Tire with tread having improved durability properties

Abstract

The invention relates to a tyre, the tread of which has at least one circumferential groove (7) and at least one sipe (9) opening into the at least one circumferential groove (7). According to the invention, the tread is composed of a first elastomer blend and the wall (10) of the at least one circumferential groove (7) is composed of a second elastomer blend over a thickness (E) of at least 1 mm around at least a part of the region of intersection with the at least one sipe (9), the tearability coefficient of the second elastomer blend is at least 20% greater than the tearability coefficient of the first elastomer blend.

Description

Technical Field

[0001] The present invention relates to tires having radial carcass reinforcements, and more particularly to tires intended for mounting on vehicles (such as, for example, trucks, tractors, trailers, or buses) that bear heavy loads and travel at continuous speeds. Background Technology

[0002] Typically, in tires used in heavy-duty vehicles, the carcass reinforcement is anchored in the bead regions on both sides and is radially covered by a crown reinforcement consisting of at least two stacked layers formed of yarns or cords. These yarns or cords are parallel within each layer and cross from one layer to the other, forming an angle between 10° and 45° with respect to the circumferential direction. The working layer forming the working reinforcement may also be covered with at least one layer called a protective layer, formed of a stretchable reinforcing element (called an elastic reinforcing element), which is advantageously metallic. This protective layer may also include a layer of low-elongation metal yarns or cords forming an angle between 45° and 90° with respect to the circumferential direction. This ply layer is called a triangular ply layer and is located radially between the carcass reinforcement and the first crown ply layer (called the working ply layer), which are formed of parallel yarns or cords with an absolute angle of at most 45°. The triangular cord layer together with at least the working cord layer forms a triangular reinforcement that undergoes almost no deformation under various stresses. The triangular cord layer is essentially used to absorb lateral compressive forces applied to all reinforcing elements in the tire crown region.

[0003] A cord is said to be inextensible when it exhibits a relative elongation of at most 0.2% under a tensile force equal to 10% of its breaking force.

[0004] A cord is said to be elastic when it exhibits a relative elongation of at least 3% and a maximum tangential modulus of less than 150 GPa under a tensile force equal to the breaking load.

[0005] A circumferential reinforcing element is a reinforcing element that forms an angle with the circumferential direction in the range of +2.5° to -2.5° (relative to 0°).

[0006] The circumferential or longitudinal direction of a tire is the direction corresponding to the outer circumference of the tire and defined by the tire's direction of travel.

[0007] The lateral or axial direction of the tire is parallel to the tire's axis of rotation.

[0008] The radial direction is the direction that intersects with and is perpendicular to the axis of rotation of the tire.

[0009] The axis of rotation of a tire is the axis around which the tire rotates during normal use.

[0010] The radial plane or meridional plane is the plane that contains the axis of rotation of the tire.

[0011] The circumferential midplane or equatorial plane is a plane perpendicular to the tire's axis of rotation and that divides the tire into two halves.

[0012] Due to improvements in road networks and the expansion of the global highway network, some tires today, known as "highway tires," are designed to travel increasingly longer distances at higher speeds. While this combination of driving conditions undoubtedly increases mileage due to reduced wear on the tire, it also negatively impacts the tire's durability, particularly the durability of the tread reinforcement.

[0013] This is because there is stress in the crown reinforcement, and more specifically, shear stress between the crown layers. These stresses, combined with the non-negligible increase in operating temperature at the end of the shortest axial crown layer, result in cracks appearing and propagating in the rubber at said end.

[0014] To improve the durability of the crown reinforcement of the tire type studied, solutions have been proposed related to the structure and quality of the rubber compound layers and / or molding elements arranged between and / or around the ends of the ply layers (more specifically, the ends of the shortest axial ply layers).

[0015] A well-known practice is to introduce a rubber compound layer between the ends of the working layer to create a disengagement bond between the ends, thereby limiting shear stress. However, such a disengaged layer needs to have very good cohesion. For example, such a rubber compound layer is described in patent application WO 2004 / 076204.

[0016] Tires produced in this way can effectively improve performance, especially in terms of durability.

[0017] Furthermore, in order to produce tires with very wide treads or to impart greater load-bearing capacity to tires of a certain size, it is known to introduce a circumferential reinforcing element layer. For example, patent application WO 99 / 24269 describes the presence of such a circumferential reinforcing element layer.

[0018] The circumferential reinforcement element layer typically consists of at least one metal cord wound together to form a coil with a layup angle of less than 2.5° relative to the circumferential direction.

[0019] In conjunction with this internal tire structure, it is known to provide a tread with a tread pattern formed by raised elements defined by slits (i.e., the part of the tire intended to contact the ground during driving and intended to wear during driving). The purpose of this tread pattern is to impart good tread performance when driving on dry roads and water-covered roads (especially when it is raining).

[0020] For the purposes of this invention, a cut generally refers to a groove or notch, and corresponds to a space defined by material walls facing each other and spaced a non-zero distance apart (referred to as the "width of the cut"). It is this distance that distinguishes a notch from a groove; in the case of a notch, this distance is suitable so that the opposing walls defining the notch are at least partially in contact upon entering a contact surface with the road surface. In the case of a groove, the walls of the groove do not contact each other under normal rolling conditions.

[0021] Heavy vehicle tires typically include circumferential grooves that form circumferential ribs.

[0022] For the purposes of this invention, a longitudinally oriented or circumferential cut is a cut in which the average plane of at least a portion of the wall of the cut forms an angle of less than 10° with the longitudinal plane. This angle with the longitudinal plane can be oriented in one direction or another relative to the longitudinal plane. A longitudinally oriented cut can also be a cut in which the wall is wavy or zigzag around the average plane as described above.

[0023] To improve tread performance without unduly reducing the tread's shear stiffness, a known practice is to form multiple laterally oriented or obliquely oriented edges on the tread surface to cut through the water film on the road surface, thereby ensuring good contact between the tread and the road surface. One method of obtaining such edges involves providing multiple lateral or oblique cuts to the tread, particularly lateral sipes or oblique sipes.

[0024] For the purposes of this invention, a laterally oriented cut is one in which the average plane of at least a portion of the cut's wall forms an angle of less than 35° with the radial plane. This angle with the radial plane can be oriented in one direction or another relative to the radial plane. A laterally oriented cut can also be one that continuously passes through both sides of the average plane as described above; it can also be one in which the walls of the cut are wavy or zigzag-shaped around the average plane as described above.

[0025] For the purposes of this invention, the obliquely oriented cut is one in which the average plane of at least a portion of the wall of the cut forms an angle between 35° and 80° with the radial plane. This angle with the radial plane can be oriented in one direction or another relative to the radial plane. The obliquely oriented cut can also be one that continuously passes through both sides of the average plane as described above; it can also be one in which the walls of the cut are wavy or zigzag-shaped around the average plane as described above.

[0026] When tires produced in this way are driven under conditions that apply particularly high stress to the tread, especially in the case of a violent impact with a curb, the tread will be damaged, which is particularly manifested as tearing or chipping of the rubber blocks. Summary of the Invention

[0027] The object of the present invention is to provide a tire with improved tread durability properties, while maintaining tire properties (especially wear and overall durability) under normal use conditions, regardless of usage.

[0028] According to the invention, this objective is achieved by a tire having radial carcass reinforcements, the tire including crown reinforcements that are themselves radially covered by a tread, the tread being connected to two bead via two sidewalls, the tread including a tread surface intended to contact the road and form a contact surface, the tread having a plurality of cuts, each cut consisting of at least one circumferential groove at least partially present on the tire circumference and at least one sipe leading to the at least one circumferential groove, the tread being composed of at least one first elastomer compound, the first elastomer being... The compound forms at least a portion of the tread surface when the tire is new, and the walls of the at least one circumferential groove are composed of a second elastomer compound at a thickness of at least 1 mm around at least a portion of the intersection area between the at least one circumferential groove and the at least one sipe. The tear coefficient (expressed in N / m) of the second elastomer compound is at least 25% greater than that of the first elastomer compound. The tear coefficient is the product of the breaking force per unit thickness (expressed in N / mm thickness) and the elongation at break (expressed as %), which are measured at 100°C.

[0029] The thickness of the second elastomer compound is locally measured in a direction perpendicular to the surface of the wall of the at least one circumferential groove.

[0030] The breaking force and elongation at break, for tear resistance, were measured on a specimen subjected to a tensile test at 500 mm / min for fracture, using a dynamic tensile testing machine equipped with a system for measuring and acquiring the force and displacement of the moving crossbeam. The tensile specimen consisted of a parallelepiped-shaped rubber sheet with a thickness of 2.5 mm, a length of 145 mm, and a width of 10 mm. Before the test, three very fine notches, 3 mm deep and perpendicular to the specimen length, were cut along one edge of the specimen using a razor blade: one in the middle, and two on either side of the first notch, 6 mm apart. The force applied to achieve fracture was determined (expressed in N / mm specimen thickness), and the elongation at break was measured (expressed as a percentage). The test was conducted in air at 100°C. Higher values ​​reflect good cohesion of the rubber composition, despite the presence of crack initiation sites.

[0031] According to a variant embodiment of the invention, the depth of the at least one cutting groove is greater than or equal to 50% of the depth of the at least one circumferential groove.

[0032] According to a first embodiment of the present invention, the at least one cutting groove is a transversely oriented cutting groove.

[0033] According to a second embodiment of the present invention, the at least one cutting groove is an inclined cutting groove.

[0034] For the purposes of this invention, the depth of the cut (groove or notch) is the radial distance between the tread surface and the innermost point of the cut, measured on a brand new tire.

[0035] Compared to tires with more conventional designs, the tires produced according to this invention are able to drive effectively under conditions of particularly high stress without tread chipping.

[0036] The inventors believe they have demonstrated that, when a conventionally designed tire is driven under conditions of exceptionally high stress on the tread, tread chipping appears to begin in the area where the sipes lead to the circumferential grooves. The inventors believe this phenomenon can be explained by the fact that the intersection between the bottom of the sipes and the walls of the circumferential grooves tends to induce longitudinal fracture upon impact. During driving, when the tire experiences impact loads on the tread, these fractures lead to chipping, resulting in partial tread tearing.

[0037] The compound according to the invention, being present at least partially in areas sensitive to crack initiation, can limit or at least delay the occurrence of such cracks, and thus reduce the risk of partial tread chipping, regardless of driving conditions.

[0038] According to a preferred embodiment of the invention, the entire wall of the at least one circumferential groove is composed of a second elastomer compound with a thickness of at least 1 mm, such that the second compound forms the entire surface of the at least one circumferential groove.

[0039] This preferred embodiment of the invention simplifies the production of tires according to the invention. According to those skilled in the art, the second compound is placed in place before molding, so that the tire according to the invention is obtained after the tread is cured and molded to form the tread pattern.

[0040] According to a preferred embodiment of the invention, the thickness of the second elastomer compound is less than 5 mm. Therefore, the volume of the second compound is still limited compared to the volume of the first compound, and thus the first compound makes a major contribution to the desired properties of the tread (e.g., grip and wear).

[0041] According to a preferred embodiment of the present invention, the tear coefficient of the second elastomer compound is at least 50% greater than that of the first elastomer compound, and more preferably at least 100% greater.

[0042] According to an advantageous variant of the invention, the maximum value of tan(δ) of the first elastomer compound (in terms of tan(δ)) max (This indicates that) is less than 0.25.

[0043] The loss factor tan(δ) is a kinetic property of the rubber compound layer. It is measured on a viscosity analyzer (Metravib VA4000) according to ASTM D5992-96 standard. A vulcanized composition sample (2 mm thick and 78 mm cross-section) subjected to simple alternating sinusoidal shear stress at 10 Hz at 60 °C was recorded. 2 The response of a cylindrical specimen was measured. Strain amplitude scans were performed from 0.1% to 50% (outward cycle) and then from 50% to 1% (backward cycle). For the backward cycle, the maximum observed tan(δ) value is shown, with tan(δ) as the maximum value. max express.

[0044] When the material thickness is between 1 mm and 2 mm, the same method as described above is used under the same conditions in a cylindrical specimen (1 mm thick and 78 mm cross-section). 2 The loss factor tan(δ) was measured on a vulcanized composition sample in the form of )

[0045] Rolling resistance is the resistance that occurs when a tire rolls. It is represented by the hysteresis loss related to the tire's deformation during rotation. The frequency values ​​related to tire rotation correspond to the tan(δ) values ​​measured between 30°C and 100°C. Therefore, the tan(δ) value at 60°C corresponds to the rolling resistance index when the tire is rolling.

[0046] Furthermore, the tests conducted demonstrated that by selecting a second elastomer compound, the rolling resistance properties were maintained or even improved, as the second elastomer compound may have better rolling resistance performance than the first elastomer compound.

[0047] Advantageously, according to the invention, the first elastomer compound is a rubber composition based on at least one elastomer matrix and at least one reinforcing filler, wherein the elastomer matrix comprises a copolymer based on styrene and butadiene.

[0048] The term "elastomer matrix" or "elastic matrix" refers to all elastomers present in a rubber composition.

[0049] "Diene" elastomers (or equivalent rubbers) (whether natural or synthetic) should be understood to mean elastomers that are at least partially (i.e., homopolymers or copolymers) composed of diene monomers (i.e., monomers with two conjugated or non-conjugated carbon-carbon double bonds).

[0050] Here, a styrene-butadiene-based copolymer is understood to mean a copolymer of at least one styrene monomer and at least one butadiene monomer (including, of course, any mixture of these copolymers); in other words, by definition, the styrene-butadiene-based copolymer contains at least styrene units (derived from styrene monomers) and butadiene units (derived from butadiene monomers).

[0051] Advantageously, according to the invention, the second elastomer compound is a rubber composition based on at least one elastomer matrix and at least one reinforcing filler, wherein the elastomer matrix comprises primarily (i.e., at least 80%) natural rubber.

[0052] According to a preferred embodiment of the present invention, the second elastomer compound is a rubber composition based on at least one elastomer matrix comprising 100% natural rubber.

[0053] The rubber composition for the first or second compound according to the present invention may contain one or more reinforcing fillers.

[0054] Any type of "reinforcing" filler known to be able to reinforce rubber compositions that can be specifically used in the manufacture of tires can be used, such as organic fillers (e.g., carbon black), inorganic fillers (e.g., silica), or mixtures of both.

[0055] All carbon blacks are suitable as carbon blacks, especially those commonly used in tires or their treads. Among the carbon blacks commonly used in tires or their treads, the 100, 200, and 300 series reinforced carbon blacks, or the 500, 600, or 700 series carbon blacks (ASTM D-1765-2017 grade), will be mentioned more specifically, such as, for example, N115, N134, N234, N326, N330, N339, N347, N375, N550, N683, and N772 carbon blacks.

[0056] Here, the term "inorganic reinforcing filler" should be understood to refer to any inorganic or mineral filler (regardless of its color and origin, whether natural or synthetic) that, in contrast to carbon black, is also called "white filler," "transparent filler," or even "non-black filler." This inorganic filler can reinforce rubber compositions intended for use in tire manufacturing without the need for any means other than an intermediate coupling agent; in other words, it can replace conventional tire-grade carbon black in its reinforcing function. In a known manner, such fillers are typically characterized by the presence of hydroxyl (-OH) groups on their surface, and in order to be used as reinforcing fillers, a coupling agent or coupling system designed to provide a stable chemical bond between the filler and the elastomer matrix is ​​required.

[0057] Silica-type mineral fillers (preferably silica (SiO2)) are particularly suitable as inorganic reinforcing fillers. The silica used can be any reinforcing silica known to those skilled in the art, especially those with a BET specific surface area and CTAB specific surface area both less than 450 m². 2 / g, preferably 30m 2 / g to 400m 2 / g, especially at 60m 2 / g and 300m 2 Any precipitated or pyrolytic silica between / g.

[0058] Of course, the term "inorganic reinforcing filler" is also understood to refer to mixtures of various inorganic reinforcing fillers, particularly mixtures of highly dispersible silica as described above, or mixtures of siliceous and non-siliceous inorganic fillers. As non-siliceous inorganic fillers, aluminous mineral fillers (particularly alumina (Al₂O₃) or aluminum (oxide) hydroxides) or reinforcing titanium oxides (e.g., as described in US 6 610 261 and US 6 747 087) may be mentioned. When present, non-siliceous inorganic fillers constitute a smaller amount in the reinforcing filler.

[0059] It does not matter what physical state the inorganic reinforcing filler is provided in, whether it is in the form of powder, microspheres, granules or beads.

[0060] Those skilled in the art will understand that, as fillers equivalent to the inorganic reinforcing fillers described in this section, reinforcing fillers with other properties (particularly organic properties) (e.g., carbon black) can be used, provided that the reinforcing filler is covered with an inorganic layer (e.g., silica) or contains functional sites (particularly hydroxyl sites) on its surface that require the use of a coupling agent to establish bonds between the filler and the elastomer. Examples include carbon black for tires, as described, for example, in patent documents WO 96 / 37547 and WO 99 / 28380.

[0061] According to a variant of the invention, the reinforcing filler in the first and / or second blends is primarily carbon black, i.e., it contains more than 50% by weight (>50% by weight) of carbon black relative to the total weight of the reinforcing filler. Optionally, according to this variant, the reinforcing filler may also contain silica or another reinforcing inorganic filler.

[0062] According to another variant of the invention, the reinforcing filler of the first blend and / or the second blend is composed of carbon black.

[0063] According to another variation of the invention, the reinforcing filler in the first and / or second blends is primarily an inorganic reinforcing filler (preferably silica); that is, it comprises more than 50% by weight (>50% by weight) of inorganic reinforcing filler (e.g., silica) relative to the total weight of the reinforcing filler. Optionally, according to this variation, the reinforcing filler also comprises carbon black. According to this choice, carbon black is used in a content of less than or equal to 20 phr, more preferably less than or equal to 10 phr (e.g., the carbon black content can range from 0.5 phr to 20 phr, particularly from 1 phr to 10 phr). Within the indicated range, the coloring properties (black colorant) and UV resistance properties of carbon black are utilized without compromising the typical performance qualities provided by the reinforcing inorganic filler.

[0064] The elastomeric composition of the tire tread according to the invention may optionally contain all or part of common additives known to those skilled in the art and commonly used in treads, such as, for example, processing aids, fillers (reinforcing or non-reinforcing fillers other than those described above), pigments, protective agents (e.g., anti-ozone waxes, chemical anti-ozone agents (6PPD, TMQ) or antioxidants), anti-fatigue agents, and reinforcing resins (such as those described, for example, in application WO 02 / 10269).

[0065] According to a variant embodiment of the invention, the tire crown reinforcement is formed of at least two working crown layers having reinforcing elements.

[0066] According to a preferred embodiment of the present invention, the reinforcing element of the working crown layer is a non-stretchable metal cord.

[0067] The preferred metal component is steel cord.

[0068] Advantageously, according to the invention, the reinforcing elements of the working crown layer of the crown reinforcement cross from one layer to another and form an angle between 10° and 45° with the circumferential direction.

[0069] Furthermore, according to the invention, the working crown reinforcement includes a circumferential reinforcing element layer, which is preferably arranged radially between two working crown layers.

[0070] According to an advantageous embodiment of the invention, the reinforcing element of at least one circumferential reinforcing element layer is a metal reinforcing element having a secant modulus at 0.7% elongation between 10 GPa and 120 GPa and a maximum tangent modulus of less than 150 GPa.

[0071] A preferred embodiment of the invention further provides that the radially outer side of the crown reinforcement is supplemented by at least one additional layer (referred to as a protective layer) having a so-called elastic reinforcing element oriented at an angle between 10° and 45° relative to the circumferential direction, and the direction of said angle is the same as that formed by the non-extendable element of the working layer radially adjacent to it.

[0072] According to any of the above embodiments of the present invention, the crown reinforcement may be supplemented on the radially inner side between the carcass reinforcement and the radially inner working layer closest to the carcass reinforcement by a triangular layer having a non-extendable metal reinforcement element made of steel, the non-extendable metal reinforcement element being made of steel and forming an angle greater than 45° with the circumferential direction, and the direction of the angle being the same as the angle formed by the reinforcement element along the radial direction closest to the carcass reinforcement layer. Attached Figure Description

[0073] By reference Figures 1 to 3 Other details and advantageous features of the invention will become apparent from the following description of exemplary embodiments of the invention, wherein:

[0074] - Figure 1 A radial schematic diagram of a tire according to the present invention is shown.

[0075] - Figure 2 A schematic projection of a portion of the surface of a tire tread according to the invention is shown.

[0076] - Figure 3 A partial cross-sectional view is shown on a cross-sectional plane parallel to the average plane of the wall of the transverse sipe of the tire according to the invention.

[0077] For ease of understanding, the accompanying drawings are not to scale. Detailed Implementation

[0078] exist Figure 1 In this tire 1, with a size of 315 / 70R 22.5, a radial carcass reinforcement 2 is included, which is anchored in two bead 3 by being rolled up around a bead cord 4. The carcass reinforcement is formed of a single layer of metal cord. The carcass reinforcement 2 is encircled by a crown reinforcement 5, which is formed radially from the inside out as follows:

[0079] - A first working layer formed of non-wound, non-extendable 9.35 metallic cords, said non-wound, non-extendable 9.35 metallic cords being continuous across the entire width of the fabric layer and oriented at an angle equal to 22°.

[0080] - A circumferential reinforcing element layer, which is formed of 21×23 type steel metal cords.

[0081] - A second working layer formed of unwound, non-extensible 9.35mm metal cords, which are continuous across the entire width of the fabric layer, oriented at an angle of 18°, and intersecting with the metal cords of the first working layer.

[0082] - A protective layer formed of elastic 6.35 metal cord.

[0083] The combination of these layers constituting the crown reinforcement 5 is not shown in the attached figures.

[0084] The crown reinforcement itself is covered by the tread, which has a surface 6 designed to contact the ground. The tread surface 6 is formed by four circumferential grooves 7, which form circumferential ribs 8 constituting the tread.

[0085] Figure 2 A schematic projection of a portion of the surface 6 of the tire 1 tread is shown. The axis XX' represents the circumferential midplane of the tire. The surface 6 of the tread consists of five circumferential ribs 8, which are separated by four circumferential grooves 7. The ribs 8 also include lateral sipes 9 that lead to the circumferential grooves 7.

[0086] Figure 3 The cross-section of the circumferential groove 7 is schematically shown on the average plane of the wall of the transverse sipe 9 and the cross-sectional plane that is tangent to the surface 6 of the tread.

[0087] The depth d7 of the circumferential groove 7 is 14 mm. The depth d9 of the transverse groove 9 is 10 mm. Therefore, the depth d9 of the transverse groove 9 is basically more than half the depth d7 of the circumferential groove 7.

[0088] The tread is mainly composed of the first compound. Figure 3The thickness E of the second compound forming the wall 10 of the circumferential groove 7 is also shown.

[0089] The average thickness E of the second compound is 2 mm. This thickness E is measured in a direction perpendicular to the inner surface of the circumferential groove 7.

[0090] Tests were conducted using tires according to the invention.

[0091] The same tests were performed using a reference tire. The reference tires differ from the tires according to the invention in that they do not have a second compound, i.e., the tread is composed entirely of the first compound.

[0092] The following lists the various formulations used in tire treads:

[0093] First blend Second blend NR(1) 60 100 BR(2) 20 SBR(3) 20 Carbon black N134(4) 58 Carbon black N115(5) 47 Paraffin (6) 1 1 Antioxidant (6PPD)(7) 2 1.5 Accelerator CBS(8) 1.1 0.7 CTP(9) 0.06 Stearic acid (10) 1.5 2.5 Zinc oxide (11) 2.5 4 soluble sulfur 1.1 1

[0094] (1) Natural rubber

[0095] (2) Neodymium polybutadiene with 98% cis-1,4 units, Tg = -108℃

[0096] (3) Anionic styrene-butadiene copolymer containing 15% by weight of styrene units and 24% by weight of butadiene moiety (Tg-65℃)

[0097] (4) N134 grade carbon black according to standard ASTM D-1765-2017

[0098] (5) N115 grade carbon black according to standard ASTM D-1765-2017

[0099] (6) SER 6266 from SER

[0100] (7) N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, Santoflex 6PPD from Flexys

[0101] (8) N-cyclohexyl-2-benzothiazole sulfenamide, from Santocure CBS of Flexsys

[0102] (9) N-Cyclohexylthio-phthalimide (CTP / PVI) sold by Shandong Derek New Materials Co.

[0103] (10) Stearic acid, from Pristerene 4931 of Uniqema

[0104] (11) Industrial-grade zinc oxide from Umicore

[0105] The values ​​of the components are expressed in phr (parts by weight per hundred parts of rubber / elastomer).

[0106] The table below shows the properties measured for each blend:

[0107] First blend Second blend Fracture force per unit thickness (N / mm) 380 550 Elongation at break (%) 185 390 Tear coefficient (N / m) 70 215 <![CDATA[tan(δ) max (at 60℃) 0.22 0.16

[0108] The first durability test is performed on the testing machine, in which each tire is rolled in a straight line at an initial load of 4000 kg at a speed equal to the maximum speed rating (or speed index) specified for the tire, and the initial load is gradually increased to shorten the duration of the test.

[0109] Other durability tests were performed on the testing machine, applying lateral forces and dynamic overloads to the tire in a cyclic manner. The tire according to the invention was tested under the same conditions applied to a reference tire.

[0110] The tests conducted in this manner demonstrated that the tires according to the invention traveled at least as much as, or even more than, the distance traveled by the reference tires in each of these tests.

[0111] A final test was conducted to reproduce the impact of curb stones that the tires might experience.

[0112] The test included an initial step of driving at 120 km / h for one and a half hours, during which the tires were subjected to a load of 4,000 kg.

[0113] Then, the vehicle travels along a track that allows the tires to pass over curbs with a height between 15cm and 20cm.

[0114] The tire is driven continuously along three different tracks, at a speed of 10 km / h, so that the tire tread overlaps the curb by a few centimeters at varying degrees. These three consecutive tracks are repeated four times, resulting in the tire crossing the curb twelve times.

[0115] Repeat the entire test, subjecting each tire to two trials.

[0116] At the end of these tests, the tires are inspected and peeled using staggered speckle interferometry to allow for analysis of any damage. This is a visual analysis that allows for comparison between any cracks and crack propagation. The tires are scored and compared to each other. Scores greater than 100 correspond to tires with less damage. A score of 100 is assigned to the reference tire with the most severe damage.

[0117] Reference Tires The tire of the present invention Fraction 100 Greater than 130

[0118] At the end of the driving period, the tire according to the invention exhibited a lower degree of damage than the reference tire.

[0119] Rolling resistance was also measured.

[0120] The results of the tests are shown below. Rolling resistance measurements are expressed in kg / t, with a value of 100 assigned to the reference tire. A value greater than 100 indicates better rolling resistance performance.

[0121] Reference Tires The tire of the present invention Rolling resistance 100 101

[0122] These tests show that, compared to the reference tire, the tire according to the present invention can maintain or even slightly improve its rolling resistance performance.

Claims

1. A tire (1) having a radial carcass reinforcement (2), the tire (1) including a crown reinforcement (5) itself being radially covered by a tread, the tread being connected to two bead via two sidewalls, the tread including a tread surface (6) intended to contact a road and form a contact surface, the tread having a plurality of cuts, the cuts consisting of at least one circumferential groove (7) at least partially present on the tire circumference and at least one sipe (9) leading to said at least one circumferential groove (7), characterized in that, The tread is composed of at least one first elastomer compound, which forms at least a portion of the tread surface (6) when the tire is new. The wall (10) of the at least one circumferential groove (7) is composed of a second elastomer compound with a thickness of at least 1 mm around at least a portion of the intersection area between the at least one circumferential groove and the at least one sipe. The tear coefficient (in N / m) of the second elastomer compound is at least 25% greater than that of the first elastomer compound. The tear coefficient is the product of the breaking force per unit thickness (in N / mm thickness) and the elongation at break (in %), which are measured at 100°C.

2. The tire (1) according to claim 1, characterized in that, The depth of the at least one cutting groove (9) is greater than or equal to 50% of the depth of the at least one circumferential groove (7).

3. The tire (1) according to claim 1 or 2, characterized in that, The at least one cutting groove (9) is a transversely oriented cutting groove.

4. The tire according to claim 1 or 2, characterized in that, The at least one cutting groove (9) is an inclined cutting groove.

5. The tire (1) according to any one of claims 1 to 4, characterized in that, The entire wall (10) of the at least one circumferential groove (7) is composed of a second elastomer compound with a thickness of at least 1 mm.

6. The tire (1) according to any one of the preceding claims, characterized in that, The thickness of the second elastomer compound is less than 5 mm.

7. The tire (1) according to any one of the preceding claims, characterized in that, The tear coefficient of the second elastomer compound is at least 50% greater than that of the first elastomer compound.

8. The tire (1) according to any one of the preceding claims, characterized in that, The first elastomer compound is tan(δ) max The maximum value of tan(δ) is less than 0.

25. tan(δ) is measured at 60°C according to standard ASTM D 5992-96.

9. The tire (1) according to any one of the preceding claims, characterized in that, The first elastomer compound is a rubber composition based on at least one elastomer matrix and at least one reinforcing filler, wherein the elastomer matrix comprises a copolymer based on styrene and butadiene.

10. The tire (1) according to any one of the preceding claims, characterized in that, The second elastomer compound is a rubber composition based on at least one elastomer matrix and at least one reinforcing filler, wherein the elastomer matrix mainly comprises natural rubber, i.e., contains at least 80% natural rubber.

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