Patent Description:
Heavy commercial truck tires have a tread area that engages the road surface, and a carcass with sidewalls that extend from the tread area. The sidewalls terminate in beads that are designed to engage a rim of the wheel. The beads include a bead core made of steel and other bead tissues that can be composed of rubber. In order to improve performance of the truck tire it is desirable to lighten the weight of the bead core, for example by reducing the number of rods of the bead core. However, reduction in the size of the bead core causes more flexing in the tire. To compensate for this flexing the area radially above the bead core, sometimes referred to as bead filler, includes a rubber portion that is more stiff. This bead filler is coextruded so that the stiffer rubber first portion is on the inboard side of the tire in the axial direction, and the more flexible second portion is on the outboard side of the tire in the axial direction. However, the use of a two zone bead filler requires these products to be formed via coextrusion which can add cost and complexity to the manufacturing process. Additionally, the use of a two zone bead filler does not eliminate the magnitude of bending caused by the bead core, but simply moves this bending to a location more outward in the radial direction. With this design, additional products outboard in the radial direction, which are sometimes referred to as a first bead layer and a second bead layer, are made of rubber materials that have the same stiffness as the flexible second portion.

The first and second bead layers are made of materials that are more flexible than the stiff first portion of the bead filler, and may have a stiffness of <NUM> with reasonably high cohesion properties. It is also known to provide first and second bead layers that have a higher stiffness at <NUM> MPa that achieve lower hysteresis but with the compromise of lower cohesion. Even at <NUM> MPa, the material making up the bead layers in this version is still more flexible than the stiffer mixes in the stiffer rubber first portion of the bead filler. In addition to the coextruded, two portion bead core, a chafer is included that wraps completely around the bead core. These configurations are difficult to build, expensive, and leaves the end of the turnup ply exposed. As such, there is a need to reduce or eliminate a bending hot spot in heavy truck tires, and to improve heated rim performance of the tire without adding significant cost to the tire.

The use of identical or similar reference numerals in different figures denotes identical or similar features.

Reference will now be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, and not meant as a limitation of the invention. For example, features illustrated or described as part of one embodiment can be used with another embodiment to yield still a third embodiment.

The present invention provides for a bead <NUM> design of a heavy duty truck tire <NUM> that features first and second bead layers <NUM>, <NUM> that are stiffer than a bead filler <NUM> portion of the bead <NUM>. The stiffness of the first and second bead layers <NUM>, <NUM> is <NUM> MPa to 14MPa. This configuration of the bead <NUM> reduces or eliminates a bending hot spot that may or may not be present just above the bead core <NUM>. Further, this configuration may achieve higher heat resistance in the tire <NUM> such as improved heated rim performance. The provided design achieves casing ply unwrapping under high heat and load while at the same time providing improved resistance to casing ply fatigue in the bead zone. The provided configuration offers a way to avoid extending the chafer ply under the bead core <NUM>, which poses significant fabrication issues, including uniformity, which increases fabrication costs.

<FIG> shows a tire <NUM> that is a heavy duty truck tire <NUM>. In this regard, the tire <NUM> is not designed for nor used with a car, motorcycle, or light truck (payload capacity less than <NUM>,<NUM> pounds), but is instead designed for and used with heavy duty trucks such as <NUM> wheelers, garbage trucks, or box trucks. The tire <NUM> may be a steer tire, a drive tire, a trailer tire, or an all position tire. The tire <NUM> includes a casing <NUM> onto which a tread <NUM> is disposed thereon. The bead <NUM> is a part of the casing <NUM> that is at the inner radial end of the casing <NUM> closest to the central axis <NUM>. The central axis <NUM> of the tire <NUM> extends through the center of the casing <NUM>, and the axial direction <NUM> of the tire <NUM> is parallel to the central axis <NUM>. The radial direction <NUM> of the tire <NUM> is perpendicular to the central axis <NUM>, and the tread <NUM> is located farther from the central axis <NUM> in the radial direction <NUM> than the casing <NUM>. The tread <NUM> extends all the way around the casing <NUM> in the circumferential direction <NUM> of the tire <NUM> and circles the central axis <NUM> by <NUM> degrees.

<FIG> is a radial cut of a tire <NUM> in accordance with one exemplary embodiment. Various tissues, sometimes called products, composed of different materials can be present throughout the tire <NUM>. The tread <NUM> of the tire <NUM> is shown as being located farthest from the axial center of the tire <NUM> in the radial direction <NUM>. A first belt layer <NUM> and a second belt layer <NUM> are located below the tread <NUM> in the radial direction <NUM> and comprise belts for use in strengthening and holding the form of the tire <NUM>. The reinforcement belts of the layers <NUM>, <NUM> may be crossed relative to one another, and in some instances they can be arranged at an angle of <NUM> degrees to one another. The casing <NUM>, or carcass, extends from the tread <NUM> and includes sidewalls of the tire <NUM> terminating in a pair of beads <NUM> that are arranged for mounting onto the rim of the wheel of the vehicle. A bead core <NUM> is located in each one of the beads <NUM> and is present to provide strength and a gripping force in the bead <NUM> for retention onto the rim. The left hand side bead <NUM> can be a mirror image of the right hand side bead <NUM> and both beads <NUM> can have products that are made of the same material. Some of the tissues/products are located only in the bead <NUM>, while others are located in the bead <NUM> and extend therefrom. For instance, an inner liner <NUM> is inside of the bead <NUM> and extends to an inner, exterior side of the bead <NUM> before extending up the sidewall of the casing <NUM>. The inner liner <NUM> then extends across the entire inner side of the crown in the axial direction <NUM> before extending into and forming the inner side of the right hand side wall of the casing <NUM>. The inner liner <NUM> then terminates inside of the right hand side bead <NUM> and is arranged in a similar mirror-image manner to its presence in the left hand side bead <NUM>. The inner liner <NUM> is thus a product of the tire <NUM> that extends all the way from one bead <NUM> to the other bead <NUM> and is made of a material that is fluid tight so that fluid between the tire <NUM> and rim is maintained therein for purposes of maintaining inflation pressure of the tire <NUM>.

The tire <NUM> includes a tissue designated as a reinforcement ply <NUM> that is located within one of the beads <NUM> and extends through the casing <NUM> and crown to the other bead <NUM>. The reinforcement ply <NUM> wraps around the bead core <NUM> and is designated as a return casing ply <NUM> in the location outward in the axial direction <NUM> from the bead core <NUM>. Other tissues in the tire <NUM> such as a stiffener layer <NUM> and a bead filler <NUM> do not extend into the sidewalls of the casing <NUM> or the crown, but are instead only located in the bead <NUM>. Relative positions in the axial direction <NUM> can be described with respect to inboard and outboard positions. The most inboard point of the tire <NUM> may be the radial direction line <NUM> shown in <FIG> as it is located at the center of the tire <NUM> in the axial direction <NUM>. The center of the tire <NUM> is inboard of both of the beads <NUM> in the axial direction <NUM>. As another example, the second bead layer <NUM> is outboard of the bead core <NUM> in the axial direction <NUM>.

<FIG> is a close up view of the left hand side bead <NUM> in accordance with another exemplary embodiment. The bead core <NUM> is made up of one or more steel rods. The bead core <NUM> is surrounded by the padding gum <NUM> and in some instances may be completely surrounded on all sides by the padding gum <NUM>. Surrounding the bead core <NUM> is a wrapping tissue <NUM> that can be made of nylon in some embodiments. The rod making up the bead core <NUM> is shown as a single piece and has a rectangular cross-sectional shape. This single piece can actually be many rods arranged together in the shape of a rectangle. However, in other embodiments the bead core <NUM> can be made of multiple components and these components could have any cross-sectional shape. The wrapping tissue <NUM> wraps around the padding gum <NUM> and overlaps itself to form an overlap. The wrapping tissue <NUM> may have a stiffness of <NUM> MPa and can be made of a rubber mix and textile which in some instances can be a nylon ply, the padding gum <NUM> can be a rubber mix and may have a stiffness of <NUM> MPa, and the bead core <NUM> can be made of steel or aluminum and can have a stiffness of <NUM>,<NUM>,<NUM> MPa in some embodiments. The bead core <NUM> can be lightened so that a smaller rod can be used to improve performance properties of the tire <NUM>.

The bead <NUM> includes bead filler <NUM>, sometimes referred to as gum stuffing, that is between and engages both the reinforcement ply <NUM> and the return casing ply <NUM>. The wrapping tissue <NUM> engages the bead filler <NUM>, the reinforcement ply <NUM>, and the return casing ply <NUM>. The wrapping tissue <NUM> functions to stabilize the geometry of the padding gum <NUM> and the bead core <NUM>. If the wrapping tissue <NUM> were not present, the padding gum <NUM> would assume a more square shape upon formation, and would assume a more oval shape when the tire <NUM> is used. The wrapping tissue <NUM> thus causes the tissues of the bead <NUM> to be desirably shaped so that they can function in an intended manner. It is to be understood that other truck tires <NUM> can be made without a wrapping tissue <NUM> and can function in a completely normal and safe manner. The addition of a wrapping tissue <NUM> may provide an even higher bead <NUM> endurance performance than in those instances in which a wrapping tissue <NUM> is absent in the bead <NUM>. However, various truck tire <NUM> designs exist that are fully functional and safe that both include and do not include a wrapping tissue <NUM>.

The bead filler <NUM> is a rubber mix that is different than the rubber mix making up the padding gum <NUM>. The material making up the bead filler <NUM> is more flexible than the material making up the padding gum <NUM>. The bead filler <NUM> can have a stiffness from <NUM> MPa to <NUM>. The bead filler <NUM> engages the wrapping tissue <NUM>, the reinforcement ply <NUM> and the return casing ply <NUM>, and may extend from the reinforcement ply <NUM> to the return casing ply <NUM> in the axial direction <NUM>. The bead filler <NUM> can be a material or composite material that has the same stiffness at all points, as distinguished from a two zone bead filler <NUM> that has a stiffer portion and a more flexible portion. The configuration of the bead <NUM> provides a way to use softer rubber which is desirable for impact and aging resistance. The bead filler <NUM> is a product that is not coextruded and can be a single, soft product as compared to some other stiffer products of the bead <NUM>. In some exemplary embodiments, no product/portion of the bead <NUM> is formed by coextrusion or is a coextruded product. The return casing ply <NUM> is a portion of the reinforcement ply <NUM> that is on the outboard side of the bead core <NUM> in the axial direction <NUM>. The return casing ply <NUM> may begin at the most inward portion of the reinforcement ply <NUM> in the radial direction <NUM>. The bead filler <NUM> ends in the bead <NUM> or in some instances may be a product that extends into the sidewall of the tire <NUM>. However, the bead filler <NUM> does not extend all the way under the belt layers <NUM>, <NUM> to the other sidewall of the tire <NUM>. The reinforcement ply <NUM> is a composite material that includes metal cords and a rubber mix. The reinforcement ply <NUM> in the direction of its cords is stiffer than the wrapping tissue <NUM>, the bead filler <NUM>, and the padding gum <NUM>. The reinforcement ply <NUM> extends from the bead <NUM>, through the sidewall, under the belt layers <NUM>, <NUM>, and then into the opposite sidewall and down into the bead <NUM> on the right hand side of the tire <NUM>.

The stiffener layer <NUM> is located outboard from the return casing ply <NUM> in the axial direction <NUM> and contacts the return casing ply <NUM> along a portion of its length. The stiffener layer <NUM> terminates in the bead <NUM> so that some of it is located inward in the radial direction <NUM> from the bead core <NUM>. Other portions of the stiffener layer <NUM> are outward in the radial direction <NUM> from the bead core <NUM>. The stiffener layer <NUM> can be made of a combination of steel and rubber, and this rubber may have a stiffness of <NUM> MPa. The bead <NUM> includes an anti-abrasive strip <NUM> that is on the outside of the bead <NUM> and designed to engage the rim. The anti-abrasive strip <NUM> engages the stiffener layer <NUM>, but need not in other arrangements. The stiffener layer <NUM> in <FIG> extends outward in the radial direction <NUM> to have a portion outward of the bead core <NUM>, and the return casing ply <NUM> in the radial direction <NUM>.

The first bead layer <NUM> is a product of the tire <NUM> made of rubber that has a portion located between and engaging the return casing ply <NUM> and the stiffener layer <NUM> in the axial direction <NUM>. The first bead layer <NUM> extends outward in the radial direction <NUM> and engages the bead filler <NUM>. The first bead layer <NUM> terminates at an outward radial terminal end <NUM> that is positioned inward of a portion of the bead filler <NUM> in the radial direction <NUM>. The first bead layer <NUM> may terminate in the bead <NUM>, and may or may not extend to the sidewall of the tire <NUM>. However, the first bead layer <NUM> does not extend to be under the belt layers <NUM>, <NUM>, and does not extend to the right hand side sidewall or right hand side bead <NUM>. The second bead layer <NUM> is likewise a product of the tire <NUM> made of rubber, and has a portion between and engaging the stiffener layer <NUM> and the anti-abrasive strip <NUM>. The second bead layer <NUM> extends outward in the radial direction <NUM> and engages the first bead layer <NUM>, terminating at an outward radial terminal end <NUM> that is short of the outward radial terminal end <NUM> so that a portion of the first bead layer <NUM> is outward in the radial direction <NUM> from the entire second bead layer <NUM>. The outward radial terminal end <NUM> is outward in the radial direction <NUM> from the outward radial terminal end <NUM>. An opposite inner radial terminal end <NUM> of the second bead layer <NUM> is located at an inner radial terminal end of the stiffener layer <NUM> and is outboard of the bead core <NUM> in the axial direction <NUM>. As with the first bead layer <NUM>, the second bead layer <NUM> may extend into the sidewall of the tire <NUM>, but does not extend over to the second sidewall or the right hand side bead <NUM> of the tire <NUM>. The second bead layer <NUM> engages a sidewall product <NUM> that is in the sidewall and that may have a stiffness that is <NUM> to <NUM> MPa. The first bead layer <NUM> and the second bead layer <NUM> are both interior products of the tire <NUM> and do not have any portions that form the outer surface of the tire <NUM>.

The first bead layer <NUM> has a stiffness that is <NUM>-<NUM> MPa. Likewise, the second bead layer <NUM> has a stiffness that is <NUM>-<NUM> MPa. In some embodiments the stiffness of the first bead layer <NUM> is the same as the stiffness of the second bead layer <NUM>. In other embodiments the stiffness of the second bead layer <NUM> is different from the stiffness of the first bead layer <NUM>. The first bead layer <NUM> can have a stiffness that is <NUM> MPa, <NUM> MPa, <NUM> MPa, <NUM> MPa, 11MPa, <NUM> MPa, from <NUM>-<NUM> MPa, from <NUM>-<NUM> MPa, or from <NUM>-<NUM> MPa in accordance with certain exemplary embodiments. The second bead layer <NUM> can have a stiffness that is <NUM> MPa, <NUM> MPa, <NUM> MPa, <NUM> MPa, <NUM> IMPa, <NUM> MPa, from <NUM>-<NUM> MPa, from <NUM>-<NUM> MPa, or from <NUM>-<NUM> MPa in accordance with certain exemplary embodiments. The stiffness of the first bead layer <NUM> and the stiffness of the second bead layer <NUM> are both greater than the stiffness of the bead filler <NUM> so that the first bead layer <NUM> and the second bead layer <NUM> are each more stiff than the bead filler <NUM>. Although various stiffness amounts for the first and second bead layers <NUM>, <NUM> are provided, the preferred embodiment employs a first bead layer <NUM> that has an <NUM> MPa stiffness, and a second bead layer <NUM> that has an <NUM> MPa stiffness.

The first and second bead layers <NUM>, <NUM> extend so as to have a portion be inward in the radial direction <NUM> from the farthest inward radial extent of the return casing ply <NUM>. The first bead layer <NUM> completely fills the void, with the exception possibly of tape <NUM>, between the return casing ply <NUM> and the stiffener layer <NUM>, sometimes referred to as a chafer. The second bead layer <NUM> should completely fill the void, with the exception of possibly tape <NUM>, between the stiffener layer <NUM> and the anti-abrasive strip <NUM>. The provided design thus utilizes stiffer products <NUM>, <NUM> in the outboard zone of the bead <NUM>. Further, the provided design does not use a stiff product directly against the reinforcement ply <NUM> interior (inboard in the axial direction <NUM>) side. The current design spreads hydrostatic stresses from the rim flange over a much larger zone than if the stiff layer were against the reinforcement ply <NUM>. This spreading reduces concentrated bending spots in the reinforcement ply <NUM> over the entire region of the bead <NUM>, thus improving fatigue performance of the reinforcement ply <NUM>. The present configuration provides resistance to casing ply unwrapping because of the rigid and cohesive first bead layer <NUM> shearing against the return side of the casing ply. The first and second bead layers <NUM> and <NUM> also provide rigidity to the working (interior side) of the casing ply to resist fatigue.

The present application describes the stiffness of a product or material. The stiffness that is being referred to is the Young's modulus which is the stiffness of an elastic material, or elastic modulus. The stiffness is provided in measurements of mega pascals (MPa). The stiffness material property in question that is being referred to is MA10. This stiffness property can be calculated using French standard NF T <NUM>-<NUM>, September <NUM>.

Tape <NUM> is located in the bead <NUM> and engages the second bead layer <NUM>, the stiffener layer <NUM>, and the first bead layer <NUM>. The tape <NUM> may be present on the end of the stiffener layer <NUM> when the stiffener layer <NUM> is assembled into the green tire <NUM> before curing. The tape could be wrapped around the outward radial terminal end <NUM> in this regard before and after assembly of the stiffener layer <NUM> into the tire <NUM>. Although the tape <NUM> is shown as being present, it is to be understood that the tape <NUM> is not present in the tire <NUM> in other exemplary embodiments of the tire <NUM>. The provided configuration of the bead <NUM> allows the elimination of tape <NUM> at the ends of all products thus decreasing cost of the tire <NUM> and reducing complexity of the tire <NUM>.

An alternate design of the bead <NUM> is illustrated in <FIG> which again shows the left hand bead <NUM> (the right side bead <NUM> being a mirror image) in cross-section. The products of the <FIG> design and their arrangement are the same as that previously discussed and a repeat of this information is not necessary. However, there are some differences in the configuration of the first and second bead layers <NUM> and <NUM>. The lengths of the bead layers <NUM>, <NUM> are shortened in the radial direction <NUM> so that they are shorter in the <FIG> embodiment than in the <FIG> embodiment. The bead layers <NUM>, <NUM> extend in the radial direction <NUM> so that the outward radial terminal ends <NUM>, <NUM> terminate at an outward radial terminal end <NUM> of the stiffener layer <NUM> in the radial direction <NUM>. This termination may be exactly at the radial position of the end <NUM>, or the three ends <NUM>, <NUM>, <NUM> could be not exactly at the same position in the radial direction <NUM> but could be very close to one another such as a few millimeters to one another in the radial direction <NUM>. As such, when described as having ends that terminate in the same radial location it is to be understood that there can be some tolerance in the regard, and the ends <NUM>, <NUM>, <NUM> could be up to <NUM> millimeters difference in location in the radial direction <NUM> but still be considered to be terminating at the same radial location due to this close proximity.

The <FIG> embodiment likewise differs from the <FIG> embodiment in that a product that is a first flexible layer <NUM> is present that engages the outward radial terminal end <NUM> and extends outward in the radial direction <NUM> to engage the bead filler <NUM>, the sidewall product <NUM>, and the second flexible layer <NUM>. The first flexible layer <NUM> extends farther outward in the radial direction <NUM> than the second flexible layer <NUM>. The second flexible layer <NUM> engages the outward radial terminal end <NUM> and extends outward in the radial direction <NUM> terminating short of the termination point of the first flexible layer <NUM>. The second flexible layer <NUM> additionally engages the first flexible layer <NUM>, the sidewall product <NUM>, and the anti-abrasive strip <NUM>. The majority of the second flexible layer <NUM> is located outboard from the first flexible layer <NUM> in the axial direction <NUM>.

The stiffness of the first flexible layer <NUM> is less than the stiffness of the first bead layer <NUM> and the stiffness of the second bead layer <NUM>. Likewise, the stiffness of the second flexible layer <NUM> is less than the stiffness of layers <NUM> and <NUM>. The stiffness of the first flexible layer <NUM> is <NUM>-<NUM> MPa, and the stiffness of the second flexible layer <NUM> is <NUM>-<NUM> MPa. The first and second flexible layers <NUM>, <NUM> are softer and have lower hysteresis than the layers <NUM> and <NUM>. The stiffness of the first flexible layer <NUM> may be the same as the stiffness of the second flexible layer <NUM>, or they can be different from one another. The stiffness of the bead filler <NUM> may be the same as the stiffness of the first flexible layer <NUM>, and can be the same as the stiffness of the second flexible layer <NUM>, or can be different than these layers <NUM> and <NUM>. The configuration in <FIG> still provides the cohesion and rigidity needed to resist reinforcement ply <NUM> fatigue and unwrapping, while keeping lower hysteresis and rigidity in the upper part of the bead <NUM> zone where there is more deflection. In this upper zone, the rigidity is not needed and the higher hysteresis contributes to a higher rolling resistance of the tire <NUM> which is not desired.

Another exemplary embodiment of the tire <NUM> is shown in <FIG> that includes products configured like those of <FIG> such that a repeat of this information is not necessary. The difference in <FIG> concerns the second bead layer <NUM> that extends a farther distance inward in the radial direction <NUM> than it does in the <FIG> or <FIG> embodiments. Here, the second bead layer <NUM> wraps around a portion of the bead core <NUM> and terminates at a location in the radial direction <NUM> that is inward of the entire bead core <NUM>, the entire bead filler <NUM>, the entire first bead layer <NUM>, and the entire stiffener layer <NUM>. As described herein, when a component is wrapped around another it may or may not engage that component. The second bead layer <NUM> engages the return casing ply <NUM>. If the second bead layer <NUM> is extended far enough, additional casing ply unwrapping performance could be expected as well as resistance to mounting damage. The illustrated arrangement of the second bead layer <NUM> in <FIG> can be used with any of the variously described embodiments of the bead <NUM> of the tire <NUM> herein and need not be only used in connection with the <FIG> embodiment.

Another exemplary embodiment of the bead <NUM> of the tire <NUM> is shown in <FIG> that includes an additional product that is the third bead layer <NUM>. The third bead layer <NUM> is located between the bead filler <NUM> and the return casing ply <NUM> in the axial direction <NUM> and engages both of these products, and the third bead layer <NUM> engages the wrapping tissue <NUM> of the bead <NUM> and extends outward in the radial direction <NUM> from the bead <NUM>. The third bead layer <NUM> has a stiffness that is <NUM>-<NUM> MPa. The stiffness of the third bead layer <NUM> can be the same as the stiffness of the first and second bead layers <NUM> and <NUM> and may be greater than the stiffness of the bead filler36, and the first and second flexible layers <NUM>, <NUM> if these layers <NUM>, <NUM> are present. The third bead layer <NUM> extends in the radial direction <NUM> outward to the outer terminal end of the return casing ply <NUM> and terminates here to share the same location in the radial direction <NUM>. The third bead layer <NUM> will add additional casing <NUM> ply unwrapping and fatigue performance. The third bead layer <NUM> has a cross-sectional size that is less than the bead filler <NUM>, and is located in an outboard region in the axial direction <NUM> of the bead <NUM> where stiffness is strategically employed as herein described. Although shown in connection with the <FIG> embodiment, the third bead layer <NUM> can be inserted into any of the other embodiments shown and described.

Claim 1:
A heavy truck tire (<NUM>) that has a central axis (<NUM>), a radial direction (<NUM>), and an axial direction (<NUM>), comprising:
a tread (<NUM>);
a casing (<NUM>) that carries the tread (<NUM>), wherein the casing (<NUM>) has a bead (<NUM>, <NUM>) that has:
a bead core (<NUM>, <NUM>) that has a rod and padding gum (<NUM>);
a reinforcement ply (<NUM>) that wraps around a section of the bead core (<NUM>, <NUM>), wherein the reinforcement ply (<NUM>) has a return casing ply (<NUM>) a portion of which is outboard in the axial direction (<NUM>) from the bead core (<NUM>, <NUM>);
a bead filler (<NUM>) that has a portion radially outward from the bead core (<NUM>, <NUM>) in the radial direction (<NUM>) and axially inboard from the return casing ply (<NUM>) in the axial direction (<NUM>);
a stiffener layer (<NUM>) that has a portion located outboard from the return casing ply (<NUM>) in the axial direction (<NUM>);
a first bead layer (<NUM>) that has a portion that is between the return casing ply (<NUM>) and the stiffener layer (<NUM>) in the axial direction (<NUM>);
a second bead layer (<NUM>) that has a portion that is outboard from the stiffener layer (<NUM>);
characterized in that
the stiffness of the first bead layer (<NUM>) is <NUM> MPa to <NUM> MPa when calculated as the Young's modulus MA10 using French standard NF T <NUM>-<NUM>, September <NUM>;
the stiffness of the second bead layer (<NUM>) is <NUM> MPa to <NUM> MPa when calculated as the Young's modulus MA10 using French standard NF T <NUM>-<NUM>, September <NUM>;
wherein the stiffness of the bead filler (<NUM>) is less than the stiffness of the first bead layer (<NUM>), and wherein the stiffness of the bead filler (<NUM>) is less than the stiffness of the second bead layer (<NUM>).