Tire with a tread having improved endurance properties

Abstract

The invention relates to a tire, the tread of which has at least one groove. According to the invention, the tread consists of a first elastomer blend, and at least a portion of the bottom and / or the walls (10) of at least one groove (7) surrounding the junction zones between the bottom and the two walls (10) of the at least one groove (7) is made of a second elastomer blend over a thickness (E) of at least 1 mm, the first elastomer blend has a fatigue resistance of less than 130 kcycle measured at 23°C until 108% elongation according to ISO standard 6943-2017, and the second elastomer blend has a fatigue resistance that is at least 30% greater than that of the first elastomer blend, measured at 23°C until 108% elongation according to ISO standard 6943-2017.

Description

TIRE WITH A TREAD WITH IMPROVED ENDURANCE PROPERTIES

[0001] The present invention relates to a tire, with a radial carcass reinforcement and more particularly a tire intended to equip vehicles carrying heavy loads and traveling at high speed, such as, for example, trucks, tractors, trailers or road buses.

[0002] Generally speaking, in heavy goods vehicle type tires, the carcass reinforcement is anchored on both sides in the bead area and is surmounted radially by a crown reinforcement consisting of at least two layers, superimposed and formed of parallel wires or cables in each layer and crossed from one layer to the next, making angles of between 10° and 45° with the circumferential direction. Said working layers, forming the working reinforcement, may also be covered with at least one so-called protective layer and formed of advantageously metallic and extensible reinforcement elements, called elastic.It may also comprise a layer of low-extensibility metal wires or cables forming an angle of between 45° and 90° with the circumferential direction, this ply, called the triangulation ply, being radially located between the carcass reinforcement and the first crown ply, called the working ply, formed of parallel wires or cables having angles at most equal to 45° in absolute value. The triangulation ply forms with at least said working ply a triangulated reinforcement, which, under the various stresses to which it is subjected, exhibits little deformation, the triangulation ply having the essential role of absorbing the transverse compression forces to which all the reinforcing elements are subjected in the area of ​​the crown of the tire.

[0003] Cables are said to be inextensible when, under a tensile force equal to 10% of the breaking force, the said cables exhibit a relative elongation of at most 0.2%.

[0004] Cables are said to be elastic when, under a tensile force equal to the breaking load, the said cables exhibit a relative elongation of at least 3% with a maximum tangent modulus of less than 150 GPa.

[0005] Circumferential reinforcing elements are reinforcing elements which make angles with the circumferential direction in the range + 2.5°, - 2.5° around 0°.

[0006] The circumferential direction of the tire, or longitudinal direction, is the direction corresponding to the periphery of the tire and defined by the rolling direction of the tire.

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

[0008] The radial direction is a direction intersecting the axis of rotation of the tire and perpendicular to it.

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

[0010] A radial or meridian plane is a plane that contains the tire's axis of rotation.

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

[0012] Some current tires, called "road tires", are designed to travel at high speeds and on increasingly long journeys, due to the improvement of the road network and the growth of the motorway network throughout the world. All the conditions under which such a tire is called upon to travel undoubtedly allow an increase in the number of kilometers traveled, the wear of the tire being less; on the other hand, the endurance of the latter and in particular of the crown reinforcement is penalized.

[0013] There are indeed constraints at the level of the crown reinforcement and more particularly shear constraints between the crown layers, combined with a significant increase in the operating temperature at the ends of the axially shortest crown layer, which result in the appearance and propagation of cracks in the rubber at the said ends.

[0014] In order to improve the endurance of the crown reinforcement of the type of tire studied, solutions relating to the structure and quality of the layers and / or profiles of rubber compounds which are arranged between and / or around the ends of the plies and more particularly the ends of the axially shortest ply have already been provided.

[0015] It is known in particular to introduce a layer of rubber mixture between the ends of the working layers to create a decoupling between said ends to limit the shear stresses. Such decoupling layers must however exhibit very good cohesion. Such layers of rubber mixtures are, for example, described in patent application WO 2004 / 076204.

[0016] The tires thus produced effectively improve performance, particularly in terms of endurance.

[0017] Furthermore, it is known to introduce a layer of circumferential reinforcing elements to produce tires with a very wide tread or to give tires of a given size greater load capacities. Patent application WO 99 / 24269 describes, for example, the presence of such a layer of circumferential reinforcing elements.

[0018] The layer of circumferential reinforcing elements is usually made up of at least one metal cable wound to form a turn whose laying angle relative to the circumferential direction is less than 2.5°.

[0019] In combination with this internal tire structure, it is known to provide the tread, that is to say the part of the tire intended to come into contact with the ground during rolling and to wear during rolling, with a sculpture formed of relief elements delimited by cutouts whether circumferential, transverse or oblique. The objective of such a sculpture is to give the tread good performance when rolling on dry roads and on water-covered roads, particularly in wet weather.

[0020] For the purposes of the invention, a cutout generically designates either a groove or an incision and corresponds to the space delimited by walls of material facing each other and spaced apart from each other by a non-zero distance (called "width of the cutout"). What differentiates an incision from a groove is precisely this distance; in the case of an incision, this distance is appropriate to allow at least partial contact of the opposite walls delimiting said incision at least when passing into contact with the roadway. In the case of a groove, the walls of this groove cannot come into contact with each other under normal driving conditions.

[0021] For the purposes of the invention, a circumferentially or longitudinally oriented cutout is a cutout whose mean plane of at least part of the walls of said cutout forms an angle with a longitudinal plane of less than 10°. This angle formed with a longitudinal plane may be oriented in one direction or the other relative to said plane. longitudinal. A longitudinally oriented cutout can also be a cutout whose walls undulate or zigzag around a mean plane as just described.

[0022] For the purposes of the invention, a transversely oriented cutout is a cutout whose mean plane of at least part of the walls of said cutout forms an angle with a radial plane of less than 35°. This angle formed with a radial plane may be oriented in one direction or the other relative to said radial plane. A transversely oriented cutout may also be a cutout which runs continuously on either side of a mean plane as just described; it may also be a cutout whose walls undulate or zigzag around a mean plane as just described.

[0023] For the purposes of the invention, an obliquely oriented cutout is a cutout whose mean plane of at least part of the walls of said cutout forms an angle with a radial plane of between 35° and 80°. This angle formed with a radial plane may be oriented in one direction or the other relative to said radial plane. An obliquely oriented cutout may also be a cutout which runs continuously on either side of a mean plane as just described; it may also be a cutout whose walls undulate or zigzag around a mean plane as just described.

[0024] When running tires produced in this way subjected to constraints that are particularly demanding on the tread, particularly when running in very severe drift and / or on steep slopes, damage to the tread has appeared, resulting in particular in the tearing of rubber blocks.

[0025] An aim of the invention is to provide tires whose tread endurance properties are improved regardless of use, the properties in particular of wear and overall endurance of the tire being preserved for normal uses.

[0026] This object is achieved according to the invention by a tire with a radial carcass reinforcement comprising a crown reinforcement, itself radially capped with a tread, said tread being joined to two beads by means of two sidewalls, said tread comprising a tread surface intended to come into contact with a roadway and form a contact surface, said tread having a plurality of cutouts consisting of at least one groove consisting of two walls opening onto the tread surface and a surface connecting the two walls forming the bottom of said at least one groove, said bottom of said at least one groove being connected to said two walls by junction zones, the tread being made up of at least a first elastomeric mixture forming at least a part of the rolling surface when the tire is new, at least a part of the bottom and / or of the walls of said at least one groove surrounding the junction zones between said bottom and said two walls of said at least one groove being made up of a second elastomeric mixture over a thickness of at least 1 mm, the first elastomeric mixture having a fatigue resistance, measured at 23°C up to an elongation of 108% according to the ISO 6943-2017 standard, of less than 130 kcycle and the second elastomeric mixture having a fatigue resistance at least 30% higher than the fatigue resistance of the first elastomeric mixture, measured at 23°C up to an elongation of 108% according to the ISO 6943-2017 standard.

[0027] The thickness of the second elastomeric mixture is measured locally in a direction normal to the surface of the wall of said at least one circumferential groove.

[0028] Fatigue resistance, expressed in number of cycles or in relative unit (ur), is measured in a known manner on 12 dumbbell-type specimens (H2), subjected to repeated low-frequency tractions up to an elongation of 108%, at 23°C, until rupture of the specimen, according to ISO 6943-2017. During the measurement, compensation for remanence is imposed. A higher value indicates better fatigue resistance.

[0029] According to a first embodiment of the invention, said at least one groove is a longitudinally oriented groove.

[0030] According to a second embodiment of the invention, said at least one groove is a transversely oriented groove.

[0031] According to a third embodiment of the invention, said at least one groove is an obliquely oriented groove.

[0032] The tires thus produced according to the invention effectively allow driving in particularly demanding conditions without seeing any tearing on the tread appearing in comparison with tires of more conventional design.

[0033] The inventors believe they have demonstrated that when driving in conditions that are particularly demanding on the tread with tires of usual design, the tears which occur on the tread seem to start at the junction zones between the bottom and the walls of a groove. The inventors believe to interpret this phenomenon due to the extremely small radii of curvature which are formed for example at the level of these junction zones and which are conducive to the initiation of cracking under the effect of cyclic stresses during rolling, in particular in the presence of small stones which become stuck. During rolling, under heavy stresses on the tread, in particular when drifting and / or on steep slopes leading to a load transfer to the tires furthest to the front of the vehicle, the cracks propagate and can lead to the tearing of part of the tread.

[0034] The presence of a mixture in accordance with the invention, at least locally in the area sensitive to the initiation of cracks, makes it possible to limit or at least delay the appearance of these cracks and therefore reduces the risk of tearing off part of the tread whatever the driving conditions.

[0035] According to a preferred embodiment of the invention, the entire bottom and walls of said at least one groove are made of the second elastomeric mixture over a thickness of at least 1 mm so that the second mixture forms the complete surface of said at least one groove.

[0036] This preferred embodiment of the invention simplifies the production of the tire according to the invention, the second mixture being positioned before molding according to the knowledge of a person skilled in the art to obtain the tire according to the invention after curing and molding of the tread forming the sculpture.

[0037] According to a preferred embodiment of the invention, the thickness of the second elastomeric mixture is less than 5 mm. The volume of the second mixture thus remains limited in comparison with the volume of the first mixture which thus contributes mainly to the desired properties of the tread such as grip and wear.

[0038] According to a preferred embodiment of the invention, the second elastomeric mixture has a fatigue resistance at least 50% higher and preferably still greater than 75% than the fatigue resistance of the first elastomeric mixture, measured at 23°C up to an elongation of 108% according to standard ISO 6943-2017.

[0039] According to an advantageous variant of the invention, the first elastomeric mixture has a maximum value of tan(ô), noted tan(ô)max, less than 0.25.

[0040] The loss factor tan(ô) is a dynamic property of the rubber compound layer. It is measured on a viscoanalyzer (Metravib VA4000), according to ASTM D 5992-96. The response of a sample of vulcanized compound (cylindrical specimen 2 mm thick and 78 mm 2 of section), subjected to sinusoidal stress in alternating simple shear, at a frequency of 10 Hz, at a temperature of 60°C. A strain amplitude sweep is carried out from 0.1 to 50% (forward cycle), then from 50% to 1% (return cycle). For the return cycle, the maximum value of tan(ô) observed is indicated, noted tan(ô) ma x.

[0041] In the case where the thickness of the material is between 1 and 2 mm, the loss factor tan(ô) is measured using the same method and under the same conditions, as described previously, on a sample of vulcanized composition which is in the form of a cylindrical test piece 1 mm thick and 78 mm2 in cross-section.

[0042] Rolling resistance is the resistance that appears when the tire rolls. It is represented by the hysteretic losses linked to the deformation of the tire during a revolution. The frequency values ​​linked to the revolution of the tire correspond to values ​​of tan(ô) measured between 30 and 100°C. The value of tan(ô) at 60°C thus corresponds to an indicator of the rolling resistance of the tire while rolling.

[0043] Furthermore, the tests carried out have shown that the rolling resistance properties are maintained or even improved by the choice of the second elastomeric compound, which can offer even better rolling resistance performance.

[0044] Advantageously according to the invention, the first elastomeric mixture is a rubber composition based on at least one elastomeric matrix comprising a copolymer based on styrene and butadiene and at least one reinforcing filler.

[0045] By "elastomer matrix" or "elastomeric matrix" is meant all of the elastomer(s) present in the rubber composition.

[0046] By “diene” elastomer (or indistinctly rubber), whether natural or synthetic, must be understood an elastomer made up at least in part (i.e. a homopolymer or copolymer) of diene monomer(s) (i.e., carrier(s) of two carbon-carbon double bonds, conjugated or not).

[0047] By copolymer based on styrene and butadiene is meant here a copolymer of at least one styrene monomer and at least one butadiene monomer (and of course also any mixture of such copolymers); in other words, said copolymer based on styrene and butadiene comprises by definition at least styrene units (derived from the styrene monomer) and butadiene units (derived from the butadiene monomer).

[0048] Advantageously according to the invention, the second elastomeric mixture is a rubber composition based on at least one elastomeric matrix comprising at least 25% of at least one synthetic elastomer based on butadiene and at least one reinforcing filler.

[0049] According to a preferred embodiment of the invention, the second elastomeric mixture is a rubber composition based on at least one elastomeric matrix comprising at least 30% and more preferably at least 40% of at least one synthetic elastomer based on butadiene.

[0050] More preferably according to the invention, said at least one synthetic elastomer based on butadiene is an SBR and / or a BR (cis or anionic) and more advantageously said at least one synthetic elastomer is a cis BR.

[0051] The rubber compositions according to the invention of the first mixture or of the second mixture may comprise one or more reinforcing fillers.

[0052] Any type of so-called reinforcing filler, known for its ability to reinforce a rubber composition that can be used in particular for the manufacture of tires, can be used, for example an organic filler such as carbon black, an inorganic filler such as silica or a mixture of these two types of fillers.

[0053] Suitable carbon blacks include all carbon blacks, including those conventionally used in tires or tire treads. These include, in particular, reinforcing carbon blacks of the 100, 200, and 300 series, or blacks of the 500, 600, or 700 series (ASTM D-1765-2017 grades), such as blacks NI 15, N134, N234, N326, N330, N339, N347, N375, N550, N683, and N772.

[0054] By "reinforcing inorganic filler" is meant here any inorganic or mineral filler, whatever its color and origin (natural or synthetic), also called "white" filler, "clear" filler or even "non-black" filler ("non-black filler") as opposed to carbon black; this inorganic filler being capable of reinforcing on its own, without any other means than an intermediate coupling agent, a rubber composition intended for the manufacture of pneumatic tires, in other words capable of replacing, in its reinforcing function, a conventional tire-grade carbon black. Such a filler is generally characterized, in a known manner, by the presence of hydroxyl groups (-OH) on its surface, requiring, in order to be used as a reinforcing filler, the use of a coupling agent or system intended to ensure a stable chemical bond between the filler and the elastomeric matrix.

[0055] Suitable inorganic reinforcing fillers are, in particular, siliceous mineral fillers, preferably silica (SiCh). The silica used may be any reinforcing silica known to those skilled in the art, in particular any precipitated or pyrogenic silica having a BET surface area and a CTAB specific surface area both less than 450 m 2 / g, preferably 30 to 400 m 2 / g, especially between 60 and 300 m 2 / g.

[0056] Of course, the term inorganic reinforcing filler also means mixtures of different reinforcing inorganic fillers, in particular highly dispersible silicas as described above or a mixture of inorganic fillers of the siliceous type and non-siliceous inorganic fillers. As non-siliceous inorganic fillers, mention may be made of mineral fillers of the aluminous type, in particular alumina (AI2O3) or aluminum (oxide)hydroxides, or even reinforcing titanium oxides, for example described in US 6,610,261 and US 6,747,087. The non-siliceous inorganic fillers, when present, are in the minority in the reinforcing filler.

[0057] The physical state in which the inorganic reinforcing filler is presented is indifferent, whether in the form of powder, microbeads, granules, or even balls.

[0058] A person skilled in the art will understand that, as a filler equivalent to the reinforcing inorganic filler described in this paragraph, a reinforcing filler of another nature, in particular organic such as carbon black, could be used, provided that this reinforcing filler is covered with an inorganic layer such as silica, or else comprises functional sites on its surface, in particular hydroxyl sites, requiring the use of a coupling agent to establish the bond between the filler and the elastomer. For example, carbon blacks for tires may be mentioned, for example, as described in patent documents WO 96 / 37547, WO 99 / 28380.

[0059] According to a variant of the invention, the reinforcing filler of the first mixture and / or of the second mixture is predominantly carbon black, that is to say that it comprises more than 50% (>50%) by weight of carbon black relative to the total weight of reinforcing filler. Optionally according to this variant, the reinforcing filler may also comprise silica or another reinforcing inorganic filler.

[0060] According to another variant of the invention, the reinforcing filler of the first mixture and / or of the second mixture consists of carbon black.

[0061] According to another variant of the invention, the reinforcing filler of the first mixture and / or of the second mixture is predominantly an inorganic reinforcing filler (preferably silica), that is to say that it comprises more than 50% (>50%) by weight of an inorganic reinforcing filler such as silica relative to the total weight of the reinforcing filler. Optionally according to this variant, the reinforcing filler also comprises carbon black. According to this option, the carbon black is used at a rate less than or equal to 20 phr, more preferably less than or equal to 10 phr (for example the carbon black rate may be in a range from 0.5 to 20 phr, in particular from 1 to 10 phr). In the indicated ranges, the coloring (black pigmenting agent) and anti-UV properties of carbon blacks are benefited from, without otherwise penalizing the typical performances provided by the reinforcing inorganic filler.

[0062] The elastomeric compositions of the tread of the tire according to the invention may optionally also comprise all or part of the usual additives, known to those skilled in the art and usually used in treads, such as for example processing aids, fillers (reinforcing or non-reinforcing, other than those mentioned above), pigments, protective agents such as anti-ozone waxes, chemical anti-ozonants (6PPD, TMQ), antioxidants, anti-fatigue agents and reinforcing resins (such as those described for example in application WO 02 / 10269).

[0063] According to an alternative embodiment of the invention, the crown reinforcement of the tire is formed from at least two working crown layers of reinforcing elements.

[0064] According to a preferred embodiment of the invention, the reinforcing elements of the working crown layers are inextensible metal cables.

[0065] The metal elements are preferably steel cables.

[0066] Advantageously according to the invention, the reinforcing elements of the working crown layers of the crown reinforcement are crossed from one layer to the other making angles of between 10° and 45° with the circumferential direction.

[0067] Advantageously still according to the invention, the working crown reinforcement comprises a layer of circumferential reinforcing elements, preferably arranged radially between two working crown layers.

[0068] According to an advantageous embodiment of the invention, the reinforcing elements of at least one layer of circumferential reinforcing elements are metallic reinforcing elements having a secant modulus at 0.7% elongation of between 10 and 120 GPa and a maximum tangent modulus of less than 150 GPa.

[0069] A preferred embodiment of the invention also provides that the crown reinforcement is completed radially on the outside by at least one additional layer, called a protective layer, of so-called elastic reinforcing elements, oriented relative to the circumferential direction with an angle of between 10° and 45° and in the same direction as the angle formed by the inextensible elements of the working layer which is radially adjacent to it.

[0070] According to any of the embodiments of the invention mentioned above, the crown reinforcement can also be completed, radially inside between the carcass reinforcement and the radially inner working layer closest to said carcass reinforcement, by a triangulation layer of inextensible metallic steel reinforcing elements making, with the circumferential direction, an angle greater than 45° and in the same direction as that of the angle formed by the reinforcing elements of the layer radially closest to the carcass reinforcement.

[0071] Other advantageous details and characteristics of the invention will emerge below from the description of the exemplary embodiments of the invention with reference to Figures 1 and 2 which represent: Figure 1, a meridian view of a diagram of a tire according to the invention, Figure 2, a radial sectional view of a groove of a tire according to the invention.

[0072] Figures are not drawn to scale to simplify understanding.

[0073] In Figure 1, the tire 1, of dimension 315 / 70 R 22.5, comprises a radial carcass reinforcement 2 anchored in two beads 3 by turning around rods 4. The carcass reinforcement is formed of a single layer of metal cables. This carcass reinforcement 2 is hooped by a crown reinforcement 5, formed radially from the inside to the outside: of a first working layer formed of non-hooped inextensible metal cables 9.35, continuous over the entire width of the ply, oriented at an angle equal to 22°, of a layer of circumferential reinforcing elements formed of 21x23 steel metal cables, of a second working layer formed of non-hooped inextensible metal cables 9.35, continuous over the entire width of the ply, oriented at an angle equal to 18° and crossed with the metal cables of the first working layer, of a protective layer formed of elastic metal cables 6.35.

[0074] All of these layers forming the crown reinforcement 5 are not shown in the figures.

[0075] The crown reinforcement is itself topped with a tread having a surface 6 intended to come into contact with the ground. The surface 6 of the tread is formed of four circumferential grooves 7 forming circumferential ribs 8 constituting the tread.

[0076] In Figure 2, a circumferential groove 7 is schematically represented in section along a radial plane.

[0077] The tread is mainly made up of a first mixture. In Figure 2, a thickness E of a second mixture forming the wall 10 of the circumferential groove 7 is also shown.

[0078] The average thickness E of the second mixture is equal to 2 mm. This thickness E is measured in the direction normal to the inner surface of the circumferential groove 7.

[0079] Tests are carried out with tires according to the invention.

[0080] The same tests are carried out with reference tires. The reference tires differ from the tires according to the invention by the absence of the second mixture, that is to say that the tread is entirely made up of the first mixture.

[0081] The different compounds used for treads are listed below: (1) Natural rubber (2) 98% neodymium polybutadiene of 1,4-cis unit; Tg=-108°C (3) Anionic styrene-butadiene copolymer containing 15% by weight of styrene unit and 24% of vinyl of the butadiene part (Tg -65°C) (4) Carbon black grade N 134 according to ASTM D-1765 -2017 (5) Carbon black grade N234 according to ASTM D-1765 -2017 (6) SER 6266 from SER (7) N-(l,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine “Santoflex 6PPD” from Flexys (8) N-cyclohexyl-2-benzothiazol-sulfenamide “Santocure CBS” from Flexsys (9) N-cyclohexylthio-phthalimide (CTP / PVI) marketed by Shandong Derek New Materials Co. (10) Stearic acid “Pristerene 4931” from Uniqema (11) Industrial grade Zinc Oxide from Umicore

[0082] The values ​​of the constituents are expressed in pce (parts by weight per hundred parts of elastomers).

[0083] The measured properties are expressed in the following table for each of the mixtures:

[0084] The result of fatigue resistance measurements is expressed in relative units (ur). A value higher than that of the control, arbitrarily set at 100, indicates an improved result, i.e. better fatigue resistance of the rubber samples.

[0085] The fatigue resistance of the first mixture is equal to 128 kcycle.

[0086] Initial endurance tests were carried out on a test machine requiring each of the tires to run in a straight line at a speed equal to the maximum speed index prescribed for the said tire (speed index) under an initial load of 4000 kg, gradually increased to reduce the duration of the test.

[0087] Further endurance tests were carried out on a test machine cyclically imposing a transverse force and a dynamic overload on the tires. The tests were carried out for the tires according to the invention under conditions identical to those applied to the reference tires.

[0088] The tests thus carried out have shown that the distances covered during each of these tests are at least as long or even longer for the tires according to the invention than the reference tires.

[0089] A final test aimed at reproducing a very severe drift of the tires was carried out. It consists of imposing a drift simulating the limit beyond which the vehicle can overturn.

[0090] This test consists of a preliminary step of placing the tire in an oven in a dry environment at 65°C for 15 weeks.

[0091] A test machine run is then carried out to cover more than 25,000 km with the tire at a speed of 40 km / h, the tire being put into drift for approximately 20% of the driving time. The tire is subjected to a load close to the nominal in a straight line and increased by approximately 40% in drift. The drift phases correspond to maximum lateral acceleration before a vehicle rolls over.

[0092] At the end of these tests, the tires are inspected using shearography and dissected to analyze any damage. This is a visual analysis that allows for comparison of any cracks and their propagation. The tires are rated and compared with each other. A score above 100 corresponds to a less damaged tire. A value of 100 is assigned to the reference tire that is the most damaged.

[0093] At the end of the rolling, the tires according to the invention show less extensive damage than the reference tires.

[0094] In addition, rolling resistance measurements were carried out.

[0095] The test results are presented in the following table. Rolling resistance measurements are expressed in kg / t, with a value of 100 being assigned to the reference tire. Values ​​above 100 show better rolling resistance performance.

[0096] These tests show that the tires according to the invention make it possible to maintain, or even slightly improve, performance in terms of rolling resistance compared to the reference tire.

Claims

CLAIMS 1 - Tire (1) with radial carcass reinforcement (2) comprising a crown reinforcement (5), itself radially capped with a tread, said tread being joined to two beads (3) by means of two sidewalls, said tread comprising a tread surface (6) intended to come into contact with a roadway and form a contact surface, said tread having a plurality of cutouts consisting of at least one groove (7) consisting of two substantially radially oriented walls opening onto the tread surface (6) and a surface connecting the two walls forming the bottom of said at least one groove (7), said bottom of said at least one groove (7) being connected to said two walls by junction zones, characterized in that the tread consists of at least a first elastomeric mixture forming at least part of the tread surface (6) when the tire is new,in that at least a portion of the bottom and / or walls of said at least one groove (7) surrounding the junction zones between said bottom and said two walls of said at least one groove (7) is made of a second elastomeric mixture over a thickness of at least 1 mm, in that the first elastomeric mixture has a fatigue resistance, measured at 23°C up to an elongation of 108% according to standard ISO 6943-2017, of less than 130 kcycle and in that the second elastomeric mixture has a fatigue resistance at least 30% higher than the fatigue resistance of the first elastomeric mixture, measured at 23°C up to an elongation of 108% according to standard ISO 6943-2017., 2 - Tire (1) according to claim 1, characterized in that said at least one groove is a groove (7) of longitudinal orientation. 3 - Tire (1) according to claim 1, characterized in that said at least one groove is a transversely oriented groove. 4 - Tire (1) according to claim 1, characterized in that said at least one groove is an obliquely oriented groove. 5 - Tire (1) according to one of claims 1 to 4, characterized in that the entire bottom and walls of said at least one groove (7) are made of the second elastomeric mixture over a thickness of at least 1 mm. 6 - Tire (1) according to one of the preceding claims, characterized in that the thickness of the second elastomeric mixture is less than 5 mm. 7 - Tire (1) according to one of the preceding claims, characterized in that the second elastomeric mixture has a fatigue resistance at least 50% greater than the fatigue resistance of the first elastomeric mixture, measured at 23°C up to an elongation of 108% according to standard ISO 6943-2017. 8 - Tire (1) according to one of the preceding claims, characterized in that the first elastomeric mixture has a maximum value of tan(ô), noted tan(ô) ma x, less than 0.

25. 9 - Tire (1) according to one of the preceding claims, characterized in that the first elastomeric mixture is a rubber composition based on at least one elastomeric matrix comprising a copolymer based on styrene and butadiene and at least one reinforcing filler. 10 - Tire according to one of the preceding claims, characterized in that the second elastomeric mixture is a rubber composition based on at least one elastomeric matrix comprising at least 25% of at least one synthetic elastomer based on butadiene and at least one reinforcing filler.

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