JP2009132177A - 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 land parts 4 are divided between main grooves 3, 3 by providing the shoulder main grooves 3 extending from tread ground-contact ends E to the inside of tire axial direction at intervals in the tire circumferential direction on each shoulder part Sh of a tread part 2. On the center part Ce, center blocks 6 are provided between the shoulder land parts 4, 4 arranged at both sides in the tire axial direction. Thereby, the center blocks 6 and the shoulder land parts 4 are adjacent to each other via vertical groove-like parts 7 extending in the tire circumferential direction. The vertical groove-like parts 7 have narrow-width parts 7a, whose narrowest groove width of the tire axial direction is 3 to 6 mm, and increased-width parts 7b, whose groove width increases gradually from the narrow-width parts 7a to both sides of the tire circumferential direction. <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 circumstances, and the groove width in the tire axial direction is minimized in the vertical groove-like portion extending in the tire circumferential direction between the shoulder land portion and the center block. Based on the inclusion of a narrow part and an amplifying part in which the groove width gradually increases from the narrow part to both sides in the tire circumferential direction, water is smoothly introduced into and discharged from the vertical groove part. Thus, the main object is to provide a pneumatic tire that can improve the handling stability on a wet road surface.

  The invention according to claim 1 of the present invention is a pneumatic tire having a tread portion, wherein the tread portion includes a center portion that forms an area of 50% of a tread contact width centered on the tire equator, Shoulder shoulder grooves on both sides, and shoulder main grooves extending from the outer side in the tire axial direction of the tread grounding end to the inner side are provided in the shoulder circumferential direction. A center block is provided between the shoulder land portions disposed on both sides in the tire axial direction, so that the center block and the shoulder land portion are arranged in the tire circumferential direction. The vertical groove-shaped portions are adjacent to each other through the extending vertical groove-shaped portion. The vertical groove-shaped portion includes a narrow width portion having a minimum groove width of 3 to 6 mm in the tire axial direction, and a tie from the narrow width portion. The groove width of the circumferential direction of the tire axial direction on both sides and having an amplifying section for increasing respectively.

  In the invention according to claim 2, the shoulder land portion has a tapered shape in which the tire circumferential direction length gradually decreases inward in the tire axial direction, and the narrow portion is formed by the apex of the tapered portion. The pneumatic tire according to claim 1.

  The invention according to claim 3 is the pneumatic tire according to claim 2, wherein an internal angle γ of the tapered portion is 100 to 150 degrees.

  According to a fourth aspect of the present invention, the shoulder land portion is formed in two blocks by providing a shoulder sub-groove having a smaller groove width than the shoulder main groove between the shoulder main grooves. The pneumatic tire according to any one of claims 1 to 3, which is classified.

  The invention according to claim 5 is the pneumatic tire according to claim 4, wherein both inner end portions of the shoulder main groove and the shoulder sub-groove in the tire axial direction communicate with the amplifying portion. .

  In the present invention, the vertical groove-shaped portion provided between the shoulder land portion and the center block includes a narrow width portion having a minimum groove width of 3 to 6 mm in the tire axial direction, and a tire circumferential direction from the narrow width portion. And amplifying sections each having a groove width gradually increasing. Such a vertical groove-like portion can maintain the rigidity of the ground contact portion high without impairing drainage. In particular, the narrow width portion increases the torsional rigidity of the center block and the shoulder land portion facing the vertical groove-like portion, and suppresses deformation when a slip angle is given. Therefore, high steering stability can be obtained even during wet travel.

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.

  In addition, the shoulder main groove 3 of the present embodiment includes an axial portion 3a extending outward in the tire axial direction from the tread grounding end E at an angle of 5 degrees or less with respect to the tire axial direction, and a tread on the axial portion 3a. And an inclined portion 3b extending in the vicinity of the ground contact E and inclined at an angle θ of about 15 to 45 degrees with respect to the tire axial direction and extending from the tread ground contact E to the crown portion 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. In addition, the tread part 2 of this embodiment is only this center block 6 and the said shoulder land part 4 as a land part which contacts a road surface.

  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 FIG. 2 in an enlarged manner, the tread surface of the center block 6 has a width 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. While gradually decreasing, 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 on the rear arrival side. The apex K1 of the tip 6a and the overhanging position M are connected by a smooth first arc 6c. Further, a second arc portion 6d connects between the overhanging 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.

  Further, as shown in FIG. 1 and FIG. 3 which is an enlarged view of a main part thereof, the shoulder land portion 4 (the first land portion 4) is formed on the first arc portion 6c and / or the second arc portion 6d of the center block 6. The shoulder block 4a) of the shoulder block 4a is arranged facing each other. Accordingly, the vertical groove-like portion 7 includes a narrow width portion 7a in which the groove width Wa in the tire axial direction is minimized, and an amplifying portion in which the groove width gradually increases from the narrow width portion 7a to both sides in the tire circumferential direction. 7b, 7b are formed. That is, the narrow width portion 7a is formed by the inner end portion 4e1 that forms the apex on the inner side in the tire axial direction of the tapered portion 12.

  Since each of the amplifying parts 7b can provide a sufficiently large drainage or storage space, the water on the road surface can be smoothly and efficiently drained to the vertical groove-like part 7 when the center block 6 starts to ground. Is desirable. Further, since the amplifying unit 7b communicates with the horizontal groove-shaped portion 8, water accumulated in the concave portion 6b and the horizontal groove-shaped portion 8 is also effectively discharged to the rear arrival side of the tire rotation direction R. can do. Further, as apparent from FIG. 3, since the inner ends of the shoulder main groove 3 and the shoulder sub-groove 5 in the tire axial direction communicate with the amplifying part 7b, the amplifying part 7b on the rear arrival side of the tire rotation direction R is connected. The drainage led to can be efficiently discharged from the tread ground end E to the outside through the shoulder main groove 3 and the shoulder subgroove 5. In order to make these effects more reliable, the width Wb of the amplifying portion 7b in the tire axial direction is preferably 3 mm or more, more preferably 4 mm or more, and further preferably 8 mm or more.

  On the other hand, if the groove width of the vertical groove-like portion 7 is increased in order to improve drainage, the rigidity of that portion tends to decrease and steering stability (turning performance) tends to decrease. Therefore, in the present invention, by providing the vertical groove-like portion 7 with the narrow width portion 7a having the groove width Wa of 3 to 6 mm and the amplification portion 7b, the steering stability can be improved without impairing drainage. Reduction is prevented. In particular, the narrow width portion 7a partially increases the torsional rigidity of the center block 6 and the shoulder land portion 4 on both sides in the tire axial direction, and suppresses large deformation of this portion even when a slip angle is given. Therefore, high steering stability can be obtained even during wet travel.

  If the groove width Wa in the tire axial direction of the narrow width portion 7a is too small, the drainage resistance at this portion increases, and there is a risk that the grip performance during wet running may be lowered. From such a viewpoint, the groove width in the tire axial direction of the narrow width portion 7a needs to be set to 3 mm or more as described above. On the other hand, if the groove width Wa in the tire axial direction of the narrow width portion 7a is too large, the pattern rigidity of the tread portion 2, in particular, the torsional rigidity is lowered, and the steering stability may be lowered. From such a viewpoint, the width Wa of the narrow portion 7a needs to be set to 6 mm or less.

  Further, as shown in FIG. 3, the taper portion 12 of the first shoulder block 4a preferably has an inner angle γ of 100 to 150 degrees. When the internal angle γ is less than 100 degrees, the tapered portion 12 becomes excessively sharp, and the rigidity in the tire axial direction and the torsional rigidity tend to decrease. This may cause a deterioration in responsiveness at the start of steering of the steering wheel. On the other hand, if the internal angle γ exceeds 150 degrees, the vertical groove-like portion 7 cannot form the amplifying portion 7b having a sufficiently large groove width, and there is a possibility that improvement in wet performance cannot be expected sufficiently. From such a viewpoint, the internal angle γ is preferably 120 degrees or more and 145 degrees or less.

  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 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 internal angle α of the tip portion 6a is less than 100 degrees, the rigidity of the tip portion 6a tends to decrease, and the responsiveness during steering of the steering wheel tends to decrease. There is a tendency for the water transfer effect to decrease. The inner angle α of the front end portion 6a is such that when the front end portion 6a is formed in a smooth arc, a distance S of 2 mm from the apex K1 to the tire circumferential direction on the tread surface is the rearward side of the tire rotation direction R. It is measured as an angle formed by a tangent line that is in contact with the center block 6 at a position j separated from each other.

  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.

  Furthermore, the land ratio of the center portion Ce is preferably set to 40 to 55%, for example. Thus, by setting the land ratio of the center portion Ce small, it is possible to improve drainage performance in the center portion Ce that is originally difficult to drain. That is, 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.

  On the other hand, the land ratio between the tread ground end E and the outer edge Ec of the center portion Ce in each shoulder portion Sh (hereinafter, the land ratio of such a region may be simply referred to as “land ratio of the shoulder portion Sh”). Is preferably set to 57 to 72%. At the time of turning, the shoulder portion Sh mainly receives a lateral force. By making the land ratio of the shoulder portion Sh larger than that of the center portion Ce in this manner, the pattern rigidity of the shoulder portion Sh is maintained high and the steering is performed. Stability can be improved.

  That is, 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 may be 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.

  The tread portion 2 is formed by repeating substantially the same pattern pitch P in the tire circumferential direction. In the present embodiment, the pattern pitch P is composed of the one shoulder main groove 3 and one shoulder land portion 4 adjacent to the shoulder main groove 3 with the position of the tread ground contact E as a reference (between the line segments Pa and Pb). portion). 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.

  FIG. 4 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 part Ce is particularly suitable for a rear wheel of a racing cart that requires a large gripping force, for example, since the drainage performance 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 center block 6A (or 6B) and the shoulder land portion 4 are adjacent to each other via a vertical groove-shaped portion 7 extending in the tire circumferential direction, and the vertical groove-shaped portion 7 is The narrow-width portion 7a, which has a minimum groove width of 3 to 6 mm in the tire axial direction, and amplification portions 7b and 7b in which the groove width gradually increases from the narrow-width portion 7a to both sides in the tire circumferential direction are provided.

  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. Specific dimensions are as follows.

(Front / Rear of Example 1)
Width of shoulder main groove GW1: 9mm / 10mm
Shoulder main groove depth: 5mm / 5mm
The angle θ of the inclined portion of the shoulder main groove: 22 degrees / 15 degrees The groove width GW2 of the shoulder sub groove: 3 mm / 2 mm
Shoulder minor groove depth: 5mm / 5mm
Depth of vertical groove: 5mm / 5mm
Horizontal groove depth: 5mm / 5mm
Maximum width of center block BW: 28mm / 27mm

(Front / Rear of Comparative Example 1)
Width of shoulder main groove GW1: 6mm / 9.5mm
Shoulder main groove depth: 6mm / 6mm
Shoulder minor groove width GW2: 1.5mm / 1.5mm
Shoulder minor groove depth: 0.5mm / 0.5mm
Vertical groove width Ga: 6mm / 7.5mm
Groove width Gb of vertical groove: No front / 9.5mm
Vertical groove width Gc: No front / 8mm
Vertical groove depth: 6mm / 6mm
Maximum width of center block: 18mm / 26mm
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 enlarged view of a vertical groove-shaped part. 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 7 vertical groove portion 7a narrow portion 7b amplifying portion 12 taper portion C tire equator Ce Crown part Sh Shoulder part E Tread grounding end

Claims (5)

A pneumatic tire with a tread,
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.
In each shoulder portion, a shoulder main groove extending inward from the outer side in the tire axial direction of the tread ground end is provided in the tire circumferential direction so that a shoulder land portion is divided between the shoulder main grooves, and the center portion In the center block is provided between the shoulder land portions arranged on both sides in the tire axial direction,
The center block and the shoulder land portion are adjacent to each other via a vertical groove-shaped portion extending in the tire circumferential direction,
The vertical groove-shaped portion includes a narrow width portion having a minimum groove width of 3 to 6 mm in the tire axial direction, and an amplifying portion in which the groove width in the tire axial direction gradually increases from the narrow width portion to both sides in the tire circumferential direction. And a pneumatic tire.   2. The pneumatic tire according to claim 1, wherein the shoulder land portion has a tapered shape in which a tire circumferential direction length gradually decreases toward an inner side in a tire axial direction, and the narrow portion is formed by an apex of the tapered portion.   The pneumatic tire according to claim 2, wherein an internal angle γ of the tapered portion is 100 to 150 degrees.   The shoulder portion is divided into two blocks by providing a shoulder sub-groove having a smaller groove width than the shoulder main groove between the shoulder main grooves. The pneumatic tire according to any one of the above.   5. The pneumatic tire according to claim 4, wherein inner end portions of the shoulder main groove and the shoulder sub-groove in the tire axial direction are both communicated with the amplifying portion.

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