JP2009132235A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire that improves driving stability on a wet road surface. <P>SOLUTION: Shoulder main grooves 3, which extend from tread ground-contact ends E to the inside of the tire axial direction, are provided on shoulder parts, and shoulder land parts 4 are divided between the shoulder main grooves 3, 3. The land ratio of the shoulder parts is 57 to 72%. On the center part Ce, center blocks 6 are provided with gaps in the tire circumferential direction between the shoulder land parts 4, 4 arranged at both sides of the tire axial direction. The land ratio of the center part Ce is 40 to 55%. When one shoulder main groove 3 and one shoulder land part 4 adjacent to each other are regarded as one pattern pitch P, each pattern pitch P has high land ratio regions Z, in which the sum of lengths (A1+A2+A3) in the tire axial direction of parts which contact road surfaces on the line of the tire axial direction occupies 78 to 93% of the tread ground-contact width TW. The high land ratio regions Z continue by 20 to 35% of the length PL of the circumferential direction of the pattern pitch P. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a pneumatic tire that can improve steering stability on a wet road surface.

  Increasing the rigidity of the tread pattern is effective for improving the turning performance of the tires for four-wheeled vehicles. Specifically, in addition to hardening the rubber in the tread portion, a groove provided in the tread portion is shallowed. Related technologies include the following.

JP 2006-82735 A

  However, if the rubber of the tread portion is hardened, it is difficult to obtain a sufficient grip when traveling on a wet road surface with a small friction coefficient. Similarly, if the groove of the tread portion is shallow, sufficient drainage performance cannot be obtained, and there is a drawback in that a significant decrease in steering stability occurs when traveling on a wet road surface.

  The present invention has been devised in view of the above situation, and in the center portion and the shoulder portion of the tread portion, each land ratio is limited to a certain range, and each pattern pitch constituting the tread pattern is defined. On the basis of providing a high land ratio region in which the sum of the length in the tire axial direction of the portion contacting the road surface on the tire axial direction line passing through the pattern pitch forms 78 to 93% of the tread contact width, The main purpose is to provide a pneumatic tire capable of improving the steering stability of the vehicle.

  The invention according to claim 1 of the present invention is a pneumatic tire including a tread portion having a tread pattern in which a pattern pitch having substantially the same pattern is repeatedly formed in a tire circumferential direction, and the tread The center portion has a center portion forming 50% of the tread contact width centered on the tire equator, and shoulder portions on both sides thereof, and each shoulder portion has an inner side from the outer side in the tire axial direction of the tread contact end. By extending the shoulder main groove extending in the tire circumferential direction, the shoulder land portion is divided between the shoulder main grooves, and the land ratio between the tread grounding end of the shoulder portion and the outer edge of the center portion is 57. ~ 72%, the center portion is provided with a center block between the shoulder land portions disposed on both sides in the tire axial direction, and When the land ratio of the center portion is 40 to 55% and the one shoulder main groove and one shoulder land portion adjacent thereto are set as one pattern pitch, each pattern pitch passes through the pattern pitch. The sum of the lengths in the tire axial direction of the portion contacting the road surface on the tire axial direction line has a high land ratio region forming 78 to 93% of the tread contact width, and the high land ratio region is the pattern pitch. It is characterized by being continuous in the tire circumferential direction at 20 to 35% of the length in the tire circumferential direction.

  The invention according to claim 2 is the pneumatic tire according to claim 1, wherein the tread portion is provided with the high land ratio regions at intervals of 30 to 60 mm in the tire circumferential direction.

  According to a third aspect of the present invention, in the shoulder land portion, the maximum ground contact length in the tire axial direction is greater than 30% and not more than 40% of the tread ground contact width. This is a pneumatic tire.

  In the present invention, the land ratio of the center portion and the shoulder portion is limited to a certain range, and the land ratio of the center portion is set to be relatively smaller than the land ratio of the shoulder portion. Thereby, the drainage of the center part which is difficult to be drained is improved. Further, at the time of turning, the shoulder portion mainly receives a lateral force, but since the shoulder portion has a higher land ratio than the center portion, the pattern rigidity is high, and thus the steering stability is improved. Further, the pattern pitch of the repetitive pattern constituting the tread pattern is such that the total sum of the lengths in the tire axial direction of the portion contacting the road surface on the tire axial direction line passing through the pattern pitch forms 78 to 93% of the tread ground contact width. It has a high land ratio region, and this high land ratio region is continuous in the tire circumferential direction by 20 to 35% of the length of the pattern pitch in the tire circumferential direction. Thereby, in the whole tread part, pattern rigidity is maintained, without impairing drainage, and the steering stability on a wet road surface improves by extension.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a development view of the tread portion 2 of the pneumatic tire (not shown) of the present embodiment. The pneumatic tire (not shown) shown in FIG. 1 is preferably used as a front wheel for a four-wheel racing cart.

  The tread portion 2 includes a directional tread pattern. The directional tread pattern means a tread pattern in which a performance difference occurs depending on the rotation direction. Accordingly, in order to maximize the performance of the pattern, the tire is designated with a tire rotation direction R and is attached to the vehicle in this direction.

  Further, the tread portion 2 is divided into a center portion Ce that forms an area of 50% of the tread contact width TW centered on the tire equator C, and shoulder portions Sh on both sides thereof. Here, the tread ground contact width TW is the distance between the tread ground contact ends E and E when the tire is assembled to a regular rim and filled with a regular internal pressure and loaded with a regular load and grounded to a plane with a camber angle of 0 degrees. The distance in the tire axial direction.

  In addition, the regular rim is a rim determined for each tire in a standard system including a standard on which a tire is based. For example, JATMA is a standard rim, TRA is “Design Rim”, and ETRTO is a standard rim. If there is no applicable standard, the rim is recommended by the manufacturer.

  The normal internal pressure is an air pressure determined by each standard for each tire in the standard system including the standard on which the tire is based. The maximum air pressure is JATMA, and the table "TIRE LOAD LIMITS AT" is TRA. The maximum value described in “VARIOUS COLD INFLATION PRESSURES”, “INFLATION PRESSURE” if it is ETRTO, but if there is no applicable standard, it is the internal pressure recommended by the manufacturer. However, when the tire is for a racing cart, it is set to 100 kPa.

  Further, the normal load is a load determined by each standard for each tire in the standard system including the standard on which the tire is based. The maximum load capacity is determined by JATMA, and the table “TIRE LOAD LIMITS” is determined by TRA. The maximum value described in "AT VARIOUS COLD INFLATION PRESSURES". If ETRTO, "LOAD CAPACITY". However, if the tire is for a racing cart, it is 392N.

  In each of the shoulder portions Sh, shoulder main grooves 3 extending from the outer side in the tire axial direction of the tread ground end E to the inner side are spaced apart in the tire circumferential direction. The shoulder main groove 3 has a length that reaches at least the center portion Ce from the tread ground contact end E. Thereby, in each shoulder part Sh, the shoulder land part 4 is divided between the shoulder main grooves 3 and 3 adjacent in the tire circumferential direction. In the present embodiment, the shoulder portions Sh on both sides are formed substantially line-symmetric with respect to the tire equator C.

  Further, the shoulder main groove 3 of the present embodiment is connected to the axial direction portion 3a extending outward from the tread grounding end E in the tire axial direction at an angle of 5 degrees or less with respect to the tire axial direction, and the axial direction portion 3a. And it is comprised including the inclination part 3b which inclines with the angle (theta) of about 15-45 degree | times with respect to a tire axial direction, and extends from the tread grounding end E to the crown part Ce. The ratio of the length in the tire axial direction between the axial portion 3a and the inclined portion 3b is preferably about 4: 6 to 6: 4. The inclined portion 3b is preferably inclined toward the first arrival side in the tire rotation direction R.

  Such shoulder main grooves 3 extend to the center portion Ce, thereby improving the drainage performance of the center portion Ce, which is inherently difficult to drain water from the road surface. Further, the shoulder main groove 3 uses the pressure at the time of ground contact to pump water from the inclined portion 3b that contacts the road surface first to the axial direction portion 3a and effectively discharges the water from the tread ground end E. The axial direction portion 3a of the shoulder main groove 3 is not substantially grounded during straight traveling, but is grounded to the road surface during turning when a lateral force is applied. Such an axial portion 3a is useful for preventing a decrease in lateral rigidity on the outer side in the tire axial direction of the shoulder land portion 4 that is grounded during turning, and thus improving steering stability.

  The groove width GW1 (measured perpendicular to the groove center line) of the shoulder main groove 3 is not particularly limited, but if the groove width GW1 is too small, sufficient drainage tends not to be obtained. There is. On the other hand, if the groove width GW1 is too large, the pattern rigidity of the shoulder portion Sh is lowered and the steering stability may be lowered. From such a viewpoint, the groove width GW1 is preferably 6 mm or more, more preferably 7 mm or more, and preferably 10 mm or less, more preferably 9 mm or less. Similarly, the depth of the shoulder main groove 3 is preferably 4 mm or more, more preferably 5 mm or more, and preferably 7 mm or less, more preferably 6 mm or less. Needless to say, the groove width and / or the groove depth may be constant or partially different.

  In addition, each shoulder land portion 4 of the present embodiment includes two blocks 4a and 4b which are divided into two in the tire circumferential direction by a shoulder sub-groove 5. This is useful for improving the wear resistance by adjusting the drainage of the shoulder portion Sh and the pattern rigidity. However, the shoulder land portion 4 may be formed by a block of blocks without being divided by such a shoulder sub-groove 5.

  A groove width GW2 of the shoulder sub-groove 5 is formed to be smaller than a groove width GW1 of the shoulder main groove 3. Although not particularly limited, the groove width GW2 is preferably about 1 to 5 mm, for example, in order to satisfy the drainage and the pattern rigidity of the shoulder portion Sh in a well-balanced manner, and the groove depth is, for example, 2 About 4 mm is desirable. The shoulder sub-groove 5 of the present embodiment is formed with a substantially constant groove width.

  Further, the shoulder sub-groove 5 extends from the outer side in the tire axial direction of the tread ground end E to the inner side in parallel with the tire axial direction at a substantially central position between the shoulder main grooves 3 and 3 adjacent in the tire circumferential direction. Note that “substantially parallel to the tire axial direction” includes at least an aspect in which the groove center line extends in the tire axial direction within a range of deflection within 5 mm in the tire circumferential direction. Further, in a preferred embodiment, the inner end in the tire axial direction of the shoulder sub-groove 5 is preferably communicated with the inclined portion 3b of the shoulder main groove 3 to provide a wide drainage or water storage space there. From such a viewpoint, it is desirable that the intersection of these grooves is provided in the vicinity of the boundary between the center portion Ce and the shoulder portion Sh.

  Each shoulder land portion 4 has a first shoulder block 4a disposed on the first arrival side in the tire rotation direction R, and a second ground contact area smaller than that of the first shoulder block 4a disposed on the rear arrival side. The shoulder block 4b.

  The first shoulder block 4a of the present embodiment has an inner end portion 4e in the tire axial direction that protrudes from the center portion Ce and ends. The first shoulder block 4a includes a main portion 10 formed between the axial direction portion 3a of the shoulder main groove 3 and the shoulder sub-groove 5 and having a substantially constant tire circumferential length. A gradually increasing portion 11 that forms a portion extending to the center portion Ce continuously with the portion 10 and that gradually increases in the tire circumferential length, and a plan view in which the tire circumferential length gradually decreases to the inner end portion 4e1 that continues to the gradually increasing portion 11. Includes a tapered portion 12 having a substantially isosceles triangular shape.

  On the other hand, the inner end 4e2 in the tire axial direction of the second shoulder block 4b terminates without reaching the center portion Ce. That is, the length of the second shoulder block 4b in the tire axial direction is smaller than that of the first shoulder block 4a. Further, the second shoulder block 4b includes a main portion 10 formed between the axial portion 3a of the shoulder main groove 3 and the shoulder sub-groove 5 and having a substantially constant tire circumferential length, and a shoulder main portion. It consists of the taper part 13 which is formed between the inclination part 3b of the groove | channel 3, and the shoulder subgroove 5, and the circumferential direction length reduces gradually to the inner end part 4e2. In the first and second shoulder blocks 4a and 4b, the main portion 10 can contact the road surface mainly during turning.

  In the center portion Ce, a center block 6 is provided between the shoulder land portions 4 and 4 disposed on both sides in the tire axial direction. In the present embodiment, each center block 6 is arranged with its center aligned on the tire equator C without protruding from the center portion Ce. Thereby, one center block row is formed in the center portion Ce.

  Further, in the center portion Ce, a vertical groove portion 7 extending in the tire circumferential direction is formed between the center block 6 and the shoulder land portion 4, and between the center blocks 6 and 6, the tire axial direction A substantially V-shaped horizontal groove-shaped portion 8 that extends is formed.

  As shown in an enlarged view in FIG. 2, the tread surface of the center block 6 of the present embodiment is directed from the overhanging position M that forms the maximum width BW in the tire axial direction toward the first arrival side and the rear arrival side in the tire rotation direction R, respectively. While the width gradually decreases, a tip portion 6a that is sharpened toward the first arrival side is provided on the first arrival side, while a concave portion 6b that is smoothly recessed toward the first arrival side is provided at an end portion on the rear arrival side. . A smooth first arc portion 6c is connected between the apex K1 of the distal end portion 6a and each of the overhang positions M. Further, a smooth second arc portion 6d is also connected between the overhang position M and the rearmost end point K3 located on the most rearward side in the tire rotation direction of the center block 6. Thus, the contour shape of the tread surface of the center block 6 is formed in a substantially heart shape that is substantially line-symmetric with respect to the tire equator C. Therefore, the entire tread pattern of the present embodiment is substantially line-symmetric with respect to the tire equator C. The overhanging position M is preferably provided at a position that is separated from the vertex K1 by 0.5 to 0.7 times the circumferential length of the block toward the rear arrival side.

  In such a center block 6, when the vehicle travels straight on a wet road surface, the tip 6 a that first contacts the road surface divides the water film on the road surface into two, and they are along a smooth arc portion 6 c. Can be led backwards. At this time, since the width of the tire block in the axial direction of the center block 6 is narrowed from the overhanging position M toward the first arrival side in the tire rotation direction R, the drainage can be effectively divided into two and smoothly backward. Can be sent (water guiding action). In addition, water tends to accumulate originally on the rear landing side of the center block 6, but the width in the tire axial direction is narrowed from the overhanging position M toward the rear landing side, and the recess 6b is provided so that the block is provided. It is possible to store water without overflowing the water that wraps around the arrival side in the direction of rotation. Therefore, high wet grip performance is exhibited. In order to enhance such an effect, the rear end width BWb, which is the distance in the tire axial direction between the rearmost end points K3 and K3 of the center block 6, is 50 to 67% of the maximum width BW of the center block 6. desirable.

  Furthermore, as shown in FIG. 1, the taper portion 12 of the shoulder land portion 4 (first shoulder block 4a) is formed on the first arc portion 6c and / or the second arc portion 6d of the center block 6. They are placed facing each other. As a result, the vertical groove-shaped portion 7 includes a narrow width portion 7a having a minimum groove width Wa in the tire axial direction, and an amplifying portion 7b in which the groove width gradually increases from the narrow width portion 7a to both sides in the tire circumferential direction. 7b are formed. Each of the amplifying sections 7b can provide a sufficiently wide drainage or storage space, so that the water on the road surface can be smoothly and efficiently drained to the vertical groove-shaped section 7 when the center block 6 starts to be grounded. Is desirable. Further, the narrow width portion 7a increases the torsional rigidity of the center block 6 and the shoulder land portion 4, and suppresses deformation when a slip angle is given. Therefore, high steering stability can be obtained even during wet travel.

  The width Wb of the amplifying portion 7b in the tire axial direction is not particularly limited, but preferably has a portion of 3 mm or more, more preferably 4 mm or more in order to ensure a sufficient amount of drainage. In addition, if the groove width Wa in the tire axial direction of the narrow width portion 7a is too small, drainage resistance may increase. On the other hand, if the groove width Wa of the narrow width portion 7a is too large, the pattern rigidity of the tread portion 2, particularly the rigidity in the vicinity of the vertical groove-shaped portion 7, may be lowered.

  Further, the center block 6 preferably has a ratio (BL / BW) of a maximum width BW in the tire axial direction and a maximum length BL in the tire circumferential direction of 1.00 to 2.20. When the ratio (BL / BW) is less than 1.00, the rigidity in the circumferential direction of the center block 6 decreases, so that the amount of deformation during braking and driving increases, and as a result, sufficient braking force and driving force can be obtained. There is a tendency not to be able to. On the other hand, when the ratio (BL / BW) exceeds 2.20, the rigidity in the tire axial direction is lowered, so that there is a possibility that sufficient lateral force cannot be exhibited during turning. Particularly, in the case of a front tire of a racing cart, since a large slip angle is given during turning, the ratio (BL / BW) is set to 1.00 to 1.20 in order to sufficiently increase the lateral rigidity of the center block 6. desirable. On the other hand, since the rear tire of the racing cart receives a large shearing force with the road surface, the ratio (BL / BW) is 1.70 to 2.20 in order to increase the tire circumferential rigidity during driving. It is desirable to enlarge it.

  Further, as shown in FIG. 2, it is desirable that the tip 6 a of the center block 6 has an internal angle α of 100 to 130 degrees. Thereby, the front-end | tip part 6a is desirable at the point from which the efficient water-conducting effect | action which divides | segments a water film into two hands more effectively at the time of road surface grounding, and guides to the both outer sides of this center block 6 is obtained. If the inner angle α of the tip portion 6a is less than 100 degrees, the rigidity of the tip portion 6a decreases, and thus the responsiveness at the time of steering the steering wheel tends to deteriorate. There is a tendency for the water-conducting action of the to decrease. The inner angle α of the tip portion 6a is a distance S of 2 mm in the tire circumferential direction from the vertex K1 on the tread surface when the tip portion 6a is formed with a smooth arc as in the present embodiment. It is measured as an angle formed by a tangent line in contact with the center block 6 at a position j separated from the rear arrival side in the rotation direction R.

  Further, the recess 6b of the center block 6 is located on both sides in the tire axial direction and on the rearmost side of the tire rotation direction R from the most concave point K2 located on the most first arrival side in the tire rotation direction R in the recess 6b. It is desirable that the intersecting angle β formed by the straight lines drawn at the last end point K3 is smaller than the inner angle α of the tip, and in particular, the difference between the angles β and α (α−β) is preferably 10 to 25 degrees. That is, when the angle difference (α−β) is less than 10 degrees, the water flowing into the recess 6b from the amplifier 7b may make it difficult to drain the water present in the recess 6b. On the other hand, when the angle exceeds 25 degrees, the water in the recess 6b tends to be difficult to drain diagonally rearward, such as colliding with the front end 6a of the center block located on the rear arrival side in the rotation direction.

  Further, in the pneumatic tire according to the present embodiment, the land ratio between the tread ground contact edge E and the outer edge Ec of the center portion Ce in each shoulder portion Sh (hereinafter, the land ratio of such a region is simply referred to as “the shoulder portion Sh”). The land ratio of the center portion Ce is set to 40 to 55%. Thus, by setting the land ratio of the center portion Ce to be smaller than the land ratio of the shoulder portion Sh, it is possible to improve drainage performance in the center portion Ce that is essentially difficult to drain. Further, at the time of turning, the shoulder portion Sh mainly receives lateral force, but since the shoulder portion Sh has a larger land ratio than the center portion Ce, the pattern rigidity can be maintained high and the steering stability can be improved.

  Here, when the land ratio of the center portion Ce is less than 40%, the pattern rigidity of the center portion Ce is remarkably lowered and the steering stability is deteriorated. In particular, in the case of a front wheel tire, the responsiveness at the time of steering the steering wheel is lowered, and a good time cannot be obtained during circuit driving. Further, when the land ratio of the center portion Ce exceeds 55%, the drainage at the center portion Ce is remarkably deteriorated, resulting in insufficient grip on the wet road surface. From such a viewpoint, the land ratio of the center portion Ce is particularly preferably 43% or more, and more preferably 47% or less.

  Further, when the land ratio of the shoulder portion Sh is less than 57%, the pattern rigidity of the shoulder portion Sh is lowered, and the stability at the time of turning is lowered. On the other hand, when the land ratio of the shoulder portion Sh exceeds 72%, the drainage performance at the time of turning tends to be remarkably lowered, and the controllability at the time of grip shortage and sliding tends to be greatly deteriorated. From such a viewpoint, the land ratio is preferably 62% or more, and more preferably 70% or less.

  The land ratio of the center portion Ce is calculated by a ratio (Cc / Ca) of the total area Ca of the center portion Ce in one tire turn and the total contact area Cc of the center portion Ce in one tire turn. Shall. Similarly, the land ratio of the shoulder portion Sh is defined as the total area Sa between the outer edge Ec of the center portion Ce and the tread contact end E in one round of the tire, and the sum Sc of the ground contact area of the region in one tire circumference. It is assumed that the ratio (Sc / Sa) is calculated.

  Further, the tread portion 2 is formed by repeating substantially the same pattern pitch P in the tire circumferential direction. In the present embodiment, as shown in FIG. 1, the pattern pitch P includes the one shoulder main groove 3 and one shoulder land portion 4 adjacent to the shoulder main groove 3 (a portion sandwiched between line segments Pa and Pb). . Since “substantially the same” is used, it is needless to say that a pitch variation method in which a plurality of types of lengths PL in the tire circumferential direction of the pattern pitch P are provided and the running noise is dispersed may be employed according to the custom. In addition, preferably, it is desirable to be configured with 18 to 25 pattern pitches P per tire circumference.

  Further, as shown in FIG. 3 and FIG. 4 which is an enlarged view thereof, each pattern pitch P is a portion (tread grounding end E, E) that contacts the road surface on the tire axial direction line X passing through the pattern pitch P. 4), that is, as shown in FIG. 4, the ground contact length A1 of one shoulder land portion 4 in the tire axial direction, the ground contact length A2 of the center block 6, and the other The sum (A1 + A2 + A3) of the ground contact length A3 of the shoulder land portion 4 has a high land ratio area Za forming 78 to 93% of the tread ground contact width TW. Moreover, the high land ratio region Za is continuous in the tire circumferential direction with a tire circumferential length ZaL of 20 to 35% of the pattern circumferential length PL of the pattern pitch P.

  Such a high land ratio region Za can obtain a sufficient ground contact area during traveling, and thus can exhibit high grip performance during straight traveling and turning. Further, since the high land ratio area Za is provided in each pitch pattern P, the tire can be sequentially brought into contact with the road surface during rotation of the tire, so that the pattern rigidity of the entire tread portion 2 can be obtained without impairing drainage. Is sufficiently maintained, and as a result, steering stability on a wet road surface is improved.

  In particular, the shoulder land portion 4 (first shoulder block 4a) desirably has a maximum contact length B in the tire axial direction that is greater than 30% and less than 40% of the tread contact width TW. As a result, the rigidity of the shoulder land portion 4 that receives a large lateral force during turning is reliably improved, and the turning performance can be significantly improved.

  Note that if the sum of the contact lengths on the tire axial line X is less than 78% of the tread contact width TW, the contact area may be insufficient and the gripping power may be reduced. On the contrary, if the sum of the contact lengths exceeds 93% of the tread contact width TW, the so-called hydroplaning phenomenon in which the drainage performance is remarkably deteriorated and the tire rides on the water film easily occurs in the high land ratio region Za. Become.

  Further, if the length ZaL in the tire circumferential direction of the high land ratio area Za is less than 20% of the length PL in the tire circumferential direction of the pattern pitch P, the rigidity of the pattern pitch cannot be sufficiently increased, and consequently the turning performance is improved. It cannot be improved sufficiently. On the other hand, when the length ZaL of the high land ratio area Za exceeds 35% of the length PL in the tire circumferential direction of the pattern pitch P, the drainage of this portion is significantly deteriorated, and the hydroplaning phenomenon is likely to occur. Become. From this point of view, the length ZaL of the high land ratio region Za is preferably 25% or more of the length PL of the pattern pitch P, and preferably 32% or less. Such a high land ratio region Za can be formed in a size within the above range by adjusting the shape of the center block 6 and the shoulder land portion 4, the relative position in the tire circumferential direction, and the like.

  Further, as shown in FIG. 3, an interval N in the tire circumferential direction of the high land ratio region Za (the length in the tire circumferential direction of a portion sandwiched between the high land ratio regions Za adjacent in the tire circumferential direction) is preferably It is desirable that the distance is 30 mm or more, more preferably 35 mm or more, and preferably 60 mm or less, more preferably 55 mm or less. If the distance is less than 30 mm, the drainage performance may be reduced. Conversely, if the distance exceeds 60 mm, the time during which the high land ratio area Za is present in the ground contact surface during tire rotation is shortened, and the grip performance is improved. There is a possibility that it cannot be expected sufficiently.

  Further, as shown in FIG. 3 and FIG. 4, each pattern pitch P has a total sum of lengths in the tire axial direction of portions contacting the road surface on the tire axial direction line X passing through the pattern pitch P. It is desirable to have a low land ratio region Zb that forms 25 to 35% of the ground contact width TW. The low land ratio region Zb is preferably continuous in the tire circumferential direction with a length ZbL of 10 to 20% of the length PL in the tire circumferential direction of the pattern pitch P.

  Thus, by providing in the pattern pitch P the low land ratio area Zb having a land ratio approximately half that of the high land ratio area Za, the above-described grip performance and drainage performance can be achieved at a higher level. . If the length ZbL in the tire circumferential direction of the low land ratio region Zb is less than 10% of the length PL of the pattern pitch P, there is a possibility that sufficient drainage effect due to the low land ratio region Zb may not be obtained. On the other hand, if it exceeds 20%, the pattern rigidity of the tread portion 2 is lowered and the steering stability may be deteriorated. 3 and 4, the high land ratio region Za and the low land ratio region Zb are displayed in light gray for easy understanding.

  FIG. 5 shows another embodiment of the present invention. In this embodiment, the center portion Ce is provided with a center main groove 20 extending linearly on the tire equator C, and a pair of center blocks 6A and 6B are provided on both sides thereof. Such a center portion Ce is more suitable for use as a rear wheel of a racing cart that requires a large gripping force, for example, because drainage is further improved. Thus, it goes without saying that the specific shape and the like of the center block 6 can be variously modified. Also in this embodiment, the high land ratio area Za is provided in the area shown in gray.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and can be implemented by being modified into various aspects.

  In order to confirm the effect of the present invention, a pneumatic tire for a racing cart (front wheel size 10 × 4.50-5 and rear wheel size 11 × 6.50-5) was prototyped based on the specifications in Table 1. Various performances were tested for them. The test method is as follows.

<Lap time>
Each test tire is mounted on a racing cart (FA category vehicle) under conditions of a rim (4.50 inches on the front wheels and 6.50 inches on the rear wheels) and an internal pressure of 100 kPa (same front and rear), and driving by a driver who is qualified for the international cart As a result, the Tsumagoi International Kart Course in wet condition was run for 5 laps and the average lap time for 1 lap was obtained. In order to make the wet condition the same, the same amount of water was sprayed just before the run.

<Steering stability>
5 points depending on the driver's sensation in response to steering (steering response performance), turning grip state (lateral grip performance) and acceleration response (acceleration performance) in fully open running under the above wet conditions Evaluated by law. The larger the value, the better. Table 1 shows the test results.

  As a result of the test, it was confirmed that the tire of the example exhibited high steering stability on the wet road surface.

It is an expanded view of the tread part which shows embodiment of this invention. It is an enlarged view of the center block. It is an expanded view of the tread part which shows a high land ratio area | region and a low land ratio area | region. It is the elements on larger scale of pattern pitch. It is an expanded view of the tread part which shows other embodiment of this invention. 3 is a development view of a tread portion of a front wheel tire of Comparative Example 1. FIG. It is an expanded view of the tread part of the rear-wheel tire of the comparative example 1.

Explanation of symbols

2 tread portion 3 shoulder main groove 4 shoulder land portion 4a first shoulder block 4b second shoulder block 5 shoulder sub-groove 6 center block Za high land ratio region Zb low land ratio region C tire equator Ce crown portion Sh shoulder portion P Pattern pitch

Claims (3)

A pneumatic tire comprising a tread portion having a tread pattern in which a pattern pitch forming a substantially identical pattern is repeatedly formed in the tire circumferential direction,
The tread portion has a center portion that forms an area of 50% of the tread contact width centered on the tire equator, and shoulder portions on both sides thereof.
The shoulder main grooves extending from the outer side in the tire axial direction to the inner side in the tire axial direction of the tread grounding end are spaced apart from each other in the tire circumferential direction. The land ratio between the tread ground contact edge and the outer edge of the center portion is 57 to 72%,
The center portion is provided with a center block between the shoulder land portions disposed on both sides in the tire axial direction, and the land ratio of the center portion is 40 to 55%, and the one shoulder main groove And when one shoulder land portion adjacent to this is defined as one pattern pitch, each pattern pitch is the sum of the lengths in the tire axial direction of the portion contacting the road surface on the tire axial direction line passing through the pattern pitch. It has a high land ratio region that forms 78 to 93% of the tread contact width, and the high land ratio region is continuous in the tire circumferential direction by 20 to 35% of the length of the pattern pitch in the tire circumferential direction. Pneumatic tire characterized by.   2. The pneumatic tire according to claim 1, wherein the tread portion is provided with the high land ratio regions at intervals of 30 to 60 mm in a tire circumferential direction.   The pneumatic tire according to any one of claims 1 to 3, wherein the shoulder land portion has a maximum contact length in a tire axial direction that is greater than 30% and less than or equal to 40% of the tread contact width.

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