Pneumatic tire

Abstract

To provide a pneumatic tire having low air resistance.SOLUTION: A pneumatic tire 1 that is one example of an embodiment includes a tread 2 and a sidewall 3. The sidewall 3 includes: a side block 3b; and within a length range equivalent to 20% of a tire cross-section height H with a tire maximum width position P as a center, a protrusion 30 protruding outward in a tire axial direction and formed in an annular shape in a tire circumferential direction. The height of the protrusion 30 is 1.1 times or more and 3.0 times or less the height of the highest portion of the side block 3b other than the protrusion 30.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to pneumatic tires.

Background Art

[0002] In recent years, from the viewpoint of improving the fuel efficiency of vehicles, etc., reduction of air resistance is also required for tires. Conventionally, in order to improve the traction performance, side cut performance, etc. during off-road driving, pneumatic tires provided with side blocks formed on the sidewalls are widely known (for example, see Patent Document 1), but when side blocks are present, it becomes more difficult to reduce air resistance. That is, the side blocks increase the air resistance of the tire.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Conventional tires cannot be said to have been sufficiently considered for reducing air resistance, and there is a large room for improvement. An object of the present invention is to provide a tire with low air resistance, and particularly to reduce air resistance in a tire provided with side blocks.

Means for Solving the Problems

[0005] A pneumatic tire according to one aspect of the present invention is a pneumatic tire having a tread and a sidewall, wherein the sidewall has side blocks and protrusions that project outward in the tire axial direction within a length range corresponding to 20% of the tire cross-sectional height centered on the tire maximum width position and are formed in an annular shape along the tire circumferential direction, and the height of the protrusions is 1.1 times or more and 3.0 times or less the height of the portion where the height of the side blocks is the highest other than the protrusions.

Advantages of the Invention

[0006] According to one aspect of the present invention, in a pneumatic tire provided with side blocks, air resistance can be effectively reduced.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0008] Hereinafter, with reference to the drawings, an example of an embodiment of a pneumatic tire according to the present invention will be described in detail. The embodiment described below is merely an example, and the present invention is not limited to the following embodiment. Also, a mode formed by selectively combining each component of a plurality of embodiments and modification examples described below is included in the present invention.

[0009] FIG. 1 is a perspective view of a pneumatic tire 1 according to an example of an embodiment. As shown in FIG. 1, the pneumatic tire 1 includes a tread 2 which is a portion in contact with a road surface, a sidewall 3 which forms a tire side surface, and a bead 4 which is a portion fixed to a rim of a wheel. The tread 2 has a tread pattern including a plurality of blocks such as shoulder blocks 2a and 2b. Further, a plurality of grooves 2c and 2d for partitioning the blocks are formed in the tread 2. The tread 2, the sidewall 3, and the bead 4 are formed in an annular shape along the tire circumferential direction.

[0010] The sidewall 3 extends radially inward from both axial ends of the tread 2 in the tire axial direction and forms the left and right side surfaces of the pneumatic tire 1 together with the bead 4. Although details will be described later, the sidewall 3 has a side block 3b and a protrusion 30 formed within a length range corresponding to 20% of the tire section height H centered on the tire maximum width position P. The side block 3b and the protrusion 30 protrude outward in the tire axial direction from the profile surface 3a of the sidewall 3. By forming the protrusion 30 at or near the tire maximum width position P, the air resistance of the tire is effectively reduced. The protrusion 30 is formed in an annular shape along the tire circumferential direction.

[0011] The side block 3b improves the traction performance and side cut performance during off-road driving. Although the presence of the side block 3b makes it more difficult to reduce air resistance, the function of the protrusion 30 greatly reduces the air resistance. The pneumatic tire 1 is suitable for, for example, a tire for a light truck. Note that light trucks include pickup trucks, sports utility vehicles (SUVs), and the like. An example of the size of the pneumatic tire 1 is LT275 / 60R20.

[0012] In the pneumatic tire 1, a side rib 5 is formed near the tread 2 on the tire sidewall. The side rib 5 is a convex portion protruding outward in the tire axial direction and is formed annularly along the tire circumferential direction. In the present embodiment, a portion from the outer axial end of the surface of the shoulder blocks 2a, 2b facing the outer side in the tire radial direction to the side rib 5 is defined as a buttless region, and a portion from the bead 4 to the side rib 5 is defined as the sidewall 3. Note that the shape of the side surfaces 6a, 6b of the shoulder blocks 2a, 2b facing the outer side in the tire axial direction affects the shape of the buttless region.

[0013] The tread 2 and the sidewall 3 are generally made of different types of rubber. The buttless region may be made of the same rubber as the tread 2 or may be made of different rubber. The bead 4 has, for example, a bead core and a bead filler. The bead core is a ring-shaped member in which bundled steel wires (bead wires) are coated with rubber. The bead filler is made of a rubber harder than the tread rubber and the sidewall rubber and has a function of enhancing the rigidity of the bead 4.

[0014] The pneumatic tire 1 includes, for example, a carcass, a belt, and an inner liner. The carcass is a cord layer coated with rubber and forms the skeleton of the pneumatic tire 1 that withstands loads, impacts, air pressure, etc. The belt is a reinforcing band disposed between the rubber constituting the tread 2 and the carcass. The belt strongly tightens the carcass to increase the rigidity of the pneumatic tire 1. The inner liner is a rubber layer provided on the inner peripheral surface of the carcass and holds the air pressure of the pneumatic tire 1.

[0015] FIG. 1 shows the side block 3b on the left side of the pneumatic tire 1. It is preferable that the pneumatic tire 1 has side blocks 3b on the left and right sidewalls 3. And it is preferable that projections 30 are formed on both the left and right sidewalls 3. However, the left and right side blocks 3b are not limited to blocks of the same shape and may have completely different shapes. The side block 3b on the right side, for example, has a shape obtained by rotating the side block 3b on the left side 180° with respect to the center line passing through the tire equator and perpendicular to the tire rotation axis. The pneumatic tire 1 may be a tire without a specified mounting direction.

[0016] Hereinafter, with further reference to FIG. 2, the sidewall 3 and the buttress region of the pneumatic tire 1 will be described in detail. FIG. 2 is a left side view of the pneumatic tire 1, showing an enlarged sidewall 3 and buttress region. Hereinafter, the first direction in the tire circumferential direction may be referred to as the "X1 direction", and the second direction may be referred to as the "X2 direction". Also, the direction facing the outside in the tire radial direction may be referred to as the "Y1 direction", and the direction facing the inside in the radial direction may be referred to as the "Y2 direction".

[0017] As shown in FIGS. 1 and 2, the pneumatic tire 1 has a plurality of side blocks 3b formed on the sidewall 3. The plurality of side blocks 3b are arranged at a predetermined interval in the tire circumferential direction. The predetermined interval may be constant or may be a variable pitch in which the interval between the blocks is slightly changed in units of a predetermined number. Also, the side block 3b includes a first side block 10 and a second side block 20. A step is formed at the boundary 15 between the first side block 10 and the second side block 20, and the first side block 10 protrudes more than the second side block 20.

[0018] In the present embodiment, side blocks 3b having substantially the same shape and the same size are arranged in the tire circumferential direction, but two or more types of blocks having different shapes from each other may be arranged alternately or in a predetermined pattern in the tire circumferential direction. The number of side blocks 3b arranged in the tire circumferential direction is not particularly limited, but as an example, it is 20 or more and 30 or less.

[0019] The side block 3b is preferably formed between the side rib 5 and the tire maximum width position P. In this case, it becomes easy to reduce air resistance while ensuring good side traction performance and side cut (protection) performance. In the present specification, the "tire maximum width position P" means a position where the length in the tire axial direction is maximum on the profile surface 3a of the sidewall 3. Further, the "profile surface 3a" of the sidewall 3 means the surface facing the outside in the tire axial direction of the sidewall 3 when the side block 3b is not formed. For the virtual surface along the surface of the sidewall 3 and the surface hidden by the side block 3b, it is distinguished from the exposed surface and is referred to as "profile surface 3x".

[0020] The side block 3b is a block in which one first side block 10 and one second side block 20 are connected and integrated. In the present embodiment, a protrusion 30 is formed at the radially inner end of the side block 3b in the tire diameter direction. Note that since the protrusion 30 is formed in an annular shape along the tire circumferential direction, it is also formed in a portion where the side block 3b does not exist. The protrusion 30 is formed substantially parallel to the side rib 5, realizes the flow of air along the surface of the sidewall 3, and effectively reduces the air resistance during running.

[0021] The portion located between the side blocks 3b is at the same height as the profile surface 3a of the sidewall 3. For this reason, unevenness is formed in the tire circumferential direction in the portion of the sidewall 3 located between the side rib 5 and the tire maximum width position P. This unevenness improves the side traction performance on muddy ground, sandy ground, or snow roads. From the viewpoint of improving the side cut performance, the length of the side block 3b along the tire circumferential direction is preferably longer than the interval between the side blocks 3b.

[0022] The side blocks 3b and the shoulder blocks 2a, 2b of the tread 2 are preferably arranged in a regular pattern related to each other. In this case, a regular pattern that is integral with the sidewall 3 and the buttress area is formed. For example, the side traction performance is stabilized and the air resistance reduction effect is also improved. In the present embodiment, the first side block 10 is formed so as to be aligned with the shoulder block 2a in the tire radial direction, and the second side block 20 is formed so as to be aligned with the shoulder block 2b in the tire radial direction.

[0023] The shoulder blocks 2a, 2b are blocks formed in the outer portion in the tire axial direction of the tread 2 and are alternately arranged in the tire circumferential direction. The shoulder blocks 2a, 2b have, for example, similar sizes to each other, but are different in shape in that the side surface 6b of the shoulder block 2b is recessed more than the side surface 6a of the shoulder block 2a. The side surface 6b of the shoulder block 2b has a step formed over the entire length in the tire circumferential direction of the side surface 6b, and the block surface side is recessed more than the side rib 5 side.

[0024] The shoulder blocks 2a, 2b are divided by grooves 2c, 2d extending in the tire axial direction. The groove 2c is formed with substantially the same width from between the blocks to the side rib 5, while the groove 2d widens in the vicinity of the side rib 5. The side surfaces 6a, 6b of the shoulder blocks 2a, 2b and the grooves 2c, 2d form irregularities in the tire circumferential direction in the buttress area of the pneumatic tire 1. Similar to the side blocks 3b, these irregularities improve the side traction performance on muddy ground, sandy ground, or snowy roads.

[0025] The side block 3b is formed in a range that overlaps with the shoulder blocks 2a and 2b and the groove 2c in the tire radial direction, and is not formed in a portion that overlaps with the groove 2d in the tire radial direction. That is, the side blocks 3b are formed at the same pitch as the pair of shoulder blocks 2a and 2b in the tire circumferential direction. The interval between the side blocks 3b is wider on the tire maximum width position P side than on the side rib 5 side. In this case, for example, in muddy ground, the mud discharging property is improved and the side traction performance is enhanced.

[0026] The first side block 10 that constitutes the side block 3b is sandwiched between two second side blocks 20, is continuous with one of the second side blocks 20, and is not connected to the other second side block 20. The first side block 10 is formed in a range that overlaps with the shoulder block 2a in the tire radial direction, and the second side block 20 is formed in a range that overlaps with the shoulder block 2b and the groove 2c in the tire radial direction. The second side block 20 is larger than the first side block 10, and a part of it extends to a position that overlaps with the shoulder block 2a in the tire radial direction.

[0027] As described above, the first side block 10 and the second side block 20 have different heights, and the first side block 10 is formed higher. The height H1 of the side block 3b (see FIG. 4 described later) means the length along the normal direction of the profile surface 3x from the profile surface 3x of the sidewall 3 to the surface of the side block 3b. Due to the height difference between the two blocks that constitute the side block 3b and the height difference between the side block 3b and its gap, irregularities are formed on the sidewall 3, and these irregularities improve the side traction performance on muddy ground, sandy ground, or snowy roads.

[0028] The first side block 10 has substantially the same height, for example, except for the protrusion 30 at the inner end in the tire radial direction and the block end. On the other hand, the second side block 20 has three regions (the first region 21, the second region 22, and the third region 23) with different heights along the tire radial direction. The height of the second side block 20 is substantially constant in the first region 21 adjacent to the side rib 5, and is the lowest at the boundary between the second region 22 and the third region 23. Regarding the protrusion 30, it is formed at the same height in the first side block 10 and the second side block 20.

[0029] The portion of the first side block 10 located on the inner side in the tire radial direction has a shape convex in the X1 direction. This convex portion 11 is formed, for example, in a length range of 30% or more and 70% or less of the tire radial length of the first side block 10 from the inner end in the tire radial direction (the end in the Y2 direction). In other words, the portion of the first side block 10 located on the outer side (the Y1 direction side) closer to the side rib 5 in the tire radial direction has a shape concave in the X2 direction. Such unevenness of the first side block 10 contributes to the improvement of the side traction performance. Note that the X1 direction end of the convex portion 11 is formed in a substantially straight line shape in side view along the tire radial direction.

[0030] The block end of the side block 3b may be formed perpendicular to the profile surface 3a, or may be inclined so that the height of the block gradually decreases. At the end of the convex portion 11 of the first side block 10, a slope 12 with a gentler inclination than other block ends is formed. The slope 12 is located at the block end facing the Y1 direction. By forming a gentle slope 12 at the Y1 direction end of the convex portion 11, an air flow along the surface of the sidewall 3 is likely to occur, and an increase in air resistance can be suppressed. The inclination angle of the slope 12 with respect to the profile surface 3x is, for example, 40° or more and 75° or less.

[0031] The boundary 15 between the two blocks that make up the side block 3b extends along the tire radial direction from the side rib 5 and bends in the X1 direction at the central portion of the block in the tire radial direction. For this reason, the portion located on the Y2-direction side of the first side block 10 gradually decreases in tire circumferential length in the Y2 direction. Since the first side block 10 and the second side block 20 have different heights, a step is formed along the boundary 15.

[0032] As described above, the height of the second side block 20 changes in the tire radial direction. In the portion other than the protrusion 30, the first region 21 adjacent to the side rib 5 is the highest. The second region 22 adjacent to the first region 21 in the Y2 direction slopes so that the height gradually decreases in the Y2 direction, and the third region 23 adjacent to the second region 22 in the Y2 direction slopes so that the height gradually increases in the Y2 direction. By providing a gentle slope on the surface of the second side block 20, an air flow along the surface of the second side block 20 is likely to occur, and an increase in air resistance can be suppressed.

[0033] The end of the second side block 20 facing the X2 direction is inclined with respect to the tire radial direction so that it is gradually positioned in the X1 direction in the Y2 direction. The second side block 20 has a tapered shape in which the tire circumferential length is slightly shorter at the Y2-direction end than at the Y1-direction end.

[0034] Hereinafter, with reference to FIGS. 2 to 5, the protrusion 30 of the sidewall 3 will be described in more detail. FIG. 3 is a view showing a part of the cross section taken along line AA in FIG. 2, and FIG. 4 is a cross-sectional view of the protrusion 30 and its vicinity in FIG. 3. FIG. 5 is a view showing a part of the cross section taken along line BB in FIG. 2.

[0035] As shown in FIGS. 2 to 5, on the sidewall 3, an annular protrusion 30 protruding outward in the tire axial direction is formed within a length range corresponding to 20% of the tire section height H (see FIG. 1) centered on the tire maximum width position P. As a result of the study by the present inventor, it has been found that the air resistance of the tire can be effectively reduced by suppressing the convection and vortices generated in the vicinity of the sidewall 3 and creating an air flow along the surface of the sidewall 3. And by providing the protrusion 30 at or near the tire maximum width position P, it has been successful in realizing a smooth air flow along the surface of the sidewall 3.

[0036] The entire protrusion 30 is formed within a length range corresponding to 20% of the tire section height H from the tire maximum width position P. The annular protrusion 30 continuous in the tire circumferential direction can more effectively suppress the generation of the above-mentioned convection and vortices compared with a discontinuous protrusion, and also improve the protection effect of the sidewall 3. Since the tire rotates at high speed during vehicle running, the radial grooves do not significantly affect the air resistance. As described above, it is considered important to create an air flow along the surface of the sidewall 3 in reducing the air resistance.

[0037] The protrusion 30 is preferably formed on the tread 2 side of the tire maximum width position P. In the present embodiment, the entire protrusion 30 is formed along the Y2-direction end of the side block 3b on the tread 2 side of the tire maximum width position P. In this case, the effect of providing the protrusion 30 becomes more prominent. Also, the tip 33 of the protrusion 30 is preferably located within a length range corresponding to 10% or 5% of the tire section height H in the Y1 direction from the tire maximum width position P. The tip 33 is the portion where the height of the protrusion 30 is the highest.

[0038] The protrusion 30 is formed at the Y2-direction end of the side block 3b or is formed continuously with the Y2-direction end of the side block 3b. Here, it is not necessary to clearly distinguish whether the protrusion 30 is formed at the Y2-direction end of the side block 3b or is formed continuously with the Y2-direction end, but in either case, it is preferable to form the protrusion 30 without leaving a gap with the side block 3b. When the protrusion 30 is formed continuously with the Y2-direction end of the side block 3b, for example, a groove having substantially the same height as the profile surface 3a is formed therebetween. However, in the present embodiment, since such a deep groove is not formed, it can be said that a part of the protrusion 30 is formed at the Y2-direction end of the side block 3b.

[0039] The height H2 of the protrusion 30 is preferably 2 mm or more and 18 mm or less, more preferably 3 mm or more and 17 mm or less, and particularly preferably 5 mm or more and 15 mm or less. In this case, the effect of reducing air resistance becomes more remarkable. If the height H2 of the protrusion 30 becomes too low, it is difficult to suppress the convection and vortices generated in the vicinity of the side wall 3, and the effect of reducing air resistance becomes small. On the other hand, if the height H2 becomes too high, the drag (resistance) may increase. Further, when the side block 3b is formed, it is preferable to control the ratio of the height H2 to the height H1 of the side block 3b within a predetermined range. The height H2 of the protrusion 30 (the same applies to the height H1 of the side block 3b) means the length along the normal direction of the profile surface 3x from the profile surface 3x to the highest part (tip 33) of the protrusion 30.

[0040] The height H2 of the protrusion 30 is 1.1 times or more and 3.0 times or less the height H1 of the highest part of the side block 3b other than the protrusion 30. That is, in the side wall 3, the height from the profile surface 3x is the highest at the tip 33 of the protrusion 30. In the present embodiment, the highest part of the side block 3b other than the protrusion 30 is the surface of the first side block 10.

[0041] The height H2 of the protrusion 30 is more preferably 1.1 times or more and 2.5 times or less, particularly preferably 1.3 times or more and 2.0 times or less, and most preferably 1.4 times or more and 1.9 times or less, or 1.5 times or more and 1.7 times or less of the height H1. An example of the height H1 of the side block 3b is 1 mm or more and 15 mm or less, or 2 mm or more and 10 mm or less. Generally, if the height H1 is too low, the side traction performance and protection performance will decrease. On the other hand, if the height H1 is too high, the drag (resistance) will increase. If the ratio of the height H2 of the protrusion 30 to the height H1 of the side block 3b is within the above range, the effect of reducing air resistance will be more remarkable. If the height H2 of the protrusion 30 is too low, the effect of the protrusion 30 will be small, and if the height H2 is too high, the air resistance may instead increase.

[0042] The protrusion 30 is preferably formed on the circumference of the same circle α along the tire circumferential direction. Further, the protrusion 30 preferably has substantially the same height over the entire length. In this case, the protrusion 30 has a perfect circular shape in the side view of the tire, and the effect of reducing air resistance by the protrusion 30 becomes more remarkable. Also, by making the height H2 of the protrusion 30 constant, a stable effect of reducing air resistance can be obtained. The circle α is a perfect circle centered on the rotation axis of the pneumatic tire 1. As described above, the protrusions 30 are formed on the left and right sidewalls 3 respectively, and the protrusions 30 overlap in the tire axial direction.

[0043] The protrusion 30 includes a first inclined surface 31 formed from the tread 2 side (Y1 direction) to the tip 33 of the protrusion 30, and a second inclined surface 32 formed from the bead 4 side (Y2 direction) to the tip 33 of the protrusion 30. The first inclined surface 31 is preferably gentler in inclination than the second inclined surface 32 and has a smaller inclination angle with respect to the profile surface 3x. In this case, it becomes easier to achieve both good side traction performance and low air resistance. The tip 33 of the protrusion 30 may be sharp as shown in FIG. 4, or may be slightly curved with a chamfered corner.

[0044] In this embodiment, since the height of the portion of the second side block 20 other than the protrusion 30 is lower than the height of the first side block 10, in the second side block 20, the height difference between the protrusion 30 and the other portion is larger compared to the first side block 10. However, since a gentle slope is formed along the tire radial direction on the surface of the second side block 20, an air flow along the block surface is likely to occur. Further, in the portion where the side block 3b does not exist, since the protrusion 30 rises from the profile surface 3a, the height difference becomes larger, but in this portion, the first slope 31 is formed longer in the Y direction than the portion where the side block 3b exists.

[0045] The first slope 31 of the protrusion 30 may be a straight slope without unevenness, or may be a slope gently curved toward the Y2 direction. Also, the inclination angle of the first slope 31 may gradually increase toward the tip 33. In any case, it is preferable that the inclination angles of the slope with respect to the profile surface 3x, both the maximum value and the average value, are such that the first slope 31 < the second slope 32. Note that at the Y2-direction end of the side block 3b, the starting end of the first slope 31 is the position where the height of the side block 3b starts to increase when viewed from the Y1 direction. Note that the second slope 32 is a slope continuous with the slope at the block end, and the boundary position with the slope at the block end may not be clear.

[0046] The first slope 31 of the protrusion 30 is formed from the profile surface 3a in the portion where the side block 3b does not exist. It is preferable that the inclination of the first slope 31 with respect to the profile surface 3x is the same over the entire length of the protrusion 30. For this reason, in the portion where the side block 3b does not exist, the first slope 31 is formed longer and wider in the Y direction compared to the portion where the side block 3b exists. The first slope 31 is preferably smoothly continuous with the profile surface 3a so that no step is formed between the first slope 31 and the profile surface 3a.

[0047] Similar to the first inclined surface 31, the second inclined surface 32 of the protrusion 30 may be a flat inclined surface without irregularities, or may be an inclined surface curved to be convex in the Y1 direction. Further, the inclination angle of the second inclined surface 32 may gradually increase toward the tip 33, and at least a part of the second inclined surface 32 may be formed substantially perpendicular to the profile surface 3x. The second inclined surface 32 of the present embodiment is located at the block end of the side block 3b and is largely curved to be convex in the Y1 direction. Since the inclination of the first inclined surface 31 affects air resistance, it is preferably gentle. However, since the inclination of the second inclined surface 32 is considered to have little effect on air resistance, the traction performance can be improved by making the inclination steep.

[0048] Regarding the pneumatic tire 1 having the above configuration, by simulation using FEM that analyzes the air flow around the rotating tire, the shape of the protrusion, the formation position of the protrusion, the height H1 of the side block 3b, and the height H2 of the protrusion 30 were changed, and the air resistance and traction performance were evaluated by the following method. The evaluation results are shown in Table 1. The evaluation results shown in Table 1 are relative values when the value of the tire without protrusions is set to 100, and the larger the numerical value, the smaller the air resistance.

[0049] [Evaluation of Air Resistance] For each test tire, the drag force (the force acting on the tire placed in the air flow and in the same direction as the flow) was measured, and the drag coefficient Cd was calculated from the following formula. The drag force was obtained from the pressure difference before and after the tire by simulation. Cd = D / (1 / 2ρU2S) In the formula, D is the generated drag force. ρ is the air density, which was set to 1.225 [kg / m 3 . U is the representative speed of the relative speed between the tire and the air, which was set to 27.8 [m / s]. S is the representative area (front projected area) of the tire.

[0050]

Table 1

[0051] Tires No1 to No3 are provided with side blocks 3b and protrusions 30 having the shapes shown in FIGS. 1 to 5. Tire No3 has a non-circular protrusion formed only at the Y2-direction end of the side block 3b. In tires No1 to No3 and No5, the tip of the protrusion is located at a position 5% of the tire cross-sectional height H in the Y1 direction from the tire maximum width position P. In this simulation, even if the position of the tip of the protrusion is changed within a range of 20% of the tire cross-sectional height H centered on the tire maximum width position P, an air resistance index exceeding 100 can be obtained, but when the position of the tip of the protrusion is within 5% in the Y1 direction from the tire maximum width position P, the air resistance index increases. Tire No4 has a circular protrusion on the sidewall, and the tip of the protrusion is located at a position 30% of the tire cross-sectional height H in the Y1 direction from the tire maximum width position P. Also, for tire No5, the value of H2 / H1 is large and is 3.3.

[0052] As shown in Table 1, it is understood that when a circular protrusion 30 exists within a length range corresponding to 20% of the tire cross-sectional height H from the tire maximum width position P, and when H2 / H1 is 1.1 or more and 3.0 or less, air resistance can be effectively reduced. When the protrusion is not formed circularly as in No3, the effect of reducing air resistance can be obtained compared to the case of not having a protrusion, but the effect is small. Also, when the protrusion is formed far from the tire maximum width position P as in No4, and when H2 / H1 exceeds 3.0, the effect of reducing air resistance cannot be obtained.

[0053] As described above, according to the pneumatic tire 1 provided with the circular protrusion 30, air resistance can be effectively reduced. By forming the circular protrusion 30 at or near the tire maximum width position P, an air flow along the surface of the sidewall 3 can be created, thereby greatly reducing air resistance. Also, according to the pneumatic tire 1, even if a large side block 3b is provided, an increase in air resistance can be suppressed.

[0054] According to the pneumatic tire 1, while reducing air resistance, side traction performance and side cut performance equal to or higher than those of the conventional tires can be ensured. The pneumatic tire 1 is particularly suitable for tires for light trucks.

[0055] In addition, the above-described embodiment can be appropriately modified within a range that does not impair the object of the present invention. For example, in the above-described embodiment, the annular protrusion 30 is formed along the Y2-direction end of the side block 3b, but an annular protrusion may be formed at a position away from the side block 3b. Further, even when an annular protrusion is formed on the sidewall without a side block, the effect of reducing air resistance can be obtained due to the effect of the protrusion. However, when the protrusion is formed at the Y2-direction end of the side block or continuously with the Y2-direction end, the effect of reducing air resistance is more remarkable.

[0056] Further, instead of the side block, a recess having a surface recessed more than the profile surface 3a may be formed on the sidewall. In this case, the profile surface 3a becomes a convex portion, and unevenness for exhibiting side traction performance is formed. The shape of the recess in side view may be the same as that of the side block 3b. The annular protrusion may be formed so as to be continuous with the Y2-direction end of the recess.

Explanation of Reference Numerals

[0057] 1 Pneumatic tire, 2 Tread, 2a, 2b Shoulder block, 2c, 2d Groove, 3 Sidewall, 3a, 3x Profile surface, 3b Side block, 4 Bead, 5 Side rib, 6a, 6b Side surface, 10 First side block, 11 Convex portion, 12 Inclined surface, 15 Boundary, 20 Second side block, 21 First region, 22 Second region, 23 Third region, 30 Protrusion, 31 First inclined surface, 32 Second inclined surface, 33 Tip, P Tire maximum width position

Claims

1. A pneumatic tire comprising a tread, a sidewall, and a bead, wherein the sidewall has a side block and a protrusion that protrudes outward in the tire axial direction within a length range corresponding to 20% of the tire cross-sectional height centered on the tire maximum width position and is formed annularly along the tire circumferential direction, the height of the protrusion is 1.1 times or more and 3.0 times or less the height of the portion where the height of the side block is highest other than the protrusion, the pneumatic tire.

2. The pneumatic tire according to claim 1, wherein the height of the protrusion is 2 mm or more and 18 mm or less.

3. The pneumatic tire according to claim 2, wherein the protrusion is formed on the tread side rather than the tire maximum width position.

4. The pneumatic tire according to claim 3, wherein the protrusion is formed at the radially inner end of the side block or is formed continuously with the radially inner end.

5. The protrusion includes a first slope formed from the tread side to the tip of the protrusion and a second slope formed from the bead side to the tip of the protrusion, the pneumatic tire according to any one of claims 1 to 4, wherein the first slope has a smaller inclination angle with respect to the profile surface of the sidewall than the second slope.

6. The pneumatic tire according to any one of claims 1 to 4, wherein the protrusion is formed on the circumference of the same circle α along the tire circumferential direction and has substantially the same height over the entire length.

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