers 16E.

[0066] Each scuff layer 18 is located radially inward of the bead 10. The scuff layer 18 is in contact with the bead seat E of the rim R. The scuff layer 18 of the tire 2 is composed of cloth and rubber impregnated in the cloth.

[0067] The inner liner 20 is located inside the carcass 12. The inner liner 20 forms the inner surface of the tire 2. The inner liner 20 is made of a cross-linked rubber having a low gas permeability coefficient. The inner liner 20 maintains the internal pressure of the tire 2.

[0068] The profile of the tire 2 is obtained, for example, by measuring the outer surface shape of the tire 2 in a standard state using a displacement sensor. In a meridian cross-section, the profile of the outer surface of the tire 2 (hereinafter referred to as the tire outer surface TS) is constructed by connecting multiple contour lines formed by straight lines or circular arcs. In this disclosure, contour lines formed by straight lines or circular arcs are simply referred to as contour lines. Contour lines formed by straight lines are referred to as linear contour lines, while contour lines formed by circular arcs are referred to as curved contour lines.

[0069] The tire outer surface TS includes a tread surface T and a pair of side surfaces S connected to one end of the tread surface T. In this disclosure, the profile of the tread surface T is described using the profile of a hypothetical outer surface (also referred to as a hypothetical tread surface) assuming no grooves. The tread surface T includes the aforementioned equator PC. The profile of the side surfaces S is described using the profile of a hypothetical outer surface (also referred to as a hypothetical side surface) assuming no decoration such as patterns or text. The side surfaces S include the aforementioned maximum width position PW.

[0070] In a meridian cross section, the profile of the tread surface T includes a plurality of curved contour lines having different radii. In this tire 2, the curved contour line having the smallest radius among the plurality of curved contour lines included in the profile of the tread surface T is located at the end of the tread surface T and is connected to the side surface S. In a meridian cross section, the profile of the tire outer surface TS is formed by the arc having the smallest radius among the plurality of curved contour lines included in the profile of the tread surface T, and the portion at the end of the tread surface T includes the curved contour line connected to the side surface S, i.e., the curved portion. Figure 1 In FIG, the curved portion is represented by the symbol RS.

[0071] In the profile of the tire's outer surface TS, the curved portion RS touches the contour line adjacent to its axially inner side (hereinafter referred to as the inner adjacent contour line NT) at a tangent point CT. The curved portion RS touches the contour line forming the contour of the side surface S adjacent to its axially outer side (hereinafter referred to as the outer adjacent contour line NS) at a tangent point CS. The profile of the tire's outer surface TS includes the inner adjacent contour line NT, located axially inward of the curved portion RS and in contact with the curved portion RS, and the outer adjacent contour line NS, located axially outward of the curved portion RS and in contact with the curved portion RS.

[0072] Figure 1 In the figure, solid line LT is a tangent to the curved portion RS at the tangent point CT between the inner adjacent contour line NT and the curved portion RS. Solid line LS is a tangent to the curved portion RS at the tangent point CS between the outer adjacent contour line NS and the curved portion RS. The position denoted by symbol PE is the intersection of a straight line extending radially through the intersection of tangent lines LT and LS with the tread surface T. In this tire 2, this intersection point PE is the tread reference end. The tangent point CS is the boundary between the tread surface T and the side surface S.

[0073] Figure 1 In FIG. 1 , symbol B1 denotes a specific position on the side surface S. The solid line LG is a straight line extending radially through the radially outer end of the flange G. The specific position B1 is the intersection of the straight line LG and the side surface S. The specific position B1 is the flange reference position.

[0074] Figure 1 In the figure, symbol B2 denotes a specific position on the side surface S. The length indicated by the double-headed arrow D is the radial distance from the bead baseline BBL to the specific position B2. In this tire 2, radial distance D is set to 0.77 times the cross-sectional height H. Specific position B2 indicates a position on the side surface S where the radial distance D from the bead baseline BBL is 0.77 times the cross-sectional height H. This specific position B2 is the sidewall reference position.

[0075] As described above, side surface S includes a maximum width position PW. In a meridian cross section, the profile of side surface S comprises two curved contour lines, or arcs, that connect at maximum width position PW. Of the two arcs connecting at maximum width position PW, the arc radially inward of maximum width position PW is the first arc, and the arc radially outward of maximum width position PW is the second arc. The curved contour line formed by the first arc is also referred to as the first curved contour line, and the curved contour line formed by the second arc is also referred to as the second curved contour line.

[0076] Figure 1 In FIG. 1 , the arrow indicated by symbol R1 is the radius of the first arc, and the arrow indicated by symbol R2 is the radius of the second arc. The centers of the first arc and the second arc pass through the maximum width position PW and are located on a straight line extending in the axial direction.

[0077] In the tire 2, the radius R1 of the first arc is smaller than the radius R2 of the second arc. Specifically, the ratio (R1 / R2) of the radius R1 of the first arc to the radius R2 of the second arc is less than 91%. As a result, the carcass 12 can be arranged on the outer side of the meridian cross section. Since the carcass 12 is long, the longitudinal rigidity of the tire 2 is effectively reduced. Due to the low longitudinal rigidity, a wider contact surface of the tire 2 can be ensured when braking with a large load. From this point of view, the ratio (R1 / R2) is preferably less than 90%, more preferably less than 88%, and even more preferably less than 86%.

[0078] In this tire 2, the ratio (R1 / R2) of the radius R1 of the first arc to the radius R2 of the second arc is 70% or greater. This maintains an appropriate contact area between the bead portion and the flange G. This effectively suppresses fluctuations in friction and strain caused by the repeated deformation and recovery of the bead portion during driving, thereby maintaining excellent durability. From this perspective, the ratio (R1 / R2) is preferably 75% or greater, more preferably 78% or greater, and even more preferably 80% or greater.

[0079] Figure 1 In the tire 2, the position indicated by symbol PM is the center of the axial width of the contact surface of the apex 32 with the core 30. The length indicated by symbol A is the radial distance from the width center PM to the front end PA of the apex 32. In this tire 2, the radial distance A is the height of the apex 32.

[0080] In this tire 2, the ratio of the height A of the apex 32 to the cross-sectional height H (A / H) is 15% or less. This ratio (A / H) is typically set at approximately 20% or greater. The height A of the apex 32 is relatively low. The apex 32 with a low height A helps reduce longitudinal rigidity. The apex 32 also helps position the carcass 12 closer to the outside in the meridian cross section. This tire 2 effectively reduces longitudinal rigidity. The apex 32 helps ensure a secure contact patch. The apex 32 also helps reduce rolling resistance.

[0081] In this tire 2, the ratio (A / H) of the height A of the apex 32 to the cross-sectional height H is 5% or greater. This tire 2 is configured with the apex 32 having the required height A. This apex 32 effectively restrains the core 30 assembled in the bead portion of the rim R. This suppresses movement of the core 30 during driving, thereby ensuring the required durability of the tire 2.

[0082] In this tire 2, the ratio of the radius R1 of the first arc to the radius R2 of the second arc (R1 / R2) is less than 91%, and the ratio of the height A of the apex rubber 32 to the cross-sectional height H (A / H) is less than 15%. The wider contact width of the tire 2 increases the contact area. The increase in contact area increases the friction coefficient of the tire 2. In this tire 2, good braking performance can be achieved even if low-heat-generating rubber is used for the tread 4. There is no need to use heat-generating rubber that focuses on grip for the tread 4 in order to increase the friction coefficient. This tire 2 can achieve improved braking performance without a significant increase in rolling resistance.

[0083] In the tire 2, the ratio of the radius R1 of the first arc to the radius R2 of the second arc (R1 / R2) is 70% or greater, and the ratio of the height A of the apex 32 to the cross-sectional height H (A / H) is 5% or greater. This tire 2 can ensure the necessary durability.

[0084] In this tire 2, the ratio of the radius R1 of the first arc to the radius R2 of the second arc (R1 / R2) is 70% to 91%, and the ratio of the height A of the apex 32 to the cross-sectional height H (A / H) is 5% to 15%. This tire 2 can achieve improved braking performance without a significant increase in rolling resistance or a significant decrease in durability.

[0085] In the tire 2, it is preferred that the radius R1 of the first arc is not less than 50 mm and not more than 65 mm. By setting the radius R1 to be not less than 50 mm, the contact area between the bead portion and the flange G can be appropriately maintained. Since the friction and strain changes caused by the repeated deformation and restoration of the bead portion during driving can be effectively suppressed, good durability can be maintained. From this point of view, the radius R1 is more preferably not less than 53 mm, and further preferably not less than 55 mm. By setting the radius R1 to be less than 65 mm, the carcass 12 can be arranged on the outer side in the meridian cross section. Since the long carcass 12 is formed, the longitudinal rigidity of the tire 2 is effectively reduced. When braking with a large load, a wider contact surface of the tire 2 can be ensured. The tire 2 can obtain good braking performance. From this point of view, the radius R1 is more preferably not more than 62 mm, and further preferably not more than 60 mm.

[0086] Figure 1 In the diagram, the position indicated by symbol G1 is the endpoint of the first arc when the maximum width position PW is set as the starting point of the first arc. The length indicated by symbol C1 is the radial distance from the maximum width position PW to the endpoint G1. The length indicated by symbol W1 is the radial distance from the maximum width position PW to the flange reference position B1.

[0087] In this tire 2, in the portion of the side surface S represented by the first arc, from the viewpoint of effectively contributing to a reduction in longitudinal rigidity, the ratio (C1 / W1) of the radial distance C1 from the maximum width position PW to the end point G1 of the first arc to the radial distance W1 from the maximum width position PW to the flange reference position B1 is preferably 0.70 or greater, more preferably 0.80 or greater, and even more preferably 0.90 or greater. This ratio (C1 / W1) is particularly preferably 1.00.

[0088] Figure 1 In the diagram, the position indicated by symbol G2 is the end point of the second arc when the maximum width position PW is set as the starting point of the second arc. The length indicated by symbol C2 is the radial distance from the maximum width position PW to the end point G2. The length indicated by symbol W2 is the radial distance from the maximum width position PW to the sidewall reference position B2.

[0089] In this tire 2, in the portion of the side surface S represented by the second arc, from the viewpoint of effectively contributing to a reduction in longitudinal rigidity, the ratio (C2 / W2) of the radial distance C2 from the maximum width position PW to the end point G2 of the second arc to the radial distance W2 from the maximum width position PW to the sidewall reference position B2 is preferably 0.70 or greater, more preferably 0.80 or greater, and even more preferably 0.90 or greater. This ratio (C2 / W2) is particularly preferably 1.00.

[0090] Figure 2 express Figure 1 A portion of the meridian cross section is shown. Figure 2 The bead portion of the tire 2 is shown in FIG. Figure 2 In the figure, the left and right directions are the axial directions of the tire 2, and the up and down directions are the radial directions of the tire 2. Figure 2 The direction of the paper surface is the circumferential direction of the tire 2.

[0091] Figure 2 In the figure, the position indicated by the symbol PF is one end of the folded portion 34b. The length indicated by the symbol F is the radial distance from the bead baseline BBL to the one end PF of the folded portion 34b. This radial distance F is the height of the folded portion 34b. The length indicated by the symbol W is the radial distance from the bead baseline BBL to the maximum width position PW. This radial distance W is the maximum width height.

[0092] In the tire 2 , the ratio (F / W) of the height F of the folded portion 34 b to the maximum width height W is preferably 48% or more and 68% or less.

[0093] By setting the ratio (F / W) to 48% or more, the concentration of strain on the end PF of the folded portion 34b when a force acts on the bead portion can be suppressed. The tire 2 can obtain good durability. From this point of view, the ratio (F / W) is more preferably 50% or more. By setting the ratio (F / W) to 68% or less, the longitudinal rigidity can be effectively reduced, so that a wider contact patch of the tire 2 can be ensured when braking with a large load. The tire 2 can obtain good braking performance. The low folded portion 34b also helps to reduce rolling resistance. From this point of view, the ratio (F / W) is more preferably 65% ​​or less.

[0094] Figure 2 In FIG. 1 , the solid line LAM is a straight line passing through the front end PA and the width center PM of the apex 32. The solid line LAF is a straight line passing through the front end PA of the apex 32 and one end PF of the folded portion 34b. Angle θ is the angle formed by the lines LAM and LAF.

[0095] In the tire 2, when the ratio (F / W) of the height F of the turn-back portion 34b to the maximum width height W is 48% to 68%, the angle θ formed by the straight line LAM passing through the front end PA and the width center PM of the apex 32 and the straight line LAF passing through the front end PA and the one end PF of the turn-back portion 34b is preferably 35 degrees to 50 degrees.

[0096] By setting the angle θ to 35 degrees or greater, the carcass 12 can be positioned further outward in the meridian cross-section. Due to the long carcass 12, the tire 2 effectively reduces longitudinal rigidity. From this perspective, the angle θ is more preferably 38 degrees or greater, and even more preferably 40 degrees or greater. By setting the angle θ to 50 degrees or less, the contact area between the bead portion and the flange G can be appropriately maintained. This effectively suppresses the friction and strain fluctuations caused by the repeated deformation and restoration of the bead portion during driving, thereby maintaining good durability. From this perspective, the angle θ is more preferably 48 degrees or less, and even more preferably 45 degrees or less.

[0097] Figure 3 A portion of the outer surface of the tread 4 is shown in FIG. Figure 3 In the figure, the left and right directions are the axial directions of the tire 2, and the up and down directions are the circumferential directions of the tire 2. Figure 3 The direction of the paper is the radial direction of the tire 2. Figure 3 In the embodiment, the tread reference end PE on the left is the first tread reference end PE1, and the tread reference end PE on the right is the second tread reference end PE2. When the tire 2 is mounted on a vehicle, the first tread reference end PE1 is arranged on the outer side in the width direction of the vehicle.

[0098] As described above, the tread 4 of the tire 2 is formed with grooves 22 to form a tread pattern. Among the grooves 22 forming the tread pattern, grooves having a groove width of 1.5 mm or less are called sipes.

[0099] In the present disclosure, the phrase "grooves extending in a substantially axial direction" means that the angle formed by the grooves with respect to the axial direction is 45 degrees or less. Sipes extending in a substantially axial direction are also referred to as transverse sipes.

[0100] As described above, in this tire 2, multiple circumferential grooves 24 are engraved in the tread 4. These grooves form multiple land portions 38. In this tire 2, three circumferential grooves 24 are engraved in the tread 4, forming four axially aligned land portions 38. Of the four land portions 38, the axially outer land portion 38 is the shoulder land portion 38s. The land portion 38 located inboard of the shoulder land portion 38s is the middle land portion 38m.

[0101] The shoulder land portion 38s is engraved with transverse grooves 40. The transverse grooves 40 have a groove width of at least 2.0 mm. The transverse grooves 40 have ends within the shoulder land portion 38s. The transverse grooves 40 extend from one end toward the tread reference end PE. The transverse grooves 40 extend in a generally axial direction. The inclination direction of the transverse grooves 40 in the shoulder land portion 38s on the first tread reference end PE1 side is the same as the inclination direction of the transverse grooves 40 in the shoulder land portion 38s on the second tread reference end PE2 side. The shoulder land portion 38s is engraved with a plurality of transverse grooves 40. These transverse grooves 40 are arranged at intervals in the circumferential direction.

[0102] The shoulder land portion 38s is engraved with stop sipes 44 serving as transverse sipes 42. The stop sipes 44 have ends within the shoulder land portion 38s. The stop sipes 44 extend from one end toward the tread reference end PE. The inclination of the stop sipes 44 is aligned with the inclination of the transverse grooves 40. The shoulder land portion 38s is engraved with a plurality of stop sipes 44. In this tire 2, the transverse grooves 40 and the stop sipes 44 are arranged alternately in the circumferential direction.

[0103] The shoulder land portion 38s on the second tread reference end PE2 side has connecting sipes 46, which serve as transverse sipes 42. The connecting sipes 46 span the shoulder circumferential grooves 24s and the transverse grooves 40. The connecting sipes 46 are inclined in the same direction as the transverse grooves 40. The shoulder land portion 38s has the same number of connecting sipes 46 as the transverse grooves 40.

[0104] The middle land portion 38m is engraved with a main stopper sipe 48 serving as the transverse sipe 42. The main stopper sipe 48 has an end portion within the middle land portion 38m. The main stopper sipe 48 extends from one end toward the circumferential groove 24. In this tire 2, the main stopper sipe 48 connecting the end portion with the shoulder circumferential groove 24s is the outer main stopper sipe 48s. The main stopper sipe 48 connecting the end portion with the middle circumferential groove 24m is the inner main stopper sipe 48u.

[0105] The middle land portion 38m is engraved with a plurality of outer main row stopper sipes 48s. These outer main row stopper sipes 48s are spaced apart in the circumferential direction. The middle land portion 38m is engraved with a plurality of inner main row stopper sipes 48u. These inner main row stopper sipes 48u are spaced apart in the circumferential direction. The pitch of the outer main row stopper sipes 48s is the same as the pitch of the inner main row stopper sipes 48u.

[0106] The outer main row stopper sipe 48s is inclined in the same direction as the inner main row stopper sipe 48u. The inner main row stopper sipe 48u located on the first tread reference end PE1 side is inclined in the same direction as the inner main row stopper sipe 48u located on the second tread reference end PE2 side.

[0107] In this tire 2, the inclination angle of the inner main stopper sipe 48u is greater than the inclination angle of the outer main stopper sipe 48s. The outer main stopper sipe 48s and the inner main stopper sipe 48u are arranged so that the inclination angle of the line segment connecting one end of the outer main stopper sipe 48s and one end of the inner main stopper sipe 48u is greater than the inclination angle of the outer main stopper sipe 48s and less than the inclination angle of the inner main stopper sipe 48u. In this tire 2, the combination of the outer main stopper sipe 48s and the inner main stopper sipe 48u adjacent to the outer main stopper sipe 48s is also referred to as a pair of sipes.

[0108] The middle land portion 38m on the first tread reference end PE1 side is engraved with a sub-row stop sipe 50 serving as the transverse sipe 42. The sub-row stop sipe 50 has an end portion within the middle land portion 38m. The sub-row stop sipe 50 extends from one end toward the shoulder circumferential groove 24s. The inclination of the sub-row stop sipe 50 is the same as that of the outer main row stop sipe 48s. The sub-row stop sipe 50 is longer than the outer main row stop sipe 48s. The middle land portion 38m is engraved with a plurality of sub-row stop sipes 50. In this tire 2, the sub-row stop sipes 50 and the outer main row stop sipes 48s are arranged alternately in the circumferential direction.

[0109] The middle land portion 38m on the second tread reference end PE2 side is engraved with transverse sipes 52, serving as transverse sipes 42. The transverse sipes 52 span the shoulder circumferential groove 24s and the middle circumferential groove 24m. The portion of the transverse sipe 52 on the shoulder circumferential groove 24s side is tilted in the same direction as the outer main stopper sipe 48s. The portion of the transverse sipe 52 on the middle circumferential groove 24m side is tilted in the same direction as the inner main stopper sipe 48u. Multiple transverse sipes 52 are engraved in the middle land portion 38m on the second tread reference end PE2 side. The transverse sipes 52 and paired sipes are arranged alternately in the circumferential direction.

[0110] Figure 4 FIG. 3 shows an enlarged cross-sectional view of the middle land portion 38m. Figure 4 3 shows a modified example of the middle land portion 38m.

[0111] Figure 4 In FIG. 4 , the two-dot chain line represented by the symbol T is the aforementioned tread surface T. The tread surface T passes through the left and right edges 54 of the middle land portion 38 m. The tread surface T is a reference surface of the outer surface of the tread 4 . Figure 4 An outer surface 56 of the illustrated middle land portion 38m is located radially outside of the tread surface T.

[0112] like Figure 4As shown, the outer surface 56 of the middle land portion 38m has an outwardly curved profile. In a meridian cross section, the profile of the outer surface 56 of the middle land portion 38m is represented by an arc passing through the left and right edges 54 and the top 58.

[0113] In this tire 2, the outer surface 56 of the middle land portion 38m has an outwardly curved profile, effectively suppressing increases in ground contact pressure at the edge 54 of the middle land portion 38m. This provides a ground contact pressure distribution that minimizes uneven ground contact pressure, allowing the tread 4 to adhere effectively to the road surface. This increases the coefficient of friction of the tire 2, resulting in excellent braking performance. From this perspective, it is preferable that the outer surface 56 of the middle land portion 38m in this tire 2 have an outwardly curved profile.

[0114] Figure 4 In FIG. 5 , the length indicated by symbol DX is the maximum height of the outer surface 56 of the middle land portion 38 m. The maximum height DX is represented by the shortest distance from the tread surface T to the top 58.

[0115] In this tire 2, from the perspective of achieving good braking performance, the maximum height DX of the outer surface 56 of the middle land portion 38m is preferably 0.05 mm or greater, and more preferably 0.08 mm or greater. From the perspective of appropriately maintaining the volume of the middle land portion 38m and suppressing an increase in rolling resistance, the maximum height DX is preferably 0.15 mm or less, and more preferably 0.12 mm or less.

[0116] Figure 5 FIG. 4 shows a cross section of the transverse groove 40 engraved in the shoulder land portion 38s. Figure 5 2 shows a modified example of the transverse groove 40 .

[0117] As mentioned above, the transverse groove 40 extends in a substantially axial direction. The edge 60 of the transverse groove 40 also extends in a substantially axial direction. Figure 5 As shown, the edge 60 of the transverse groove 40 is chamfered. This can suppress the concentration of strain toward the edge 60 of the transverse groove 40 during braking. A ground pressure distribution that can suppress the height difference of the ground pressure can be obtained, so that the tread 4 is fully in contact with the road surface. The friction coefficient of the tire 2 is improved, and good braking performance can be obtained. From this point of view, in the tire 2, it is preferred that the edge 60 of the transverse groove 40 is chamfered. In this case, from the point of view that the tread 4 can be more fully in contact with the road surface and the friction coefficient of the tire 2 can be effectively improved, it is more preferred that the two edges 60 of the transverse groove 40 are chamfered.

[0118] although Figure 5 3 shows an example in which the edge 60 of the transverse groove 40 is subjected to C-chamfering processing, but the edge 60 of the transverse groove 40 may also be subjected to R-chamfering processing.

[0119] Figure 6FIG. 4 shows a cross section of a stop sipe 44 engraved on the shoulder land portion 38s as an example of a transverse sipe 42 engraved on the land portion 38. Figure 6 2 shows a modified example of the transverse sipe 42 .

[0120] As previously mentioned, the transverse sipe 42 extends in a generally axial direction. The edge 62 of the transverse sipe 42 also extends in a generally axial direction. Figure 6 As shown, in the transverse groove pattern 42, the edge 62 is chamfered. This can suppress the concentration of strain toward the edge 62 of the transverse groove pattern 42 during braking. Since a ground pressure distribution that suppresses the height difference of the ground pressure can be obtained, the tread 4 is fully in contact with the road surface. The friction coefficient of the tire 2 is improved, and good braking performance can be obtained. From this point of view, in the tire 2, it is preferred that the edge 62 of the transverse groove pattern 42 is chamfered. In this case, from the point of view that the tread 4 can fully fit with the road surface and can effectively improve the friction coefficient of the tire 2, it is preferred that the two edges 62 of the transverse groove pattern 42 are chamfered.

[0121] Figure 6 3 shows an example in which the edge 62 of the transverse sipe 42 is subjected to C-chamfering, but the edge 62 of the transverse sipe 42 may be subjected to R-chamfering.

[0122] Figure 5 In FIG. 4 , the double arrow Dg is the chamfer depth of the edge 60 of the transverse groove 40. The double arrow Wg is the chamfer width. Figure 6 In FIG. 4 , the double arrow Ds is the chamfer depth of the edge 62 of the transverse sipe 42. The double arrow Ws is the chamfer width.

[0123] In this tire 2, the chamfer depth Dg of the edge 60 of the transverse groove 40 is preferably greater than the chamfer depth Ds of the edge 62 of the transverse sipe 42. This effectively improves the friction coefficient of the tire 2. From this perspective, the chamfer depth Dg of the edge 60 of the transverse groove 40 is preferably 2.0 mm to 3.0 mm, and the chamfer depth Ds of the edge 62 of the transverse sipe 42 is preferably 1.0 mm to 2.0 mm.

[0124] In this tire 2, from the perspective of effectively improving the friction coefficient of the tire 2, the chamfer width Wg of the edge 60 of the transverse groove 40 is preferably 1.0 mm or more and 2.0 mm or less. From the same perspective, the chamfer width Ws of the edge 62 of the transverse sipe 42 is preferably 1.0 mm or more and 2.0 mm or less. In this case, the chamfer width Wg and the chamfer width Ws may be the same or different.

[0125] In this tire 2, from the perspective of effectively improving the coefficient of friction, it is preferred that the middle land portion 38m include transverse sipes 42 extending substantially in the axial direction, with the edges 62 of the transverse sipes 42 being chamfered. In this case, it is more preferred that both edges 62 of the transverse sipes 42 be chamfered. In this tire 2, when the outer surface 56 of the middle land portion 38m has an outwardly curved profile, the coefficient of friction can be more effectively improved by including transverse sipes 42 extending substantially in the axial direction in the middle land portion 38m and chamfering the edges 62 of the transverse sipes 42.

[0126] In this tire 2, from the perspective of effectively improving the coefficient of friction, it is preferred that the shoulder land portion 38s include transverse grooves 40 and transverse sipes 42 extending substantially in the axial direction, and that the edges 60 of the transverse grooves 40 and the edges 62 of the transverse sipes 42 are chamfered. In this case, it is more preferred that both edges 60 of the transverse grooves 40 and both edges 62 of the transverse sipes 42 are chamfered.

[0127] In the case where the shoulder land portion 38s is engraved with a transverse groove 40 extending approximately axially and a transverse sipe pattern 42, and the edge 60 of the transverse groove 40 and the edge 62 of the transverse sipe pattern 42 are chamfered, from the viewpoint of more effectively improving the friction coefficient of the tire 2, it is preferred that the chamfer depth Dg of the edge 60 of the transverse groove 40 is deeper than the chamfer depth Ds of the edge 62 of the transverse sipe pattern 42.

[0128] As described above, according to the present invention, it is possible to obtain the tire 2 capable of achieving improved braking performance without a significant increase in rolling resistance.

[0129] [Example]

[0130] Hereinafter, the present invention will be described in more detail with reference to Examples and the like, but the present invention is not limited to the Examples.

[0131] [Example 1]

[0132] Get equipped Figure 1 A pneumatic tire for a passenger car (tire size = 205 / 60R16) having the basic structure shown in FIG. 1 and the specifications shown in Table 1 below.

[0133] The ratio (R1 / R2) of the radius R1 of the first arc to the radius R2 of the second arc included in the side profile is 86%. The radius R1 is 55 mm.

[0134] The ratio (A / H) of the height A of the apex to the cross-sectional height H was 10%.

[0135] The carcass was composed of a single carcass ply, and the ratio of the height F of the folded portion to the maximum width height W (F / W) was 58%.

[0136] [Comparative Example 1]

[0137] Comparative Example 1 is a conventional tire. In Comparative Example 1, the ratio (R1 / R2) of the radius R1 of the first arc to the radius R2 of the second arc included in the side profile is 100%. The radius R1 is 70 mm.

[0138] The ratio (A / H) of the height A of the apex to the cross-sectional height H was 20%.

[0139] The carcass is composed of two carcass plies. Although not shown, the two carcass plies are folded around the tire beads from the axially inner side to the outer side. The height ratio of the first folded portion, located axially outward, to the maximum width is 65%. The height ratio of the second folded portion, located axially inward of the first folded portion, to the maximum width is 20%.

[0140] [Example 2-7 and Comparative Example 2-4]

[0141] Tires of Examples 2-7 and Comparative Examples 2-4 were obtained in the same manner as in Example 1, except that the radius R2 of the second arc was adjusted and the radius R1 of the first arc and the ratio (R1 / R2) were set as shown in Tables 1 and 2 below.

[0142] [Examples 8-9]

[0143] Tires of Examples 8-9 were obtained in the same manner as in Example 1 except that the ratio (A / H) was set as shown in Table 3 below.

[0144] [Examples 10-11]

[0145] Tires of Examples 10-11 were obtained in the same manner as in Example 1 except that the ratio (F / W) was set as shown in Table 3 below.

[0146] [Example 12]

[0147] In addition to changing the middle land part to Figure 4 Except for the middle land portion having the structure shown, a tire of Example 12 was obtained in the same manner as in Example 1. The maximum height DX was set to 0.10 mm.

[0148] [Example 13]

[0149] The tire of Example 13 was produced in the same manner as Example 12, except that both edges of the transverse grooves and transverse sipes engraved in the land portion were chamfered. The transverse grooves had a chamfer width Wg of 1.5 mm and a chamfer depth Dg of 2.5 mm. The transverse sipes had a chamfer width Ws of 1.5 mm and a chamfer depth Ds of 1.5 mm. The presence of chamfering is indicated by "Y" in the "Chamfering Treatment" column of Table 3 below. Furthermore, "N" in the "Chamfering Treatment" column of each table indicates that chamfering was not performed.

[0150] [Braking performance]

[0151] The prototype tire was assembled onto a rim (size = 16 x 6.5), filled with air, and the internal pressure of the tire was adjusted to 250 kPa. The tire was then mounted on a test vehicle (passenger car) and driven on a test course for evaluating braking performance. The braking distance was measured from a speed of 110 km / h. The results are shown in Tables 1-3 below as indices. The larger the numerical value, the shorter the braking distance and the better the tire's braking performance.

[0152] Rolling resistance coefficient (RRC)

[0153] A rolling resistance tester was used to measure the rolling resistance coefficient (RRC) of the test tires when running on a roller at 80 km / h under the following conditions. The results are shown in Tables 1-3 below as indices. The larger the value, the lower the rolling resistance of the tire. In this evaluation, if the index is above 95, the rolling resistance has not increased significantly and is acceptable.

[0154] Rim: 16×6.5J

[0155] Internal pressure: 250kPa

[0156] Longitudinal load: 5.43kN

[0157] [Achievement Degree]

[0158] The sum of the indices obtained from the evaluations related to braking performance and rolling resistance was calculated. The results are shown in the "Achievement" column of Table 1-3 below. The larger the value, the better.

[0159] Durability

[0160] The prototype tire was assembled onto a rim (size = 16 x 6.5), filled with air, and the internal pressure of the tire was adjusted to 250 kPa. Durability testing was conducted using a roller tester using a walking speed method, in accordance with the load / speed performance test specified in ECE 30. The distance the tire traveled until failure was measured. The results are presented as an index in Tables 1-3 below. The larger the value, the better the tire's durability. In this evaluation, an index of 95 or higher indicates no significant decrease in durability and is acceptable.

[0161]

Table 1

[0162]

[0163]

Table 2

[0164]

[0165]

Table 3

[0166]

[0167] As shown in Tables 1 to 3, it was confirmed that the Examples were able to achieve an improvement in braking performance without a significant increase in rolling resistance. The superiority of the present invention is evident from these evaluation results.

[0168] Industrial Applicability

[0169] The above-described technology capable of achieving improved braking performance without a significant increase in rolling resistance can also be applied to various tires.

[0170]

Explanation of symbols

[0171] 2···Tires;

[0172] 4···tread;

[0173] 6···Sidewall;

[0174] 10···bead;

[0175] 12···fetal body;

[0176] 24, 24s, 24m···circumferential groove;

[0177] 30···Core;

[0178] 32···Triangle glue;

[0179] 34, 34a, 34b···carcass cord;

[0180] 38, 38s, 38m···Land Department;

[0181] 40 horizontal slots;

[0182] 42 horizontal groove pattern.

Claims

1. A tire comprising a tread that contacts a road surface, a pair of sidewalls connected to one end of the tread and located radially inward of the tread, a pair of beads located radially inward of the sidewalls, and a carcass located inward of the tread and the pair of sidewalls. The tire bead includes a core and an apex located radially outside the core. The ratio of the height of the apex to the cross-sectional height is not less than 5% and not more than 15%. When assembled to a standard rim and the internal pressure is adjusted to 250 kPa, in the meridian cross-section under no-load conditions, the profile of the side surface including the maximum width position includes two arcs that meet at the maximum width position. Of the two arcs, the arc located radially inside the maximum width position is a first arc, and the arc located radially outside the maximum width position is a second arc. The ratio of the radius of the first arc to the radius of the second arc is greater than or equal to 75% and less than or equal to 86%. The radius of the first arc is greater than or equal to 53 mm and less than or equal to 65 mm.

2. The tire according to claim 1, wherein The carcass is provided with a carcass ply, The carcass ply includes a ply main body spanned between one bead and the other bead, and a pair of folded portions connected to the ply main body and folded back from the axial inside to the outside around the bead. A ratio of a radial distance from the bead base line to one end of the folded portion to a radial distance from the bead base line to the maximum width position is 48% or more and 68% or less.

3. The tire according to claim 2, wherein: An angle formed by a straight line passing through the front end of the apex and the width center of the contact surface of the apex with the core and a straight line passing through the front end of the apex and one end of the folded portion is 35 degrees or more and 50 degrees or less.

4. The tire according to any one of claims 1 to 3, wherein The tread is engraved with a plurality of circumferential grooves to form a plurality of land portions. Among the plurality of land portions, the land portion located on the outer side in the axial direction is a shoulder land portion, and the land portion located on the inner side of the shoulder land portion is a middle land portion. The outer surface of the middle land portion has an outwardly curved profile. The maximum height of the outer surface is not less than 0.05 mm and not more than 0.15 mm.

5. The tire according to claim 4, wherein: The middle land portion is engraved with a transverse sipe pattern extending substantially axially. The edges of the transverse sipes are chamfered.

6. The tire according to claim 4, wherein: The shoulder land portion is engraved with transverse grooves and transverse sipes extending substantially in the axial direction, and the edges of the transverse grooves and transverse sipes are chamfered.

7. The tire according to claim 5, wherein: The shoulder land portion is engraved with transverse grooves and transverse sipes extending substantially in the axial direction, and the edges of the transverse grooves and transverse sipes are chamfered.

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