Tires having treads comprising oriented fibers

Abstract

The present invention relates to a tire with a radial carcass reinforcement, comprising a crown reinforcement radially surmounted by a tread joined to two beads by two sidewalls. According to the invention, the layer of elastomeric compound forming the tread surface of the tire is reinforced with non-metallic fibers, thereby improving grip on wet surfaces.

Description

Technical Field

[0001] The present invention relates to a tire with a radial carcass reinforcement, and more particularly to a tire intended to be mounted on vehicles carrying heavy loads, such as trucks, tractors, trailers or buses. Background Art

[0002] Typically, in heavy-duty tires, the carcass reinforcement is anchored on both sides in the bead region and radially covered by a crown reinforcement composed of at least two superimposed layers formed of threads or cords that are parallel in each layer and cross from one layer to the other, making angles of between 10° and 45° with the circumferential direction. The working layers forming the working reinforcement may also be covered with at least one layer, known as a protective layer, formed of reinforcing elements that are advantageously metallic and extensible and known as elastic reinforcing elements. The working layers may also comprise a layer of less extensible metal threads or cords that make angles of between 45° and 90° with the circumferential direction, this ply (known as a triangular ply) being radially positioned between the carcass reinforcement and a first crown ply (known as a working ply), said working ply being formed of parallel threads or cords making angles of at most 45° in absolute value. The triangular ply forms, at least with the working plies, a triangular reinforcement which exhibits hardly any deformation under the various stresses to which it is subjected, its key function being to absorb the transverse compression forces to which all the reinforcing elements in the crown region of the tire are subjected.

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

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

[0005] The circumferential direction or longitudinal direction of the tire is the direction corresponding to the circumference of the tire and defined by the direction of travel of the tire.

[0006] The tyre's axis of rotation is the axis about which the tyre rotates in normal use.

[0007] A radial plane or meridian plane is a plane containing the axis of rotation of the tire.

[0008] The circumferential median plane or equatorial plane is the plane perpendicular to the tire's axis of rotation and dividing the tire into two halves.

[0009] The transverse or axial direction of a tire is parallel to its axis of rotation. An axial distance is a distance measured along the axial direction. The expression "axially inside or axially outside, respectively" means "the axial distance, measured from the equatorial plane, is smaller or larger, respectively."

[0010] A radial direction is a direction that intersects and is perpendicular to the tire's axis of rotation. A radial distance is a distance measured along the radial direction. The expression "radially inside or radially outside, respectively" means "the radial distance, measured from the tire's axis of rotation, is smaller than or larger than, respectively."

[0011] Radially on the outside of the crown reinforcement is the tread, generally made of polymer material and intended to come into contact with the ground in the contact patch where the tire comes into contact with the ground.

[0012] It is known to provide the tread (i.e. the portion of the tire intended to come into contact with the ground during rolling and intended to wear during rolling) with a tread pattern formed by raised elements delimited by cutouts (e.g. grooves, whether circumferentially, transversely or obliquely oriented). The purpose of this tread pattern is to give the tread good performance both when running on dry roads and on roads covered with water, in particular when it rains.

[0013] However, in order to improve the performance of the tread without significantly reducing its shear stiffness, it is known to form on the tread surface a plurality of transversely or obliquely oriented edges designed to cut through the film of water on the road surface, thereby ensuring good contact between the tread and the road surface. One method of achieving such edges consists in providing the tread with a plurality of cuts in the form of grooves or sipes. In the present context, the distinction between sipes and grooves lies in the fact that the width of the sipes is adapted to allow at least partial contact between the opposing walls delimiting them during driving, in particular in the contact patch with the ground, which is not the case with grooves under normal conditions of tire use.

[0014] For the purposes of the present invention, a longitudinally oriented incision is one in which a plane bisecting at least a portion of the wall of the incision forms an angle of less than 10° with the longitudinal plane. This angle with the longitudinal plane can be oriented in one direction or the other relative to the longitudinal plane. A longitudinally oriented incision can further be one in which the wall undulates or zigzags about the bisecting plane (as described above).

[0015] For the purposes of the present invention, a transversely oriented incision is one in which a plane bisecting at least a portion of the wall of the incision forms an angle of less than 35° with a radial plane. This angle with the radial plane can be oriented in one direction or the other relative to the radial plane. A transversely oriented incision can further be one in which the wall undulates or zigzags about the bisecting plane (as described above).

[0016] For the purposes of the present invention, an obliquely oriented incision is one in which a plane bisecting at least a portion of the wall of the incision forms an angle between 35° and 80° with a radial plane. This angle with the radial plane can be oriented in one direction or the other relative to the radial plane. An obliquely oriented incision can further be one in which the wall undulates or zigzags about the bisecting plane (as described above).

[0017] As road networks improve and motorway networks grow worldwide, certain existing tires, known as "road" tires, are designed to travel longer and longer distances at high speeds. This allows for increased mileage and less wear on the tire.

[0018] In order to further increase the service life of the tire, it is common practice to select polymer materials to prepare treads with improved wear resistance. On the other hand, it is known that such materials are not conducive to grip, especially on wet ground.

[0019] Such a tire is described, for example, in document US 6,247, 512. This document describes the superposition of two layers of material forming the tread, the outer layer in contact with the ground being more effective, in particular in terms of wear. Summary of the Invention

[0020] The inventors have set themselves the task of being able to provide a tire which allows a greater rolling distance and has improved grip on wet ground.

[0021] This object is achieved according to the invention by a tire having a radial carcass reinforcement and comprising a crown reinforcement, said crown reinforcement itself being radially covered by a tread, said tread being joined to two beads by two sidewalls, said tread comprising grooves forming at least one tread pattern element, said tread comprising at least one layer of elastomeric compound forming the tread surface of the tire, said at least one layer of elastomeric compound being reinforced with non-metallic fibers, said non-metallic fibers being arranged substantially parallel to the outer surface of the tread, at least 40% of the non-metallic fibers being oriented in a direction forming an angle of less than 30° with respect to the main axis of inertia, Said principal axis of inertia is associated with the maximum moment of inertia of the ground-contacting surface of said at least one tread pattern element, said ground-contacting surface having its center in a longitudinal direction passing through the center of gravity of said ground-contacting surface being longitudinally located at the center of the contact patch, the tire being subjected to its nominal load on a nominal rim and inflated to its nominal pressure, and said at least one elastomeric compound layer having a value of longitudinal elastic modulus measured at ambient temperature in at least one direction parallel to the tread surface being greater than 5 times the value of longitudinal elastic modulus of said at least one elastomeric compound layer measured at ambient temperature in a direction perpendicular to the tread surface.

[0022] According to the present invention, preferably, the value of the longitudinal elastic modulus of the at least one elastomeric compound layer measured along at least one direction parallel to the tread surface at ambient temperature is less than 20 times the value of the longitudinal elastic modulus of the at least one elastomeric compound layer measured along a direction perpendicular to the tread surface at ambient temperature, and preferably less than 10 times the value of the longitudinal elastic modulus of the at least one elastomeric compound layer measured along a direction perpendicular to the tread surface at ambient temperature.

[0023] For the purposes of the present invention, the nominal load and pressure conditions and the nominal rim are defined according to ETRTO, TRA or JATMA regulations.

[0024] The longitudinal modulus of elasticity is measured according to standard NF ISO 37 of December 2005 on dumbbell test specimens type 2 by measuring the modulus of elasticity at 5% deformation and 23°C.

[0025] The angle of the short fibers in the tread is measured on a sample taken from the tread, preferably by removing half the width of a rib along a plane parallel to the tread surface, thereby revealing the interface containing the short fibers, and then cutting the tread along a plane parallel to the tread surface to obtain a material sample. According to the recommendations of "Orientation of short fibers in parts made of reinforced thermoplastic - Observation of fiber orientation" (Engineering techniques, reference AM 3729, July 10, 2003, Michel Vincent), a histogram of the orientation of the fibers relative to the longitudinal direction is established on a sample of at least 100 fibers by optical reflection microscopy.

[0026] According to a preferred embodiment of the present invention, the at least one elastomeric compound reinforced with non-metallic fibers has a tan(δ)-20° C. value strictly less than 0.50.

[0027] The dynamic property tan (δ)-20° C. is measured on a viscoanalyzer (Metravib VA4000) according to standard ASTM D 5992-96. The response of a test specimen consisting of two cylindrical pellets 2 mm thick and 1 cm in diameter (the test specimen is made from a tire sample taken at the mid-height of the area closest to the equatorial plane of the relevant layer, the thickness of which is sufficient to form the test specimen) is recorded, subjected to a simple alternating sinusoidal shear stress at a frequency of 10 Hz.

[0028] To measure tan(δ)-20°C, a temperature sweep is performed between -80°C and +100°C under a stress of 0.7 MPa, and the tan(δ) value observed at -20°C is recorded. It should be recalled that, in a manner known to those skilled in the art, this value represents the grip potential on wet surfaces: the higher the tan(δ)-20°C value, the better the grip. An arbitrary value of 100 is assigned to the control composition; a result greater than 100 indicates an increase in the tan(δ)-20°C value, corresponding to an improvement in grip on wet surfaces.

[0029] For example, a tire's grip is characterized by the force it can transmit to the ground under braking stress. This force is specifically expressed by the hysteresis losses associated with the deformation of the tread when stress is applied. Thus, the tan(δ)-20°C value represents an indicator of a tire's grip on wet ground when braking between 80 km / h and 0 km / h.

[0030] The various measurements are performed on brand new tires that have not been driven at all.

[0031] The inventors have been able to demonstrate that an elastomeric compound reinforced with non-metallic fibers as described above leads to a satisfactory compromise between wear resistance and grip of the tire on wet ground.

[0032] In particular, the elastomeric compound constituting the radially outer portion of the tread has a stiffness measured perpendicular to the tread surface that allows it to have satisfactory wear properties.

[0033] When the tire is squeezed in the contact patch, the presence of fibers oriented as described above in the elastomeric compound imparts the aforementioned stiffness to the mixture, resulting in less deformation of the tire tread. The inventors have been able to demonstrate that the presence of the non-metallic fibers limits so-called lateral deformations associated with the incompressibility of the elastomeric compound forming the radially outer portion of the tread. The inventors have also been able to demonstrate that deformation of the elastomeric compound layer forming the tire tread induces so-called parasitic forces in the contact patch. These so-called parasitic forces, described in "Effect of friction on rolling tire–pavement interaction" (H. Wang, I.L. Al-Qadi & I. Stanciulescu, NEXTRANS Project No. 049IY02, USDOT Region V Regional University Transportation Center Final Report), correspondingly reduce the amount of force that can be transmitted in the contact patch before the maximum force that can be transmitted is reached, characterized by the tire sliding on the ground. In other words, these so-called parasitic forces consume a portion of the grip potential. The presence of the non-metallic fibers in the elastomeric compound limits deformation of the tread, thereby contributing to better grip of the tire.

[0034] Preferably according to the invention the average length of the non-metallic fibers is between 0.5 and 10 mm, even more preferably between 2 and 5 mm.

[0035] The measurement of the staple length is carried out according to the invention by optical microscopy using automated optical analysis according to ISO 16065 or by one of the methods described in "AREVIEW OF IMAGE ANALYSIS BASED METHODS TO EVALUATE FIBER PROPERTIES" (Ulrich Hirn and Wolfgang Bauer, Lenzinger Berichte, 86 (2006) 96-105).

[0036] Preferably according to the invention, the average thickness of the non-metallic fibers is between 5 and 40 μm, even more preferably between 10 and 30 μm.

[0037] The measurement of the staple fiber thickness is carried out according to the invention by optical microscopy using automated optical analysis according to ISO 16065 or by one of the methods described in "AREVIEW OF IMAGE ANALYSIS BASED METHODS TO EVALUATE FIBER PROPERTIES" (Ulrich Hirn and Wolfgang Bauer, Lenzinger Berichte, 86 (2006) 96-105).

[0038] Advantageously according to the invention, the shape factor of the non-metallic fibers (ie the ratio between the length and thickness of the fibers) is between 12.5 and 2000. Also advantageously, the shape factor is between 50 and 1500, more preferably between 100 and 1000.

[0039] The non-metallic fibers can have any known cross section, such as cubic, cylindrical or star-shaped. According to the invention, preferably, the fibers have a cylindrical cross section. In this case, the thickness corresponds to the diameter of the short fibers.

[0040] According to a preferred variant embodiment of the invention, the Young's modulus of the non-metallic fibers is between 0.5 and 500 GPa, preferably between 0.5 and 200 GPa, more preferably between 0.5 and 50 GPa.

[0041] The Young's modulus of the staple fibers is measured according to ASTM D885.

[0042] According to an advantageous embodiment of the invention, the content of non-metallic fibers present in the layer of elastomeric compound forming the tread surface of the tire is between 2.5 and 10% by volume, preferably between 5 and 7.5% by volume.

[0043] For the purposes of the present invention, the fiber content of an elastomeric compound expressed as a volume percentage is determined using an X-ray tomography method as described in the paper "Multi-resolution imaging by X-ray tomography: application to local tomography in materials science" (Tao Zhang, University of Grenoble, 2012 (NNT: 2012GRENI020.tel-00876871). A person skilled in the art would know how to use acquisition parameters, filters, and appropriate image processing to identify the fibers within the matrix and the corresponding volumes, and thus determine the volume fraction of the fibers.

[0044] Advantageously according to the invention, the non-metallic fibers are selected from natural fibers such as cotton, flax or bamboo, etc. The advantage of this choice is that the biodegradable reinforcing elements can be released into the natural world as the tire tread wears away.

[0045] According to one embodiment of the invention, the elastomeric compound forming the tread surface of the tire comprises non-metallic fibers in two main orientations substantially perpendicular to each other, so that the value of the longitudinal elastic modulus measured at ambient temperature along at least two directions parallel to the tread surface is greater than 5 times the value of the longitudinal elastic modulus measured at ambient temperature along a direction perpendicular to the tread surface.

[0046] According to this embodiment of the invention, in order to determine the orientation of the fibers, a series of cuts are made parallel to the tread surface in order to reveal the fibers and a histogram of the orientation of the fibers in these planes parallel to the tread surface with respect to the longitudinal direction is established by optical reflection microscopy on a sample of at least 100 fibers, according to the recommendations in "Orientation of short fibres in parts made of reinforced thermoplastic - Observation of fibre orientation" (Engineering techniques, Reference AM3729, July 10, 2003, Michel VINCENT).

[0047] According to this embodiment, in order to measure the longitudinal elastic modulus, at least two samples with a thickness of 1 mm are extracted from the tread in a plane parallel to the tread surface along the two main orientations that are essentially perpendicular to each other, and a sample with a thickness of 1 mm is extracted in a plane perpendicular to the tread surface and in a direction perpendicular to the tread surface.

[0048] According to one embodiment of the invention, the crown reinforcement of the tire is formed from at least two working crown layers of inextensible reinforcing elements crossing from one layer to the other and forming angles of between 10° and 45° with the circumferential direction.

[0049] According to other embodiments of the invention, the crown reinforcement also comprises at least one layer of circumferential reinforcing elements.

[0050] One embodiment of the invention also provides for the crown reinforcement to be supplemented radially on the outside by at least one additional layer (called protective layer) having reinforcing elements (called elastic reinforcing elements) oriented at angles of between 10° and 45° with respect to the circumferential direction and in the same direction as the angles formed by the inextensible elements of the working layers radially adjacent thereto.

[0051] According to any of the above-described embodiments of the invention, the crown reinforcement may also be supplemented radially on the inside between the carcass reinforcement and the radially inner working layer closest to said carcass reinforcement by a triangulation layer made of inextensible steel metal reinforcement elements forming an angle greater than 60° with the circumferential direction and in the same direction as the angle formed by the reinforcement elements of the layer radially closest to the carcass reinforcement. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Further advantageous features and details of the invention will be seen from the following references Figures 1 to 4 A description of exemplary embodiments of the present invention will become apparent from the accompanying drawings in which:

[0053] - Figure 1 shows a meridian diagram of a tire according to one embodiment of the present invention,

[0054] - Figure 2 A schematic diagram showing the contact patch of a tire,

[0055] - Figure 3 A schematic diagram of a portion of the contact patch of a tire is shown, illustrating the directions associated with the maximum and minimum moments of inertia of the tread blocks of the tire,

[0056] - Figure 4 A partial schematic diagram of the contact patch of a tire is shown, illustrating the directions associated with the maximum and minimum moments of inertia of the tire's ribs.

[0057] To facilitate understanding, the drawings are not drawn to scale. DETAILED DESCRIPTION

[0058] exist Figure 1 In FIG. 1 , a tire 1 of size 315 / 70R22.5 comprises a radial carcass reinforcement 2 anchored in two beads around bead wires (not shown). The carcass reinforcement 2 is formed by a single layer of metal cords. The carcass reinforcement 2 is surrounded by a crown reinforcement 5, which is itself covered by a tread 6. The tread has four grooves 3 forming five ribs 4.

[0059] The lower region and beads of the tire 1 are not specifically shown in the drawings.

[0060] exist Figure 1 In the embodiment, the crown reinforcement 5 is formed radially from the inside to the outside by:

[0061] a first working layer 51 formed of unsheathed inextensible 11.35 metal cords continuous over the entire width of the ply and oriented at an angle equal to 18°,

[0062] a second working layer 52 formed of unsheathed inextensible 11.35 metal cords continuous over the entire width of the ply and oriented at an angle equal to 26° and crossing the metal cords of the first working layer,

[0063] A protective layer 53 formed of unsheathed elastic 6.35 metal cords continuous over the entire width of the ply, oriented at an angle equal to 26° and in the same direction as the metal cords of the working layer 52 .

[0064] According to the invention, the tread 6 is composed of a layer of elastomeric compound in which the fibers are embedded.

[0065] The elastomeric compound has a longitudinal modulus of elasticity, measured perpendicular to the tread surface at ambient temperature and 5% deformation, equal to 5.2 MPa.

[0066] The elastomeric compound had a tan(δ)-20°C value equal to 0.35.

[0067] The fibers are PET fibers with an average length equal to 4 mm and an average diameter of 23 microns.

[0068] The volume percentage of fibers in the elastomeric compound layer was 5%.

[0069] The tread is made by stacking layers of an elastomeric compound reinforced with non-metallic fibers with a thickness of 2 mm and prepared according to the method described in patent WO2017 / 109336. The reinforced elastomeric compound layers are oriented so that the fibers are oriented axially, and the tread is formed by stacking multiple layers to achieve the desired thickness.

[0070] The longitudinal elastic modulus of the elastomeric compound reinforced with non-metallic fibers, measured in the direction of the fibers at ambient temperature and 5% deformation, is equal to 49 MPa.

[0071] Figure 2 The diagram schematically shows a contact patch 21 of a tire surface 22 in contact with the ground, the tire being mounted on its nominal rim, inflated to its nominal pressure, and subjected to its nominal load. On this tire surface 22, it can be seen that the tread pattern consists of a block 23 in the axially central portion, sandwiched between two circumferential ribs 24 located axially outside the tire surface 22.

[0072] In this Figure 2 Further shown in FIG. 2 is an axis 25 oriented in the axial direction and longitudinally at the center of the contact patch.

[0073] Figure 3The tread block 23 is shown schematically, wherein the center of the ground contact surface in the longitudinal direction passing through the center of gravity of the ground contact surface is located longitudinally at the center of the contact patch, thus on the axis 25. Figure 3 Also shown are the two directions associated with the maximum moment of inertia (straight line 26) and the minimum moment of inertia (straight line 27) of the surface of the block 23 in contact with the ground. Around the direction associated with the maximum moment of inertia 26, the orientation range of the non-metallic fiber according to the present invention is shown between two straight lines 28, 29, which are arranged at 30° on either side of direction 26.

[0074] Figure 4 The tread pattern rib 24 is shown schematically. In the case of circumferential continuity of the rib 24, the center of the ground contact surface in the longitudinal direction passing through the center of gravity of the ground contact surface is located continuously longitudinally at the center of the contact patch, thus on the axis 25. Figure 4 3 shows two directions associated with the maximum moment of inertia (straight line 36) and the minimum moment of inertia (straight line 37) of the surface of the rib 24 in contact with the ground. Around the direction associated with the maximum moment of inertia 36, ​​the orientation range of the non-metallic fiber according to the present invention is shown between two straight lines 38, 39, which are respectively arranged at 30° on both sides of direction 36.

[0075] In such Figure 1 In the case of the tire according to the invention shown, the non-metallic fibers are oriented in the axial direction, so that they form a substantially zero angle with the direction associated with the maximum moment of inertia of the surface of the rib 4 in contact with the ground.

[0076] In the tread pattern Figure 2 In the case of tires with similar tread patterns, the present invention can be configured such that the orientation of the non-metallic fibers varies according to the axial position of the measurement. In other words, the orientation of the non-metallic fibers can be varied according to Figure 2 The arrangement is different depending on whether the position is the block 23 or the rib 24 .

[0077] Tires were prepared based on the elastomeric compound A described below and its properties.

[0078]

[0079] The values ​​for the components are expressed in phr (parts by weight per hundred parts of rubber / elastomer).

[0080] A reference tire R was prepared according to a configuration corresponding to conventional production, comprising no fibers in the layer of elastomeric compound forming the tread surface.

[0081] According to Figure 1The tire T of the invention shown incorporates a mixture A forming a layer of elastomeric compound, in which the fibers described above are inserted, forming the tread surface, to form the tread.

[0082] The grip of each tire on wet surfaces was measured under the same driving conditions according to ISO 15222. The results are shown in the table below, with tire R assigned a value of 100.

[0083] A value greater than 100 indicates better grip performance.

[0084] Tire R Tire T 100 103

[0085] These values ​​demonstrate that the advantage of the presence of non-metallic fibers in the elastomeric compound forming the tread surface is to limit the deformation of the tread when passing through the contact patch with the ground (said deformation giving rise to parasitic forces), thus contributing to better grip of the tire on wet ground.

[0086] Wear tests were carried out on a track simulating a motorway-type loop.A tyre T according to the invention was compared with a reference tyre R.

[0087] The driving conditions for all tires were the same: the inflation pressure was 9 bar and the tires were subjected to a load of 3750 kg, with the tires mounted at two locations on the steering axle of a heavy vehicle. The average driving speed was 70 km / h.

[0088] In a wear test carried out on track, the average weight loss after a given mileage is measured. The tests carried out have shown that the tire T according to the invention has covered a mileage equivalent to that of the reference tire R, for the same weight loss.

Claims

1. Tire (1) having a radial carcass reinforcement (2) and comprising a crown reinforcement (5), said crown reinforcement (5) itself being radially covered by a tread (6), said tread (6) being joined to two beads by two sidewalls, said tread (6) comprising grooves forming at least one tread pattern element, said tread comprising at least one layer of elastomeric compound forming the tread surface of the tire, characterized in that The at least one elastomeric compound layer is reinforced with non-metallic fibers arranged substantially parallel to the outer surface of the tread, wherein at least 40% of the non-metallic fibers are oriented in a direction forming an angle of less than 30° with respect to a principal axis of inertia associated with the maximum moment of inertia of the ground-contacting surface of the at least one tread pattern element, the center of the ground-contacting surface in a longitudinal direction passing through the center of gravity of the ground-contacting surface being longitudinally located at the center of the contact patch, the tire being subjected to its nominal load on a nominal rim and inflated to its nominal pressure, and the value of the longitudinal elastic modulus of the at least one elastomeric compound layer measured at ambient temperature in at least one direction parallel to the tread surface is greater than 5 times the value of the longitudinal elastic modulus of the at least one elastomeric compound layer measured at ambient temperature in a direction perpendicular to the tread surface.

2. The tire (1) according to claim 1, characterized in that The value of the longitudinal elastic modulus of the at least one elastomeric compound layer measured at ambient temperature along at least one direction parallel to the tread surface is less than 20 times the value of the longitudinal elastic modulus of the at least one elastomeric compound layer measured at ambient temperature along a direction perpendicular to the tread surface.

3. The tire (1) according to any one of claims 1 or 2, characterized in that The tan(δ)-20° C. value of the non-metallic fiber-reinforced elastomeric compound of the layer forming the tread surface is strictly less than 0.

50.

4. The tire (1) according to any one of claims 1 or 2, characterized in that The length of the non-metallic fibers is between 0.5 and 10 mm.

5. The tire (1) according to any one of claims 1 or 2, characterized in that The average thickness of the non-metallic fibers is between 5 and 40 μm.

6. The tire (1) according to any one of claims 1 or 2, characterized in that The shape factor of the non-metallic fibers is between 12.5 and 2000, the shape factor being the ratio between the length and thickness of the fiber.

7. The tire (1) according to any one of claims 1 or 2, characterized in that The Young's modulus of the non-metallic fibers is between 0.5 and 500 GPa.

8. The tire (1) according to any one of claims 1 or 2, characterized in that The non-metallic fibers are present in the elastomeric compound layer forming the tread surface of the tire in an amount between 2.5 and 10% by volume.

9. The tire (1) according to any one of claims 1 or 2, characterized in that The non-metallic fibers are selected from natural fibers.

10. The tire (1) according to any one of claims 1 or 2, characterized in that The at least one elastomeric compound layer comprises non-metallic fibers in two main orientations that are substantially perpendicular to each other, and the at least one elastomeric compound layer has a longitudinal elastic modulus measured at ambient temperature in at least two directions parallel to the tread surface that is greater than 5 times the value of the longitudinal elastic modulus of the at least one elastomeric compound layer measured at ambient temperature in a direction perpendicular to the tread surface.

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