TIRE HAVING IMPROVED TREAD PORTION FOR REDUCING FORMATION OF ANOMALIES CAUSING USER DISSATISFACTION

Abstract: The invention is directed to a shoulder construction of the tread area of pneumatic tires which provides increased stability and reduced wear. The shoulder construction comprises a decoupling rib having an outer surface arranged circumferentially about the tire on an outer edge of the tread portion. A shoulder rib, which also has an outer surface, is arranged inwardly of an adjacent the decoupling rib. A groove, which is defined by the inner and outer side faces of the decoupling rib and the shoulder rib, extends from its base radially beneath the outer surface of the decoupling rib first diagonally toward and then away from the central radial axis of the shoulder rib. The groove configures the inner and outer side faces of the decoupling and shoulder ribs in conforming image and forms an unsupported outer surface area on the shoulder rib. This construction, under nominal pressure and load at the foot portion, provides radial stress which is substantially equalized from an outer edge over a major portion of the outer surface of the shoulder rib and provides for a portion of the inner side surface of the decoupling rib and a portion of the outer side surface of the shoulder rib to move into mutual contact providing reduced wear and increased lateral stability of the shoulder rib.

Description: TITLE OF THE INVENTION Tire Having Improved Tread Portion For Reducing Formation of Anomalies Causing User Dissatisfaction BACKGROUND OF THE INVENTION The present invention relates to a vehicle tire. Specifically, the invention relates to a pneumatic vehicle tire having an improved tread portion that reduces the formation of anomalies causing subjective user dissatisfaction. Tires, especially commercial vehicle tires sometimes have to be removed from service due to anomalies on the tread region and particularly the shoulder tread region . These anomalies are depressions in the tread rib or tread blocks forming the rib. The anomalies are generally caused by unequal radial stress distribution laterally across the rib or blocks. The highest stress concentration occurs at the outer edges of the rib or blocks. This high stress concentration at the edges and particularly the outer edges of the rib or blocks is known as the edge effect. The central portion of the rib or blocks experiences lower stress than the edges. As a result, the anomalies typically begin to form at the edges of the rib or blocks. Once an anomaly forms at the edge of the rib or blocks, the anomaly will propagate to the remainder of the rib or blocks; and often to adjacent ribs or blocks. The propagation of the anomaly occurs quickly as the tire continues to roll. The decision to remove a tire is subjective and may depend on the location of the tire on the truck/trailer combination. Generally, a driver can feel an anomaly on a steering tire by the ride of the vehicle. In that case, the driver pulls the tire when uncomfortable with the ride of the vehicle. However, if a tire having an anomaly is a drive tire or is located on the trailer, the driver may not sense any discomfort. The driver may, however, hear an increase in tire noise. If the driver does not sense discomfort or an increase in noise, the driver will pull the tire during a subsequent visual inspection of the vehicle. The removal of a tire due to anomalies causing subj ective user dissatisfaction is premature when considering the portions of the tire without the anomaly. The portions of the tire without the anomaly are capable of substantial additional service on the vehicle. Extending the time until the onset of an anomaly or decreasing the severity of the anomaly once found may extend the life of the tire. The extended life of the tire reduces the cost of purchase and installation of new tires. In the commercial trucking field, these potential cost savings are significant. Accordingly it is an object of the present invention to provide an improved tread portion that reduces the formation of anomalies causing subjective user dissatisfaction. It is a further object of the present invention to reduce or eliminate the high normal stress distribution at the lateral edges of a tread rib or blocks. It is a further object of the present invention to more uniformly distribute the normal stress laterally across the tread rib or blocks. It is a further object of the present invention to reduce the radial stiffness at a lateral edge of a tread rib or blocks. It is a further object of the present invention to maintain the lateral rigidity of a tread rib or blocks while reducing the radial stiffness at the edge of the rib or blocks. It is a further object of the invention to provide sequential radial and lateral support for the shoulder ribs or blocks. It is a further object of the invention to provide an improved shoulder construction of the tread portion of a tire. It is a further object of the invention to provide conforming image support structure for the shoulder ribs and blocks It is a further object of the present invention to provide a tread rib or block capable of resisting tearing or cracking during. SUMMARY OF THE INVENTION Accordingly, the invention provides a tire comprising a pair of beads, a carcass ply having ends anchored to respective ones of the beads, a belt ply extending circumferentially around the tire and disposed axially outward of the carcass ply, and a tread portion disposed axially outward of the belt ply. The tread portion includes a first or a shoulder rib having a side surface formed to have a positively tapered portion extending along a radially innermost extend of the rib, a negatively tapered portion extending radially outward from the outer portion of the positively tapered portion, and a straight portion extending radially from the outer extension of the negatively tapered portion to the outer surface. A second or decoupling rib is formed adjacent the shoulder rib. The decoupling rib has a side surface facing the side surface of the shoulder rib which includes a negatively tapered portion extending along the radially innermost extent thereof, and a positively tapered portion interconnected with the outermost portion of the negatively tapered portion and extending radially outward therefrom. A groove of selected width is formed between the two side surfaces separating the ribs a desired distance. The base of the groove, at the radially inner extent of the positively and negatively tapered portions of the shoulder and decoupling ribs respectively, is positioned laterally and radially outward from an outer edge of the belt ply for providing additional strength for the base of the shoulder rib to prevent cracking. The transition areas between the tapered portions and between the negative taper portion and the straight portion form arcuate angles, which also prevents cracking. The radial outward height of the shoulder rib is greater, by up to 20% of its total height, than the outward height of the decoupling rib. This requires that the shoulder rib, on contact with the support surface under nominal operating conditions, be moved radially inward in order for an outer surface of the decoupling rib to be in contact with the support surface. In addition, under nominal inflation pressure and tire loading, the sidewalls of the tire in the footprint area are urged laterally outward. These radially inward and laterally outward movements deflect the opposed shoulders carrying the decoupling ribs laterally inwardly a distance sufficient to close the grooves and bring at least a portion of the tapered portions of the decoupling rib into contact with the tapered portions of the shoulder ribs and to further bring the outer surface of the decoupling rib in contact with the support surface. In this position the decoupling ribs provide lateral support and a degree of radial support for the shoulder ribs at the footprint; which stabilizes the shoulder rib's lateral edge reducing wear and the formation of anomalies. BRIEF DESCRIPTION OF THE DRAWINGS Other objects of the present invention will become apparent from the following description with reference to the accompanying drawings, wherein: Figure 1 is a perspective view of a tire having a tread portion of the present invention; Figure 2 is a cross-sectional view of the tire in Figure 1; Figure 3 is an exploded cross-sectional view of the shoulder region of the tire of Figure 2; Figure 4 is an exploded cross-sectional view of a shoulder rib of the tire of Figure 3; Figure 5 is an exploded cross-sectional view similar to Figure 3 showing the effect on the tread and sidewall of the tire from normal weight and pressure above the footprint; Figure 6 is a schematic view showing nominal radial pressure across a conventional shoulder rib at the footprint; and, Figure 7 is a schematic view showing the radial pressure across the shoulder rib of the invention at the footprint. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS This application uses numerous phrases and terms of art. The phrase "mid-circumferential plane" refers to the plane passing through the center of the tread and being perpendicular to the axis of rotation of the tire. The term "rib or blocks" refers to a rib of the tread portion which may be formed continuous about the circumference of the tire or which may be formed by a plurality of juxtaposed blocks arranged about the circumference of the tire. The specification, in all instances, when referring to rib or ribs refers to both the continuous structure and the block structure. The term "radial" refers to the direction perpendicular to the axis of rotation of the tire. The term "axial" refers to the direction parallel to the axis of rotation of the tire. The term "lateral" refers to the direction along the tread of the tire going from one sidewall of the tire toward the other sidewall. The term "groove" refers to an elongated void area in the tread that may extend circumferentially or laterally in a straight, curved of zig-zag manner. The term "footprint" or "foot area" refers to that portion of the tread area engaged with a support surface. The phrase "tread width" refers to the greatest axial distance across the crown or the portion of the tread in contact with a road surface, as measured from a footprint of the tire, when the tire is mounted on a rim, subjected to a load, and inflated to a pressure corresponding to the load. All of the other tire dimensions are measured when the tire is mounted on a rim and inflated to a given pressure, but not subjected to a load. The phrase "tread height" refers to the radial extent, or height, of a rib of the tread portion of a tire. The term "taper" is defined as progressively narrowing or widening in the radially outward direction the width of the rib. Thus, the phrase "negative taper" is defined as progressively widening of the rib in the radially outward direction and the phrase "positive taper" is defined as progressively narrowing of the rib in the radially outward direction. The radial or normal pressure on the ribs of a conventional tire when contacting the supporting surface, is known to vary laterally across each rib. The normal pressure is greater at both lateral edges of each rib than it is in the center portion of each rib. This greater normal pressure accelerates wear along these edges. In addition, the most lateral ribs experience more wear that cause anomalies than the center ribs experience. As illustrated in Figure 2, the shoulder rib 23 construction of this invention has a unique outermost lateral side surface configuration to undercut ribs 23 and reduce the accelerated wear producing the formation of anomalies formed along the lateral outer edges of the shoulder ribs. The side surface configuration is further reflected in each decoupling rib 25 to form a narrow groove 29. The decoupling ribs further support the shoulder ribs by contacting the supporting surface as well as the shoulder ribs when the tire contacts the supporting surface in the footprint of the tire. Turning now to Figure 1 , tire 10 is mounted on a rim R and includes sidewalls S and a tread portion T having a tread width TW. Tread portion T of tire 10 comprises a pair of shoulder portions which include associated shoulder ribs and decoupling ribs of unique design. Figure 2 is a cross-sectional view of tire 10 which includes a pair of annular beads 11 on opposite sides of a mid-circumferential plane M. Opposite ends of at least one carcass ply 13 anchor with beads 11 while belt plies 15 are positioned radially outward of carcass ply 13 at crown C beneath tread portion T. Tread portion T, which includes shoulder portions 19 merge with the sidewalls S. A footprint of tread portion T contacts the supporting surface during rolling movement of tire 10. The inner area of tread portion T may include any desired conventional tire tread sculpture features, such as one with inner circumferential grooves 27, and ribs 21. Lateral grooves (not shown), and sipes may also form the tread portion. The particular inner area structure selected is irrelevant to the present invention. Each shoulder region 19 of tread portion T is constructed to include a shoulder rib 23 and a decoupling, or sacrificial, rib 25. The desirability of a decoupling rib on the shoulder portion of a tire is discussed in U.S. Patent number 4,480,671 to Giron. Figures 3 and 4 are cross-sectional views of a shoulder region containing the unique shoulder construction of the invention. Decoupling groove 29 separates decoupling rib 25 and shoulder rib 23. As clearly shown the facing lateral or side surfaces of shoulder rib 23 and decoupling rib 25 are shaped in conforming image to form the uniquely constructed decoupling groove 29 therebetween. Figures 3 and 4 show the actual lateral profile of tread area T and outer surface A of shoulder rib 23. As indicated in the drawings these areas are slightly arcuate and do not extend laterally along a single plane across the tire width. The lateral outer side surface of shoulder rib 23 faces the lateral inner side surface of decoupling rib 25. The lateral outer side of the shoulder rib includes a positively tapered portion 31 , transition area 33, negatively tapered portion 35 and substantially straight portion 37. The opposite, or lateral inner side surface of shoulder rib 23 generally conforms with the side surfaces of ribs 21 and is not relevant to the present invention. Grooves 27 separate tread ribs 21 from shoulder ribs 23. Positively tapered portion 31 , which begins at transition or base 34, forms the radially innermost, or proximal, part of the outer side surface of shoulder rib 23. Preferably, positively tapered portion 31 encompasses between 30%> and 40%> of the total radial height H of shoulder rib 23 with 35%> being preferred. In, for example, a long-haul commercial vehicle tire, a shoulder rib can have a total radial height of between approximately 10 and 25 mm. Thus, preferably positively tapered portion 31 encompasses between approximately 3.5 and 8J5 mm of the radial height of shoulder rib 23. Positively tapered portion 31 has a taper angle α as shown in Figure 4. Taper angle α, is measured from a radial line R extending from the axis of rotation of the tire. Taper angle α, is between approximately 30 and 60° with the preferred taper angle being approximately 53°. Negatively tapered portion 35 extends radially outward from transition area 33. Negatively tapered portion 35 encompasses between approximately 30%o and 40%> of the total radial height of shoulder rib 23 with approximately 35%. prefeπed. In, for example, a long-haul commercial vehicle tire, negatively tapered portion 35 encompasses between approximately 3.5 and 8J5 mm of the radial height H of shoulder rib 23, which is between approximately 10 and 25 mm. Negatively tapered portion 31 has a taper angle β, (see Figure 4). Taper angle βj is measured from a radial line extending from the axis of rotation of the tire. Taper angle R>_ is between approximately 20 and 45°. Preferably, taper angle β[ is approximately 37°. Straight portion 37 preferably extends radially outward from negatively tapered portion 35 although it could extend at a slight angle from the radial line or be curved. Straight portion 37 forms the radially outermost, or distal, part of the lateral side of shoulder rib 23; extending the remaining radial height of the shoulder rib and terminating with outer surface A. Preferably, the straight portion 37 extends approximately 30%> of the radial height of shoulder rib 23. In, for example, a long-haul commercial vehicle tire, straight portion 37 encompasses between approximately 3 and7.5 mm of the radial height of shoulder rib 23, which is between approximately between 10 and 25 mm. Transition area 33 forms a connecting area between positively tapered portion 31 and negatively tapered portion 35. Transition area 33 is preferably rounded to prevent cracking and can have a radius of curvature, for example, of between approximately 1.5 and 3.5 mm. Preferably, the radius of curvature of transition area 33 is approximately 3 mm. In an alternative aπangement transition area 33 does not require a radius of curvature. The interface between straight portion 37 and negatively tapered portion 35 is also preferably a rounded profile. The rounded profile of the interface between straight portion 37 and negatively tapered portion 35 also helps to prevent cracking on shoulder rib 23. Decoupling rib 25 has a smaller radial height than shoulder rib 23 and includes a radially outer or crown surface. The lateral inner side surface of decoupling rib 25 faces the lateral outer side surface of shoulder rib 23. The lateral inner side surface consists of a negatively tapered portion 39, transition area 41 and a positively tapered portion 43. The 10 inner lateral side surface of the decoupling rib has all of the features and is generally formed in conforming image of the lateral outer side surface of shoulder rib 23, save straight portion 37. The lateral outer side surface of decoupling rib 25 is substantially aligned with and merges into shoulder 19 in the usual manner. Negatively tapered portion 39 which begins at transition or base 34 forms the radially innermost, or proximal, part of the side portion of decoupling rib 25. Negatively tapered portion 39 has a taper angle α 2 , as illustrated in Figure 4. Taper angle α 2 is measured from a radial line R extending from the axis of rotation of the tire. Transition area 41 is formed between negatively tapered portion 39 and a positively tapered portion 43. Transition area 41 preferably forms a rounded interface between the negatively tapered portion 39 and positively tapered portion 43; which helps prevent cracking of decoupling rib 25. The outer extremity of positively tapered portion 43 aligns with the radially outer, or crown surface of decoupling rib 25. Positively tapered portion 43 has a taper angle β 2 (see Figure 4). Taper angle β 2 is measured from a radial line R extending from the axis of rotation A- A of the tire. Radial innermost ends of positive and negative tapered portions 31 and 39 respectively are interconnected with a rounded transition area 34 with a radius of curvature of between 2 mm and 3 mm at the bottom of the groove 29. In the prefeπed embodiment, the shape of the laterally inner side surface of decoupling rib 25 conforms with the shape of the laterally outer side surface of shoulder rib 23. The inner side surface of decoupling rib 25 is offset from the outer side surface of shoulder rib 23 by a distance M between about 1 mm and 3 mm, as illustrated in Figures 3 and 4. This offset may be constant along the length of the groove 29 or may 11 progressively vary. The radially outer surface of decoupling rib 25 is radially offset from the lateral profile of the outer surface A of shoulder rib 23 from between approximately 0%> and 20% of the rib height H of tread T. In, for example, a long haul commercial vehicle tire, the radial offset is between approximately 0 and 5 mm and is, preferably, approximately 2.5 mm. In order for the inner side surface of decoupling rib 25 to follow the shape of the laterally outer side surface of shoulder rib 23, taper angle 2 should approximately equal taper angle c^; and taper angle β 2 should approximately equal taper angle β,. Preferably, decoupling rib 25 has a lateral width W of approximately 30% of the tread height H of tire 10 at the radial outer surface of decoupling rib 25. Thus, in, for example, a long-haul commercial tire, the lateral width of decoupling rib 25 at its radially outermost extent is between approximately 3 and 7.5 mm. The lateral width of decoupling rib 25 can be adjusted by radially positioning the radially outermost extent of its outer surface. The lateral outer surface of decoupling rib 25 extends radially inward at an acute angle with respect to the radial axis R and merges with sidewall S. Straight portion 37 is provided to strengthen the radially outer surface of the shoulder rib 23 to resist tearing or cutting the lateral edge of shoulder rib during use of tire 10. Straight portion 37 also assists in providing the lateral stability to shoulder rib 23 and reducing its tendency for wear due to scrubbing. Groove 29 has a lateral outward slant near its base 34 to provide for an increased base area for shoulder rib 23 adjacent the edge of belt 15. This increased base area provides increased strength between the base of the groove and the edge of the belt and further prevents cracking at the bottom of the groove. 12 Groove 29 is designed to reduce the radial rigidity of the lateral outer portion of shoulder rib 23. This reduces the normal stress against the footprint on the lateral outer surface of the rib to be substantially equal to the average radial stress distribution on the rib, as shown in the graph N2 of normal stresses of Figure 7. This equalization of stress brings about an equalization of wear laterally across the outer surface of shoulder rib 23 which reduces the formation of anomalies. A graph Nl of normal stresses for a tire with conventional shoulder grooves is illustrated in Figure 6. Turning now to Figure 6, graph Nl depicts the radial or normal pressure at the footprint of a conventional tire of normal tread construction across or laterally of shoulder rib 23' under nominal inflation pressure and load. As shown, by the graph, normal pressure at the outer edge Al of the surface of the rib is greater than the radial pressure along the central area of the rib and somewhat greater than the pressure at inner edge B, as shown by graph Nl. This radial pressure at edge Al helps create accelerated wear in this area. The excessive normal pressure may also causes chunking along rib edges. These phenomenons cause anomalies to form along outer edge Al . Figure 7 shows a shoulder construction generally defining the structure of the invention in which edge A2 of rib 23 has been under cut by the design configuration of groove 29. The structure of groove 29 reduces the radial stiffness of the shoulder rib at edge A2, which reduces the normal pressure on the outer rib surface at the footprint to be substantially constant from edge A2 to just before edge B as shown by graph N2. The reduced pressure helps to relieve accelerated wear and the formation of anomalies along edge A2 under nominal operating conditions. Therefore, the groove 29 configuration of 13 this invention reduces the normal pressure on the shoulder rib at edges A2 of the tire's footprint. In all areas except the area in contact with the supporting surface (footprint), the contour of the tire under nominal inflation pressure appears substantially as shown in Figure 2 with sides S and tread T extending along arcuate paths. Grooves 29 and 27 are shown in their normal open conditions. When the tread surface makes contact at the footprint the configuration of the tire changes drastically, as illustrated in Figure 5. Sides S of the tire are forced outwardly and downwardly in the direction of the arrows from the position shown in dashed lines to the position shown in solid lines. Tread T of the tire is moved inwardly from its normal arcuate configuration shown in the dashed lines into the substantially horizontal position shown in solid lines. It can also be seen that ribs 21 and shoulder rib 23 are compressed narrowing grooves 27 and 29 and moving surface 35 laterally outwardly a slight amount. The configuration and the movement of sides S laterally outwardly and downwardly and the movement of tread T inwardly allows decoupling rib 25 of shoulder 19 to move radially and laterally inwardly, bringing side face 43 into contact with side face 35 of shoulder rib 23. Also, the radial outer surface of decoupling rib 25 is brought into contact with the support surface. At least a portion of groove 29 is now closed to help support the shoulder rib and further improve the stresses on the shoulder ribs. The configuration of groove 29 provides reduced normal stress of the outer portion of outer surface A of shoulder rib 23 while the engagement between side faces 35 and 43 provides increased lateral stability to the outer side surface of shoulder rib 23 during straight ahead rolling of the tire. During turns, in which increased lateral stress is 14 applied against the shoulder rib 23 and the decoupling rib. The decoupling rib 25 is moved even further than depicted in Figure 5 causing groove 29 to further close and increase the lateral support. In the above described relative positions, decoupling rib 25 in combination with the configuration of groove 29 provides increased lateral stability and reduced radial stress of the lateral outer edge of shoulder rib 23 along its height providing a higher degree of lateral support for the shoulder rib. In use, the configuration of tire 10 continuously alternates between the configuration shown in Figure 2 to that shown in Figure 5 so that at the footprint, shoulder rib 23 is always provided additional lateral and radial support. The additional lateral support combined with the reduction of radial stress along the outer area of the outer surface of the shoulder rib prevent abnormal deformation and excessive wear of the shoulder rib. The above description is given in reference to the prefeπed embodiment of a tire having a tread portion for reducing the formation of anomalies causing subjective user dissatisfaction. However, it is understood that many variations are apparent to one of ordinary skill in the art from a reading of the disclosure of the invention. Such variations and modifications apparent to those skilled in the art are within the scope and spirit of the instant invention as defined by the following appended claims. 15

Claims: CLAIMS I claim: 1. A tire comprising: a pair of beads; a carcass ply having ends, each of said ends anchored to a respective one of said beads; at least one belt ply extending circumferentially around the tire and disposed axially outward of said carcass ply; and a tread portion disposed axially outward of said at least one belt ply, said tread portion including: a first rib having a side surface, said side surface: having apositively tapered portion extending along a radially innermost extent of said first rib; a negatively tapered portion extending radially outward of said positively tapered portion; and a straight portion located radially outward of said negatively tapered portion and extending to said outer surface; a second rib having a side surface facing said side surface of said first rib, said side of said second rib having a negatively tapered portion extending along a radially innermost extent of said second rib; and a positively tapered portion extending radially outward of said negatively tapered portion; said first and second ribs forming a groove therebetween. 16 2. The tire as recited in claim 1 , including transition areas interconnecting said tapered portions of said first rib and interconnecting said tapered portions of said second rib. 3. The tire as recited in claim 2, wherein said transition areas of said first and second ribs are rounded. 4. The tire as recited in claim 3, including a rounded interface at the convergence of said straight portion and said negative taper portion of said first rib. 5. The tire as recited in claim 1 , wherein said negatively tapered portion of said second rib tapers at an angle approximately equal to the angle of taper of said positively tapered portion of said first rib; and said positively tapered portion of said second rib tapers at an angle approximately equal to the angle of taper said negatively tapered portion of said first rib. 6. The tire as recited in claim 5, wherein said second rib is laterally offset from said first rib. 7. The tire as recited in claim 6, wherein said first and second ribs have a radial outward height, the radial outward height of said second rib being offset inwardly from said first rib between approximately 0%. and 20%> of the height of said first rib. 8. The tire as recited in claim 1 , wherein said first rib has a radial height; said straight portion of said first rib comprises approximately 30%> of the height of said first rib; said negative taper portion of said first rib comprises approximately 35%> of the height of said first rib; and said tapered portion of said first rib comprises approximately 35%o of the height of said first rib. 17 9. The tire as recited in claim 1, wherein said first rib is a shoulder rib; and said second rib is a decoupling rib. 10. The tire as recited in claim 9, wherein said tread portion has a tread height; and said decoupling rib has a lateral width of approximately 30%> of said tread height at a radially outermost extent. 11. The tire as recited in claim 1, wherein said first rib is adjacent said second rib. 12. A tire having a carcass, at least one circumferentially and axially extending belt ply and a tread layer having a pair of shoulders, said shoulders comprising: a first circumferentially extending rib adj acent an outer side of said tread layer having an outwardly directed first side surface, a second inwardly side surface and a lateral outer surface interconnected with outer extremities of said first and second side surfaces; a second circumferentially extending rib, located axially outwardly of said first rib, having a first outwardly directed side surface, a second inwardly directed side surface and a lateral outer surface interconnected with outer extremities of said first and second side surfaces; a circumferentially extending groove separating said first side surface of said first rib and said second side surface of said second rib; said first side surface of said first rib having a negative tapered position extending along an innermost extend thereof, a positive tapered portion extending radially outward from said negative tapered portion, and a straight portion extending radially outward of said positive tapered portion to said outer surface, said positive and negative 18 tapered portions forming a circumferentially extending side groove about said first side of said first rib which underlays a portion of said outer surface; said second side surface of said second rib having a negative tapered portion extending along an innermost extend thereof and a positively tapered portion extending radially outward of said negative tapered portion, said negative and positive tapered portions of said second rib forming said second side surface of said second rib in conforming image of said first side surface of said first rib; whereby, said side groove and said circumferential groove function to lower radial stiffness of said first side of said first rib of said shoulder. 13. The tread layer of a tire as recited in claim 12, wherein said first side surface of said first rib further includes a transition area between said positively tapered portion and said negatively tapered portion; and said side surface of said second rib further includes a transition area between said negatively tapered portion and said positively tapered portion. 14. The tread layer of a tire as recited in claim 13, wherein said transition areas are rounded. 15. The tread layer of a tire as recited in claim 12, wherein said first side surface of said first rib comprises a rounded interface at a convergence of said straight portion and said negative taper portion. 16. The tread layer of a tire as recited in claim 12, wherein said first rib has a radial height; said straight portion of said first rib occupies approximately 30%> of the height of said first rib; said negative taper portion of said first rib occupies approximately 19 35% of the height of said first rib; and said tapered portion of said first rib occupies approximately 35%> of the height of said first rib. 17. The tire of claim 12 wherein said groove has a width of between 1 mm and 2.5 mm. 18. A shoulder construction of a tread, for pneumatic tires providing increased stability and reduced wear, said tire having a carcass ply, at least one belt ply extending circumferentially around and disposed axially of said carcass ply, said tread portion being disposed outwardly and axially of said belt ply, said shoulder construction comprising: a decoupling rib having an outer surface arranged circumferentially about said tire on an outer edge of said tread portion; a shoulder rib having an outer surface arranged circumferentially about said tire and inwardly of and adjacent said decoupling rib; a groove, defined by an inner side face of said decoupling rib and an outer side face of said shoulder rib, said groove extending from its radially inward extent beneath said outer surface of said decoupling rib first diagonally toward the central radial axis of said shoulder rib and secondly diagonally away from said central radial axis configuring said inner and outer side faces in conforming image and forming an unsupported outer surface area on said shoulder rib; whereby, under nominal pressure and load at the foot portion stress is substantially equalized from an outer edge over a major portion of said outer surface of said shoulder rib and a portion of said inner side surface of said decoupling rib is contacted with a 20 portion of said outer side surface of said shoulder rib providing increased lateral stability and reduced wear of said shoulder rib. 19. The shoulder construction of claim 18 wherein said groove is of equal width along its length. 20. The shoulder construction of claim 19 wherein said groove provides a base area of said shoulder rib of increased size and a base area of said coupling rib of reduced size. 21. The shoulder construction of claim 19 wherein said groove extends in each diagonal direction at an angle of between 30° and 60°. 22. The shoulder construction of claim 18 wherein said groove is of progressively varying width along its length. 23. The shoulder construction of claim 18 wherein said outer surface of said shoulder rib is radially spaced outward of said outer face of said decoupling rib. 24. The shoulder construction of claim 18 wherein the width of said groove is between 1 mm and 2.5 mm. 25. The shoulder construction of claim 18 wherein said shoulder rib has a radial height and said decoupling rib has a radial height of up to 40% less than said radial height of said shoulder rib. 26. The shoulder construction of claim 18 wherein a rounded surface forms said base of said groove. 27. The shoulder construction of claim 18 wherein intersections of engaging ends of diagonal extensions of said inner and outer faces of said decoupling and shoulder ribs are rounded. 21

Inventors: JANAJREH IBRAHIM MUSTAFA, JANAJREH, IBRAHIM, MUSTAFA
Applicants: JANAJREH IBRAHIM MUSTAFA, MICHELIN RECH TECH, JANAJREH, IBRAHIM, MUSTAFA, MICHELIN RECHERCHE ET TECHNIQUE S.A.
Application year: 1999
Main classification: B60C11
IPC codes: B60C11