JP2019043233A - Pneumatic radial tire - Google Patents

Abstract

To provide a pneumatic radial tire that does good to improve turning performance of a four-wheel vehicle.SOLUTION: A pneumatic radial tire 1 for a passenger vehicle includes a carcass 6 of a radial structure, a belt layer 7 and a tread part 2. The tread part 2 has an outer tread end To and an inner tread end Ti, where a tread pattern is formed in an asymmetric shape with respect to a tire equator C. The tread part 2 is partitioned by three main grooves 10 into four circumferential land parts. The circumferential land parts include an outer shoulder land part 16, an inner shoulder land part 17 and a middle land part 18 arranged between the land parts. The number of inner shoulder lug grooves 21 are above 1.1 times the number of outer shoulder lug grooves 28, and angles of the outer shoulder lug grooves 28 with respect to a tire shaft direction are smaller than angles of the inner shoulder lug grooves 21 with respect to the tire shaft direction.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a pneumatic radial tire for a passenger car, and more particularly, to a pneumatic radial tire useful for improving the turning performance of a four-wheeled vehicle.

  FIG. 13 shows time-series changes in turning operation of a general four-wheeled vehicle having a steering mechanism on the front wheels. First, as in state A, when the steering wheel is operated by the driver while traveling straight ahead, a slip angle is given to the tire b of the front wheel, and the tire b of the front wheel generates a cornering force (state B). Here, the "slip angle" is an angle between the traveling direction of the vehicle body c and the tire b. Further, “cornering force” is a component of force acting laterally with respect to the traveling direction among the frictional force generated on the ground contact surface of the tire b when the four-wheeled vehicle a turns, and in particular, the slip angle is 1 degree. The cornering force at the time may be called cornering power.

  The cornering force generated by the front wheel tire b brings about a pivoting movement of the vehicle body c with yaw. Since this turning motion gives a slip angle to the tire b of the rear wheel, the tire b of the rear wheel also generates a cornering force (state C). When the moment based on the cornering force of the front tire b and the moment based on the cornering force of the rear wheel tire b substantially balance around the center of gravity CG of the vehicle (state D), the vehicle body c has yaw acceleration Is a stationary state (hereinafter, such a traveling state may be referred to as a "revolution traveling state") in which the vehicle moves obliquely at substantially zero.

  The inventors are aware that it is important to shift the vehicle body to the revolving state as soon as possible after turning and steering in order to improve the turning performance of the four-wheeled vehicle. Repeated research.

Generally, when a tire is mounted on a vehicle, the cornering power generated by the tire is referred to as equivalent cornering power (hereinafter "equivalent CP"). The equivalent CP has a relationship of the following formula (1) with the cornering power (hereinafter referred to as “stand-up CP”) of the tire unit measured in the bench test and the like.
Equivalent CP = bench CP × CP amplification factor ... (1)
The equivalent CP is the cornering power including the effects of so-called roll steer, compliance steer, etc., and is the cornering power when assuming that the roll characteristics and the suspension characteristics of the vehicle are taken into the tire. These characteristics are represented by CP amplification factor.

  FIG. 13 is a graph showing the relationship between the stand CP of a general pneumatic radial tire and the load acting thereon. Generally, it is found that after the CP rises up with the increase of load and reaches a peak, it gradually decreases. The graph also shows the approximate load area of a tire mounted on a FF four wheel vehicle during turning. First, in FF four-wheeled vehicles, the front tires tend to be loaded more than rear tires (Fr load> Rr load). In addition, in each of the front wheel and the rear wheel, a larger load tends to act on the tire on the outside of the turning than in the tire on the inside of the turning. Therefore, a relatively large difference occurs between the front wheel tire and the rear wheel tire with respect to the average bench CP values Ff and Fr generated at the time of turning.

  Assuming that the above load distribution to each tire is premised, during the turning operation of the vehicle, the equivalent CP of the front wheel tire is relatively lowered in order to shift to the revolving state as soon as possible to improve the turning performance. On the other hand, it is considered effective to relatively increase the equivalent CP of the rear wheel tire, that is, to make both equivalent CPs close to each other or improve them so as to approach early.

  The inventors focused on self aligning torque (hereinafter sometimes referred to simply as “SAT”), which has not been paid much attention so far, in order to relatively lower the equivalent CP of the front wheel tire.

  Here, we will briefly describe SAT. FIG. 15 shows a contact surface of the tire b turning at a slip angle α with respect to the traveling direction Y, as viewed from the road surface side. As shown in FIG. 15, the tread rubber of the contact surface P is elastically deformed to generate CF in the lateral direction. If the point of action G of the CF (corresponding to the centroid of the hatched contact surface) is behind the contact center point Pc of the tire, the tire has a small slip angle α around the contact center point Pc. SAT, which is a moment in the direction of movement, works. That is, SAT works in a direction to reduce the slip angle around the tire contact center point Pc. The distance NT along the traveling direction Y between the ground contact point Pc and the action point G of the CF is defined as a pneumatic trail.

  Also, as a result of various experiments by the inventors, it has been found that the CP amplification factor of the above-mentioned formula (1) is approximately proportional to the reciprocal of SAT. For this reason, a tire with a large SAT results in relatively lowering the equivalent CP.

  On the other hand, since the rear wheel has no steering mechanism and is not affected by SAT, the equivalent CP can be increased by raising the stand CP as a tire.

  As is apparent from the above, in a four-wheeled vehicle, in particular an FF four-wheeled vehicle in which a large load is applied to the front wheels, a large SAT can be used as a tire to quickly shift to a revolving state during turning. Characteristics that generate the

  The inventors further studied the relationship between SAT and the tread pattern of the tire and found that the shoulder portion has the largest contribution to SAT among the tread portion of the tire. The inventors of the present invention generate a large SAT by improving the configuration of the outer shoulder land portion located outside of the vehicle at the time of turning and the lug groove formed at the inside shoulder land portion located at the inside of the vehicle at the time of turning. I got the knowledge that I could get it.

JP, 2012-017011, A JP, 2009-162482, A

  The present invention has been made in view of the above problems, and has as its main object to provide a pneumatic radial tire which is useful for improving the turning performance of a four-wheeled vehicle.

According to the present invention, a carcass having a radial structure, a belt layer consisting of at least two belt plies disposed on the outside of the carcass, and a tread portion having a tread pattern in which the direction of mounting on a vehicle is specified Pneumatic radial tires for passenger cars, including:
The tread portion has an outer tread end and an inner tread end located on the outer side and the inner side of the vehicle, respectively, when the vehicle is mounted.
The tread pattern is formed asymmetrically with respect to the tire equator,
The tread portion is divided into four circumferential land portions by three main grooves continuously extending in the tire circumferential direction,
The circumferential land portion includes an outer shoulder land portion including the outer tread end, an inner shoulder land portion including the inner tread end, and at least one middle land portion disposed therebetween.
The outer shoulder land portion is provided with a plurality of outer shoulder lug grooves that extend inward in the tire axial direction from the outer tread end and are interrupted in the outer shoulder land portion,
The inner shoulder land portion is provided with a plurality of inner shoulder lug grooves that extend inward in the tire axial direction from the inner tread end and are interrupted within the inner shoulder land portion.
The number of the inner shoulder lug grooves is at least 1.1 times the number of the outer shoulder lug grooves,
The angle of the outer shoulder lug grooves with respect to the tire axial direction is smaller than the angle of the inner shoulder lug grooves with respect to the tire axial direction.
It is a pneumatic radial tire.

  In another aspect of the present invention, the number of the inner shoulder lug grooves may be 2.0 times or less the number of the outer shoulder lug grooves.

  In another aspect of the present invention, the inner shoulder lug groove may have an angle of 30 to 60 degrees with respect to the axial direction of the tire.

  In another aspect of the present invention, the outer shoulder lug groove may have an angle of 15 degrees or less with respect to the axial direction of the tire.

  In another aspect of the present invention, the sum of the angle of the outer shoulder lug grooves with respect to the tire axial direction and the angle of the inner shoulder lug grooves with respect to the tire axial direction may be 30 to 60 degrees.

  In another aspect of the present invention, the axial length of the outer shoulder lug groove may be 0.5 to 0.9 times the maximum contact width in the tire axial direction of the outer shoulder land portion.

  In another aspect of the present invention, the axial length of the inner shoulder lug groove may be 0.5 to 0.9 times the maximum contact width in the tire axial direction of the inner shoulder land portion.

  In another aspect of the present invention, the number of the outer shoulder lug grooves may be in the range of 55 to 75.

  In another aspect of the present invention, the outer shoulder land portion may be larger than the inner shoulder land portion in terms of tire circumferential stiffness and tire axial stiffness.

According to another aspect of the present invention, the following equation (1) can be satisfied under the following traveling conditions.
Mounting rim: Normal rim Tire internal pressure: Normal internal pressure Load applied to the tire: 70% of the normal load
Speed: 10 km / h
Slip angle: 0.7 degree Camber angle:-(minus) 1.0 degree
SAT ≧ 0.18 × L × CF (1)
Here, "SAT" is the self aligning torque (N · m), "L" is the maximum contact length (m) of the tread in the tire circumferential direction, and "CF" is the cornering force (N).

  In the pneumatic radial tire according to the present invention, as described above, by improving the configuration of the outer side shoulder lug groove and the inner side shoulder lug groove, the outer side shoulder land portion relates to tire circumferential rigidity and tire axial direction rigidity; It can be made larger than the land, which in turn can enhance the SAT. Therefore, the four-wheeled vehicle equipped with the pneumatic radial tire according to the present invention on four wheels can be rapidly shifted to the revolving state during turning and can provide excellent turning performance.

1 is a cross-sectional view of an embodiment of a pneumatic radial tire according to the present invention. It is an expanded view of the tread part of the tire of FIG. It is an explanatory view showing SAT which acts on a front wheel tire when a vehicle is turning left. (A) And (b) is explanatory drawing of the measuring method of the rigidity of a land part. It is an enlarged view of the inside shoulder land part of FIG. It is the BB sectional drawing of FIG. It is an enlarged view of the outer side shoulder land part of FIG. It is the CC sectional view taken on the line of FIG. It is an enlarged view of the middle land part of FIG. (A) is the DD sectional view taken on the line of FIG. 9, (b) is an EE sectional view taken on the line of FIG. It is an expanded view of the tread part of the pneumatic radial tire of other embodiment of this invention. It is an expanded view of the tread part of the pneumatic radial tire of other embodiment of this invention. It is an explanatory view showing turning operation of a four-wheeled passenger car. It is a graph which shows the relationship between stand CP of a common pneumatic radial tire, and the load which acts on it. It is an explanatory view showing the contact surface of the tire of the front wheel at the time of turning of the vehicle.

Hereinafter, an embodiment of the present invention will be described based on the drawings.
FIG. 1 is a cross-sectional view including a tire rotation axis of a pneumatic radial tire 1 (hereinafter sometimes simply referred to as “tire”) of the present embodiment. FIG. 2 is a development view of the tread portion 2 of the tire 1 of FIG. FIG. 1 corresponds to a cross-sectional view taken along line A-A of FIG. The tire 1 of the present embodiment is configured as a pneumatic radial tire for a passenger car. The tire 1 of the present embodiment is suitable for use in a passenger car in which the vertical load acting on the front wheels is larger than the vertical load acting on the rear wheels in a stationary state, and is particularly suitably used for a passenger car of the FF.

  As shown in FIG. 1, the tire 1 of the present embodiment includes a carcass 6 of a radial structure and a belt layer 7.

  The carcass 6 passes from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4. The carcass 6 is formed of, for example, one carcass ply 6A. The carcass ply 6A is made of, for example, a carcass cord made of organic fibers arranged at an angle of 75 to 90 degrees with respect to the circumferential direction of the tire.

  The belt layer 7 is composed of at least two belt plies 7A and 7B. The belt plies 7A, 7B are made of, for example, steel cords arranged at an angle of 10 to 45 degrees with respect to the tire circumferential direction. The belt ply 7A is made of, for example, a steel cord inclined in the opposite direction to the steel cord of the adjacent belt ply 7B. On the outside of the belt layer 7, a further reinforcing layer such as a band layer may be arranged.

  As shown in FIG. 2, the tread portion 2 is formed with a tread pattern in which the direction of attachment to the vehicle is designated. The tread pattern of the tread portion 2 is formed asymmetrically with respect to the tire equator C. The direction of attachment of the tire 1 to the vehicle is displayed, for example, in the side wall portion 3 or the like by characters or symbols.

  The tread portion 2 has an outer tread end To and an inner tread end Ti. The outer tread end To is located outside the vehicle (right side in FIG. 2) when the vehicle is mounted. The inner tread end Ti is located inside the vehicle (left side in FIG. 2) when the vehicle is mounted.

  Each tread end To, Ti is a contact position on the outermost side in the tire axial direction when a normal load is applied to the tire 1 in a normal state and the tire is grounded on a plane at a camber angle of 0 °. The normal state is a state in which the tire is rim-assembled on a normal rim, filled with a normal internal pressure, and unloaded. In the present specification, unless otherwise noted, the dimensions and the like of each part of the tire are values measured in the normal state. In the normal state, the axial axial distance between the outer tread end To and the inner tread end Ti is defined as the tread width TW.

  In the standard system including the standard to which the tire is based, the “regular rim” is the rim which the standard defines for each tire, and if it is JATMA, “standard rim”, if it is TRA, “design rim” or ETRTO. For example, "Measuring Rim".

  The “normal internal pressure” is the air pressure specified by each standard in the standard system including the standard on which the tire is based, and in the case of JATMA, the “maximum air pressure”; in the case of TRA, the table “TIRE LOAD LIMITS AT The maximum value described in VARIOUS COLD INFlation PRESSURES, and in the case of ETRTO, it is “INFLATION PRESSURE”.

  "Normal load" is the load defined by each standard in the standard system including the standard on which the tire is based, and if it is JATMA, "maximum load capacity", if it is TRA, the table "TIRE LOAD LIMITS At the time of ETRTO, it is "LOAD CAPACITY".

  The tread portion 2 of the present embodiment is divided into four circumferential land portions by three main grooves 10 continuously extending in the tire circumferential direction. As the main groove 10, an inner shoulder main groove 11, an outer shoulder main groove 12, and a crown main groove 13 are included.

  The inner shoulder main groove 11 is provided, for example, on the innermost tread end Ti side among the plurality of main grooves 10. The inner shoulder main groove 11 is provided on the inner tread end Ti side with respect to the tire equator C.

  The outer shoulder main groove 12 is provided, for example, on the outermost tread end To side among the plurality of main grooves 10. The outer shoulder main groove 12 is provided closer to the outer tread end To than the tire equator C.

  The crown main groove 13 is provided between the inner shoulder main groove 11 and the outer shoulder main groove 12. For example, one crown main groove 13 is provided on the tire equator C. In another aspect, the crown main groove 13 may be provided, for example, at a position deviated from the tire equator C in the tire axial direction.

  In the present embodiment, the main groove 10 extends linearly, for example, along the tire circumferential direction. In another aspect, the main groove 10 may extend in a wavy or zigzag manner, for example. The groove width of the main groove (the groove width W1 of the inner shoulder main groove 11, the groove width W2 of the outer shoulder main groove 12, and the groove width W3 of the crown main groove 13) can be arbitrarily determined according to conventional practice. In order to provide sufficient drainage performance while maintaining the pattern rigidity of the tread portion 2, for example, about 2.5% to 5.0% of the tread width TW is desirable for each of the groove widths W1, W2 and W3. The depth of each of the main grooves 11 to 13 is preferably, for example, about 5 to 10 mm in the case of a radial tire for a passenger car.

  The tread portion 2 of the present embodiment includes, as circumferential land portions, an outer shoulder land portion 16, an inner shoulder land portion 17, and middle land portions 19 and 20 disposed therebetween.

  In the present embodiment, the outer shoulder land portion 16 and the inner shoulder land portion 17 are provided with an outer shoulder lug groove 28 and an inner shoulder lug groove 21, respectively. The number of the lug grooves 28 and 21 and the angle with respect to the axial direction of the tire are different. Specifically, the number of the inner shoulder lug grooves 21 is 1.1 or more times the number of the outer shoulder lug grooves 28. Further, the angle of the outer shoulder lug groove 28 with respect to the tire axial direction is smaller than the angle of the inner shoulder lug groove 21 with respect to the tire axial direction.

  By configuring the outer shoulder lug groove 28 and the inner shoulder lug groove 21 as described above, in the tire 1 of the present embodiment, the outer shoulder land portion 16 has the rigidity in the tire circumferential direction (front and rear) and the tire axial direction (lateral). The rigidity is larger than the inner shoulder land portion 17.

  As described above, it is effective to generate a large SAT in order to improve the turning performance by shifting the vehicle to the revolving state as soon as possible during turning of the four-wheeled vehicle. The inventors analyzed the pressure distribution on the contact surface during turning of the tire in detail. According to the tire circumferential rigidity and the tire axial rigidity of the outer shoulder land portion 16 and the inner shoulder land portion 17 of the tread portion, to SAT It was found that the contribution of was the largest. Hereinafter, this point will be described with reference to the case where the vehicle is turning left, as shown in FIG.

  In the front wheel tire having a slip angle with respect to the traveling direction, the circumferential land portion is deformed counterclockwise due to the friction between the road surface and the tread surface. When the slip angle becomes almost constant, each deformed circumferential land portion tries to return to the original state, and generates a reaction force, that is, SAT clockwise as shown by the arrow in the figure. In order to increase the SAT, that is, the clockwise torque around the tread center point Pc of the tread portion, the contact area of the outer shoulder land portion 16 of the turning outer tire (right tire) having a high contribution to the SAT It is effective to generate a large driving direction force in the rear region X1. In order to generate such force, it is important to increase the tire circumferential rigidity of the outer shoulder land portion 16.

  On the other hand, with regard to the inner shoulder land portion 17, in order to increase the SAT, a large braking direction is obtained in the front region X2 of the contact region of the inner shoulder land portion 17 of the turning outer tire (right tire) having a high contribution to SAT. It is effective to generate force. In order to generate such a force in the braking direction, the inner shoulder land portion 16 lowers the rigidity in the circumferential direction of the tire contrary to the outer shoulder land portion 17 and has a ground contact ability to flexibly follow the road surface. It is effective to improve.

  Therefore, as in the present invention, the tire 1 in which the outer shoulder land portion 16 is larger than the inner shoulder land portion 17 with respect to the tire circumferential rigidity can effectively enhance the SAT. Therefore, the four-wheeled vehicle equipped with the tire 1 of the present invention on four wheels can quickly shift to the revolving state during turning and can provide excellent turning performance.

  Further, the outer diameter of the pneumatic radial tire gradually decreases toward the axial outer side at the shoulder land portion. Therefore, in the tire on the turning outer side of the front wheel, the outer shoulder land portion 16 generates a camber thrust which is a force opposite to the cornering force of the tire. The inner shoulder land portion 17 generates a camber thrust in the same direction as the cornering force of the tire. The outer shoulder land portion 16 is configured to be larger than the inner shoulder land portion 17 with respect to axial axial rigidity, and therefore, generates a camber thrust greater than the inner shoulder land portion 17. Accordingly, the camber thrust generated by the outer shoulder land portion 16 helps to reduce the cornering force of the front wheel tire, and thus the vehicle in cornering can be more rapidly transferred to the revolving state.

  When the number of the inner shoulder lug grooves 21 is less than 1.1 times the number of the outer shoulder lug grooves 28 or the angle of the outer shoulder lug grooves 28 with respect to the axial direction of the tire is the tire of the inner shoulder lug grooves 21. When the angle with respect to the axial direction is exceeded, the tire circumferential direction (front and rear) rigidity and the tire axial direction (lateral) rigidity of the outer shoulder land portion 16 can not be sufficiently improved with respect to the inner shoulder land portion 17. Tend.

  Hereinafter, although a more preferable tread pattern is described in detail, it is pointed out that the present invention is not construed as being limited to such a tread pattern.

[Configuration of inner shoulder land portion]
An enlarged view of the inner shoulder land portion 17 is shown in FIG. As shown in FIG. 5, the inner shoulder land portion 17 is formed between the inner tread end Ti and the inner shoulder main groove 11. The inner shoulder land portion 17 has, for example, an axial width in the axial direction of 0.25 to 0.35 times the tread width TW (the width at the contact surface, and the same applies to the width of the land portion hereinafter). It has W4.

  The inner shoulder land portion 17 is provided with a plurality of the inner shoulder lug grooves 21 described above. Each inner shoulder lug groove 21 extends inward in the axial direction of the tire from the inner tread end Ti and is interrupted at the inside of the inner shoulder land portion 17.

  As described above, the number of the inner shoulder lug grooves 21 (total number) is 1.1 times or more, more preferably 1.2 times, more preferably 1.3 times the number of the outer shoulder lug grooves 28 (total number). It is set to be On the other hand, when the number of the inner shoulder lug grooves 21 becomes significantly larger than the number of the outer shoulder lug grooves 28, there is a possibility that the basic performance required for the tire such as steering stability and uneven wear resistance is deteriorated. From such a point of view, it is desirable that the number of the inner shoulder lug grooves 21 be equal to or less than 2.0 times the number of the outer shoulder lug grooves 28.

  The inner shoulder lug groove 21 needs to be inclined with respect to the axial direction of the tire in order to relatively reduce the rigidity of the inner shoulder land portion 17. In a preferred embodiment, the inner shoulder lug groove 21 is inclined at an angle θ1 of, for example, 30 to 60 degrees with respect to the tire axial direction. The inner shoulder lug groove 21 of the present embodiment is, for example, linearly extended so as to be inclined at a predetermined angle with respect to the tire axial direction.

  The axial length L1 of the inner shoulder lug groove 21 is preferably 0.5 to 0.9 times the axial width W4 of the inner shoulder land portion 17, for example. The groove width W5 of the inner shoulder lug groove 21 is desirably 0.30 to 0.45 times the groove width W1 of the inner shoulder main groove 11, for example. In the present embodiment, the groove width W5 is fixed, but may be changed. When the length L1 and the groove width W5 of the inner shoulder lug groove 21 are defined, good wet performance is provided while reducing the tire circumferential rigidity and the tire axial rigidity of the inner shoulder land portion 17 in a more preferable range. be able to.

  6 is a cross-sectional view taken along the line B-B of FIG. As shown in FIG. 6, in the inner shoulder lug groove 21, for example, in the region between the inner tread end Ti and the inner shoulder main groove 11, the groove depth gradually decreases toward the inner shoulder main groove 11. There is. As described above, when a large number of inner shoulder lug grooves 21 are arranged to reduce the rigidity of the inner shoulder land portion 17, the pumping noise during traveling tends to be large. However, the sound pressure of such pumping noise can be reduced by largely reducing the groove volume on the inner end side in the tire axial direction of the inner shoulder lug groove 21 as in the present embodiment. In a particularly preferred embodiment, the depth d1 at the inner end side of the inner shoulder lug groove 21 is preferably 40% to 60% of the depth d2 at the inner tread end Ti of the inner shoulder lug groove 21. The depth d2 on the inner end side is measured from the inner end of the inner shoulder lug groove 21 at a position at which 25% of the length L1 in the axial direction of the tire is L5 outside the axial direction of the tire. It shall be.

  As shown in FIG. 5, in order to reduce the tire circumferential rigidity and the tire axial rigidity of the inner shoulder land portion 17 to a preferable range, the number N1 of the inner shoulder lug grooves 21 is, for example, in the range of 65 to 85. Is desirable.

  The inner shoulder land portion 17 is an inner shoulder block piece divided between the inner shoulder rib-shaped portion 25 between the inner shoulder main groove 11 and each inner shoulder lug groove 21 and the inner shoulder lug grooves adjacent in the tire circumferential direction. And 26.

  The inner shoulder rib-shaped portion 25 is not provided with a groove, for example, and land portions extend continuously in the tire circumferential direction. Such an inner shoulder rib-like portion 25 enhances the tire circumferential rigidity in the tire axial direction inner region of the inner shoulder land portion 17 and thus helps to obtain a large equivalent CP. The axial width W6 of the inner shoulder rib-shaped portion 25 is preferably, for example, 0.15 to 0.30 times the width W4 of the inner shoulder land portion 17.

  The inner shoulder block piece 26 has a tire circumferential length Sbi. It is desirable that the tire circumferential direction length Sbi of the inner shoulder block piece 26 of the present embodiment is, for example, 0.9% to 1.2% of the circumferential length of one tire of the inner shoulder land portion 17. In a more desirable aspect, the inner shoulder block piece 26 extends obliquely in the tire axial direction with a constant tire circumferential length Sbi.

  The inner shoulder land portion 17 desirably has a land ratio of 75 to 85%, for example. In the present specification, “land ratio” is defined as the ratio Sb / Sa of the total ground area Sb of the actual land area to the total area Sa of the virtual ground plane in which all the grooves provided in the target land area are filled. It is defined.

[Configuration of outer shoulder land portion]
An enlarged view of the outer shoulder land portion 16 is shown in FIG. As shown in FIG. 7, the outer shoulder land portion 16 is formed between the outer tread end To and the outer shoulder main groove 12. The outer shoulder land portion 16 has, for example, an axial width W7 of 0.25 to 0.35 times the tread width TW. As a desirable aspect, the outer shoulder land portion 16 of the present embodiment is configured to have the same width as the inner shoulder land portion 17 (shown in FIG. 5).

  The outer side shoulder land portion 16 is provided with a plurality of the outer side shoulder lug grooves 28 described above. Each outer shoulder lug groove 28 extends inward in the tire axial direction from the outer tread end To and is interrupted in the outer shoulder land portion 16. In the present embodiment, each outer shoulder lug groove 28 has the same shape, but is not limited to such an aspect.

  As described above, the number of the outer shoulder lug grooves 28 (total number) is associated with the number of the inner shoulder lug grooves 21 (total number), and is set smaller than that. As described above, by providing a difference in the numbers of the inner shoulder lug grooves 21 and the outer shoulder lug grooves 28, the tire circumferential rigidity and the tire axial stiffness of the outer shoulder land portion 16 are compared with those of the inner shoulder land portion 17. It can be relatively enhanced. In a preferred embodiment, the number N2 of the outer shoulder lug grooves 28 is set in the range of 55-75.

  Further, the angle θ2 (not shown) of the outer shoulder lug groove 28 with respect to the tire axial direction is smaller than the angle θ1 with respect to the tire axial direction of the inner shoulder lug groove 21 (shown in FIG. 5 and the same hereinafter). It is done. The angle θ2 is preferably, for example, 15 degrees or less, and more preferably 0 to 10 degrees. In the present embodiment, the outer shoulder lug grooves 28 extend linearly along the tire axial direction, and the angle θ2 = 0 degrees. In a particularly preferred embodiment, the sum of the angle θ2 of the outer shoulder lug groove 28 with respect to the tire axial direction and the angle θ2 of the inner shoulder lug groove 21 with respect to the tire axial direction (this is the sum of absolute values) is 30 to 60 degrees. Is desirable. By configuring the outer shoulder lug groove 28 in this manner, the tire axial stiffness of the outer shoulder land portion 16 is effectively greater than the inner shoulder land portion 17, which helps to increase the SAT.

  The axial length L 2 of the outer shoulder lug groove 28 is preferably 0.5 to 0.9 times the axial width W 7 of the outer shoulder land portion 16. In another aspect, the axial length L2 of the outer shoulder lug grooves 28 may be smaller than the axial length L1 of the inner shoulder lug grooves 21. For example, the length L2 of the outer shoulder lug groove 28 is preferably 0.90 to 0.98 times the length L1 of the inner shoulder lug groove 21. Such an outer shoulder lug groove 28 can also relatively increase the tire circumferential rigidity of the outer shoulder land portion 16 and thus enhance the SAT.

  The outer shoulder lug groove 28 preferably has a groove width W8 equal to or smaller than the groove width W5 of the inner shoulder lug groove 21, for example. Specifically, the groove width W8 of the outer shoulder lug groove 28 is desirably about 0.80 to 1.0 times the groove width W5 of the inner shoulder lug groove 21. In the present embodiment, the groove width W8 is constant, but may be changed.

  The CC sectional view taken on the line of FIG. 7 is shown by FIG. As shown in FIG. 8, the outer shoulder lug grooves 28 have, for example, a gradually decreasing groove depth inward in the tire axial direction from the outer tread end To. Such outer shoulder lug grooves 28 serve to reduce pumping noise during travel, as described above. In order to further enhance the above-mentioned effect, the depth d3 at the inner end side of the outer shoulder lug groove 28 is set to 40% to 60% of the depth d4 at the outer tread end To of the outer shoulder lug groove 28. It is desirable to make a large change (decrease) in volume. The depth d3 on the inner end side is measured from the inner end of the outer shoulder lug groove 28 at a position where 25% of the axial length L2 in the axial direction of the tire is separated on the outer side in the axial direction of the tire I assume.

  As shown in FIG. 7, the outer shoulder land portion 16 is, for example, an outer shoulder rib 33 adjacent to the outer shoulder rib-shaped portion 33 between the outer shoulder main groove 12 and each outer shoulder lug groove 28 in the tire circumferential direction. And an outer shoulder block piece 34 divided between the grooves 28, 28.

  For example, the outer shoulder rib-shaped portion 33 is not provided with a groove, and the land portion extends continuously in the tire circumferential direction. Such an outer shoulder rib-like portion 33 can effectively enhance the tire circumferential rigidity of the outer shoulder land portion 16.

  The outer shoulder rib-shaped portion 33 preferably has, for example, a width W 9 in the tire axial direction larger than that of the inner shoulder rib-shaped portion 25. The width W 9 of the outer shoulder rib-shaped portion 33 is preferably 1.10 to 1.20 times the width W 6 of the inner shoulder rib-shaped portion 25, for example. As a result, the outer shoulder land portion 16 has relatively higher rigidity than the inner shoulder land portion 17, and thus, high SAT can be generated.

  The outer shoulder block piece 34 has a tire circumferential length Sbo. In the present embodiment, the tire circumferential direction length Sbo of the outer shoulder block piece 34 is formed larger than the tire circumferential direction length Sbi of the inner shoulder block piece 26. In a preferred embodiment, the ratio Sbi / Sbo of the tire circumferential direction length between the inner shoulder block piece 26 and the outer shoulder block piece 34 is, for example, in the range of 0.6 to 0.9. This gives a high SAT and thus an excellent turning performance.

  From the same point of view, the outer shoulder land portion 16 desirably has a land ratio greater than, for example, the inner shoulder land portion 17. The land ratio of the outer shoulder land portion 16 is desirably, for example, in the range of 1.05 to 1.10 times the land ratio of the inner shoulder land portion 17.

  In the preferred embodiment, with respect to the circumferential rigidity of the tire, the outer shoulder land portion 16 is 1.05 to 1.40 times as stiff as the inner shoulder land portion 17 in order to prevent occurrence of uneven wear while generating a larger SAT. It is desirable to have the ratio σ 1. Similarly, with regard to tire axial stiffness, the outer shoulder land portion 16 desirably has a rigidity ratio σ2 that is 1.05 to 1.40 times that of the inner shoulder land portion 17.

  The tire circumferential rigidity and the tire axial rigidity of the land portions 16 and 17 are indicated by the force required to generate a unit deformation amount in each direction. Specific measurement methods include the following. In FIG. 4A, the inner shoulder land portion 17 is shown as an example of the land portion. As shown in FIG. 4A, the inner shoulder land portion 17 to be measured is cut out from the tire 1 with a tire circumferential direction length of two or more pitches. At this time, the land portion test piece TP is cut out by a surface PS1 parallel to the tread surface of the tread portion through the groove bottom 10b of the main groove 10 and a surface PS2 extending along the tire radial direction through the inner tread end Ti. (Shown in FIG. 4 (b)). Next, the ground contact surface of the land portion test piece TP is pressed against a flat test surface, for example, with a normal load to maintain the ground contact state. Next, the test surface is moved with a force F in the tire circumferential direction Y or the tire axial direction X, and the displacement of the land portion in each direction X or Y is measured. Then, the force F is divided by the amount of displacement of the land portion test piece TP in each direction to obtain the land portion rigidity in each of the directions Y and X.

[Middle land section composition]
An enlarged view of an embodiment of the middle land portion is shown in FIG. As shown in FIG. 9, the middle land portion of the present embodiment includes an outer middle land portion 19 and an inner middle land portion 20. The outer middle land portion 19 is divided, for example, between the crown main groove 13 and the outer shoulder main groove 12. In this embodiment, the outer middle land portion 19 and the inner middle land portion 20 have axial axial widths W13 and W10 of 0.10 to 0.20 times the tread width TW, respectively. In the present embodiment, W13 = W10, but it may be W13> W10.

  In the present invention, the specific pattern of the middle land portion 18 is not particularly limited. However, as a result of various experiments by the inventors shown in FIG. 3, the tire circumferential rigidity and the tire axial rigidity of the outer middle land portion 19 are not limited to the contribution to the SAT. Therefore, by increasing the tire circumferential rigidity and the tire axial rigidity of the outer middle land portion 19 more than that of the inner middle land portion 20, the SAT can be increased by a mechanism similar to the above.

  In a preferred embodiment, the outer middle land portion 19 is also formed to be the same as or larger than the inner middle land portion 20 with respect to tire circumferential rigidity and tire axial rigidity. In the present embodiment, the outer middle land portion 19 is formed larger than the inner middle land portion 20 in terms of tire circumferential rigidity and tire axial rigidity. In this case, in an exemplary embodiment, the outer middle land portion 19 has a land ratio greater than, for example, the inner middle land portion 20.

  As shown in FIG. 9, in the preferred embodiment, regarding the circumferential rigidity of the tire, the outer middle land portion 19 is formed of 1. of the inner middle land portion 20 in order to prevent occurrence of uneven wear while generating SAT larger. It is desirable to have a rigidity ratio σ3 of 05 to 1.40. Similarly, regarding the tire axial stiffness, the outer middle land portion 19 desirably has a rigidity ratio σ 4 that is 1.05 to 1.40 times that of the inner middle land portion 20. Hereinafter, the configuration of a specific pattern that can realize the above-described difference in rigidity will be described.

[Configuration of inner middle land portion]
The inner middle land portion 20 is provided with, for example, a plurality of inner middle lug grooves 36. Each inner middle lug groove 36 extends from the edge 20 A on the inner tread end Ti side of the inner middle land portion 20 toward the outer tread end To and is interrupted in the inner middle land portion 20. Thereby, the outer half 20o of the inner middle land portion 20 is formed to be equal to or larger than the inner half 20i of the inner middle land 20 with respect to the tire circumferential rigidity and the tire axial rigidity (this embodiment) In form, it is formed large.). Thus, SAT can be further enhanced and, in turn, cornering performance can be enhanced by providing a difference in rigidity in the inner middle land portion 20 alone.

  In the preferred embodiment, with respect to the circumferential rigidity of the tire, the outer half 20o of the inner middle land 20 has 1.05 to 1 of its inner half 20i in order to prevent occurrence of uneven wear while generating SAT more largely. It is desirable to have a rigidity ratio σ5 of 50 times. Similarly, regarding tire axial rigidity, it is desirable that the outer half 20o of the inner middle land portion 20 have a rigidity ratio σ6 that is 1.05 to 1.20 times that of the inner half 20i.

  Here, the outer half portion 20o is a portion on the outer tread end To side with respect to the center position 20C of the inner middle land portion 20 in the tire axial direction. The inner half portion 20i is a portion on the inner tread end Ti side with respect to the center position 20C of the inner middle land portion 20 in the tire axial direction. The tire circumferential rigidity and tire axial rigidity of the outer half 20o and the inner half 20i of the inner middle land portion 20 are measured by cutting out the lands from the tread portion 2 as described above.

  The inner middle lug groove 36 extends at an angle θ7 (not shown) smaller than the inner shoulder lug groove 21 with respect to the axial direction of the tire, for example. The angle θ7 of the inner middle lug groove 36 is desirably, for example, 0 to 10 degrees, and in the present embodiment, linearly extends along the tire axial direction (angle θ7 = 0 degrees). Such an inner middle lug groove 36 can sufficiently maintain the axial rigidity of the inner middle land portion 20, and can provide a large equivalent CP, particularly when the tire 1 is mounted on the rear wheel of the vehicle.

  The axial length L3 of the inner middle lug groove 36 is preferably, for example, 0.45 to 0.55 times the width W10 of the inner middle land portion 20. The groove width W11 of the inner middle lug groove 36 is, for example, the same as the groove width W5 (shown in FIG. 5) of the inner shoulder lug groove 21 but may be different. FIG. 10A shows a cross-sectional view taken along the line D-D in FIG. As shown in FIG. 10A, the depth d6 of the inner middle lug groove 36 is desirably, for example, about 0.20 to 0.90 times the groove depth d5 of the crown main groove 13.

  As shown in FIG. 9, it is desirable that the number (total number) N3 of the inner middle lug grooves 36 provided in the inner middle land portion 20 be, for example, in the range of 80 to 100.

  The inner middle land portion 20 is, for example, an inner middle block piece 38 divided between the inner middle rib-like portion 37 between the crown main groove 13 and each inner middle lug groove 36 and the inner middle lug groove 36 adjacent in the tire circumferential direction. And contains.

  For example, the inner middle rib-shaped portion 37 is not provided with a groove, and the land portion extends continuously in the tire circumferential direction. Such an inner middle rib-like portion 37 can increase the rigidity of the inner middle land portion 20 on the tire equator side, and thus can enhance SAT.

  The inner middle block piece 38 has a tire circumferential length Mbi. The tire circumferential direction length Mbi of the inner middle block piece 38 is, for example, 0.7% to 0.9% of the circumferential length of the tire of the inner middle land portion 20 by setting the number N3 of grooves as described above. It is said to be about%.

  The inner middle land portion 20 preferably has a land ratio of 75 to 85%, for example. Such an inner middle land portion 20 can improve the wet performance and the steering stability in a well-balanced manner.

[Configuration of outer middle land portion]
The outer middle land portion 19 is provided with, for example, a plurality of outer middle lug grooves 40. Each outer middle lug groove 40 extends, for example, from the edge on the inner tread end Ti side of the outer middle land portion 19 toward the outer tread end To, and is interrupted in the outer middle land portion 19. Thereby, the outer half 19o of the outer middle land 19 is formed to be equal to or larger than the inner half 19i of the outer middle land 19 with respect to the tire circumferential rigidity and the tire axial rigidity (the present embodiment). In form, it is formed large.). Such an outer middle land portion 19 further contributes to the enhancement of SAT, which in turn can enhance the turning performance.

  In the preferred embodiment, with respect to the circumferential rigidity of the tire, the outer half portion 19o of the outer middle land portion is 1.05-1. It is desirable to have a stiffness ratio σ7 of 50 times. Similarly, with regard to tire axial stiffness, it is desirable that the outer half portion 19o of the outer middle land portion have a rigidity ratio σ8 that is 1.05 to 1.20 times that of the inner half portion 19i.

  Here, the outer half portion 19 o is a portion on the outer tread end To side of the center position 19 C in the tire axial direction of the outer middle land portion 19. The inner half portion 19i is a portion on the inner tread end Ti side with respect to the center position 19C of the outer middle land portion 19 in the tire axial direction. The tire circumferential rigidity and tire axial rigidity of the outer half portion 19 o and the inner half portion 19 i of the outer middle land portion 19 are measured by cutting out the land portions from the tread portion 2 as described above.

  The outer middle lug groove 40 extends, for example, at an angle θ8 (not shown) smaller than the inner shoulder lug groove 21 with respect to the axial direction of the tire. The angle θ 8 of the outer middle lug groove 40 is desirably, for example, 0 to 10 degrees, and in the present embodiment, the outer middle lug groove 40 linearly extends along the tire axial direction (angle θ 8 = 0 degree).

  Each outer middle lug groove 40 preferably has an axial length L4 smaller than that of the inner middle lug groove 36, for example. The length L4 of the outer middle lug groove 40 is preferably, for example, 0.70 to 0.80 times the length L3 of the inner middle lug groove 36. The groove width W14 of the outer middle lug groove 40 is, for example, the same as the groove width W11 of the inner middle lug groove 36, but may be different. The EE sectional view taken on the line of FIG. 9 is shown by FIG.10 (b). As shown in FIG. 10 (b), it is desirable that the groove depth d7 of the outer middle lug groove 40 be smaller than the groove depth d6 of the inner middle lug groove 36, for example.

  The number (total number) N4 of the outer middle lug grooves 40 provided in the outer middle land portion 19 is preferably smaller than the number N3 of the inner middle lug grooves 36, for example, and in particular, 0.5 of the number N3. It is desirable to be in the range of ̃0.7 times. Such an outer middle lug groove 40 relatively enhances the rigidity of the outer middle land portion 19 and can provide high SAT.

  In a more desirable aspect, a ratio N4 / N3 of the number N4 of the outer middle lug grooves 40 to the number N3 of the inner middle lug grooves is a ratio N2 / N1 of the number N2 of the outer shoulder lug grooves 28 to the number N1 of the inner shoulder lug grooves 21. Less than. Such an aspect can relatively reduce the difference in rigidity between the outer middle land portion 19 and the inner middle land portion 20, and in turn can suppress these uneven wear.

  The outer middle land portion 19 is, for example, an outer middle block piece divided between the outer middle rib-shaped portion 41 between the outer shoulder main groove 12 and each outer middle lug groove 40 and the outer middle lug groove 40 adjacent in the tire circumferential direction. And 42.

  For example, it is desirable that the outer middle rib-shaped portion 41 is not provided with a groove, and continuously extended in the tire circumferential direction. Such an outer middle rib-like portion 41 has high rigidity and thus can provide high SAT. From the same point of view, it is desirable that the outer middle rib portion 41 have, for example, a width W15 in the tire axial direction larger than the width W12 of the inner middle rib portion 37.

  The outer middle block piece 42 has a tire circumferential length Mbo. In the desirable aspect, the tire circumferential direction length Mbo of the outer middle block piece 42 is formed larger than the tire circumferential direction length Mbi of the inner middle block piece 38 by setting the number N4 of grooves as described above. Is desirable. In a particularly preferred embodiment, the ratio Mbi / Mbo of the tire circumferential length between the inner middle block piece 38 and the outer middle block piece 42 is preferably in the range of 0.7 to 0.9. Thereby, the rigidity balance between the inner middle land portion 20 and the outer middle land portion 19 is further enhanced.

[Specific SAT]
In a preferred embodiment, it is desirable that the tire 1 satisfy the following formula (1) under the following traveling conditions in, for example, a bench test (for example, a test using a flat belt type tire tester). .
Mounting rim: Normal rim Tire internal pressure: Normal internal pressure Load applied to the tire: 70% of the normal load
Speed: 10 km / h
Slip angle: 0.7 degree Camber angle:-(minus) 1.0 degree
SAT ≧ 0.18 × L × CF (1)
Here, "SAT" is the self aligning torque (N · m), "L" is the maximum contact length (m) of the tread in the tire circumferential direction, and "CF" is the cornering force (N). Also, "minus" of the camber angle means an inclination such that the upper part of the tire is directed to the center of the vehicle.

  The above measurement conditions are based on the condition of the front wheels in a turning state (lateral acceleration of about 0.2 G) which tends to occur frequently in four-wheeled vehicles. The inventors mount various sensors on a four-wheeled vehicle, measure the condition (load, camber angle, slip angle, and angle) of the tire in the above-mentioned turning state, and approximate it by bench test As a thing, the above-mentioned running condition was obtained. Therefore, the tire 1 satisfying the above equation (1) can generate SAT reliably and sufficiently large in a normal turning state. That is, it is possible to more rapidly shift the vehicle on which it is turning to the revolving state.

[Other embodiments]
FIG. 11 shows a development view of the tread portion 2 of the tire 1 according to another embodiment of the present invention. In FIG. 11, the elements common to the above-described embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  A sipe is added to the tire 1 of this embodiment. The sipe includes, for example, an inner middle sipe 45 provided on the inner middle land portion 20. The inner middle sipes 45 of the present embodiment are formed between the inner middle lug grooves 36 adjacent in the tire circumferential direction, and extend in the tire axial direction.

  Preferably, at least one end of the inner middle sipe 45 communicates with the main groove 10. The inner middle sipe 45 of the present embodiment completely crosses the inner middle land portion 20 in the tire axial direction. The inner middle sipe 45 can increase the frictional force during wet running by the edge without excessively reducing the rigidity of the inner middle land portion 20 in the tire circumferential direction. In the present specification, “sipe” is defined as a slit having a width of 0.8 mm or less, and is distinguished from a “groove” having a width larger than this.

  In the embodiment of FIG. 11, the inner middle lug groove 36 includes a first inner middle lug groove 36A and a second inner middle lug groove 36B having a tire axial length greater than the first inner middle lug groove 36A. A first inner middle lug groove 36A and a second inner middle lug groove 36B are provided between the inner middle sipes 45 adjacent in the tire circumferential direction. This helps to suppress uneven wear of the inner middle land portion 20.

  The sipe further includes an outer middle sipe 46 provided on the outer middle land portion 19. The outer middle sipes 46 are provided with outer middle sipes 46 penetrating the outer middle land portion 19 in the tire axial direction between the outer middle lug grooves 40 adjacent in the tire circumferential direction. Such an outer middle sipe 46 can increase the frictional force during wet running by the edge.

  The outer middle lug groove 40 preferably includes, for example, a first outer middle lug groove 40A and a second outer middle lug groove 40B having a greater axial length than the first outer middle lug groove 40A.

  As a further preferable aspect, one first outer middle lug groove 40A and one second outer middle lug groove 40B are provided between the outer middle sipes 46 adjacent in the tire circumferential direction. As a result, uneven wear of the outer middle land portion 19 is suppressed.

  The outer shoulder lug groove 28 in this embodiment has, for example, an inner shoulder lug groove 21, an inner middle lug groove 36, and a groove width W 8 smaller than the outer middle lug groove 40. Such outer shoulder lug grooves 28 can further enhance the rigidity of the outer shoulder land portion 16 and thus provide high SAT.

  FIG. 12 shows a development view of the tread portion 2 of the tire 1 according to still another embodiment of the present invention. Also in FIG. 12, the elements common to the above-described embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  In this embodiment, the outer middle land portion 19 and the inner middle land portion 20 are respectively formed with an outer middle lug groove 40 and an inner middle lug groove 36 whose both ends communicate with the main groove.

  As mentioned above, although the tire of one embodiment of the present invention was explained in detail, the present invention can be changed and carried out in various modes, without being limited to the above-mentioned specific embodiment.

  A pneumatic tire of size 235 / 45R18 was prototyped based on the specifications in Table 1. The following tests were conducted for each test tire.

[Tire specifications]
For the comparative example, Examples 1-7, the middle land is configured as a plain rib essentially free of grooves, otherwise as essentially as shown in FIG. For Example 8, a lug groove according to FIG. 2 was further formed in the middle land portion.

[Table test]
Using the flat belt type tire testing machine, the SAT and the maximum contact length L and CF in the tire circumferential direction of the tread portion are measured under the following conditions, and whether each test tire satisfies the following equation (1) It was investigated.
Mounting rim: 18 × 6.5 JJ
Tire internal pressure: 220kPa
Speed: 10 km / h
Slip angle: 0.7 degree Camber angle: -1.0 degree Tire load: 70% of normal load
SAT ≧ 0.18 × L × CF (1)
[Swirl performance]
A test tire was attached to four wheels of an FF passenger car having a displacement of 2000 cc, and it was allowed to turn on a dry road surface with one driver, and the turning performance at that time was evaluated by the driver's function. The result is a score of 100 for the comparative example. The larger the value is, the faster the vehicle has shifted to the revolving state during turning.
The results of the test are shown in Table 1.

  As a result of the test, it was confirmed that the tire of the example exhibited superior turning performance as compared with the tire of the comparative example.

Reference Signs List 2 tread portion 6 carcass 7 belt layer 10 main groove 16 outer shoulder land portion 17 inner shoulder land portion 18 middle land portion 21 inner shoulder lug groove 28 outer shoulder lug groove C tire equator To outer tread end Ti inner tread end

Claims (10)

For a passenger car including a carcass of radial structure, a belt layer consisting of at least two belt plies disposed outside the carcass, and a tread portion on which a tread pattern having a designated direction of mounting on a vehicle is formed A pneumatic radial tire,
The tread portion has an outer tread end and an inner tread end located on the outer side and the inner side of the vehicle, respectively, when the vehicle is mounted.
The tread pattern is formed asymmetrically with respect to the tire equator,
The tread portion is divided into four circumferential land portions by three main grooves continuously extending in the tire circumferential direction,
The circumferential land portion includes an outer shoulder land portion including the outer tread end, an inner shoulder land portion including the inner tread end, and a pair of middle land portions disposed therebetween.
The outer shoulder land portion is provided with a plurality of outer shoulder lug grooves that extend inward in the tire axial direction from the outer tread end and are interrupted in the outer shoulder land portion,
The inner shoulder land portion is provided with a plurality of inner shoulder lug grooves that extend inward in the tire axial direction from the inner tread end and are interrupted within the inner shoulder land portion.
The number of the inner shoulder lug grooves is at least 1.1 times the number of the outer shoulder lug grooves,
The angle of the outer shoulder lug grooves with respect to the tire axial direction is smaller than the angle of the inner shoulder lug grooves with respect to the tire axial direction.
Pneumatic radial tire.   The pneumatic radial tire according to claim 1, wherein the number of the inner shoulder lug grooves is 2.0 times or less of the number of the outer shoulder lug grooves.   The pneumatic radial tire according to claim 1 or 2, wherein an angle of the inner shoulder lug grooves with respect to the tire axial direction is 30 to 60 degrees.   The pneumatic radial tire according to any one of claims 1 to 3, wherein an angle of the outer shoulder lug grooves with respect to the tire axial direction is 15 degrees or less.   The pneumatic radial tire according to any one of claims 1 to 4, wherein the sum of the angle of the outer shoulder lug grooves with respect to the tire axial direction and the angle of the inner shoulder lug grooves with respect to the tire axial direction is 30 to 60 degrees.   The pneumatic radial according to any one of claims 1 to 5, wherein the axial length of the outer shoulder lug groove is 0.5 to 0.9 times the axial width of the outer shoulder land portion. tire.   The pneumatic radial according to any one of claims 1 to 6, wherein the axial length of the inner shoulder lug groove is 0.5 to 0.9 times the axial width of the inner shoulder land portion. tire.   The pneumatic radial tire according to any one of claims 1 to 7, wherein the number of the outer shoulder lug grooves is in the range of 55 to 75.   The pneumatic radial tire according to any one of claims 1 to 8, wherein the outer shoulder land portion is larger than the inner shoulder land portion in terms of tire circumferential rigidity and tire axial rigidity. The pneumatic radial tire according to any one of claims 1 to 9, wherein the following formula (1) is satisfied under the following traveling conditions.
Mounting rim: Normal rim Tire internal pressure: Normal internal pressure Load applied to the tire: 70% of the normal load
Speed: 10 km / h
Slip angle: 0.7 degree Camber angle:-(minus) 1.0 degree
SAT ≧ 0.18 × L × CF (1)
Here, "SAT" is the self aligning torque (N · m), "L" is the maximum contact length (m) of the tread in the tire circumferential direction, and "CF" is the cornering force (N).