Patent Publication Number: US-2004055683-A1

Title: Truck steer tire, a mold and a method of molding

Description:
FIELD OF THE INVENTION  
       [0001] The present invention relates to truck tires for steer axles, a unique mold and method of molding same.  
       BACKGROUND OF THE INVENTION  
       [0002] The use of treads specifically designed for the steer axle of truck tires has been directed to various forms of rib-type tires. This nondriving axle exhibits cornering and turning loads as well as straight line running loads. Some skilled in the art believe the tread ribs should ideally have a sharp edge adjacent to the circumferential grooves to provide improved handling.  
       [0003] These sharp edges during normal use can exhibit irregular tread wear. High wear erosion is common in the shoulder region of the tread. This problem was addressed in U.S. Pat. No. 4,480,671 issued Nov. 6, 1984, to Giron. As shown in FIG. 2, Giron disclosed the use of a laterally located circumferentially continuous rib  4  that under normal driving conditions is in contact with the road. The force or pressure exerted by the rib  4  on the road being less than the force or pressure of the shoulder rib  6 . This prior art tire  2  relied on the laterally located rib to protect the sharp edge of the shoulder rib. One such tire  2  is believed to be the Michelin XZA-1+ steer tire.  
       [0004] An alternative design approach was to have a nonrecessed circumferential rib  3  adjacent a narrow circumferentially continuous groove  7  and shoulder rib  5 . Such a tire was commercially sold as the Goodyear G259 steer tire and that tire  1  exhibits a static footprint or tread contact patch as shown in FIG. 3.  
       [0005] Yet another design approach was demonstrated by Bridgestone Tire &amp; Rubber Company&#39;s R227 Steer Tire which has a narrow circumferentially continuous bent groove in the side of a shoulder rib. The narrow bent groove creates reduced shoulder pressure and acts as a decoupling groove as is taught in U.S. Pat. No. 4,995,437.  
       [0006] All of these design approaches rely on a decoupling groove in the tread. These features will effectively reduce shoulder wear when the tread is new. This has the remarkable benefit of inhibiting the onset of irregular wear. The tread shoulder is most prone to setting up irregular wear when the tread is new and is at a maximum tread thickness.  
       [0007] What is troubling though is that the decoupling ribs in the tread are prone to tearing and cutting while the decoupling groove can be prone to stone holding. As a result, this portion of the tread is potentially vulnerable to damage when the tire strikes a curb or other hard obstruction.  
       [0008] Another problem associated with the use of decoupling grooves in a tread is the inability to reliably mold a good decoupling groove in a lateral orientation. In the past, it has been common practice to use tire molds in a steer tire application where the decoupling groove was in the segmented tread ring. Accordingly, steer tires when molded with a tread design suitable for use on a steer wheel position had been easier to mold with decoupling grooves exending radially or vertically inwardly. Laterally extending decoupling grooves had problems at least to the degree that is associated with molding and uniformity.  
       [0009] In order to insure that the tread is effectively decoupled from the sidewall, that is the tread shoulder remains somewhat independent of the forces exerted by the sidewall, a new and vastly improved way of decoupling must be provided.  
       [0010] The present invention provides a way to effectively decouple the tread shoulder.  
       [0011] The effective decoupling of the tread shoulder occurs in the treadwall region of the tread at a location radially outward or preferably directly above the belt structure and, thus, above a tread buff line when the tire casing is prepared for retreading.  
       SUMMARY OF THE INVENTION  
       [0012] A radial ply pneumatic tire for the steer axle of a commercial truck is described. The tire has a tread and a casing. The casing has at least one radial ply extending to a pair of radially inner beads and a belt reinforcing structures disposed radially outward of the ply.  
       [0013] The tread is disposed radially outward of the casing. The tread has a pair of shoulder tread ribs; each shoulder rib has an axially outer treadwall. Each axially outer treadwall has a laterally inward extending circumferentially continuous side groove. The side groove has a groove depth (d) and a minimum groove width (w). The minimum groove width (w) is about 5 mm or greater, preferably in the range of 5 mm and 7 mm and the ratio of groove depth to the minimum groove width is 1.0 to 2.4, preferably 1.6 to 2.4. The side groove has a groove base having a radiused profile R, the radially inner portion of R being at least equal to one half the minimum groove width (w).  
       [0014] The tire also has a pair of sidewalls, one sidewall extending radially inwardly from each shoulder rib toward each radially inner bead.  
       [0015] Each side groove has a centerline C defined as the midway line between the groove walls. The centerline C between groove walls relative to a normal line to sidewall preferred angle is zero. The acceptable range would be no greater than +10 degrees above horizontal (axis of rotation) and not exceeding an angle which is concentric or tangent to the tread radius to −10 degrees below the normal line to the sidewall.  
       [0016] The groove walls of the side groove may have a positive draft angle. In at least one embodiment the radially upper groove wall has a negative angle θ 
       [0017] Alternatively, the distance between groove walls of the side grooves can narrow as the side groove extends from the base of the side groove to the axially outer treadwall.  
       [0018] The tread has at least one full depth groove extending from the surface of the tread to a bottom, the radial depth of the at least one full depth groove defines the tread&#39;s nonskid depth, wherein the radial thickness of the tread at the axially outer tread wall as measured from the side groove to the tread surface at least equals at least 50% of the tread&#39;s nonskid depth.  
       [0019] The present invention also includes a mold for forming the tire. The mold has a radially outer tread forming portion, the radially outer tread forming portion forms an annular closed ring by two segments abutting circumferentially or a plurality of segments abutting radially. The mold has a pair of treadwall/sidewall forming plates. Each of the treadwall/sidewall forming plates extends radially outwardly beyond the casing. Each treadwall/sidewall forming plate has a laterally inwardly extending annular rib for forming a side groove in the tread, the side groove being circumferentially continuous and located at or radially outward of the belt reinforcing structure.  
       [0020] The invention further includes a method of molding the tire, the method having the steps of:  
       [0021] placing the tire in a mold, the mold having a tread forming portion and a pair of annular treadwall/sidewall forming plates;  
       [0022] applying heat and pressure to form the tread and sidewalls of the tire&#39;s exterior;  
       [0023] forming a laterally extending circumferentially continuous side groove radially at or outward of the belt reinforcing structure and radially inward of the outer surface of the tread along each lateral tread edge, wherein the step of forming the side grooves is accomplished by an annular rib in each of the annular treadwall/sidewall forming plates;  
       [0024] curing the tire;  
       [0025] opening the mold; and  
       [0026] removing the cured tire.  
       [0027] Definitions  
       [0028] “Apex” means an elastomeric filler located radially above the bead core and between the plies and the turnup ply.  
       [0029] “Bead” means that part of the tire comprising an annular tensile member wrapped by or otherwise anchored by ply cords and shaped, with or without other reinforcement elements such as flippers, chippers, apexes, toe guards and chafers, to fit the design rim.  
       [0030] “Belt Structure” means at least two annular layers or plies of parallel cords, woven or unwoven, underlying the tread, unanchored to the bead, and having both left and right cord angles in the range from 15° to  70 ° with respect to the circumferential centerline of the tire.  
       [0031] “Casing” means the carcass, belt structure, beads, sidewalls, and all other components of the tire excepting the tread and undertread. The casing may be new, unvulcanized rubber or previously vulcanized rubber to be fitted with a new tread.  
       [0032] “Chafers” refers to narrow strips of material placed around the outside of the bead to protect cord plies from the rim, distribute flexing above the rim, and to seal the tire.  
       [0033] “Circumferential” means lines or directions extending along the perimeter of the surface of the annular tread perpendicular to the axial direction.  
       [0034] “Cord” means one of the reinforcement strands of which the belts and plies in the tire are comprised.  
       [0035] “Lateral” means an axial direction.  
       [0036] “Ply” means a continuous layer of elastomeric rubber-coated parallel cords.  
       [0037] “Radial” and “radially” mean directions radially toward or away from the axis of rotation of the tire.  
       [0038] “Radial Ply Tire” means a belted or circumferentially-restricted pneumatic tire in which the ply cords which extend from bead to bead are laid at cord angles between 65° and 90° with respect to the equatorial plane of the tire.  
       [0039] “Shoulder” means the upper portion of sidewall just below the tread edge; tread shoulder or shoulder rib means that portion of the tread near the shoulder.  
       [0040] “Sidewall” means that portion of a tire between the tread and the bead.  
       [0041] “Tread” means a rubber or elastomeric component including that portion of the tire that comes into contact with the road under normal inflation and load. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0042] The invention will be described by way of example and with reference to the accompanying drawings in which:  
     [0043]FIG. 1 is a cross-sectional view of the tire  10  according to the present invention.  
     [0044]FIG. 2 is a partial cross-sectional view of a prior art tire  2  disclosed in U.S. Pat. No. 4,480,671.  
     [0045]FIG. 3 is an exemplary static footprint of a prior art tire  1  commercially sold as the Goodyear G259.  
     [0046]FIG. 4 is an illustration of a prior art exemplary tire footprint exhibiting shoulder rib cupping after 100,000 miles of use.  
     [0047]FIG. 5 is an exemplary tire footprint of the present invention depicting the pressure distribution of the tire as molded.  
     [0048]FIG. 6 is an enlarged cross-section of one-of the tire shoulders of the preferred tire according to the invention.  
     [0049]FIGS. 7A, 7B,  7 C,  7 D and  7 E are cross-sections of an alternative embodiment ire shoulders of the present invention.  
     [0050]FIG. 8 is a mold for the present invention shown in a half portion closed about a tire to be molded, the mold for molding the tire of the present invention.  
     [0051]FIG. 9 is one of the two annular treadwall/sidewall plates taken from FIG. 8 and shown in a perspective view.  
     [0052]FIG. 10 is an enlarged cross-sectional view of the tire of the present invention showing a multiple radiused profile decoupling groove.  
     [0053]FIGS. 11A and 11B show a test result comparison of the decoupling grooves having a full single radius and the multiple radiused profile of FIG. 10, respectively. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0054] With reference to FIG. 1, a cross-section of the pneumatic radial tire  10  for use on steering axles is illustrated.  
     [0055] The tire  10  has a tread  20  and a casing  12 . The casing  12  has two sidewalls  14 ,  16  one or more radial plies  18  extending from and preferably wrapped about or otherwise secured to two annular beads  13  and a belt reinforcement structure  15  located radially between the tread  20  and the plies  18 .  
     [0056] The plies  18  and the belt reinforcement structure  15  are cord reinforced elastomeric material, the cords being preferably steel wire filaments and the elastomer preferably being a vulcanized rubber material. Similarly, the annular beads  13  have steel wires wrapped into a bundle known as the bead core.  
     [0057] A liner  19  component of preferably halobutyl rubber forms a somewhat air impervious chamber to contain the air pressure when the tire  10  is inflated.  
     [0058] The casing  12  of the preferred embodiment of the invention, as illustrated in FIG. 1, employed a bead  13  having an 8×10×9 hexagonal bead core having an elastomeric apex  61  radially above the bead  13 . The ply turnup  18 A in the bead area was reinforced with a flipper  67 , chipper  62 , gum and fabric chafers  64 ,  65 , gum strips  66  and elastomeric wedges  63 .  
     [0059] Additionally, the belt reinforcement structure  15  included gum strip of rubber material  75  and a plurality of elastomeric strips or wedges  72  in the lateral extremes of the belts  15  in proximity of the side grooves  24 . Although not required to the practice of the inventive concept, these features are disclosed as features employed in the preferred embodiment.  
     [0060] The tread  20  has a plurality of circumferentially continuous grooves  22  and a plurality of tread ribs  25 , including a pair of shoulder ribs  25 A, one shoulder rib  25 A being adjacent each lateral edge  21  of the tread  20 .  
     [0061] The distance halfway between the lateral edges  21  of the tread defines the circumferential centerline CL of the tread  20 .  
     [0062] The radially outer road contacting surfaces  26  of the plurality of tread ribs  25 ,  25 A define a radially outer tread surface  30 . The outer tread surface  30  is adjacent to and extends between the pair of lateral edges  21 . A plurality of sipes or incisions  54  and  56  may be employed on the tread  20  as shown in FIG. 5.  
     [0063] As shown in FIG. 1, a laterally inwardly extending circumferential side groove  24  is located in a treadwall  29  of each shoulder rib  25 A.  
     [0064] As shown in FIG. 5, the tread  20 , when new, exhibits a static footprint pressure distribution when the tire is normally loaded, such that the pressure exerted along the axial centerline C of the footprint on the shoulder rib  25 A adjacent the lateral edge  21  is P3, on the shoulder rib  25 A adjacent the circumferential groove  22  is P1, on the rib  25  laterally adjacent the shoulder rib  25 A at the groove  22  is P2. The relationship of the pressure distribution is P1 is about equal to P2; and about equal to P3 in one preferred embodiment of the invention.  
     [0065] As shown in FIG. 4, a prior art tire  1 , the G259 after 100,000 miles of wear can exhibit considerable cupping wear in the shoulder rib region  2 . The decoupling or recessed lateral rib  6  is noticeably worn away from road contact at this wear condition. The tire  10  according to the preferred embodiment of the invention, as illustrated in FIG. 1, has a much more uniform wear in the same shoulder regions of the tread  20 . Both the prior art tire  1  and the test tires  10  were of similar size, 11R22.5, and similarly loaded and inflated during the evaluations.  
     [0066] As shown in FIGS. 1 and 5, one embodiment of the invention has the above-described pressure distribution exhibited by the exemplary tire  10  which is achieved by effectively progressively increasing the width Ws of the tread shoulder rib  25 A from the point  40  of the change in curvature to the lateral edge  21 . This added rubber area effectively provides more material in an area of high wear propensity and decreases the pressure in the area by spreading the load over a wider rib. The area directly above or adjacent the side grooves  24  improves the maintenance of the shoulder radius  27  of the shoulder rib  25 A.  
     [0067] Interestingly an upper limit in the amount of pressure change must be maintained wherein P3 should not exceed P1 by 20%, preferably 10% or less. If too much rubber is added to the shoulder rib  25 A above the decoupling grooves  24 , the area adjacent the circumferential groove  22  can become too lightly loaded. When this condition occurs a phenomena known as erosion wear or river wear can occur adjacent the groove  22 . To prevent this problem from occurring a balance must be maintained. Ideally, both edges across the shoulder ribs  25 A wear at the same uniform rate. This condition achieves a most beneficial projected mileage life of the tread.  
     [0068] In the exemplary tire of FIG. 1 one embodiment of the invention shows the tread radius of curvature R i  was selected to be a single radius of curvature. A single radius R 1  provides a simple mold shape. Alternatively multiple radii of curvature R i  can be used. All of these tread shapes are feasible due in part to the side grooves  24  in the upper treadwall  29  enabling the tire engineer to select the tread shape most preferred for the particular application.  
     [0069] Ideally the side grooves  24  are positioned at a radial height at or above the edges of the belt structure as is illustrated. Under normal load the side grooves  24  compress slightly causing the tread to exhibit a lower contact pressure at the tread ribs  25 A and reduce torquing of the shoulder rib. These side grooves  24  preferably have an end formed by a large or full radius R G  in the lower portion of the radius profile R, the large or full radius R G  extending a fixed or predetermined distance (d) inwardly toward the underlying belt layers  15 .  
     [0070] As the tire rotates under load, the decoupling grooves  24  compress. This ability to compress greatly facilitates the ability of the tread to maintain its shape in turning and cornering maneuvers.  
     [0071] The tread  20  at the axially outer portion of the tread shoulder rib  25 A has a treadwall  29 . The treadwall  29  as shown may include a radially outer rounded surface  28  extending to the edge  27 . As shown, this portion of the tread shoulder rib  25 A lies radially outward of the side grooves  24 .  
     [0072] As the tread  20  wears, the edge  27  moves axially outward along the rounded surface  28 . This feature enables the tread to compensate for wear in that tread elements as they wear generally get stiffer. As the edge  27  wears, it moves outwardly. The edge  27  moves over more of the side grooves  24 . This means the stiffness-increase, due to wear, is to a large extent dampened or minimized. Additionally, as the edge  27  moves outwardly, the surface area  26  of the rib  25 A also increases in width. This means the contact pressure can actually reduce slightly as the tread  20  wears.  
     [0073] As shown in FIG. 5, when the tread is new the footprint or contact patch of the tire exhibits a contact pressure as measured along a line C spaced equidistant between a leading edge and a trailing edge of the tires normally loaded and normally inflated static condition. The normally inflated condition as used herein means the design inflation pressure P N . At the edge  27  of rib  25 A intersecting the line C a contact pressure P3 is shown. On the opposite side of the rib  25 A adjacent the groove  22  intersecting line C a contact pressure P1 is shown. On the opposite groove wall of adjacent rib  25  along the line C a contact pressure P 2  is shown. These contact pressures can be adjusted upward by elevating the edge  27  relative to the contour of the central portion of the tread  20  as defined by the radius R i  or lowered by lowering the edge  27  relative to the contour of the central portion of the tread  20 .  
     [0074] An important feature of the preferred embodiment tire is that the axial widths W C  of the tread ribs  25  are actually smaller in width than the axial width W S  of the shoulder ribs  25 A. These are average widths as measured halfway across each respective tread rib  25  and ribs  25 A. This feature helps insure the shoulder ribs  25 A can have an overall lower average pressure than the central ribs portion of the tread. Ideally the shoulder ribs  25 A have a contact pressure equal to or less than the central ribs  25 . The desired pressure distribution relationships are achieved by a combination of tread arc curvatures, rib width variations and the unique side grooves  24 . The side grooves  24  enable the tire designer to stiffen or soften the tread edge  27  by simply adjusting the depth, width or shape of the grooves  24 , their radial location or their axial extent. These features can be tuned individually or collectively to enhance tire performance and tread wear. This is very beneficial in several ways not the least of which is achieving a more durable tread that wears uniformly without requiring a vertical tread decoupling rib which had been considered the most reliable way to design a tread for a steer tire.  
     [0075] As shown the radial location of the side grooves  24  can be at the location of the lateral outermost edge of the belts  15  as in FIGS. 1 and 6 or radially above the outermost edge belts  15  as in FIGS.  7 A- 7 D.  
     [0076] A second and even more important feature is the side grooves  24  are located above the tread buff line  95  as shown in FIG. 6. This facilitates retreading. Currently in most commercial truck tire applications retreaded tires are not used in the front steer wheel position. This is because the single wheel position of the each steer axle means that a tread separation or sudden loss of pressure can be more problematic when compared to a dual wheel position axle such as the drive axles or the trailer axles.  
     [0077] The side grooves  24 ,  240  of the present invention allows this feature to be part of a precured tread, used in new tire manufacturing or in retreading. Unlike any other concept used to date, this feature will be perfectly positioned after mounting to the casing because it was molded into the precured tread originally and is never changed during a molding.  
     [0078] A third important point of the present invention is that this form of decoupling is very complimentary for use on the drive axle and trailer axle position when the tire is retreaded. In other words, even if the wheel axle position is changed, there appears to be no negative consequences. This is true because unlike most rib type tread decoupling concepts, there is no small appendages of rubber to cut or tear.  
     [0079] In essence the entire invention principle achieved by the use of side grooves  24  resides in the desensitization of the shoulder pressure to varying loads. The loads of a steer axle tire vary due to the vertical and lateral movements of the tire. The prior art tires exhibit a higher sensitivity of shoulder pressure to load variation when compared to the tire of the present invention.  
     [0080] Naturally the lower contact pressure achieved at the edge can be advantageous in some cases as well, but in other cases it may be beneficial to increase the contact pressure at location P 3 . The side grooves  24  allow the engineer to achieve these benefits as well as was noted earlier.  
     [0081] With reference to FIG. 6, one embodiment of the invention is shown with an enlarged view of the tire&#39;s shoulder shown in cross section.  
     [0082] As shown in FIG. 7A the side groove  24  has the centerline angled between 0 and 10° downward relative to a normal line to the upper sidewall contour. The preferred layout is normal to the upper sidewall or treadwall  29  through a point at the centerline of the groove location. The groove  24  at the closed end or base forms a dome  24 A. The engineer when designing a steer tire  10  should select the dome point to be located at or near the intersection of the groove centerline C and the nonskid baseline. The nonskid baseline is the extension of the nonskid depth as shown by the line  90 .  
     [0083] A vertical line  92  drawn from the edge of the widest reinforcing belt  15  established the lateral extent of the side groove  24 . For any particular tire the side groove  24  should have the end or dome point within plus or minus 10 mm of the line  92 .  
     [0084] Ideally the side groove  24  lies at least 2 mm above the belt reinforcing structure  15 . It is believed important that no part of the side grooves  24  should be below the tread to casing interface  94 . Furthermore, the groove  24 ,  240  lies above the casing buff line for retreading which is at least 2 mm above the belts. If possible the side groove should be entirely in the tread material and not extend beyond the tread cap/base interfacial line  93 .  
     [0085] As shown the side groove  24  has a preferred shape that is symmetrical about its centerline C although it can be asymmetrical. The width (w) of the side groove is in the range of 5.0 mm and 7.0 mm. The preferred width (w) is 6.0 mm. The depth to width ratio should be 1.6 to 2.4. The preferred ratio is 2.0. The lower portion of the radius of the dome or base of the groove should be as large as possible. A full radius is the most simple design to manufacture.  
     [0086] With reference to FIGS. 7A, 7B,  7 C and  7 D four exemplary side grooves  24  are shown. The side groove  24  of FIG. 7A is the same as was shown in FIGS. 1 and 6 and it has generally parallel groove walls. In FIG. 7B the dome (or base) has an enlarged full radius that narrows as the side groove  24  extends to the treadwall. In FIG. 7C the side groove  24  is asymmetrical about the line intersecting the dome point and extending roughly parallel to the tread surface. As shown the lower part of the groove  24  is larger and the walls of the side groove  24  are not parallel but instead have a large positive draft angle.  
     [0087] With reference to FIG. 10, a further cross-sectional view of the decoupling groove is illustrated. In this embodiment in place of a full symmetrical dome or base  244  a more sophisticated asymmetric geometric profile is shown. The upper surface  242  of the groove  240  has the upper surface substantially parallel to the tread radius. As shown the surface is inclined slightly at an angle θ of 5° or more, preferably about 7°, relative to an axially drawn line.  
     [0088] At the inner end of the groove  240 , the base  240  has a preferred profile established by two radii, R x , R y , the upper radius R x  is smaller than the larger lower radius R y , as shown. R x  is less than 50% of R y . In the embodiment shown Rx is about 1.5 mm while R y  is about 5.0 mm. As shown R x  is less than 30% of R y .  
     [0089] In testing it has been discovered that a simple full radius base experience a surface reversion or blemish line that is generally symmetrical to the base after being exposed to exaggerated test conditions on a round drum test machine with the tire under normal inflation and a very high extreme load. As shown in FIG. 11A, the full radius base has a surface reversion occurring after about 50,000 miles under these very severe test conditions.  
     [0090] By employing the groove  240  in the tread this surface reversion is dramatically diminished. Importantly, the surface reversion line as shown in FIG. 11B is also moved radially outwardly toward the tread. In the case of the compound radii base  240  the initiation of the blemish is reduced and moved a substantial distance away from the belts. Assuming new tread compounds permit even greater mileage to be achieved then the design of FIG. 10 shows the capacity to maintain a decoupling feature well beyond that achievable in the 100,000 test miles of steer tires of current production.  
     [0091] As shown in FIG. 10, the transition from radius R x  to R y  should occur at location Z. Location Z, preferably, is located at a distance X of at least 25% or preferably at least 33% above the groove centerline, as shown about 40% above the centerline based on the average groove width being 100%. The groove centerline is the distance equidistantly spaced between the groove surfaces  242  and  241 . This effectively forces the surface reversion flexure line to be as shown at location Z in FIG. 11B to be occurring well above the groove centerline.  
     [0092] As shown it is believed desirable that the axially outer portion of the surface should have a radius R t , R t  being about 2.0 mm. This prevents a sharp edge from occurring that might cause a cut or fracture. R s  has a 1.5 mm radius of curvature. Both upper radius R t  and the lower radius R s  blend into the axially outer tread wall  290  as illustrated.  
     [0093] Each of the exemplary steer tires can be molded using the mold of the present invention as illustrated in FIGS. 8 through 10.  
     [0094] As shown in FIG. 8, the mold  100  is made with a plurality of tread forming segments  104 . The tread forming segments  104  have cavities  110  for forming tread elements that may be blocks or ribs  25 ,  25 A. The lateral edges of the tread are shown in the location which forms the upper portion of the treadwall  29 .  
     [0095] Two annular treadwall/sidewall forming plates  108  are shown in FIG. 9. The plates  108  abut the segments at a mold split line  120 . The sidewall  16  is formed along the molding surface  106 . Indicia, lettering and the like are carved into these plates to mold the tire&#39;s trademarks and other tire labeling. Toward the radially outer portion of the surface  106  is found an annular rib  109 . The rib  109  forms the side groove  24 ,  240  of the tire.  
     [0096] It is understood that the segmented mold  100  can alternatively be built in a two piece mold. The advantages of uniformity and superior quality make the segmented mold more desirable.  
     [0097] As shown in FIG. 10 the mold  100  when closed with a green or unvulcanized tire inside forms the tread and the sidewall as the tire is cured. The treadwall/sidewall forming plates  108  extend well into the tread and thus enable the side groove  24 ,  240  to be very accurately positioned. Normally such features are found in the tread forming segments  104  and as one would expect the size of side grooves formed in a tread segment was very limited due to the fact the tread rubber overhangs these features. The present invention has the side grooves  24 ,  240  formed in the treadwall/sidewall forming plates and this permits much larger side grooves  24 ,  240  to be employed.  
     [0098] It has been discovered that small side grooves close with the walls under deflection becoming a fully compressed before a sufficient reduction in pressure occurs along the tread shoulders. Accordingly, the rate of treadwear was not markedly improved. By using the larger and deeper side grooves  24 ,  240  as described above much improved treadwear results have been achieved. Initiation of shoulder wear when compared to prior art commercially available tires such as the Goodyear G357, the Bridgestone R227 and the Michelin XZA2 showed that mileages up to 100,000 miles were possible with the prior art tires but the present invention tire in a 11R22.5 size achieved a remarkable 150,000 mile performance. These results are most remarkable when one considers advances of as little as 10% are often hard to achieve in such steer tires. The present invention advances the state of steer tire design.  
     [0099] Variations in the present invention are possible in light of the description of it provided herein. While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention. It is, therefore, to be understood that changes can be made in the particular embodiments described which will be within the full intended scope of the invention as defined by the following appended claims.