Patent Publication Number: US-2015083306-A1

Title: Tire treads with reduced undertread thickness

Description:
This application claims priority to, and the benefit of, International Patent Application No. PCT/US2013/032467 filed on Mar. 15, 2013, which claims priority to, and the benefit of, U.S. Provisional Patent Application No. 61/618,267, filed Mar. 30, 2012 with the U.S. Patent Office, both of which are herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to treads for retreaded tires, and more particularly, to precured treads for application to a tire carcass. 
     2. Description of the Related Art 
     Precured treads are designed to include an undertread below the grooves to provide sufficient strength and integrity to the precured tread for proper handling during retreading operations, for stability in placement on the tire carcass being recapped, and to maintain the designed groove width as the retreaded tire is put in an envelope and cured. Furthermore, this undertread is often of at least a minimum thickness to ensure that the tread does not rip or tear when handled or when the bottom side of the tread is abraded in preparation for bonding to a tire carcass. The undertread of the procured tire becomes part of the total undertread of the newly retreaded tire, and, generally, an equivalent amount of the original undertread is removed from the tire being retreaded to accommodate the new undertread thickness of the precured tread to maintain the desired total undertread thickness in the finished tire. 
     In an effort to reduce the thickness and weight of the new precured tread, which reduces waste as less tread is removed from the used tire during the retreading process, it would be advantageous to reduce the undertread of the precured tread while maintaining the tread stability and rigidity by increasing the strength and rigidity of the groove bottom itself. A thinner undertread on the precured tread would allow more of the original undertread to be retained on the tire being retreaded. The net result would be a retreaded tire with the same skid depth and undertread thickness as before, but with significantly less new rubber being spent. Furthermore, a tread having a reduced undertread would be better able to accommodate a used tire from which an insufficient amount of undertread was removed prior to application of the new precured tread. Otherwise, the effective or net undertread thickness of the retreaded tire may be thicker than desired, which may reduce tire performance. 
     Furthermore, during tire operation, there is the possibility that cracks may form and propagate along a groove bottom, such as where the groove side intersects the groove bottom. This arises, at least in part, due to the cycle deflection of the tire as the tire tread repeatedly rotates through the tire footprint during tire operation. A more rigid groove bottom could serve to prevent the formation of these cracks. 
     SUMMARY OF THE INVENTION 
     The invention comprises a tire tread, and tire, and a method of forming a tire having the tire tread. Particular embodiments of the tire tread comprise a tread thickness bounded by a top side and a bottom side and opposing lateral sides and a groove extending into the tread thickness from the tread top side and terminating within a thickness of the tread at a groove bottom, the groove having a width defined by a pair of opposing sides and the groove bottom being spaced from the bottom side of the tread by an undertread thickness. Such tire tread further includes a plurality of strengthening members forming protrusions extending into the groove from the groove bottom and from at least one side of the pair of opposing groove sides, the plurality of strengthening members being arranged along a length of the groove. 
     Further embodiments of the invention comprise a method of forming a tire, which includes the step of applying a tire tread to a tire carcass. Such methods further include the step of forming or molding the tire tread to include a tread thickness bounded by a top side and a bottom side and opposing lateral sides and a groove extending into the tread thickness from the tread top side and terminating within a thickness of the tread at a groove bottom, the groove having a width defined by a pair of opposing sides and the groove bottom being spaced from the bottom side of the tread by an undertread thickness. The tread is formed or molded to further include a plurality of strengthening members forming protrusions extending into the groove from the groove bottom and from at least one side of the pair of opposing groove sides, the plurality of strengthening members being arranged along a length of the groove. 
     The foregoing and other objects, features and advantages of the invention will be apparent from the following more detailed descriptions of particular embodiments of the invention, as illustrated in the accompanying drawings wherein like reference numbers represent like parts of the invention. 
    
    
     
       DETAILED DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side cross sectional view taken laterally across a retreated tire comprising a prior art tread arranged atop a tire carcass, the tread including longitudinal grooves extending between a top side and an undertread. 
         FIG. 2  is a cross-sectional view of a tire tread separated from a tire carcass taken laterally across the tread and showing an undertread having a number of protrusions, in accordance with an embodiment of the invention. 
         FIG. 3  is a front cross sectional perspective view of the tread separated from the tire carcass and taken along line  3 - 3  in  FIG. 2 , the tread having longitudinal and lateral grooves extending across the width of the tire with an arrangement of protrusions extending into the groove in accordance with an embodiment of the invention. 
         FIG. 4  is a top view of the tread shown in  FIGS. 2 and 3  illustrating the lateral and longitudinal grooves having protrusions extending from the undertread into the tread. 
         FIG. 5  is a top view of a first embodiment of the undertread having a number of protruding strengthening members forming a stone ejector arrangement. 
         FIG. 6  is a top view of a second embodiment of the undertread having a number of protruding strengthening members. 
         FIG. 7  is a top view of a third embodiment of the undertread having a number of protruding strengthening members. 
         FIG. 8  is a top view of a fourth embodiment tread, the tread having strengthening members arranged along a length of a groove bottom and extending from opposing sides of the groove in an alternating arrangement in accordance with a particular embodiment of the invention. 
         FIG. 9  is a front sectional view of a tread along line  9 - 9  in  FIG. 8  showing the tapering strengthening members protruding from the groove bottom and from opposing sides of the groove. 
         FIG. 10  is a cross-sectional view of an alternative tire tread separated from a tire carcass taken laterally across the tread having an offset undertread and a number of protruding strengthening members. 
         FIG. 11  is a front cross-sectional view of a sixth embodiment tire tread taken across a retreaded tire with the tread arranged atop a tire carcass, the tread having offset undertread and a number of protruding strengthening members. 
         FIG. 12  is a side sectional view of a seventh embodiment tire tread taken along the direction of the groove length showing non-linear protruding strengthening members and an offset undertread, providing a variable-depth groove. 
         FIG. 13  is a side sectional view of an eighth embodiment tire tread taken along the direction of the groove length showing a non-liner outer side of an offset undertread, where the outer side of the offset undertread and of the bottom side of the tread has a plurality of apexes arranged along a length of the undertread and of the associated groove. 
         FIG. 14  is a side sectional view of yet another embodiment tire tread taken along the direction of the groove length showing a non-linear groove bottom and outer side of an offset undertread, where the outer side of the offset undertread and of the bottom side of the tread has a plurality of apexes arranged along a length of the undertread and of the associated groove, and where the offset undertread thickness is constant. 
     
    
    
     DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS 
     Particular embodiments of the invention provide a tire tread, tires incorporating such treads, and methods for forming a tire. The tire tread may comprise a molded new tire tread, the tread either being molded prior to application to a tire carcass, such as to form a retreaded tire, or being molded with the tire during new tire formation. The invention includes the addition of strengthening members (which may also be referred to as stiffening members) comprising protrusions extending into a groove arranged within a tread from the bottom of a groove. By the addition of strengthening members along the groove bottom, at least locally the tread is stiffer or stronger in the area of the grooves. This allows the thickness of the tread underneath the grooves, which is referred to as the undertread, to be reduced while not significantly reducing stiffness of the tread, including portions of the tread proximate the groove bottom. By reducing the undertread, a higher percentage of tread is maintained above the undertread for use during the normal wear life of the tread. By maintaining the stiffness of the tread, proper handling of the tread is maintained without risk of tearing. By providing the strengthening members along the groove bottom, crack initiation and/or propagation along a groove bottom may be avoided or significantly reduced during tire operation. Furthermore, by arranging stiffening members along the groove bottom, any peaking or raising of the reduced thickness undertread is generally avoided, or at least significantly reduced (relative a reduced thickness undertread not including strengthening members) during curing operations, where otherwise the bonding layer (identified as element  22  in  FIG. 1 ) would push the undertread upwards into the depth of the groove (identified as element  16  in  FIG. 1 ). 
     Particular embodiments of such methods of forming a retreaded tire comprise the step of applying a tire tread to a tire carcass. The tire carcass generally includes a pair of beads, a pair of sidewalls, body plies, and a belt package if the tire is a radial tire (otherwise, if not including a belt package, the tire is a biased ply tire). The body plies and belt package generally comprise plies of rubber containing strands of reinforcements. When retreading a tire, a used tire carcass is provided, which generally comprises a cured tire having at least a portion of the old tread removed so that a new tread may be attached to the tire carcass to form a retreaded tire. Commonly, at least a portion of the old tread is removed to a desired depth by performing a buffing or abrading operation. The old tread may be complete or partially removed. When forming a new tire, in lieu of a retreaded tire, a new tire carcass is provided, where such tire carcass is generally uncured. 
     When applying the tread to the tire, bonding material may be employed to attach or improve attachment of the tread to the tire carcass. For example, a bonding rubber (comprising natural or synthetic rubber) may be arranged between the tread and the tire carcass. By further example, bonding material comprising an adhesive may be arranged between the tread and the tire carcass. In such instances, the methods further include the step of providing a bonding agent between said tire carcass and said bottom side. 
     Particular embodiments of such methods include the step of forming the tire tread to include a tread thickness bounded by a top side (also referred to as a ground-engaging side of the tread, configured to engage a surface upon which the tire operates during vehicle operation) and a bottom side (configured for attachment to a tire carcass) and opposing lateral sides and a groove extending into the tread thickness from the tread top side and terminating within a thickness of the tread at a groove bottom, the groove having a width defined by a pair of opposing sides and the groove bottom being spaced from the bottom side of the tread by an undertread thickness. It is understood that the groove may comprise any type of groove having a groove bottom, where the groove is characterized as having any desired size, shape, and geometry that may be employed in any desired tire tread. The tread is formed to further include a plurality of strengthening members forming protrusions extending into the groove from the groove bottom and from at least one side of the pair of opposing groove sides, the plurality of strengthening members being arranged along a length of the groove. For example, when retreading a tire, the tread may be molded and cured according to any known method and operation of retreading, which includes molding and curing the tread prior to applying the tread to the tire carcass to provide a precured tire tread. By further example, when the tire being formed is a new tire, the tread may be molded and cured according to any known method or operation of forming a new tire, which includes molding and curing the tread while attached to the tire carcass. 
     The strengthening members may be arranged in any one or more grooves, where such one or more grooves may comprise longitudinal and/or lateral grooves. The strengthening members may also extend partially or fully across the groove width, and in any path or direction. In particular embodiments, for example, each of the strengthening members extend from one or both sides of a groove. Furthermore, the strengthening members may form any desired shape. For example, in particular embodiments, the cross-sectional shape of the strengthening members (as taken in a plane extending in a direction of the tread thickness and either in a direction of the tread length or width) may be block-shaped, polygonal, arcuate, rounded, or other shapes as desired. Finally, the size, shape, and direction of extension may vary amongst any plurality of strengthening members along the length of any groove or between different grooves within the tire tread. The strengthening members increase the stiffness of the tread so that the thickness of the tread arranged under the groove, that is, between the groove and the bottom side of the tread, which is referred to as the undertread, may be of a reduced thickness. By providing a reduced thickness undertread, a higher percentage of the tread thickness is arranged at or above the bottom of the groove bottom, which places a higher percentage of the tread within the useable portion of the tread. The overall tread thickness may also shrink with the reduction in undertread thickness. In providing a reduced undertread, any reduction from a normal undertread thickness is possible. For example, in particular exemplary embodiments, the undertread may be reduced to have a thickness less than 5 millimeters (mm), less than of 4 mm, that is or equal to 3.5 to 3 mm. Of course other reductions are contemplated. It is also understood, however, that the strengthening members may be used in any tread, whether or not being characterized as being a reduced thickness, normal thickness, or even increased thickness tread or as having a reduced thickness, normal thickness, or increased thickness undertread, as it is understood that the strengthening members can be useful for any such tread to provide additional strength and/or reduce or eliminate cracking, for example. 
     In more particular embodiments of the tire tread having a plurality of strengthening members arranged within a groove, the tire tread includes a thickness of the tread extending from the groove bottom to form a protruding portion of the bottom side arranged below the groove bottom such that adjacent portions of the bottom side located adjacent the protruding portion are recessed within the tread thickness from an outer surface of the protruding portion. In such embodiments, the groove and strengthening members may comprise any groove and strengthening member contemplated above and otherwise herein, of any design, size, configuration, or arrangement. More generally, a tread having a projecting portion may comprise any tread otherwise contemplated herein having a plurality of strengthening members arranged therein. 
     With regard to the protruding portion, the protruding portion may comprise any shaped protruding member or structure extending outwardly along the bottom side, and may define any constant or variable undertread thickness extending between the groove bottom and an outer side or surface of the protruding portion, which is also the outer side or surface of the undertread and of the bottom side. For example, protruding portion, which at least partially comprises an undertread (or undertread thickness) arranged below a groove bottom and between the groove bottom and the tread bottom side, may have a cross-section extending in a direction of the groove width that is polygonal. By further example, the outer side of the protruding member or of the undertread may be generally polygonal and may have any planar or non-planar outer side surface. For example, in particular embodiments to assist in the penetration of the protruding portion or undertread into a bonding layer arranged along the tire carcass, the outer side of the protruding portion has an apex defining maximum extent of the protruding portion relative the adjacent portions of the bottom side. In achieving an apex, the outer side may extend in a direction of the groove width along an arcuate path, to provide an arcuate cross-sectional shape, or along a V-shaped path, to provide a triangular cross-sectional shape. 
     In defining the protruding portion of the bottom side, adjacent portions of the bottom side are recessed within the tread thickness from, or relative to, the outer side of the protruding portion. For example, in particular embodiments, each of the adjacent portions comprise portions of the bottom side arranged below a tread element. In providing a protruding portion along the bottom side of the tread, it can be said that, in relation to the tire carcass, the portion of the bottom side below the groove bottom (protruding portion) forming the undertread thickness is offset in the direction of the tire carcass forming ridges in the bottom side. 
     As with other embodiments described herein, the undertread thickness associated with the protruding portion of the bottom side may comprise any desired and contemplated thickness. Furthermore, the protruding portion of the bottom side of the tread below the groove bottom may be offset (or extend from any adjacent portion forming a recess) by any desired distance. For example, the protruding portion of the bottom side is offset from any adjacent portion of the bottom side in the direction of the tire carcass by 1.5 mm. Alternatively, the offset is 2 mm. In particular embodiments, the offset is between 2 mm and 6 mm. Other offsets of the undertread thicknesses, smaller and larger, are contemplated. 
     Accordingly, in particular embodiments the invention, a method for retreading a tire (that is, forming a retreaded tire) is provided, which includes a step of providing a tire tread having: a tread thickness bounded by a top side and a bottom side and opposing lateral sides, the tire tread bottom side configured to attach to an annular tire carcass; a groove extending into the tread thickness from the top side and terminating within the tread thickness at a groove bottom arranged between a pair of opposing sides defining a width of the groove, where a thickness of the tread extends from the groove bottom to form a protruding portion of the bottom side below the groove bottom such that adjacent portions of the bottom side located adjacent the protruding portion are recessed within the tread thickness from an outer surface of the protruding portion; and a plurality of strengthening members arranged along the groove bottom, the plurality of strengthening members forming protrusions extending into the groove from the groove bottom and from at least one side of the pair of opposing groove sides, the plurality of strengthening members being arranged along a length of the groove. In further embodiments, the tread provided includes a thickness of the tread extending from the groove bottom to a protruding portion of the bottom side of the tread below the groove bottom such that portions of the bottom side adjacent the protruding portion are recessed within the tread thickness from an outer surface of the protruding portion. 
     Such methods for retreading a tire further include the steps of: providing an annular tire carcass having an annular tread-receiving portion; arranging a layer of bonding material between the tire tread and the tire carcass; and, applying the tire tread to the tire carcass, such that the protruding portion of the bottom side below the groove bottom extends into a thickness of the layer of bonding material. In particular embodiments, the step of applying the tire tread comprises extending the protruding portion into a thickness of the layer of bonding material. In doing so, the outer side of the protruding portion presses into the bonding layer displacing excess bonding material. In certain instances, at least in part due to the use of strengthening members, upon completing the step of applying the tire tread, the cross-sectional shape of the groove bottom extending in the direction of the groove width is substantially undeformed from a molded cross-sectional shape of the groove bottom. This allows the depth (that is, the skid depth) of the top side groove to remain generally unchanged so to achieve a desired or targeted depth. To better facilitate this, the outer surface of the protruding portion of the bottom side forming the undertread may be particularly shaped, such as having an apex, for example. It is understood, however, in other embodiments, that at least the thickness of the undertread, the width of the groove (and therefore the width of the undertread), and/or the pliability or viscosity of the bonding layer may be conducive to eliminating the need for any strengthening members in any configuration having a projecting portion extending outwardly along the tread bottom side below a top groove while still being able to apply the tread to the bonding layer without the projecting portion deforming in any undesired manner and/or while allowing the bottom side of the tread to be sufficiently buffed or abraded in preparation for application to the tire carcass. 
     In particular embodiments, the outer side of the protruding portion, and therefore the bottom side, includes at least one or a plurality of apexes arranged along a length of the tread facilitating penetration of the protruding portion into the bonding layer, to thereby displace bonding material for receiving at least a portion of the protruding portion. In particular embodiments, the thickness between the groove bottom and the outer side varies along the offset undertread to form an undulating or stepped portion of the outer side forming a plurality of apexes along the groove bottom. In particular embodiments, the apexes are longitudinal apexes transverse to the direction of the groove. In alternative embodiments, the apexes come to a point or rounded form. The plurality of apexes are associated with the bottom of the groove such that adjacent portions of the bottom side located adjacent the varying offset undertread are recessed within the tread thickness from an outer side of the apexes. In further embodiments, both the outer side of the projecting portion and the groove bottom extend in a direction of the groove length in a non-linear path, where the undertread thickness may be either constant or may vary along the length of the groove to provide a constant or variable-thickness undertread, respectively. In specific variations, each of the groove bottom and the outer side include at least one or a plurality of apexes. 
     Particular embodiments of the methods discussed above will now be described in further detail below in association with the figures filed herewith exemplifying the performance of the methods in association with particular embodiments of the tread. 
     With reference to  FIG. 1 , a prior art tread  10 ′ is shown in a cross-sectional view extending laterally across the tread. The tread  10 ′ is shown as having a top side  12  and a bottom side  14  (each of which may also be referred to as top and bottom faces, respectfully) and a thickness T′ extending there between. The tread also includes a plurality of grooves  16 , such as longitudinal and laterally grooves, extending from the top side  12  towards the bottom side  14 . In the figure shown, longitudinal grooves  16   long  are shown extending from the top side  12  towards the bottom side  14 . The grooves  16  terminate at a groove bottom  17   b  offset a distance T′ 18  from the tread bottom side  14  to define an undertread having a thickness T′ 18 . Typically, the prior art undertread thickness T′ 18  is equal to approximately 2.5-4.5 mm. The grooves  16  also have a width defined by opposing sides  17   a . A skid depth D 16  is defined by the difference between the thickness T′ between the top side  12  and bottom side  14  and the thickness T′ 18  of the undertread  18 . The skid depth D 16  is the thickness of useful tread contained within the precured retread, that is, a thickness designed to be available for wearing during vehicle operation. The tread  10 ′ also extends between opposing lateral sides  19 , which may be coextensive with the tire carcass  20 . The tread  10 ′ is bonded at the bottom end  14  to the tire carcass  20 , either directly or by use of a bonding material  22 , such as a layer of bonding rubber or adhesive, arranged between the tread and the tire carcass. 
     With reference to  FIGS. 2-4 , an exemplary embodiment of the invention is shown. In particular, an exemplary tread  10  is shown having a top side (or face)  12  and a bottom side (or face)  14  and a thickness T extending there between. A plurality of grooves, generally indicated as  16 , are shown, comprising lateral grooves  16   lat  and longitudinal grooves  16   long  extending into the tread thickness from the top side  12  towards the bottom side  14 . Longitudinal and lateral grooves  16   long ,  16   lat  are shown to extend longitudinally (that is, in a lengthwise direction) along a linear path, although is it understood that each may extend lengthwise along any desired path, which includes any curvilinear path or non-linear path. As best shown in  FIGS. 3-4  in a particular embodiment, longitudinal grooves  16   long  extend along a linear path while lateral grooves  16   lat  extend along a non-linear path. Furthermore, the lateral and longitudinal grooves may extend along continuous or discontinuous path. Grooves  16  also terminate at a groove bottom  17   b , offset a distance T 18  from the tread bottom side  14  to define an undertread having a thickness T 18 . The undertread thickness T 18  is thinner than the undertread thickness of the prior art tread of  FIG. 1  due to the addition of strengthening members  24  arranged along the groove bottom  17   b  to provide sufficient rigidity and strength to improve handling of the tread, to maintain dimensional stability of the tread, and to prevent tearing of the tread during the retreading process, such as when the tread is handled, transported, and applied to the tire carcass. For example, in particular embodiments, with the addition of strengthening members  24  as described herein, the undertread thickness T 18  is reduced 1 to 3 mm to approximately 1.5 mm or less, which at least equals a 40 to 67% decrease in the undertread thickness relative to a typical undertread thickness of 2.5 to 4.5 mm. In other embodiments, the undertread thickness T 18  is reduced to approximately 1.0 mm or less, which at least equals a 60% to 78% decrease in the undertread thickness relative the typical undertread thicknesses. In these exemplary embodiments, which concern truck tires, the typical overall tread thickness T is generally 12 to 30 mm. Therefore, the prior art undertread typically consumes 8% to 15% of the 30 mm thick tread and 21% to 38% of the 12 mm thick tread. However, when reducing the undertread thickness, the undertread may consume less than 8% of the tread thickness. For example, when reducing the undertread thickness from 2.5 mm to 1.5 mm, whereby a 12 mm thick tread becomes an 11 mm thick tread, the reduced undertread consumes no more than 14% (that is, 14% or less) of the thinner tread. Furthermore, when reducing the undertread thickness from 2.5 mm to 1.0 mm, and the 12 mm thick tread becomes a 10.5 mm thick tread, the reduced undertread consumes no more than 10% (that is, 10% or less) of the thinner tread. Performing similar calculations on a 30 mm thick tread for the same reduction in undertread, the reduced undertread consumes no more than 5% (that is, 5% or less) of the thinner tread (when reducing the undertread thickness to 1.5 mm) and 4% (that is, 4% or less) of the thinner tread (when reducing the undertread thickness to 1.0 mm) 
     With continued reference to  FIGS. 2-4 , strengthening members  24  comprise protrusions extending upwardly or outwardly from the groove bottom  17   b  into the corresponding groove  16  by a distance T 24 . Distance T 24  is also referred to as the thickness of the strengthening members  24 . Strengthening members  24  also have a width W 24 . In the particular embodiment shown, strengthening members extend across a full width W 16  of each groove measured at the groove bottom and from each side  17   a . In other embodiments, strengthening members  24  may extend fully or partially between opposing sides  17   a  and across the groove width W 16 . It is understood that the strengthening members  24  are sufficiently sized, oriented, and spaced to provide a sufficiently resilient and strong tread that resists tearing and improves tread stability during the retreading process. Strengthening members also provide an effective skid depth D 16  that is closer to the total tread height T than treads provided in the prior art. For example, when employing strengthening members, the undertread thickness T 18  is less than 2 mm, and in particular embodiments equal to 1.5 mm or less, or 1 mm or less. In such instances, in particular embodiments, strengthening members  24  have a thickness T 24  of 4 mm or less, which is below the groove depth that commonly remains when a tire is removed from service. Width W 24  and frequency must be sufficient to give adequate stiffness to the groove. In addition to strengthening the tread, the strengthening members may also operate as wear bars useful for determining the amount of useful tread remaining. For example, the height of the strengthening members may be preselected to become exposed to the top surface of the tread when an intended thickness of the tread remains in the normal life of the tread. Furthermore, strengthening members may operate as stone ejectors to assist in discharging any unwanted material from the groove, such as stones or other foreign matter, or noise suppressors for reducing the noise generation of the tread during tire operation. When operating as noise suppressors, extend at least halfway through the depth or height of the groove and/or at least halfway across the groove width. In particular embodiments, the strengthening members, when operating as noise suppressors, extend substantially the full depth or height of the groove and/or substantially across the groove width. It is understood, however, that any prior art wear bars, stone ejectors, and noise suppressors are not configured or arranged in sufficient frequency to operate as the strengthening members described herein, and not taught for use in conjunction with thin undertread tire treads to solve the problems described herein that may arise during retreading operations. Accordingly, while the strengthening members may be configured to operate as wear bars, stone ejectors, and/or noise suppressors, strengthening members may or may not operate as such and may be arranged within a groove in addition to other wear bars, stone ejectors, and/or noise suppressors separately provided for their intended purpose. 
     With specific reference to  FIGS. 3-4 , strengthening members are shown in further detail according to a particular embodiment. In particular, the strengthening members  24  are shown spaced along the groove bottom  17   b , extending across the full width of the groove and from each side  17   a . The strengthening members  24  are shown spaced along the groove bottom  17   b  by a distance S 24 , such that the strengthening members are separated by a distance Δ 24 . The spacing S 24  may comprise any desired spacing sufficient to provide strengthening or stiffening properties as desired for the particular tread design and use. For example, in particular embodiments, spacing S 24  is equal to 10 mm or less, although greater spacings may be employed (such as when, for example, employing strengthening members having greater widths W 24 ) for this and any other embodiments discussed or contemplated herein. It can also be said that the strengthening members are arranged in an array, at least along each tread element. Accordingly, the spacing may be constant along a length of the groove, or may be variable as desired. Nevertheless, the spacing is sufficient to provide a desired stiffness for the undertread thickness reduction. With regard to the distance of separation Δ 24  between adjacent strengthening members  24 , it is understood that such distance may be any distance desired. It is also understood that in certain embodiments, separation distance Δ 24  may be equal to zero. 
     In particular embodiments, the arrangement of strengthening members may be quantified by comparing the void defined by each groove without the presence of any strengthening members with the amount of volume the strengthening members consume within the groove. This comparison of volumes is often referred to as a void volume ratio. For example, in particular embodiments, for a length of the groove, the volume of the groove between the groove bottom and the top of the tallest strengthening member (the height of a strengthening member equals distance T 24 , shown in  FIGS. 1 and 9 ) is at least 25% filled with strengthening members. In other words, the ratio of strengthening member volume to total groove void as measured below the tallest strengthening member is 1:3. In other embodiments, the volume of the groove between the groove bottom and the top of the tallest strengthening member is at least 20% and at least 40% filled with strengthening members. 
     With continued reference to  FIGS. 3-4 , strengthening members  24  are shown to comprise rectangular cubes. As such, the sides of each strengthening member  24  generally extend normal to the groove bottom, but may be tapered or inclined such that the sides of the strengthening members intersect the bottom groove at an angle other than 90 degrees. A tapered arrangement may reduce stress concentrations that may form along the sides of the strengthening members at the groove bottom. Furthermore, the strengthening members extend laterally, normal to a longitudinal centerline of the tread. It can also be said that the strengthening members are arranged in an array, at least along each tread element  28  or rib  29 . It is understood, however, that strengthening members may comprise any shape and extend from either or both groove sides  17   a , extend across the groove width fully or partially, and may extend across the groove width W 16  in any direction. In particular exemplary embodiments, a plurality of strengthening members  24  having a width of approximately 8 mm spaced are arranged every 10 mm or less (S 24 ) to form an arrangement of strengthening members along a length of a groove. 
     It is understood that strengthening members may form any desired shape and arrangement along a length of a groove. With reference to  FIGS. 5-7 , a variety of groove  16  and strengthening member  24  arrangements are illustrated. 
     In the embodiment illustrated in  FIG. 5 , strengthening members  24  extend into the groove  16  from opposing sides  17   a  in an alternating arrangement along a length of the groove. Each strengthening member  24  has a width W 24  less than the groove width W 16 . In particular embodiments, width W 24  is greater than one-half (½), or at least three-quarters (¾), of the groove width W 16  as measured along the groove bottom (or, in other words, at least ½ or ¾ the width W 16  of the groove bottom)—such as when the groove width varies with the depth of the groove, such as is shown in the FIGURES. In other variations, W 24  extends fully across a width W 16  of the groove, such as is shown in  FIGS. 2-4  by example. As can be appreciated from this figure, the strengthening members  24  form rectangular cubes having a rounded terminal end. Further, the length dimension L 24  and spacing S 24  are such that there is space or void arranged between the strengthening members  24 . In particular exemplary embodiments, a plurality of strengthening members  24  having a width of approximately 8 mm spaced are arranged every 5 mm or less (S 24 ) to form an arrangement of strengthening members along a length of a groove. 
     In the embodiment illustrated in  FIG. 6 , strengthening members  24  extend diagonally across the groove width W 16  (that is, in a direction not perpendicular to the length of the groove or biased relative a widthwise direction of the groove) in an alternating arrangement. The strengthening members  24  are also shown connected to form a continuous arrangement of alternating strengthening members extending lengthwise along a length of the groove  16 . In the embodiment shown, the lengthwise extending of the continuous arrangement of strengthening members extends along a zigzag path, although it is understood such path may comprise any non-linear or curvilinear path. In the embodiment shown, strengthening members  24  extend from both opposing sides  17   a  diagonally across the groove, although strengthening members may only extend from one of the sides  17   a  while still extending lengthwise in a continuous, alternating path. Distance S 24  represents the length of each strengthening member of the continuous arrangement of strengthening members as the length of each such member extends to and from opposing sides  17   a  of a corresponding groove  16 . The continuous arrangement of strengthening members can also be described as a continuous strengthening member having alternating segments extending between opposing sides  17   a  of a groove  16 . In other variations, a plurality of strengthening members comprising any shape may be disconnected (that is, spaced apart) while remaining biased to the groove widthwise direction. In particular exemplary embodiments, a plurality of strengthening members  24  having a width of approximately 8 mm spaced are arranged every 10 mm or less (S 24 ) to form an arrangement of strengthening members along a length of a groove. 
     In a further embodiment illustrated in  FIG. 7 , the strengthening members  24  are arranged to form a continuous arrangement of strengthening members extending lengthwise along a length of the groove  16 , whereby the continuous arrangement forms a network or web of crisscrossing strengthening members. For example, it could be said that the continuous arrangement shown comprises the alternating zigzag arrangement of  FIG. 6  overlaid with a second alternating zigzag arrangement shifted lengthwise such that the first and second zigzag arrangements are mirror images of each other as referenced from a longitudinal centerline of the grove. The arrangement of strengthening members  24  shown can also be described as comprising “X” shaped or diamond-shaped strengthening members interconnected to form a continuous arrangement of strengthening members. It is understood that any shaped strengthening members  24  may be used to form a network or web of intersecting or crisscrossing strengthening members. Furthermore, the “X” or diamond-shaped strengthening members  24  may be disconnected, whereby such strengthening members may be separated and spaced apart in lieu of being connected in a continuous arrangement. It is understood that the embodiment of  FIG. 7  is a variation of the continuous arrangement of strengthening members shown in  FIG. 6 . In particular exemplary embodiments, a plurality of strengthening members  24  having a width of approximately 8 mm spaced are arranged every 10 mm or less (S 24 ) to form an arrangement of strengthening members along a length of a groove. 
     Yet another embodiment is illustrated in  FIGS. 8 and 9 , whereby strengthening members  24  taper in depth or thickness. Furthermore, strengthening members  24  are spaced apart along a length of the groove and extend alternatively from opposing groove sides  17   a  to form an alternating, spaced apart arrangement. and groove bottoms  17   b  within the grooves  16  may alternate. In the aspect illustrated in  FIGS. 8-9 , the design is similar to the aspect shown in  FIG. 6  with the strengthening members  24  and groove bottoms  17   b  being inverted. In this arrangement, the strengthening members  24  form a tetrahedron, or pyramidal in shape, extending from alternating sidewalls  17   a . The strengthening members are arranged such that the arrangement of groove bottom  17   b  between the strengthening members  24  forms a reduced groove  26  along the groove bottom zigzagging sideways along a length of the major groove  16 . This reduced groove  26  has a width W 26 , which is shown to be constant but may be variable in other variations. It can be said that the arrangement of strengthening members in  FIG. 5  also provide a reduced groove  26 . In the embodiment of  FIGS. 8 and 9 , strengthening member width W 24  is greater than one-half (½) of the groove width W 16  and may also be at least equal to three-quarter (¾) of groove width W 16  or equal to such groove width as measured along the groove bottom. This embodiment is especially advantageous, because it provides the needed rigidity while maintaining a continuous, full depth groove bottom. 
     Referring specifically to  FIG. 9 , the strengthening member  24  are shown as having a gradually sloped profile between sides  17   a  of the groove  16 . According to the aspect illustrated, the strengthening member  24  have the greatest thickness T 24  at the sidewalls  17   a  and taper to the groove bottom  17   b  as they approach the opposite side. As shown in  FIG. 8 , the strengthening member thickness T 24  may also taper along the length of the strengthening member L 24 , such as from the vertex of the tetrahedron whereby each strengthening member decreases in thickness in each lengthwise direction of the groove. 
     The arrangement described above provides a tire tread  10  having grooves  16  that define a tread design. The grooves  16  extend from the top side  12  towards the bottom side  14  of the tread  10  and include tapering sides  17   a  and a groove bottom  17   b  arranged at the full depth of the groove. A series of protrusions  24  extend from the undertread  18  into the grooves  16 , providing a web of connectors, thereby allowing for a thin undertread  18  at other points. In this arrangement, the skid depth D 16  is nearly equal to the tread thickness T. The strengthening members  24  arranged along the groove bottom  17   b  provide stability, strength, and rigidity to a reduced thickness undertread  18  during the demolding of the precured tread, as the bottom side of the tread is abraded for improved adhesion, and during the handling of the tread during the retreading process, which resists tearing and maintains dimensional stability during the retread process. Furthermore, in any newly formed tire or in any retreaded tire, using the tread designs described herein aid in resisting the formation of cracks within the grooves, and in particular longitudinal grooves, during tire operation. This increases the durability of the tire and the tread. 
     The performance of the strengthening members has been evaluated according to certain tests to confirm the benefits of the strengthening members. In particular, the performance of the tread generally represented by  FIGS. 8 and 9  was evaluated, treads having a reduced thickness with strengthening members generally described in  FIGS. 8 and 9  were evaluated against treads having prior art undertread thicknesses without strengthening members. (For the test, the continuous arrangement of strengthening members formed an alternating arrangement comprising a winding, curvilinear arrangement as opposed to the linear-segmented, zig-zag arrangement shown in the  FIG. 8 .) Specifically, reduced undertread-thickness treads were characterized as having an overall thickness T of 11 mm and an undertread thickness T 18  of 1.0 to 1.4 mm, with the height of the strengthening members  24  being 4 mm and being spaced a distance Δ 24  of 10 mm. The prior art tread (with reference to  FIG. 1 ) had an overall thickness T′ of 13 mm and an undertread thickness T′ 18  of 3.5 mm. Testing included verifying the durability of the reduced undertread-thickness treads as they were processed and used to form a retreaded tire. Furthermore, the retreaded tires were inspected to ascertain whether any peaking of bonding layer material (e.g., see element  22  in  FIG. 1 ) occurred, where peaking would cause excessive bonding layer material to accumulate beneath the undertread (e.g., see element  18  in  FIG. 1 ) and therefore push the undertread upwards and further into the groove to reduce the overall depth of the groove. Finally, the retreaded tires were run under common conditions to ascertain the performance of the reduced-thickness undertread tires with regard to crack initiation and propagation along the groove bottom and with regard to tread operating temperature and tire rolling resistance. In conclusion, while maintaining the same groove depth between the different tire treads while also removing 21% weight in the reduced undertread-thickness tread by reducing the thickness of the undertread, no noticeable bonding layer peaking was observed in the reduced undertread-thickness tires, which would have been expected to peak without use of the strengthening members. Furthermore, no noticeable cracking was observed along the groove bottoms for those reduced undertread-thickness treads employing the strengthening members. Finally, the operating temperature of the reduced-thickness undertread tires ran approximately 12% cooler across the tread (from shoulder to center), and exhibited a 4.5% reduction in rolling resistance. Therefore, by reducing the undertread thickness to reduce the weight of the tread without reducing the depth of any groove, the reduced undertread-thickness tread was able to avoid issues normally arising when reducing the thickness of the undertread—such as peaking and cracking. 
     In other embodiments of the inventive treads discussed above, the undertread protrudes along the bottom side to form a protruding portion of the bottom side. With reference to the exemplary embodiments of  FIGS. 10 and 11 , a variation of the tread shown in  FIG. 2  is shown, where tread  10  instead includes an undertread  18  protruding along the bottom side  14  to at least partially form a protruding portion  30  of the bottom side, such that the bottom side is non-planar. As with other treads, tread  10  has a top side  12  and a bottom side  14  defining a tread thickness T and may include any other desired feature, including void features. For example, the tread may include any combination of lateral grooves and longitudinal grooves extending longitudinally along any linear or non-linear path of any design as discussed above. In the embodiments shown, however, a plurality of grooves  16  comprising longitudinal grooves  16   long  are shown extending into the tread thickness from the top side  12  towards the bottom side  14  forming tread elements  28 . The grooves  16  terminate at a groove bottom  17   b  below which undertread  18  is arranged, the undertread having a thickness T 18  extending from groove bottom  17   b  to the bottom side  14 . Because the undertread  18  at least in part forms a protrusion along the bottom side  14 , the undertread at least partially forms a protruding portion  30  of the bottom side. Accordingly, at least a portion of the undertread thickness T 18  protrudes along the bottom side  14 , where the portion of the bottom side associated with the bottom side and defining a thickness of the undertread opposite groove bottom  17   b  is referred to as a protruding portion outer side  30   s . Adjacent each protruding portion  30  (also referred to as a protruding or offset undertread) of the bottom side is a recess  32  forming a recessed portion of the bottom side recessed (that is, spaced or offset) in a direction of the tread thickness from the outer side  30   s  of the protruding portion. In other words, protruding portion  30  (including outer side  30   s  of the protruding portion and undertread  18 ) extends (spaced or offset) a distance T O  (also referred to as an offset distance) from adjacent portions of the bottom side  14  referred to as recesses or recessed portions  32  of the bottom side. Accordingly, an undertread  18  of the protruding portion  30  can also be referred to as an offset undertread. In the embodiment shown, the recessed portions are arranged below a tread element  28  or rib. In particular embodiments, the offset distance T O  is 1.5 mm. Alternatively, the offset distance T O  is 2 mm. In particular embodiments, the offset distance T O  is between 2 mm and 6 mm. Other offsets of the undertread thicknesses, smaller and larger, are contemplated. 
     By arranging at least a portion of the undertread, which includes arranging the entire undertread, outward an adjacent recessed portion  32  of the bottom side  14 , the skid depth D 16  of the tread can be increased. The skid depth is the thickness of useful tread  10  contained within the precured retread, that is, the thickness designed for wearing during vehicle operation. In the treads discussed previously, the undertread extended from the top side  12  of the tread to the groove bottom  17   b  of a groove  16  associated with a non-protruding undertread  18 . By arranging the undertread  18  further from the top side  12  to at least partially protrude along the bottom side  14 , the skid depth D 16  may be increased. For example, with reference to the exemplary embodiment of  FIG. 11 , when the undertread  18  protrudes along the bottom side  14  such that the groove bottom  17   b  is arranged at a tread depth equal to the distance by which the recessed portion  32  is arranged from a tread top side  12  (that is, the tread thickness defined by the bottom side  14  associated with a recessed portion  32 ), skid depth D 16  is equal to the groove depth or to the tread thickness defined by the bottom side associated with each recessed portion. It is noted that the skid depth may be further increased when the undertread  18  and groove bottom  17   b  are arranged outward or below the recessed portion  32  and the bottom side  14  associated with the bottom side, such as is exemplarily shown in  FIG. 10 , where the undertread and groove bottom are spaced a distance T 17  from the recessed bottom portion  32  (where T 17  is greater than zero, unlike the prior example shown in  FIG. 11  where T 17  is equal to zero). Further, when the tread is arranged on a retreaded tire, by arranging the undertread below the recessed portions, where the protruding portion is arranged within a groove of a portion of the pre-existing tread arranged on a tire carcass, the effective skid depth of the retreaded tire tread is greater than the skid depth of the new retread tire tread since the skid depth of the retreaded tire includes a portion of the pre-existing tread extending above the bottom of the groove bottom of each protruding portion. Accordingly, by increasing the depth of the groove bottom  17   b  by protruding at least a portion of the undertread thickness along the bottom side, the skid depth of the tread is increased over the prior art tread of  FIG. 1  to thereby increase the wear life of the tread. In particular embodiments, the skid depth D 16  is increased by more than 1 mm, or alternatively more than 1.5 mm over the prior art tread depth. In particular embodiments, the skid depth is increased between 2 and 4 mm. Smaller or larger increases are contemplated. 
     In each of the embodiments shown in  FIGS. 10 through 12 , the undertread along the groove bottom includes strengthening members  24  arranged along the groove bottom  17   b . While the strengthening members may comprise any strengthening member arranged in any configuration contemplated above and otherwise herein to support the undertread and the protruding portion, it is noted that the exemplary embodiments of  FIGS. 10 and 11  include strengthening members  24  similar to those shown in  FIGS. 8 and 9 . Accordingly, as discussed above in association with other embodiments, the undertread thickness T 18  in the protruding portion  30  may be thinner than prior art undertread thickness due to the addition of strengthening members  24  arranged along the groove bottom  17   b . For example, in particular embodiments, with the addition of the strengthening members  24 , the undertread thickness T 18  is less than 3 millimeters (mm), less than 2 mm, or between about 1 and 1.5 mm. Thicker or thinner undertread thicknesses are contemplated. 
     In operation, the protruding portion below the groove bottom presses into the bonding layer displacing excess bonding material approximately retaining its offset shape and causing the thickness of the bonding material to vary across the tire across the tread width and/or along the tread length after the tire tread is applied to the tire carcass. For example, in  FIG. 11  a protruding portion  30  having an outer side  30   s  extending into the bonding layer. In particular embodiments, to assist in penetrating the bonding layer, the outer side of the protruding portion may include one or a plurality of apexes. An apex forms a lead-in or entry-point for the tread in penetrating the bonding layer for improved reception of the protruding portion. For example, in the embodiment of  FIG. 11 , the outer side  30   s  extends in a direction of the groove width along a non-linear path having an apex  31 . While the outer side  30   s  of  FIG. 11  extends along an arcuate path defining a U-shaped cross-sectional shape, outer side  30   s  may extend along any non-linear path having one or more apexes. For example, the path may include one or a plurality of segments extending along any linear or curvilinear path to form a protruding portion, such as to form a V-shaped path or cross-sectional shape. In particular embodiments, the outer side  30   s  forms a polygonal cross-sectional shape such as shown in  FIG. 10 . The use of strengthening members may assist in generally maintaining the shape of the groove and undertread as the tread is applied to the bonding layer. Furthermore, the non-planar or arcuate outer side  30   s  shown in  FIG. 11  enabled the protruding portion  18  to retain the shape of the groove bottom  17   b  and protruding portion  30  when penetrating the bonding layer. Additionally, a non-linear bottom side assists in creating additional bonding surface area for improved bonding of the tread to the tire carcass, and for improving the ability of the outer side of protruding member to be roughened in an abrading process without notable deformation. 
     In particular embodiments of the invention having a protruding portion, it is understood that the strengthening members provide a variable-depth groove, whereby the strengthening members reduce the local depth of the grooves. For example, in the exemplary embodiment of  FIG. 12 , the grooves  16  vary depthwise between a minimum depth Dmin along contoured strengthening members  24  and a maximum depth Dmax arranged between contoured strengthening members. In the embodiment shown, the strengthening members are arranged in a sinusoidal arrangement with groove bottom  17   b . The protruding portion  30  is also shown offset a distance T O  from a recessed portion of the tread bottom side. 
     In the embodiment shown in  FIG. 13 , the outer side  30   s  of the protruding portion  30  is non-planar, whereby the outer side extends along a length of groove  16  along a sinusoidal non-linear path to thereby include a plurality of apexes  31  facilitating penetration of the protruding portion into a bonding layer of a tire carcass. It is understood that the outer side  30   s  may extend in a direction of the groove length along any non-linear path to provide one or a plurality of apexes. For example, the non-linear path may form an undulating, step-function, or wave-form path. By further example, the non-linear path may comprise any repeating or non-repeating path. And because groove bottom  17   b  may also extend in any such linear or non-linear path, the undertread thickness T 18  may remain contact or vary along a length of the groove. Likewise, the depth of groove  16  may vary or remain constant in any such embodiment. For example, in the embodiment shown in  FIG. 13 , the undertread thickness T 18  varies along a length of the groove  16  because the groove bottom  17   b  does not extend along the same non-linear path, while the depth of groove  16  remains constant. By further example with reference to  FIG. 14 , the undertread thickness T 18  remains constant along a length of the groove  16 , while the groove bottom  17   b  and the outer side  30  both extend along non-linear paths, where the non-linear paths are coordinated to provide the constant thickness, and while the depth of groove  16  varies between a minimum depth Dmin and a maximum depth Dmax. In each of  FIGS. 13 and 14 , it can be said that the protruding portion is a variable protruding portion having a variable offset distance T O  and a plurality of apexes arranged along the outer side of the protruding portion. In particular embodiments, any apex has a length, such that the apex forms a ridge. In other embodiments, an apex is of pointed or rounded form. The undulating apexes on the outer side of the protruding portion may vary between any minimum and maximum depth. In certain exemplary embodiments, the difference between the minimum and maximum depths is at least 1 mm, 2 mm, or 5 mm. By further example, the undertread thickness may vary from less than 1 mm to about 4 mm. 
     The tire treads described above may be formed as a precured tread and attached to a tire carcass in a retreading operation or may be formed with a new tire according to any new tire forming operation, which may occur in a tire molding operation. In particular embodiments, the invention includes a tire comprising a tire carcass and a tire tread bonded to the tire carcass, the tire tread comprising any inventive tread contemplated herein having a protruding portion arranged along a bottom side of the tire tread. In such embodiments, the tire tread may comprise a precured tread formed prior to application to the tire carcass or a new tread molded with (that is, while arranged along) the tire carcass. When the tread is a precured tread, a bonding material may be arranged between the tread and the tire carcass. 
     The present invention may be utilized in association with retreaded heavy duty truck or trailer tires. Heavy duty truck tires include steer and drive tires and trailer tires. Nevertheless, the present invention may be utilized in association with any type of tire to form any new or retreaded tire and as such, any type of tire may provide an embodiment of the present invention. Exemplary tire types for use with the subject invention further include light truck tires, off the road tires, bus tires, aircraft tires, bicycle tires, motorcycle tires, and passenger vehicle tires. 
     The terms “comprising,” “including,” and “having,” as used in the claims and specification herein, shall be considered as indicating an open group that may include other elements not specified. The terms “a,” “an,” and the singular forms of words shall be taken to include the plural form of the same words, such that the terms mean that one or more of something is provided. The terms “at least one” and “one or more” are used interchangeably. The term “single” shall be used to indicate that one and only one of something is intended. Similarly, other specific integer values, such as “two,” are used when a specific number of things is intended. The terms “preferably,” “preferred,” “prefer,” “optionally,” “may,” and similar terms are used to indicate that an item, condition or step being referred to is an optional (i.e., not required) feature of the invention. Ranges that are described as being “between a and b” are inclusive of the values for “a” and “b” unless otherwise specified. 
     While this invention has been described with reference to particular embodiments thereof, it shall be understood that such description is by way of illustration only and should not be construed as limiting the scope of the claimed invention. Accordingly, the scope and content of the invention are to be defined only by the terms of the following claims. Furthermore, it is understood that the features of any specific embodiment discussed herein may be combined with one or more features of any one or more embodiments otherwise discussed or contemplated herein unless otherwise stated.