Abstract:
Articles of footwear may include self-adjusting studs that adjust to various types of conditions, environmental changes, and applied forces. The self-adjusting studs may have a first portion and a second portion of different levels of compressibilities and/or retractabilities that compress and extend based on the type of surface on which the wearer is walking or running. This footwear with self-adjusting studs may easily transition between surfaces of varying hardness without causing damage to the surface, but also providing the wearer with the necessary amount of traction on each type of surface. Wearers will enjoy the benefit of being able to move on various surfaces without the need to change their footwear multiple times to accommodate the wearer&#39;s varying traction needs on different surfaces.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a divisional of U.S. patent application Ser. No. 12/708,411, filed Feb. 18, 2010, and titled “Self-Adjusting Studs.” Application Ser. No. 12/708,411, in its entirety, is incorporated by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    Aspects of the invention relate generally to fraction elements for articles of manufacture and articles of wear. In some more specific examples, aspects of the invention relate to self-adjusting traction elements for articles of footwear. 
       BACKGROUND 
       [0003]    Many articles of wear benefit from traction elements. Such articles of wear come into contact with a surface or another item and benefit from the increased friction and stability provided by traction elements. Traction elements typically form a portion of the ground-contact surface of the article of wear. Many traction elements form protrusions that extend away from the surface of the article of wear toward the ground or other surface that contacts the article of wear. Some traction elements are shaped or configured to pierce the ground or surface when the article of wear comes into contact with the ground or surface. Other traction elements are shaped or have characteristics that engage with the ground in a way that increases the friction between the article of wear and the surface that it contacts. Such traction elements increase lateral stability between the fraction element and the ground or surface and reduce the risk that the article of wear will slide or slip when it contacts the ground or surface. 
         [0004]    Many people wear footwear, apparel, and athletic and protective gear and expect these articles of wear to provide traction and stability during use. For example, articles of footwear may include traction elements that are attached to a sole structure that forms the ground-contact surface of the article of footwear. The traction elements provide gripping characteristics that help create supportive and secure contact between the wearer&#39;s foot and the ground. These traction elements typically increase the surface area of the ground-contact surface of the footwear and often form protrusions that are usually shaped or configured to pierce the ground and/or create friction between the ground-contact surface of the footwear and the ground or surface that it contacts. 
         [0005]    These traction elements usually are solid protrusions that are static with respect to the article of footwear. This means that the traction elements and the footwear move as a single unit, i.e., the traction elements remain stationary with respect to the footwear. The traction elements progress through the bending and flexing motions of the step or run cycle in the same way as the rest of the sole structure of the footwear. This configuration limits traction capabilities because it cannot adapt to the various forces being applied to the article of wear or the changing environments in which the article of footwear is being used. 
         [0006]    Athletes engaged in certain sports such as soccer, baseball, and football often utilize footwear having traction elements. These athletes perform various movements that have sudden starts, stops, twisting, and turning. Additionally, most athletes wish to wear their articles of footwear in various environments with surfaces having different conditions and characteristics. On many occasions, the static traction elements are unable to provide adequate support and traction that the athlete needs to perform the various movements. The static traction elements simply cannot adapt to the changing movements of these athletes or the various environments in which the athletes wear the articles of footwear. Rather, the static traction elements provide the same type and amount of traction during all movements and in all environments, regardless of the type of movement being performed by the athlete or the characteristics of the environment in which the articles of footwear are being worn. 
         [0007]    Additionally, various surfaces on which the athlete wishes to wear their articles of footwear have many different characteristics including different hardnesses and contours. For example, an athlete may utilize studded footwear on a playing field made of grass or a synthetic material similar in nature to grass. Many of these playing fields are outdoors and the conditions of the fields are subject to weather conditions, varying degrees of maintenance performed on the surfaces, regional (geographical) surface differences, and the like. For example, athletes that usually practice on a grass field that is rather soft may find that their cleated footwear functions differently on a grass field that is hard, such as when the athlete plays a game at another location or the weather causes the field conditions to harden the surface. By wearing the same cleats on all surfaces, wearers are at greater risk of falling, sliding, and/or otherwise injuring themselves, at least under such circumstances in which the static traction elements provided on the article of footwear are not well-designed for use under the field conditions. The alternative is to purchase several different pairs of cleated footwear with varying types of traction to accommodate several different surfaces. However, this method is expensive and inconvenient. 
         [0008]    Therefore, while some traction elements are currently available, there is room for improvement in this art. For example, articles of wear having traction elements that may be self-adjusting to provide a user with traction that automatically adjusts based on the type of surface with which the article of wear is in contact and the types of forces applied to the traction elements would be a desirable advancement in the art. 
       SUMMARY 
       [0009]    The following presents a general summary of aspects of the invention in order to provide a basic understanding of at least some of its aspects. This summary is not an extensive overview of the invention. It is not intended to identify key or critical elements of the invention and/or to delineate the scope of the invention. The following summary merely presents some concepts of the invention in a general form as a prelude to the more detailed description provided below. 
         [0010]    Aspects of this invention relate to self-adjusting traction elements for articles of wear, such as footwear. In an example footwear embodiment, the article of footwear may incorporate a sole structure having one or more self-adjusting traction elements or “self-adjusting studs.” 
         [0011]    In one example, a self-adjusting stud may comprise a first portion having a first compressibility and a second portion having a second compressibility that is greater than the first compressibility. The second portion may surround the first portion. The first portion and the second portion may be substantially uncompressed when the self-adjusting stud comes into contact with a surface of a first hardness. The first portion may be substantially uncompressed and the second portion may be compressed when the self-adjusting stud comes into contact with a surface of a second hardness, wherein the first hardness is less than the second hardness. 
         [0012]    In another example, a self-adjusting stud may comprise a stud body having a hole extending therethrough and a pin extending through the hole in the stud body. At least a portion of the stud body and a tip of the pin form a ground-contact surface of the self-adjusting stud. The stud body may be in a first, extended position when the self-adjusting stud contacts a surface having a first hardness and the stud body may be in a second, retracted position when the self-adjusting stud contacts a surface having a second hardness that is greater than the first hardness. 
         [0013]    In yet another example, a sole structure may comprise a sole base member and at least one self-adjusting stud attached thereto. The self-adjusting stud may be any of the example embodiments described above. In some examples, the sole structure includes more than one self-adjusting stud, either of the same embodiment or of different embodiments of the self-adjusting stud. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    A more complete understanding of the present invention and certain advantages thereof may be acquired by referring to the following description along with the accompanying drawings, in which like reference numbers indicate like features, and wherein: 
           [0015]      FIG. 1  illustrates a bottom perspective view of the forefoot region of an article of footwear having self-adjusting studs in accordance with aspects of the invention. 
           [0016]      FIG. 2  illustrates a bottom plan view of the sole structure of an article of footwear having self-adjusting studs in accordance with aspects of the invention. 
           [0017]      FIGS. 3A and 3B  illustrate side views of the forefoot region of an article of footwear having self-adjusting studs in an uncompressed/unretracted position and in a compressed/retracted position, respectively, according to aspects of the invention. 
           [0018]      FIGS. 4A and 4B  illustrate side views of a self-adjusting stud with a compressible foam material in an uncompressed/unretracted position and in a compressed/retracted position, respectively, according to aspects of the invention. 
           [0019]      FIGS. 5A and 5B  illustrate side views of a self-adjusting stud with a spring in an uncompressed/unretracted position and in a compressed/retracted position, respectively, according to aspects of the invention. 
           [0020]      FIG. 6  illustrates a side view of a self-adjusting stud in which one portion/end is compressed more than another portion/end of the stud in accordance with aspects of the invention. 
           [0021]      FIG. 7  illustrates a self-adjusting stud having two pins according to aspects of the invention. 
       
    
    
       [0022]    The reader is advised that the attached drawings are not necessarily drawn to scale. 
       DETAILED DESCRIPTION 
       [0023]    In the following description of various example embodiments of the invention, reference is made to the accompanying drawings, which form a part hereof, and in which are shown by way of illustration various example devices, systems, and environments in which aspects of the invention may be practiced. It is to be understood that other specific arrangements of parts, example devices, systems, and environments may be utilized and structural and functional modifications may be made without departing from the scope of the present invention. 
         [0024]    The articles of footwear disclosed herein include one or more self-adjusting studs that change their fraction characteristics based on the type of surface with which the self-adjusting stud contacts, and/or the type of force that is applied to the self-adjusting stud thereby providing greater overall versatility and stability of the studded footwear and decreasing the chances that the wearers will get injured by unexpected or unfamiliar field conditions. 
       A. Definitions Section 
       [0025]    To assist and clarify the subsequent description of various embodiments, various terms are defined herein. Unless otherwise indicated, the following definitions apply throughout this specification (including the claims). 
         [0026]    The term “compressibility,” as used herein, means the ability of the first portion and/or the second portion to condense, become more compact, or otherwise become reduced in size. The term “compressibility,” as used herein, is used to describe the ability of a portion of a self-adjusting stud to become reduced in size in any way (height, width, thickness, volume, or any other reduction in size). A particular portion of the self-adjusting stud may be described as having a particular level of “compressibility,” which means that it has been constructed with an ability to compress with respect to another portion of the self-adjusting stud. 
         [0027]    For example, a first portion and a second portion of a self-adjusting stud may be assigned different “compressibilities” as they relate to each other. The first portion may compress more or less (depending on the embodiment) than the second portion with respect to a surface having a defined hardness (such as a hard surface like a gymnasium, artificial turf, or a frozen or near-frozen playing field). Atomically speaking, any force applied to a solid object will “compress” the atoms in the object to some degree (even objects made of the hardest materials available). However, the term “compressibility,” as used herein, is meant to refer to a measurable difference in the amount of compression that occurs in a particular portion of the self-adjusting stud. 
         [0028]    The terms “substantially uncompressed” and “compressed,” as used herein, are meant to describe levels of compression of various portions of the self-adjusting studs. As discussed above, atomically speaking, any force applied to an object made of even the hardest of materials will “compress” the object to some degree. The term “substantially uncompressed,” is intended to include those levels of compression in which none or only a very small amount of compression occurs (e.g., when the atoms move only slightly closer together). For example, a hard metal, such as titanium, may be used to form a portion of the self-adjusting stud. This titanium metal portion would typically be able to withstand most forces in a “substantially uncompressed” form because it does not substantially compress or become reduced in size when such forces are applied to it. 
         [0029]    Use of the term “substantially uncompressed” is meant to include the levels of compressibility in which mere atoms move, but no noticeable change in traction capabilities occurs, such as in the titanium example previously described. The term “compressed,” as used herein, is used to describe a noticeable or detectable difference in the volume or size of any portion of the self-adjusting stud from the perspective of an athlete or user or a size or volume difference that is measurable by generally available measurement tools, such as a ruler or detectable by the human eye. The difference will often, although not always, result in a size or volume change such that the traction characteristics of the self-adjusting stud will exhibit a noticeable change from the perspective of the athlete/wearer. In some example structures, the self-adjusting stud may compress up to 5-50% of its uncompressed size/shape. For example, if the compression occurs in the vertical direction, the height of the self-adjusting stud may be 25% less when it is compressed than when it is substantially uncompressed. 
         [0030]    The term “hardness,” as used herein is used to describe the type of surface that comes into contact with the self-adjusting stud. For example, a soft surface would have a lower hardness level than a hard surface. The soft surface may include a grass playing field or a field with flexible ground. The hard surface may include an artificial playing field or a playing field with firm ground. As described in greater detail below, the self-adjusting studs may be activated (compressed/retracted) on either hard or soft surfaces, depending on the embodiment. 
       B. General Description of Articles of Footwear with Self-Adjusting Studs 
       [0031]    The following description and accompanying figures disclose various articles of footwear that have self-adjusting studs. The self-adjusting studs may be incorporated into any article of manufacture or article of wear that would benefit from self-adjusting studs, such as, but not limited to, footwear, sporting equipment, protective gear, mats, and the like. 
         [0032]    Sole structures of articles of footwear may have self-adjusting studs. The self-adjusting studs may be discrete elements from the sole structure or may be integrally formed with or incorporated into the sole structure. In some examples, the self-adjusting studs may be detachable (and/or replaceable) from the sole structure altogether. In other examples, the self-adjusting studs may be permanently attached to the sole structure and may be either a separate construction or may be formed from the same piece of material as the sole structure. 
         [0033]    The sole structures may be incorporated into any type of article of footwear. In more specific examples, the sole structures are incorporated into athletic footwear for sports including, but not limited to soccer, football, baseball, track, golf, mountain climbing, hiking, and any other sport or activity in which an athlete would benefit from a sole structure having self-adjusting studs. 
         [0034]    Generally, articles of footwear comprise an upper attached to a sole structure. The sole structure extends along the length of the article of footwear and may comprise an outsole that forms the ground contacting surface of the article of footwear. Traction elements may be attached to and form portions of the sole structure and/or ground contacting surface (e.g., the outsole). In some examples, the sole structure includes a sole base member and one or more self-adjusting studs. 
         [0035]    Articles of footwear may generally be divided into three regions for explanatory purposes. The demarcation of each region is not intended to define a precise divide between the various regions of the footwear. The regions of the footwear may be a forefoot region, a midfoot region, and a heel region. The forefoot region generally relates to the portion of the foot of a wearer comprising the metatarsophalangeal joints and the phalanges. The midfoot region generally relates to the portion of the foot of a wearer comprising the metatarsals and the “arch” of the foot. The heel region generally relates to the portion of the wearer&#39;s foot comprising the heel or calcaneus bone. 
         [0036]    One or more self-adjusting studs may be positioned in any region or a combination of regions of the sole structure of the article of footwear. For example, one or more self-adjusting studs may be positioned in the forefoot region of the article of footwear. Further, self-adjusting studs may be positioned on any side of the article of footwear including the medial side and the lateral side. In more specific examples, a self-adjusting stud may be positioned along the medial or lateral edge of the sole structure of the footwear. The self-adjusting studs also may be placed in the heel region of the article of footwear. The self-adjusting studs may be strategically positioned to provide additional traction when the wearers most need it, i.e., during specific targeted activities and/or when a particular kind of force is applied to the sole structure by the ground and/or the wearer&#39;s foot. The self-adjusting studs may be positioned in any suitable configuration on the sole structure and in any region of the sole structure. 
         [0037]    Athletes may greatly benefit from the additional traction capabilities of the self-adjusting studs in their footwear during certain movements. Athletes participating in athletic activities, for example, may need to perform sudden or abrupt starting, stopping, turning, and/or twisting motions. Athletes also make quick changes in direction of their movement. Additionally, athletes may wish to compete on various surfaces (e.g., varying field conditions or terrains). Athletes may benefit from self-adjusting studs during these movements and in these different environments of use. 
         [0038]    Generally, traction elements (and specifically self-adjusting studs) cause friction between the sole structure and the ground or surface that they contact to provide support and stability to the users of the articles of footwear during various movements. Traction elements increase the surface area of the sole structure and are often shaped and/or configured to pierce the ground when contact with the ground occurs. Such contact decreases lateral and rearward slip and slide of the footwear with the ground and increases stability for the wearer. Self-adjusting studs can provide traction that is tailored to specific movements and that can change its characteristics based on the type of terrain or surface with which the sole structure comes into contact and based on the type(s) of forces being applied to the sole structure. 
         [0039]    The self-adjusting studs may be any suitable shape and size. The surfaces of the self-adjusting studs may be smooth or textured and curved or relatively flat. The self-adjusting studs may have a smooth surface or may have edges or “sides,” such as a polygon. The self-adjusting studs may be conical, rectangular, pyramid-shaped, polygonal, or other suitable shapes. In one example, an article of footwear may have a plurality of self-adjusting studs that are all uniform in shape. In another example, the plurality of self-adjusting studs on a single article of footwear may have various shapes. The self-adjusting studs may be any size. In the example configuration where a plurality of self-adjusting studs are attached to the sole structure, each of the self-adjusting studs may be the same size and/or shape or they may be of varying sizes and/or shapes. The ground-contact surface of the self-adjusting studs may be a point, a flat surface, or any other suitable configuration. 
         [0040]    The sole structure may contain one or more self-adjusting studs. In some examples, the sole structure has a single self-adjusting stud. In another example, the sole structure has a plurality of self-adjusting studs. The self-adjusting stud(s) may be positioned within the forefoot region of the sole structure or any other region of the sole structure. For example, the sole structure may include a plurality of self-adjusting studs. A first portion of the plurality of self-adjusting studs may be positioned along the medial edge of the forefoot region of the sole structure and a second portion of the plurality of self-adjusting studs may be positioned along the lateral edge of the forefoot region of the sole structure. In essence, the plurality of studs may be positioned to frame the forefoot region along the border of the sole structure. This positioning helps to provide additional traction for the wearers during side-lateral movements. 
         [0041]    In another example, the self-adjusting studs may be positioned in the heel region of the sole structure of the studded footwear. In even other examples, self-adjusting studs may be positioned in both the forefoot region and the heel region. By varying the configuration of the self-adjusting studs, the type of traction capabilities of the footwear can be varied and/or even customized to provide additional traction to the wearer when the wearer performs a particular movement or engages in activities on surfaces having various characteristics. 
         [0042]    Articles of footwear may include various types of self-adjusting studs. Some self-adjusting studs may be activated when the surface conditions change (i.e., such as the hardness and contour). For example, some of the self-adjusting studs may be activated when the surface conditions change from a relatively soft to a relatively hard condition. The self-adjusting studs may be activated by any change in the condition(s) of the surface that the article of footwear contacts. 
         [0043]    In one example, a self-adjusting stud comprises: a first portion having a first compressibility and a second portion having a second compressibility that is greater than the first compressibility. The second portion surrounds the first portion. The first portion and the second portion are substantially uncompressed when the self-adjusting stud comes into contact with a surface of a first hardness. The first portion is substantially uncompressed and the second portion is compressed when the self-adjusting stud comes into contact with a surface of a second hardness. The first hardness is less than the second hardness. 
         [0044]    The first portion may include any type of material(s), including, but not limited to hard thermoplastic polyurethane (TPU), metal, rubber, etc. A hard TPU may have a hardness rating of 90 or above on the Shore A hardness scale or a rating of greater than 40 on the Shore D hardness scale. The metal may be an alloy of metals (e.g., steel, aluminum, titanium, alloys containing one or more of these metals, etc.). The first portion may also include various plastics having a high hardness rating and other suitable materials. The first portion is a hard material, especially relative to the second portion. The first portion remains substantially uncompressed when it contacts both the surface with a first hardness (a relatively soft surface) and the surface with a second hardness (a relatively hard surface). The first portion includes a material that will not substantially compress when it contacts most surfaces, under normal conditions (e.g., normal running, jumping, and other athletic activities performed by an athlete wearing the footwear on a usual surface, such as a hard or soft field, artificial field, or other surface). 
         [0045]    The first portion may be a pin. The pin may include any suitable material(s) such as, but not limited to, hard TPU, metal, metal alloy(s), rubber, hard plastics, and the like, as described above with respect to the first portion. The pin may have a length that is greater than its width. In some example embodiments, the pin may have a length that is at least as great as the height of the second portion so that the tip of the pin is either flush or extends beyond the ground-contact surface of the second portion. The pin may have a rounded, flat, or beveled tip or any other suitable tip. The tip of the pin and the ground-contact surface of the second portion may form a ground-contact surface of the self-adjusting stud. The tip of the pin may be flush with the surface of the second portion or it may be recessed within the second portion when the second portion is substantially uncompressed. In any of the configurations, the tip of the pin extends beyond the surface of the second portion when the second portion is compressed at least a predetermined amount. The width of the pin may account for less than 25% of the ground-contact surface of the self-adjusting stud (i.e., it may be much smaller than the surface of the second portion). 
         [0046]    The second portion of this example self-adjusting stud is compressible. The second portion may include any variety of materials that are capable of being compressed, such as, compressible foam, rubber, soft thermoplastic polyurethane (TPU), and the like. The second portion may also have a two-plate structure that is capable of reducing the size of the second portion or otherwise “compressing.” This two-plate structure includes at least a first and a second plate that are spaced apart from each other such that when a force is applied to the first plate, the space between the two plates is decreased (or reduced to nothing). A compressible foam or a spring (coil spring, leaf spring, etc.) may be positioned within the space between the first plate and the second plate such that the compressible foam or spring compresses when the force is applied to the first plate and helps to bias the plates back apart from one another after the force is removed from the first plate. The second portion may compress up to 3 mm in this example construction. 
         [0047]    The second portion completely surrounds the first portion in this example of the self-adjusting stud, although this is not a requirement in all such structures. As a more specific example, the second portion may be positioned proximate to the first portion or may be positioned some distance away from the first portion. The second portion may be positioned proximate to and, in this example, in a position that physically touches the first portion. The second portion may be positioned in any suitable manner with respect to the first portion such that the second portion may be compressed along the length of the first portion. In the example described above in which the first portion is a pin, the second portion may be positioned proximate to and in direct physical contact with the first portion in a manner that permits the second portion to slide along the surface of the longitudinal length of the pin as the second portion compresses when a force is applied to the self-adjusting stud (e.g., when the self-adjusting stud comes into contact with a hard surface). 
         [0048]    In this embodiment of the self-adjusting stud, the first portion and the second portion are substantially uncompressed when the self-adjusting stud comes into contact with a surface of a first hardness. The first portion is substantially uncompressed and the second portion is compressed when the self-adjusting stud comes into contact with a surface of a second hardness. In this example, the first hardness is less than the second hardness (i.e., the surface of a first hardness is “softer” or more “flexible” than the surface of the second hardness). In this way, the second portion “peels back,” compresses, or otherwise retracts in a direction away from the ground while the first portion remains substantially uncompressed and pierces the ground. A greater amount of the first portion is exposed when the second portion is compressed. In this example in which the first portion is a pin, a greater amount of the pin&#39;s length is exposed when the second portion is compressed. This permits a greater length of the pin to pierce the ground or other surface to provide additional traction. In some example structures, the second portion compresses up to 3 mm or more along the length of the pin (away from the ground). 
         [0049]    In some examples, the pin (or first portion) is positioned such that its tip extends beyond the surface of the second portion when the second portion is substantially uncompressed. In this configuration, the tip of the pin extends slightly beyond the surface of the second portion and thus provides some degree of traction when the second portion is substantially uncompressed. When the second portion is compressed, the level of traction and/or the type of traction that the pin can provide is increased because a greater amount of the length of the pin may pierce the ground. In other examples, the pin is flush or even recessed within the second portion, in which case the pin provides little or no traction when the second portion is substantially uncompressed. In this other example, the pin is only exposed when the second portion is compressed or otherwise retracted. The pin is able to pierce the ground when the second portion is compressed/retracted, which provides the self-adjusting stud with additional traction. 
         [0050]    The second portion may be integrally formed with or attached to the sole structure or any other portion of the article of footwear. The pin may also be integrally formed with or attached to the sole structure or any other portion of the article of footwear. For example, the pin may be attached to the base plate of the sole structure of the article of footwear and the second portion may be attached to or integrally formed with the outsole of the sole structure. In this example, the pin can be cemented, glued, bonded, and/or attached via a mechanical connector to the base plate of the sole structure. 
         [0051]    These example configurations of the self-adjusting studs are useful when the self-adjusting stud contacts relatively hard ground (e.g., ground hard enough to cause the second portion to compress). These configurations will “activate” the self-adjusting stud when the hard ground contacts the second portion and causes it to compress and expose a portion of (or a greater portion of) the first portion (or pin). The pin is then able to pierce the hard ground and provide additional traction in the hard ground. The additional traction is not activated when this example self-adjusting stud contacts soft ground that does not cause the second portion to substantially compress and expose the first portion or a greater portion of the first portion. 
         [0052]    In these example configurations, the second portion may compress any suitable amount. For example, the size of the compressed second portion may be at least 5% smaller than the size of the uncompressed second portion. In another example, the size of the compressed second portion may be at least 25% smaller than the size of the uncompressed second portion or even at least 50% smaller. 
         [0053]    Specific examples of the invention are described in more detail below. The reader should understand that these specific examples are set forth merely to illustrate examples of the invention, and they should not be construed as limiting the invention. 
       C. Specific Examples of Articles of Footwear with Self-Adjusting Studs 
       [0054]    The various figures in this application illustrate examples of articles of footwear with self-adjusting studs according to this invention. When the same reference number appears in more than one drawing, that reference number is used consistently in this specification and the drawings to refer to the same or similar parts throughout. 
         [0055]      FIGS. 1-7  illustrate specific examples of embodiment 1 that is described above in the section entitled, “General Description of Articles of Footwear with Self-Adjusting Studs.”  FIG. 1  illustrates a bottom perspective view of a portion of a forefoot region of an article of footwear  100 . The article of footwear  100  has an upper  102  and a sole structure  104  attached to the upper  102 . Four self-adjusting studs  106 ,  108 ,  110 , and  112  are attached to or integrally formed with the sole structure  104 . Two static traction elements  114 ,  116  are also attached to or integrally formed with the sole structure  104 . Each of the self-adjusting studs  106 ,  108 ,  110 , and  112  includes a study body  118  and a pin  120 . The stud body  118  defines a hole extending through the stud body  118 . In this example, the hole extends through the entire height  122  of the stud body  118 . In other examples, the hole may extend through only a portion of the height  122  of stud body  118 . 
         [0056]    In the example constructions illustrated in  FIGS. 1 and 2 , the hole in the stud body  118  is sized to have a radius that is slightly greater than the radius of the pin  120  so that the stud body  118  is capable of sliding or otherwise moving along the length of the pin  120  when the stud body  118  is retracted from the first, extended position to the second, retracted position. The pin  120  has a length that extends through at least a portion of the hole in the stud body  118 . In this example, the pin  120  has a height that exceeds the height  122  of the stud body  118  when the stud body  118  is in both the first, extended position and the second, retracted position. In some examples, the pin  120  has a height that exceeds the height  122  of the stud body  118  only when the stud body  118  is in the second, retracted position (e.g., when the pin&#39;s height is less than or equal to the height of the stud body when the stud body is in the first, extended position). In other example configurations, the pin  120  may have a height that is less than or equal to the height  122  of the stud body  118 . 
         [0057]    In the examples illustrated in  FIGS. 1 and 2 , a tip  124  of the pin  120  extends beyond the surface of the second end  128  of the stud body  118 . In other examples, the tip  124  of the pin  120  is flush with the surface of the second end  128  of the stud body  118  or it may be recessed within the stud body  118 . Regardless of the positioning of the pin  120  within the stud body  118 , the length of the pin  120  of this example structure exceeds its radius (or width, depending on the shape) of the pin  120 . In essence, the pin  120  is longer than it is wide. In some examples, such as the embodiment illustrated in  FIGS. 1 and 2 , the pin  120  is generally long and slender. 
         [0058]    The stud body  118  has a first end  126  proximate to the sole structure  104 , a second end  128  opposite the first end  126 , and a side wall  130  interconnecting the first end  126  and the second end  128 . The first end  126  may be permanently attached to or integrally formed with the sole structure  104  or may be selectively removable from the sole structure  104 . In this example structure, the side wall  130  is smooth and curved so that the overall shape of the self-adjusting studs  106 ,  108 ,  110 , and  112  is generally a three-dimensional teardrop shape. Also, the side walls  130  are shaped to taper the self-adjusting studs  106 ,  108 ,  110 , and  112  as they extend away from the sole structure  104 . The self-adjusting studs  106 ,  108 ,  110 , and  112  may have one or more side walls  130  that are shaped in any suitable manner. The overall shape of the self-adjusting studs  106 ,  108 ,  110 , and  112  may be any suitable shape. The second end  128  and a tip  124  of the pin  120  form the ground-contact surface of the self-adjusting studs  106 ,  108 ,  110 , and  112 . The second end  128  of the stud body  118  is a flat surface, although it may have any other suitable configuration (e.g., beveled, pointed, angled, etc.). The tip  124  of the pin  120  is rounded in this example, and also may have any other suitable configuration (e.g., beveled, pointed, angled, etc.). 
         [0059]    The stud body  118  may include any suitable material(s), including but not limited to, soft TPUs (TPUs having a hardness rating on the Shore A scale below 90), rubber, compressible foam, and the like. The pin  120  may include any suitable material(s), including but not limited to hard TPUs (TPUs having a hardness rating on the Shore A scale above 90 or a hardness rating on the Shore D scale above 40), metal or a metal alloy, or the like. 
         [0060]      FIG. 2  illustrates a bottom plan view of the sole structure  104  of the article of footwear  100 . The sole structure  104  has four self-adjusting studs  106 ,  108 ,  110 , and  112  and four static traction elements  114 ,  116 ,  132 , and  134 . The four self-adjusting studs  106 ,  108 ,  110 , and  112  are positioned in the forefoot region of the sole structure  104 . The first and second self-adjusting studs  106  and  108  are positioned along the medial edge of the sole structure  104  in the forefoot region. The third and fourth self-adjusting studs  110  and  112  are positioned along the lateral edge of the sole structure  104  in the forefoot region. The first self-adjusting stud  106  is positioned on the sole structure  104  to extend beneath at least a portion of the first phalange (“big toe”) when the wearer&#39;s foot is positioned within the article of footwear  100 . The second self-adjusting stud  108  is positioned on the sole structure  104  to extend approximately beneath the first metatarsophalangeal joint when the wearer&#39;s foot is positioned within the article of footwear  100 . The third self-adjusting stud  110  is positioned on the sole structure  104  to extend beneath at least a portion of the fifth phalange when the wearer&#39;s foot is positioned within the article of footwear  100 . The fourth self-adjusting stud  112  is positioned on the sole structure  104  to extend beneath at least a portion of the fifth metatarsophalangeal joint of the wearer&#39;s foot when the wearer&#39;s foot is positioned within the article of footwear  100 . 
         [0061]    The pin  120  may be positioned within any portion of the stud body  118 . For example, the pin  120  may be positioned within the center of the stud body  118  or along one or more edges of the stud body  118 . In the example illustrated in  FIGS. 1 and 2 , the pin  120  is located near an edge of the stud body  118 . 
         [0062]    The sole structure  104  illustrated in  FIG. 2  also includes four static traction elements  114 ,  116 ,  132 , and  134 . The static traction elements  114 ,  116 ,  132 , and  134  remain stationary when any type of force is applied to the sole structure  104  and/or the static traction elements  114 ,  116 ,  132 , and  134 . The static traction elements  114 ,  116 ,  132 , and  134  in this example structure do not adjust or otherwise change their shape, size, or function when forces are applied to static traction elements  114 ,  116 ,  132 , and  134  and/or the sole structure  104 . The first static traction element  114  and the second static fraction element  116  are positioned in the forefoot region of the article of footwear  100 , approximately centered between the medial edge and the lateral edge. 
         [0063]    The first static traction element  114  is positioned on the sole structure  104  approximately beneath at least a portion of the second, third, and/or fourth metatarsals of the wearer&#39;s foot when the wearer&#39;s foot is positioned within the article of footwear  100 . The second static traction element  116  is positioned on the sole structure  104  approximately beneath at least a portion of the second, third, and/or fourth metatarsophalangeal joints of the wearer&#39;s foot when the wearer&#39;s foot is positioned within the article of footwear  100 . The first and the second static traction elements  114 ,  116  are shaped similarly in this example, but each may be any suitable or desired shape. The first and the second static traction elements  114 ,  116  are tapered as they extend away from the surface of the sole structure  104  to define an edge  136  at their ground-contact surfaces. The edge  136  of the first and the second static traction elements  114 ,  116  is rounded in the example illustrated in  FIGS. 1 and 2 . However, the ground-contact surface of the static traction elements  114 ,  116  may be any suitable shape or configuration (e.g., sharp point, beveled edge, flat, etc.). 
         [0064]    The third and fourth static traction elements  132 ,  134  illustrated in  FIG. 2  are positioned on the sole structure  104  in the heel region of the article of footwear  100 . The third static traction element  132  is positioned along the medial edge of the sole structure  104  in the heel region and the fourth static traction element  134  is positioned along the lateral edge of the sole structure  104  in the heel region. In this example, the third and the fourth static traction elements  132 ,  134  have two traction regions  138  and a bridge  140  interconnecting the two traction regions  138 . The third and the fourth static fraction elements  132 ,  134  may be shaped in any suitable or desired manner. 
         [0065]    At least a portion of the stud body  118  and a tip  124  of the pin  120  form a ground-contact surface of the self-adjusting studs  106 ,  108 ,  110 , and  112 . The stud body  118  is in a first, extended position when the self-adjusting studs  106 ,  108 ,  110 , and  112  contact a surface having a first hardness and the stud body  118  is in a second, retracted position when the self-adjusting studs  106 ,  108 ,  110 , and  112  contact a surface having a second hardness that is greater than the first hardness.  FIGS. 3A and 3B  illustrate the stud body  118  in the first, extended position and the second, retracted position, respectively. In the first, extended position, the tip  124  of the pin  120  extends slightly beyond the height of the stud body  122 , as illustrated in  FIG. 3A . In the second, retracted position, the stud body  118  refracts (or otherwise compresses, becomes reduced in size and/or volume, etc.) so that it exposes a larger portion of the pin  120  (e.g., the tip  124  of the pin  120  plus additional length along a body  142  of the pin  120 ), as illustrated in  FIG. 3B . This relatively thin, narrow, hard pin  120  can better pierce the hard ground when the stud body  118  retracts, thereby digging into the hard ground and providing improved traction in the hard ground. 
         [0066]      FIGS. 4A and 4B  illustrate a side view of an embodiment of the self-adjusting studs. In this example, the stud body  118  includes a compressible foam or rubber-like material that compresses when a force is applied to the stud body  118  (the force is illustrated by the arrow in  FIG. 4B ). The self-adjusting stud body  118  compresses when it contacts a surface having a sufficient hardness. “Sufficient hardness,” as used herein, is meant to include any surface that applies a force to the stud body  118  sufficient to cause it to compress/retract. When the force is removed, the stud body  118  extends back to its “uncompressed” or “unretracted” (i.e., natural) state. The compressible foam material of the stud body  118  biases the stud body  118  back to its uncompressed/unretracted position. A spring also may be included in the stud body  118  and also may help to bias the stud body  118  back to its uncompressed/unretracted position after a force has been removed from the self-adjusting stud. The spring may be any type of spring, such as a coil spring or leaf spring. 
         [0067]      FIGS. 5A and 5B  illustrate a side view of an embodiment of the self-adjusting stud. In this embodiment, the stud body  118  includes a two-plate structure that comprises a first plate  144  and a second plate  146  defining a space  148  therebetween. When the stud body  118  is in the first, extended (uncompressed) position, the space  148  between the first plate  144  and the second plate  146  is a first distance  150 . When a force is applied to the self-adjusting stud sufficient enough to compress the stud body  118  (e.g., when the self-adjusting stud contacts hard ground), the stud body  118  retracts or compresses to its second, retracted (compressed) position. In the second, retracted (compressed) position, the space  148  between the first plate  144  and the second plate  146  is a second distance  152 . The first distance  150  between the first plate  144  and the second plate  146  (when the stud body  118  is in its first, unretracted/uncompressed position) is greater than the second distance  152  between the first plate  144  and the second plate  146  (when the stud body  118  is in its second, retracted/compressed position). Within the space  148  between the first plate  144  and the second plate  146  may be positioned compressible foam, a spring (e.g., a coil spring or leaf spring), or any other mechanism that will bias the first plate  144  and the second plate  146  back apart (i.e., back to the unretracted/uncompressed position of the stud body  118  once an applied force has been removed). 
         [0068]      FIG. 6  illustrates a side view of a self-adjusting stud. In some examples, the stud body  118  has a first portion and a second portion that can compress/retract and uncompress/unretract different amounts.  FIG. 6  illustrates an example construction in which the first portion is at a first end  154  of the stud body  118  and the second portion is at a second end  156  opposite the first end  154 . In this example, when a force is applied to the self-adjusting stud, the first end  154  compresses/retracts a first distance  160  and the second end  156  compresses/retracts a second distance  158  that is greater than the first distance  160 . This capability to compress different amounts along the stud body  118  length can help provide a more natural or comfortable feel as the applied forces move along the sole structure during a step cycle. 
         [0069]      FIGS. 4A-7  illustrates various example constructions in which at least a portion of the stud body  118  is compressed. The stud body  118  may compress any desired amount. For example, the stud body  118  may compress up to 50% of the original uncompressed height of the stud body  118 . In other examples, a portion of the stud body  118  may compress up to 50% of the original uncompressed height of the stud body  118 . For example,  FIGS. 5A and 5  B illustrate the stud body  118  in an uncompressed state ( FIG. 5A ) and a compressed state ( FIG. 5B ), respectively. The compressed state of the stud body  118  illustrated in  FIG. 5B  is approximately 25% the height of the stud body  118  in the uncompressed state illustrated in  FIG. 5A . 
         [0070]      FIG. 7  illustrates a side view of another example construction of a self-adjusting stud. In this example, the self-adjusting stud comprises a stud body  118  that has a first hole and a second hole. The self-adjusting stud also includes a first pin  162  extending through the first hole and a second pin  164  extending through the second hole. The self-adjusting stud may include any suitable or desired number of pins and corresponding holes. 
         [0071]    This example embodiment of the self-adjusting stud is described and illustrated with elements that have a smooth, curved shape. Alternative embodiments may include elements that have one or more flat sides or any other configuration of contours and shapes. 
       D. Self-Adjusting Studs in Articles of Footwear 
       [0072]    Articles of footwear incorporating the self-adjusting studs may be athletic footwear known as “cleats” or “spikes.” Such cleats having self-adjusting studs may be useful in a variety of sports such as soccer, baseball, golf, football, hiking, mountain climbing, lacrosse, field hockey, and the like. 
         [0073]    Articles of footwear may include a sole structure and an upper attached to the sole structure that together define a void for receiving a foot of a wearer. The sole structure may include a sole base member and at least one of the self-adjusting studs described above. The self-adjusting studs are attached to or integrally formed with the sole base member. The sole structure may include two or more of the self-adjusting studs. In the examples in which the sole structure includes two or more self-adjusting studs, the self-adjusting studs may be all of the same construction or they may be different constructions. For example, a sole structure may include two self-adjusting studs in which one is of the construction described in the first embodiment described above and the second is of the construction described in the second embodiment described above. 
         [0074]    The self-adjusting stud(s) may be positioned on the sole base member in any region of the sole structure. For example, one or more self-adjusting studs may be positioned in the forefoot region and/or heel region of the sole structure. More specifically, one or more self-adjusting studs may be positioned along either or both of the medial edge and the lateral edge of the forefoot and/or heel region of the sole structure. 
       D. CONCLUSION 
       [0075]    While the invention has been described with respect to specific examples including presently implemented modes of carrying out the invention, numerous variations and permutations of the above described systems and methods may also be implemented. Thus, the spirit and scope of the invention should be construed broadly as set forth in the appended claims.