Method to evaluate irregular wear performance of tire tread

Abstract

A method for evaluating irregular wear of a tire is provided that involves providing a cured tire that has a tread. The tread extends 360 degrees about an axis of the tire. The tread has an outer surface. The method also provides for the formation of a depression in the outer surface via laser ablation. The depression has a length that extends in a circumferential direction of the tire, and has a width that is greater than 0.2 millimeters.

Description

DescriptionTitle of Invention: METHOD TO EVALUATE IRREGULAR WEAR PERFORMANCE OF TIRE TREADFIELD OF THE INVENTION

[0001] The subject matter of the present invention relates to a method to evaluate irregular wear on tires to gauge how the tread design and / or the tread materials impact irregular wear. More particularly, the present application involves an evaluation method in which a depression is made into the tread surface in order to accelerate the formation of irregular wear.BACKGROUND OF THE INVENTION

[0002] Manufacturers of heavy commercial vehicle tires have made progress in developing tire architectures and tire materials that causes an increase in the wear resistance of tire treads and the reduction of the rolling resistance of tires while at the same time improving their level of grip and resistance to road hazard. Irregular tread wear is a great concern for heavy commercial vehicle tires as it can progressively induce tire vibrations that become sensed by the driver through the steering wheel. It can also make for a poor looking wear pattern. Both of these undesired effects often lead to the tire being removed from service at an early stage of its wear life. Generally, the more the tire is put through a slow-wearing usage, the more irregular wear is affecting the removal mileage. This is why resistance to irregular wear is important for truck tires in the so-called long haul steer usage.

[0003] It is known to include structural features in tires to fight irregular wear. For example, a sacrificial rib can be incorporated into the tread architecture to delay the onset of irregular wear. Additionally or alternatively, the tread could include materials that resist the formation of irregular wear. In order to know how a newly designed tire resists irregular wear, the newly designed tire can be placed into a field study. This involves putting the as built tire onto a vehicle and observing the natural onset of irregular wear. Such a study requires a large number of tires be placed into the field in order to get a statistically valid and representative result. Over 100 tires of a particular design may need to be placed into the study. The as built tires that are placed into the study may be compared to a reference design that is placed into the field at the same time for determining their irregular wear performance. Field studies can take a significant amount of time, such as on the order of one to two years, to observe the irregular wear of the as built tires.

[0004] The length of time these field studies take increases the amount of time it takes for a tire to enter the marketplace. Consumers are required to wait a longer amount of timefor a product that performs better in irregular wear. The large amount of tires necessary for such studies also increases the cost, time, and complexity of executing the study, thus leading to higher consumer cost and wait times for tires with the desired irregular wear performance. As such, there remains room for variation and improvement within the art.BRIEF DESCRIPTION OF THE DRAWINGS

[0005] A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:[Fig 1]

[0006] [Fig.1] is a perspective view of a heavy truck tire that has irregular wear.[Fig 2]

[0007] [Fig.2] is a front view of a portion of a tire in which masking is applied to create a target zone.[Fig 3]

[0008] [Fig.3] is a front view of a portion of a tire with a depression formed in the outer surface.[Fig 4]

[0009] [Fig.4] is a cross-sectional view taken along line 4-4 of [Fig.3].[Fig 5]

[0010] [Fig.5] is front view of a portion of the tire of [Fig.3] that has been run so that irregular wear has formed at the depression.[Fig 6]

[0011] [Fig.6] is a cross-sectional view taken along line 6-6 of [Fig.5].[Fig 7]

[0012] [Fig.7] is a side view of a tire that illustrates the average distance compared to the roundness of the tire to identify high spots and low spots.[Fig 8]

[0013] [Fig.8] is a cross-sectional view of a depression in accordance with another embodiment taken from a shoulder groove in which the depression has tapered ends

[0014] The use of identical or similar reference numerals in different figures denotes identical or similar features.DETAILED DESCRIPTION OF THE INVENTION

[0015] Reference will now be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, and not meant as a limitation of the invention. For example, features illustrated or described as part of one embodiment can be used withanother embodiment to yield still a third embodiment. It is intended that the present invention include these and other modifications and variations.

[0016] The present invention provides for a method for preparing a tire 10 so that it more easily experiences irregular wear 64 so that field studies that examine the tire 10 can be conducted in a faster amount of time, and potentially with less cost as fewer tires 10 may need to be employed. The method involves taking a cured tire 10 that has a tread 12 with an outer surface 16 and creating a depression 18 in the outer surface 16. This depression 18 is formed through the use of laser ablation. The length 26 of the depression 18 extends in the circumferential direction 20 of the tire, and the depression 18 has a width 28 that is greater than 0.2 millimeters. The depression 18 forms a feature on the tire 10 that accelerates the formation of irregular wear 64 so that irregular wear 64 forms at this depression 18, and the irregular wear 64 forms on the tire 10 at a rate much faster than if the depression 18 were not present. This being the case, if the tire 10 were used in a field study, irregular wear 64 would occur at a much faster rate than would be the case if the tire 10 did not have the depression 18. Since irregular wear 64 occurs faster, the field study to evaluate irregular wear in the tire 10 could be completed faster and potentially less tires 10 could be needed in the field study. This method may improve the speed at which products are introduced into the marketplace and may decrease the cost of performing field studies. Also, the field study quality may be improved because the depressions 18 could be consistently formed from one tire 10 to the next in the study, thus allowing for the irregular wear 64 to be observed and compared between tires 10.

[0017] [Fig.l] shows a tire 10 that is a heavy duty truck tire 10. In this regard, the tire 10 is not designed for nor used with a car, motorcycle, or light truck (payload capacity less than 4,000 pounds), but is instead designed for and used with heavy duty trucks such as 18 wheelers, garbage trucks, or box trucks. The tire 10 may be a steer tire, a drive tire, a trailer tire, or an all position tire. The tire 10 can be a free rolling tire on a truck, such as a “pusher” or “tag” axle that is successive of the steer tires on a truck but are free rolling. The tire 10 is not limited to any particular position on the truck or trailer. The central axis 14 of the tire 10 extends through the center of the carcass, and the lateral direction 22, which can be called the axial direction 22, of the tire 10 is parallel to the axis 14. The thickness direction 24 of the tire 10 can be referred to as the radial direction 24 and is perpendicular to the axis 14. The tread 12 is located farther from the axis 14 in the thickness direction 24 than the carcass of the tire 10. The tread 12 extends all the way around the carcass in the circumferential direction 20 of the tire 10 and circles the axis 14 three hundred and sixty degrees. The circumferential direction 20 can also be referred to as the longitudinal direction 20 of the tread 12.

[0018] The tread 12 in [Fig.l] features five ribs that are separated by four circumferential grooves that extend in the circumferential direction 20 completely about the tire 10. The five ribs include a center rib between two intermediate ribs with partially hidden grooves between the center rib and the two intermediate ribs. Circumferential rib 62 is located on one lateral end and is a shoulder rib 62 of the tread 12 which extends completely 360 degrees around the axis 14. On the opposite side, a circumferential rib 46 likewise extends completely 360 degrees around the axis 14 and is the opposite shoulder rib 46 of the tread 12. A shoulder groove 66 separates the shoulder rib 46 from the intermediate rib, and shoulder groove 68 separates the shoulder rib 62 from its adjacent intermediate rib, and both of these grooves 66, 68 extend completely around the tread 12. Although five ribs are shown, any number of ribs can be present in other exemplary embodiments. The ribs can each be made up of a number of tread blocks that can have various shapes, sizes, and configurations. The inclusion of these architectural features gives the tread different performance properties in use. As shown, the center rib and intermediate ribs includes sipes that extend completely across their lateral lengths, but the two shoulder ribs 46, 62 are featureless and do not include sipes or other architectural elements. However, the shoulder ribs 46, 62 could include sipes in other embodiments. Sipes are grooves in the tread 12 that are 2 millimeters or less in width. The tire 10 can be a brand new tire with the carcass and tread 12 formed at the same time with both being brand new. Alternatively, the tread 12 may be provided as a retread band that is newly formed and then subsequently attached to an existing, used carcass through a retread process.

[0019] As the tire 10 is used on the roadway, it may experience irregular wear 64 which is wear into the outer surface 16 of the tread 12 that is not even across the entire outer surface 16. Irregular wear 64 is a localized wear of the outer surface 16 in one spot of the tread 12 that can be visually distinguished from the outer surface 16 around it which does not have such wearing. The irregular wear 64 extends some amount in the thickness direction 24 so that the irregular wear 64 forms a cavity in the outer surface 16. The top of the outer surface 16 is farther in the thickness direction 24 from the axis 14 than is the irregular wear 64 to the axis 14. [Fig.l] shows the tread 12 having five spots of irregular wear 64. Irregular wear 64 is present in the shoulder rib 46 at the rib edge 48 of the shoulder rib 46 which is located adjacent the shoulder groove 66. The irregular wear 64 extends outboard in the lateral direction 22 from the rib edge 48 across some amount of, but not all of, the outer surface 16 of the shoulder rib 46. The irregular wear 64 is separated in the circumferential direction 20 so that three distinct spots of irregular wear 64 are present. On the opposite shoulder rib 62, two spots of irregular wear 64 are present and likewise extend from the rib edge adjacent the shoulder groove 68 outboard across some but not all of the outer surface 16 of theshoulder rib 62. It is to be understood that the irregular wear 64 as shown is only one example, and the irregular wear 64 could form in many different amounts, locations, and degrees. For example, the irregular wear 64 could extend completely across the entire circumferential ribs 46, 62 instead of just across portions thereof. Also, the irregular wear 64 could extend completely 360 degrees around the axis 14 instead of just extending around a portion of the axis 14. The irregular wear 64 could be located in only one of the ribs instead of two, or the irregular wear 64 could be located in the center rib or intermediate ribs in addition to, or alternatively to, being located in the shoulder ribs 46, 62. When the tread 12 has irregular wear 64, the tire 10 may be removed early from service with large amounts of tread 12 left because the owner may view the irregular wear 64 as unsightly, or the irregular wear 64 may cause unwanted vibration in the tire 10 that detracts from the driving experience.

[0020] The irregular wear 64 may take a long time to develop on the tire 10, so if irregular wear 64 formation is to be avoided it should be studied. Shortening the time irregular wear 64 occurs will allow for such studying to be completed faster. [Fig.2] shows a method of forming irregular wear 64 faster in the tire 10. The tread 12 of [Fig.2] is the same as that shown in [Fig.l] but is a new tire 10 without any irregular wear 64 on the outer surface 16. Masking 40 is placed onto the outer surface 16 of the shoulder rib 46 so that a target zone 42 is defined by the masking 40 and the shoulder groove 66. The target zone 42 is sized so that it engages the rib edge 48 and does not extend completely across the entire shoulder rib 46 in the lateral direction 22. The tread 12 along with the rest of the tire 10 is cured. The method may be executed on a round tire 10 with the tread 12 thereon, or may be executed on a tread 12 band first which is then attached to the rest of the components of the tire 10.

[0021] The method involves making a depression 18 in the outer surface 16. The depression18 is formed via laser ablation. The laser ablation may be done though the use of a hand held laser ablation device, or may be made via a laser ablation machine in an automated process. The provision of a target zone 42 may assist the operator in directing the laser ablation device to the desired area on the outer surface 16, and the masking 40 prevents area of the outer surface 16 proximate to the target zone 42 from being inadvertently removed via the laser ablation process. The operator directs the laser ablation to the target zone 42 to remove a portion of the outer surface 16 to form a depression 18 as shown in [Fig.3]. The use of laser ablation allows for the formation of depressions 18 that have a consistent depth 44, shape, and positioning on the tire 10. The depression 18 opens into the rib edge 48 and has a width 28 that is greater than 0.2 millimeters. The depression 18 does not extend across the entire shoulder rib 46 but is blind, ending at a location spaced in the lateral direction 22 from the tread edge at the shoulder rib 46. The depression 18 has a length 26 that extends in the circumferentialdirection 20 along some, but not all of, the circumferential length of the shoulder rib 46. The length 26 thus extends less than 360 degrees about the axis 14.

[0022] The masking 40 is made of a material such as steel or aluminum that resists being cut when hit with the laser ablation. The masking 40 thus protects portions of the outer surface 16 from being cut when the laser ablation is applied. However, it is to be understood that the masking 40 is not present in other embodiments. In such embodiments, the depression 18 is cut using laser ablation without the use of the masking 40.

[0023] The depression 18 has a shape that features first and second lateral ends 56, 58 that extend linearly in the circumferential direction 20 and are parallel to one another. The lateral ends 56, 58 do not extend in the lateral direction 22, but in the circumferential direction 20. The depression 18 has a first circumferential end 52 that is curved and extends from the first lateral end 56 to the second lateral end 58. The first circumferential end 52 is concave in shape, and is completely concave from end 56 to end 58. The first circumferential end 52 does not have any portion that is not linear in shape. Oppositely disposed from the first circumferential end 52 is a second circumferential end 54 of the depression 18. The second circumferential end 54 is also curved, and is completely concave in shape from the first lateral end 56 to the second lateral end 58. The width 28 is constant along a majority of the length 26, and is measured as the distance from the first lateral end 56 to the second lateral end 58. In this embodiment, the width 28 is the distance in the lateral direction 22 the depression 18 extends. The width 28 in some embodiments may be the maximum length the depression 18 extends in the lateral direction 22, or may be simply the width from one end of the depression 18 to the other in the minor length of the depression 18, such as when the length 26 is the major length of the depression.

[0024] The circumferential rib 46 has a width 50 that is the maximum length the circumferential rib 46 extends in the lateral direction 22. The width 28 can be the maximum amount of extension of the depression 18 in the lateral direction 22. The width 28 may have an extension that is 25% or less than that of the width 50. Alternatively, the width 28 may have an extension that is 50% or less than that of the width 50. Other arrangements of the depression 18 are possible in which the width 28 is the same as the width 50. Still further, the width 28 may be from 25% to 33% of the width 50. The width 28 may be from 8 millimeters to 10 millimeters in some embodiments.

[0025] The depression 18 is formed via laser ablation to a depth 44 as shown in [Fig.4] which is a cross-sectional view taken along line 4-4 of [Fig.3]. The depth 44 is consistent along the entire length 26 of the depression 18, and the depression 18 does not taper at any point near the ends 52, 54, 58. However, with reference now to [Fig.8],another embodiment of the depression 18 is shown similar to that just discussed but with a gradual transition where the depression 18 transitions to the outer surface 16. There may be a taper at all of the ends 52, 54, 58. The taper can be a smooth taper in which the material making up the outer surface 16 extends evenly upward from the bottom of the depression 18 to the outer surface 16 outside of the depression 18. The ends 52, 54 taper in that they angle at an amount less than 90 degrees upwards from the bottom of the depression 18 to the outer surface 16. Other embodiments exist in which the taper instead of being a smooth taper is a stepped taper in that the material making up the outer surface 16 is stepped from the bottom of the depression 18 to the outer surface 16 outside of the depression 18. The depth 44 is again shown as being consistent in maximum depth, but the depth 44 could be varied along the length 26 in other designs of the depression 18.

[0026] The depth 44 may be the maximum depth of the depression 18. The depth 44 may be from 0.5 millimeters - 3.0 millimeters, from 1.0 millimeters - 2.0 millimeters, from 0.5 millimeters - 1.0 millimeters, from 1.0 millimeters - 1.5 millimeters, from 1.5 millimeters - 2.0 millimeters, from 2.0 millimeters - 2.5 millimeters, from 2.5 millimeters - 3.0 millimeters, from 0.5 millimeters - 1.5 millimeters, from 0.5 millimeters - 2.0 millimeters, from 0.5 millimeters - 2.5 millimeters, from 1.0 millimeters - 2.5 millimeters, from 1.0 millimeters - 3.0 millimeters, from 1.5 millimeters - 2.5 millimeters, or from 1.5 millimeters - 3.0 millimeters. The previously disclosed ranges include the ends of the ranges.

[0027] Once the depression 18 is formed in the outer surface 16, the tire 10 may be placed into a field study to determine how irregular wear 64 forms on the tire 10 so that this irregular wear 64 can be studied to in turn determine how portions of the tire 10 such as the material and / or tread 12 design effects irregular wear 64 formation. The presence of the depression 18 causes the irregular wear 64 to form faster than it otherwise would if the depression 18 were not present. [Fig.5] shows the formation of irregular wear 64 at the depression 18. The irregular wear 64 is formed in the shoulder rib 46 and is a cavity in the outer surface 16 that engages the depression 18. The irregular wear 64 extends in the lateral direction 22 to a location more outboard than that of the second lateral end 58. The irregular wear 64 extends from the second circumferential end 54 and wears off this second circumferential end 54 such that it is not present in [Fig.5]. With reference to the cross-sectional view of [Fig.6], the irregular wear 64 extends some amount in the circumferential direction 20 and has a depth in the thickness direction 24 that varies along its length in the circumferential direction 20. Generally, the depth of the irregular wear 64 is not as great as that of the depression 18, although it does obtain a depth the same as depth 44 at the location where it engages the depression 18.

[0028] In order to further accelerate the formation of irregular wear 64 on the tread 12, the depression 18 could be strategically placed on the tire 10 at a location that is more prone to irregular wear 64. For example, it is the case that a low spot 32 on the tire 10 is more likely to develop irregular wear 64 than other areas of the tire 10 so the depression 18 could be formed in this location. A side view of a tire 10 is shown in [Fig.7] to illustrate tire non-uniformity. Due to variations in the tire manufacturing process such as thickness extrusion variability, heavy or thin product joints, superposition of product joints, and variations in the material properties around the circumference of the tire 10, the tire 10 may be made so that is not perfectly round. This imperfection in the roundness of the tire 10 will create one or more low spots 32 and one or more high spots 34. In order to evaluate the tire 10, an average distance circle 60 can be calculated. This average distance circle 60 is a perfect circle and is located at an average distance 30 from the axis 14 to the average distance circle 60.

[0029] The average distance circle 60 represents the average distance 30 of the outer surface 16 to the axis 14 and can be calculated in a variety of manners. For example, the tire 10 could be inflated to its normal operating pressure, or if it has a range of normal operating pressures then to a pressure in the middle of this range. The tire 10 can be at a temperature of 75 degrees Fahrenheit. The midpoint in the lateral direction 22 of the outer surface 16 can be evaluated. Measurements of this midpoint can be taken at increments about the axis 14 of the tire 10, for example every 3 or 5 degrees a measurement can be made. These measurements determine the distance of the outer surface 16 at these points to the axis 14. Once all of the measurements are ascertained, they can be averaged to arrive at an average distance 30 to then ascertain the size of the average distance circle 60. However, other methods of measuring the roundness of the tire 10 are possible. For example, the tire 10 can be rotated in a measurement machine so that the outer surface 16 is scanned to determine the average distance 30. Any method of measuring the tire 10 can be used to determine the average distance 30, and it is to be understood that such measurement methods are not limited to measuring the tire 10 at its midpoint in the lateral direction 22, and are not limited to a particular pressure or temperature of the tire 10.

[0030] With reference to [Fig.7], the average distance circle 60 and its average distance 30 are illustrated along with the tire 10 that has a non-uniform roundness. Portions of the outer surface 16 are identified as being low spots 32 and high spots 34. One of the low spots 32 has a distance 38 that is from the outer surface 16 at the low spot 32 to the axis 14. The distance 38 is less than the average distance 30. One of the high spots 34 has a distance 36 that is from the outer surface 16 at the high spot 34 to the axis 14. The distance 36 is greater than the average distance 30. The outer surface 16 can be evaluated in this manner to classify almost all of the outer surface 16 as being a lowspot 32 or a high spot 34, as some portions of the outer surface 16 may be right at the average distance 30 and on the average distance circle 60 and thus neither a low spot 32 or a high spot 34.

[0031] It may be the case that tires 10 first experience irregular wear 64 at a low spot 32 since these areas are more sensitive to developing irregular wear 64. The method may therefore seek to place the depression 18 at the low spot 32 of the tire 10 so that irregular wear 64 can be generated on the tire 10 as fast as possible. In some embodiments, the depression 18 is formed in a single low spot 32 of the tire 10 and does not extend in the circumferential direction 20 outside of this single low spot 32. In other embodiments, multiple depressions 18 are formed in a single or multiple low spots 32. In yet other embodiments, depressions 18 are present in one or more low spots 32, but none of the high spots 34 or high spot 34 includes any depression 18 or portion of depression 18. As such, in these embodiments, any depression 18 present is not located in any portion of the outer surface 16 that is radially beyond the average distance circle 60. In still yet other embodiments, the lowest low spot 32 on the tire 10 is discovered, and the depression 18 is placed in it. With such a placement, it is not necessary to even ascertain an average distance circle 60 as the method need only determine the lowest low spot 32 regardless of having knowledge of the average distance 30. Surface imaging of the outer surface 16 can be made to find the low spots 32 for depression 18 placement.

[0032] The area or areas selected for placement of the depressions 18 can be made based upon design experience in anticipating which zones of the tire 10 are most sensitive for irregular wear 64. Shoulder ribs 46, 62 can be selected as they are known to experience irregular wear 64, and the low spots 32 could be used for placement of the depressions 18 as they are likewise known to experience irregular wear 64.

[0033] The depression 18 can be variously configured in other embodiments, and it is to be understood that the shape, size and positioning illustrated in the figures is only exemplary. The depression 18 need not engage the rib edge 48 in other embodiments but can be spaced from and free from engagement with the rib edge 48. Likewise, if the depression 18 is located in a shoulder rib 46, it may engage the tread edge which is the edge of the shoulder rib 46 that is most outboard. In yet other arrangements, the depression 18 can be spaced from and free from contact with both the tread edge and the rib edge 48 when placed into a shoulder rib 46. In yet other arrangements, the shoulder ribs 46, 62 do not include depressions 18, and the depressions 18 are present in the center rib or intermediate ribs. The depression 18 can extend completely around the tire 10 in the circumferential direction 20 so that the length 26 extends 360 degrees around the axis 14. Alternatively, the length 26 may extend for less than 120 degrees around the axis 14. In these instances, the length 26 may be from 20.0 millimeters to50.0 millimeters in length in the circumferential direction 20. In other embodiments, the length 26 may be 100 millimeters or less.

[0034] While the present subject matter has been described in detail with respect to specific embodiments and methods thereof, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing may readily produce alterations to, variations of, and equivalents to such embodiments. Accordingly, the scope of the present disclosure is by way of example rather than by way of limitation, and the subject disclosure does not preclude inclusion of such modifications, variations and / or additions to the present subject matter as would be apparent.

Claims

Claims

1. A method, comprising: providing a cured tire that has a tread with a tread pattern thereon, wherein the tread extends 360 degrees about an axis of the tire, wherein the tread has an outer surface; and forming through laser ablation a depression in the outer surface that has a length that extends in a circumferential direction of the tire, wherein the depression has a width that is greater than 0.2 millimeters, and wherein the depression is not a sipe.

2. The method as set forth in claim 1, further comprising operating the tire on a road until irregular wear progression occurs at the depression.

3. The method as set forth in claim 1 or 2, further comprising identifying a low spot in a roundness of the tire, wherein the depression is formed in the low spot after the identification of the low spot.

4. The method as set forth in any one of claims 1 to 3, further comprising identifying high spots of the tire that are portions of the outer surface that have a distance to the axis greater than an average distance of the outer surface to the axis, wherein the depression is not located in the high spots, and wherein no laser ablation is applied in the high spots.

5. The method as set forth in any one of claims 1 to 4, wherein the tread is a retread band that is applied to a carcass to form the tire, wherein the depression is formed in the tread before the tread is applied to the carcass.

6. The method as set forth in any one of claims 1 to 5, further comprising masking a portion of the outer surface to define a target zone on the outer surface, wherein the depression is formed in the target zone.

7. The method as set forth in any one of claims 1 to 6, wherein the width of the depression is the distance the depression extends in a lateral direction of the tire, wherein the length of the depression extends for a greater distance than does the width of the depression.

8. The method as set forth in any one of claims 1 to 7, wherein the length of the depression extends for an amount that is less than 120 degrees about the axis of the tire.

9. The method as set forth in claim 8, wherein the length of the depression is greater than or equal to 20.0 millimeters and is less than or equal to 50.0 millimeters.

10. The method as set forth in any one of claims 1 to 9, wherein the depression has a depth in a thickness direction of the tire, wherein the depth is greater than 0.5 millimeters and is less than or equal to 3.0 millimeters.

11. The method as set forth in claim 10, wherein the depth is greater than or equal to 1.0 millimeters and is less than or equal to 2.0 millimeters.

12. The method as set forth in any one of claims 1 to 11, wherein the tread has a circumferential rib that extends 360 degrees about the axis of the tire, wherein the circumferential rib has a rib edge, wherein the depression is located in the circumferential rib and engages the rib edge.

13. The method as set forth in claim 12, wherein the circumferential rib has a rib width that extends in a lateral direction of the tire, wherein the depression extends in the lateral direction across 25% or less of the rib width.

14. The method as set forth in claim 12, wherein the circumferential rib has a rib width that extends in a lateral direction of the tire, wherein the depression extends in the lateral direction across 50% or less of the rib width.

15. The method as set forth in any one of claims 1 to 14, wherein the depression has a first circumferential end and an oppositely disposed second circumferential end in the circumferential direction, wherein the first and second circumferential ends are concave in shape, wherein the depression has a first lateral end and an oppositely disposed second lateral end in the lateral direction, wherein the first and second lateral ends are linear in shape.

16. The method as set forth in any one of claims 1 to 15, wherein the width of the depression is a maximum distance the depression extends in a lateral direction of the tire.

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