Tyre comprising tread blocks with extended cutouts

Abstract

The invention relates to a tyre comprising a tread comprising so-called elongated sipes (82) located in a tread block (20) and comprising:-a central portion (84) arranged between dimension points (94, 96) defining an elongate direction (Ei) of the elongated sipes (82); -an elongated portion (86, 88), said elongated portion (86, 88) being arranged between one of the dimension points (94, 96) and one of the blind ends (90, 92). The central portion (84) and the elongated portions (86, 88) are arranged such that, when moved along the elongated sipe (82) from the elongated portions (86, 88) towards the central portion (84), the direction of movement changes relative to the elongated direction (Ei) when passing through the dimensional points (94, 96) defining the elongated direction (Ei). The ratio between the curvilinear lengths of the elongated portions (86, 88) and the central portion (84) is strictly less than 1.0.

Description

Technical Field

[0001] The present invention relates to a tyre. A tyre is understood to mean a casing intended to form a cavity by cooperating with a supporting element, such as a rim, wherein the cavity can be pressurized to a pressure greater than atmospheric pressure. The tyre according to the invention has a generally annular structure with rotational symmetry about the main axis of the tyre. Background Art

[0002] Racing tires intended for use in rally competitions, in which a vehicle equipped with such tires is driven on rocky terrain, are known in the prior art. The known tire is the MICHELIN LATITUDE tire.

[0003] These tires include a tread including a plurality of tread blocks and a plurality of cutouts. Each tread block includes a sipe arranged in the tread block.

[0004] The appearance of cracks (and even chipping) at the ends of the sipes has been observed in rally events (also called special stages). These cracks and chipping occur even more rapidly when the special stages are long and run at high temperatures on relatively aggressive surfaces. Although not dangerous, such chipping shortens the service life of the tire. Summary of the invention

[0005] The object of the present invention is to make the tyre less sensitive to the occurrence of cracks and chipping, thereby extending the service life of the tyre, in particular during intensive use, for example on aggressive terrain and / or at high temperatures.

[0006] To this end, the subject of the invention is a tire comprising a tread, said tread comprising a plurality of tread blocks, said tread blocks being delimited by a plurality of incisions, at least one of the plurality of tread blocks comprising a sipe referred to as an extended sipe, wherein the extended sipe is arranged in said tread block, said extended sipe comprising:

[0007] - a first blind end portion and a second blind end portion;

[0008] a first dimension point and a second dimension point, the first dimension point and the second dimension point defining the slenderness direction of the extended sipe and the maximum dimension of the extended sipe in the slenderness direction of the extended sipe, the first dimension point and the second dimension point each being different from the first blind end portion and the second blind end portion, respectively;

[0009] The first and second blind end portions and the first and second dimension points are arranged to define:

[0010] - a central portion of the extended sipe, the central portion being arranged between a first dimension point and a second dimension point defining the elongated length direction of the extended sipe;

[0011] - at least one extension of the extended sipe, the extension being arranged between one of the first and second dimension points defining the elongate direction of the extended sipe and one of the first and second blind end portions, wherein the or each extension is connected to the central portion;

[0012] said central portion and the or each extended portion are arranged such that when moving along the extended sipe from the or each extended portion towards the central portion, the direction of movement changes relative to the slenderness direction of the extended sipe when passing through the point at which the extended sipe defines said dimension in the slenderness direction of the extended sipe;

[0013] - the length of the curve of the or each extension; and

[0014] - the length of the curve in the central part,

[0015] The ratio is strictly less than 1.0.

[0016] Due to the extension, the first and second dimension points of the sipe are different from the first and second ends. Therefore, due to the arrangement relative to the first and second dimension points, the first and second ends of the sipe are further away from the edge of the tread block in which the sipe is arranged, which limits the occurrence of cracks. In addition, due to the blind ends, the first and second ends of the sipe do not appear in the incision, which also prevents them from cracking. In other words, the first and second ends of the sipe are not connected to the incision.

[0017] Due to the ratio of the curve length of the extended part to the central part, the invention covers extended parts whose curve length is strictly less than the curve length of the central part. In other words, the extended part provides a performance gain which, although significant, is still additional to the performance imparted by the central part.

[0018] The extension portion is able to increase the curve length of the sipe compared to a sipe that only includes a portion where the first and second dimension points coincide with the first and second ends of the sipe. In other words, in the present invention, the total curve length of the extended sipe between the first blind end and the second blind end is strictly greater than the curve length of the extended sipe between the first dimension point and the second dimension point. By changing the direction of movement relative to the slenderness direction of the extended sipe when passing through the dimension points, it is possible to benefit from the space of the tread block, thereby arranging the extension portion away from at least one edge of the tread block. The extension portion is able to increase the heat exchange surface area between the tread and the air and thus to cool the tread block more effectively than tires of the prior art. This cooling limits any temperature increase of the tread block when running on relatively aggressive ground and / or at high temperatures (especially in long special stages) and thus delays the appearance of cracks by maintaining the properties of one or more constituent materials of the tread block.

[0019] Finally, unlike straight sipes, the presence of the extension creates an edge in multiple directions, which improves the transmission of forces, can improve the drivability of the tire and increase versatility in various load directions.

[0020] The slenderness direction is the direction of the straight line connecting the first dimension point and the second dimension point. The first dimension point and the second dimension point define the maximum dimension of the extended slit in the slenderness direction, which means that the extended slit is inscribed between a first straight line and a second straight line that are substantially parallel to each other and pass through the first dimension point and the second dimension point, respectively, wherein these first straight line and the second straight line are perpendicular to the slenderness direction.

[0021] The slit length direction can travel in two directions. The direction changes when moving along the extended slit and when the component of movement in the slit length direction changes from one of the two slit length directions to the other of the two slit length directions.

[0022] The first blind end and the second blind end define the total maximum curve length of the extended grooving. In other words, if the grooving has more than two blind ends (such as in the case of a branching grooving), the first blind end and the second blind end are the blind ends that define the longest curve length (referred to as the maximum curve length).

[0023] As is well known to those skilled in the art, "blind" is understood to mean that the first and second ends are each separated from each cut of the adjacent tread block by a non-zero thickness of the constituent material or materials of the tread block. Thus, as indicated above, the first and second ends of the sipe do not appear in the cut, which means that for any point located at the radial height of each of the first and second ends, there is a non-zero thickness of the constituent material or materials of the tread block separating that point from its orthogonal projection on each face of the tread block delimiting each adjacent cut.

[0024] Any end of the trough other than the first blind end and the second blind end will be referred to as a blind end if the other ends meet the features described in the previous paragraph. For example, a branch trough may have a blind end other than the first blind end and the second blind end.

[0025] Each extended portion connected to the central portion means that the extended sipe is continuous between the or each extended portion and the central portion. The or each extended portion and the central portion are not separated from each other, for example by a portion of the tread block. In other words, when the sipe is radially closed by the ground on which the tyre runs, air can circulate freely between the or each extended portion and the central portion, and vice versa.

[0026] The tread blocks usually have a plurality of edges which define the profile of the tread blocks. These edges may be straight or curved. A distinction is made between leading edges, trailing edges and side edges. The leading edge is the edge which first comes into contact with the ground when the tyre rotates in its forward rotational direction. The trailing edge is the edge which last comes into contact with the ground when the tyre rotates in its forward rotational direction. The side edges are the edges which connect the leading edge and the trailing edge.

[0027] The angle between the two directions is an angle having the smallest absolute value among two angles defined between a first direction of the two directions and a second direction of the two directions.

[0028] The average direction formed by the edge is the direction of a straight line connecting both ends of the edge.

[0029] In the case of racing tires, the axial width of the tread is determined on an unmounted and uninflated tire by measuring the axial distance between the edges forming a first axial edge and a second axial edge of the tread, wherein these axial edges form the border between the tread and the sidewalls of the tire. Each of these first and second axial edges comprises a lateral edge of the axially outermost tread blocks of the tread.

[0030] In the case of tyres not intended for racing, the tread surface area of ​​a tyre mounted on a measuring rim and inflated to its nominal pressure (250 kPa or 290 kPa, depending on whether it is a standard tyre or a reinforced tyre) within the meaning of the ETRTO (“European Tyre and Rim Technical Organisation”) Manual of Standards (2021) is determined as the surface area in contact with the ground when the tyre is loaded to 80% of its load capacity within the meaning of the ETRTO Manual of Standards (2021), wherein this load represents the conditions of use normally encountered. Another method may involve determining the axial limits of the tread surface on an unloaded tyre mounted on a measuring rim and inflated to its nominal pressure within the meaning of the ETRTO Manual of Standards (2021) (250 kPa or 290 kPa, depending on whether it is a standard tyre or a reinforced tyre), for example by considering at each axial limit of the tread surface the point at which the angle between a tangent through the tread surface and a straight line parallel to the axial direction and passing through this point is equal to 30°. When there are a plurality of points at which the absolute value of the angle is equal to 30° in the meridian cross-sectional plane, the radially outermost point is used.

[0031] The invention relates in particular to racing tyres for motor vehicles.Racing is understood to mean officially timed events, as opposed to free running events (sometimes called "track days" or "HDPE" (High Driving Performance Events)) which cover events that are not officially timed.

[0032] Very particularly and very preferably, the invention relates to a tyre for rallying, more preferably to a tyre for rallying at least on rocky and / or gravel and / or muddy ground, very preferably to a tyre for rallying on rocky ground.

[0033] The tyre according to the invention has a generally annular shape around an axis of rotation (substantially coinciding with the axis of rotation of the tyre). This axis of rotation defines three directions commonly used by those skilled in the art: axial, circumferential and radial.

[0034] The tread surface of a tire is the surface of the tread that comes into contact with the ground when the tire is running on the ground.

[0035] An axial direction is understood to mean a direction substantially parallel to the axis of rotation of the tyre, ie the axis of rotation of the tyre.

[0036] A circumferential direction is understood to mean a direction substantially perpendicular simultaneously to the axial direction and to a radius of the tire (in other words tangential to a circle centred on the axis of rotation of the tire).

[0037] A radial direction is understood to mean a direction along a radius of the tire, ie any direction intersecting the axis of rotation of the tire and substantially perpendicular to this axis.

[0038] The median plane of the tire, denoted M, is understood to mean a plane perpendicular to the axis of rotation of the tire and axially centered between the two beads and passing through the axial center of the crown reinforcement.

[0039] The equatorial circumferential surface of the tire is understood to mean the surface which passes through the equator of the tire in a meridian section plane and is perpendicular to the median plane and to the radial direction. The equator of the tire is the axis which is parallel to the axis of rotation of the tire in a meridian section plane (a plane perpendicular to the circumferential direction and parallel to the radial and axial directions) and is situated at an equal distance between the radially outermost point of the tread intended to come into contact with the ground and the radially innermost point of the tire intended to come into contact with a support, such as a rim.

[0040] Meridian plane is understood to mean a plane parallel to and containing the axis of rotation of the tyre and perpendicular to the circumferential direction.

[0041] “Radially inside” and “radially outside” mean respectively closer to and further away from the tire's axis of rotation. “Axially inside” and “axially outside” mean respectively closer to and further away from the tire's median plane.

[0042] Bead is understood to mean the radial portion of the tire intended to attach the tire to a mounting support, such as a wheel comprising a rim. Thus, each bead is particularly intended to come into contact with a flange of the rim so that it can be attached.

[0043] Any numerical range expressed by the expression "between a and b" means a numerical range from greater than a to less than b (i.e., excluding the limits a and b), while any numerical range expressed by the expression "from a to b" means a numerical range from a to b (i.e., including the strict limits a and b).

[0044] The cuts represent grooves or sipes and form spaces that appear on the tread surface.

[0045] A sipe or groove has two main characteristic dimensions on the tread surface: a width and a curve length, satisfying that the curve length is at least equal to twice the width. Thus, a sipe or groove is delimited by at least two main side surfaces that determine its curve length and are connected by a bottom surface, wherein the two main side surfaces are separated from each other by a non-zero distance (called the width of the cut).

[0046] On a new tyre, the width of the incision is the maximum distance between the two main lateral surfaces measured at the radial dimension coinciding with the tread surface when the incision does not have a chamfer, and the width of the incision is the maximum distance between the two main lateral surfaces measured at the radially outermost radial dimension of the incision and the radially innermost dimension of the chamfer when the incision has a chamfer. The width is measured substantially perpendicular to the main lateral surfaces.

[0047] The sipes are such that the distance between the main lateral surfaces is adapted to allow the main lateral surfaces delimiting said sipes to come into at least partial contact in the contact zone, in particular when the tyre is new.

[0048] The grooves are such that the distance between the main lateral surfaces is such that these main lateral surfaces cannot touch each other, in particular when the tyre is new.

[0049] The cuts may be transverse or circumferential.

[0050] The transverse incision satisfies that the incision extends along an average direction forming an angle strictly greater than 30°, preferably greater than or equal to 45° with the circumferential direction of the tire. The average direction is the shortest curve connecting the two ends of the incision and parallel to the tread surface. The transverse incision can be continuous, that is, not interrupted by a tread block or another incision, so that the two main side surfaces that determine its length are uninterrupted over the length of the transverse incision. The transverse incision can also be discontinuous, that is, interrupted by one or more tread blocks and / or one or more incisions, so that the two main side surfaces that determine its length are interrupted by one or more tread blocks and / or one or more incisions.

[0051] A circumferential incision is such that the incision extends along an average direction forming an angle less than or equal to 30°, preferably less than or equal to 10°, with the circumferential direction of the tire. The average direction is the shortest curve connecting the two ends of the incision and parallel to the tread surface. In the case of a continuous circumferential incision, the two ends coincide with each other and are connected by a curve forming a complete circumference around the tire. The transverse incision can be continuous, i.e. not interrupted by a tread block or another incision, so that the two main side surfaces that determine its length are uninterrupted around the complete circumference of the tire. The circumferential incision can also be discontinuous, i.e. interrupted by one or more tread blocks and / or one or more incisions, so that the two main side surfaces that determine its length are interrupted by one or more tread blocks and / or one or more incisions around the complete circumference of the tire.

[0052] In some embodiments, one or each circumferential cut has a chamfer. The chamfer of the circumferential cut can be a straight chamfer or a round chamfer. The straight chamfer is formed by a plane inclined relative to the axial inner surface and the axial outer surface, and the plane continues the axial inner surface and the axial outer surface until the axial inner edge or the axial outer edge of the circumferential cut is axially defined. The round chamfer is formed by a curved surface tangent to the axial inner surface or the axial outer surface, and the curved surface continues the axial inner surface or the axial outer surface. The chamfer of the circumferential cut is characterized in that the height and width are respectively equal to the radial distance and axial distance between the common point shared by the axial inner surface or the axial outer surface continued by the chamfer and the axial inner edge or the axial outer edge of the circumferential cut axially defined.

[0053] In some embodiments, one or each transverse cut has a chamfer. In other words, each transverse cut is radially delimited by surfaces that delimit the transverse cut circumferentially and are connected to each other by a bottom surface that delimits the transverse cut radially inward. The chamfer of the transverse cut can be a straight chamfer or a rounded chamfer. The straight chamfer is formed by a plane inclined relative to the face, which continues the face until the edge that delimits the transverse groove circumferentially. The rounded chamfer is formed by a curved surface that merges tangentially with the face, which continues the face. The chamfer of the transverse cut is characterized in that the height and width are respectively equal to the radial distance and distance in a direction perpendicular to the face between the common point shared by the face continued by the chamfer and the edge that delimits the transverse cut circumferentially.

[0054] On a new tire, the depth of the cut is the maximum radial distance between the bottom of the cut and its projection on the ground when the tire is running. The maximum depth of the cut is called the tread height.

[0055] In an embodiment, particularly suitable for racing tires, in particular rally tires, the tire according to the invention is a tire having a defined inside and outside when mounted on a vehicle. This means that the tire is designed so that one side of it is arranged on the inside and the other side is arranged on the outside. The expression "outside" is understood to mean the side of the tire that is fully visible from the outside of the vehicle when the tire is mounted on the vehicle. "Inside" is understood to mean the side of the tire that faces the wheel arch of the vehicle on which the tire is mounted. Usually, the tire has a marking indicating the inside and outside.

[0056] In a preferred embodiment, the slenderness of the extended sipe is greater than or equal to 1.5, preferably 1.7, more preferably 2.0.

[0057] The slenderness of the extended sipe is the ratio of the maximum dimension of the extended sipe in the slenderness direction of the extended sipe to the maximum dimension of the extended sipe in the direction perpendicular to the slenderness direction of the extended sipe. Obviously, the dimensions are considered in the same plane.

[0058] In a preferred embodiment,

[0059] - the length of the curve of the or each extension; and

[0060] - the length of the curve in the central part,

[0061] The ratio is less than or equal to 0.7, preferably 0.5.

[0062] In an advantageous but optional embodiment, the first and second blind end portions and the first and second dimension points defining the slender length direction of the extended slit are arranged to define a first extension portion and a second extension portion, the first extension portion and the second extension portion being arranged respectively between each first and second dimension point defining the slender length direction of the extended slit and each first and second blind end portion,

[0063] The central portion and each of the first and second extended portions are arranged such that when moving along the extended sipe from each of the first and second extended portions toward the central portion, the moving direction changes relative to the sipe direction when passing through each of the first and second dimension points of the sipe defining the sipe direction of the elongation, respectively;

[0064] - the length of the curve of the first extension and the second extension, respectively; and

[0065] - the length of the curve in the central part,

[0066] The ratio is strictly less than 1.0.

[0067] Thus, the sipe is extended from each of the first dimension point and the second dimension point, which makes the extended sipe even less sensitive to the occurrence of cracks and chipping.

[0068] In a preferred variant,

[0069] - the length of the curve of the first extension and the second extension, respectively; and

[0070] - the length of the curve in the central part,

[0071] The ratio is less than or equal to 0.7, preferably 0.5.

[0072] In an embodiment using a simple manufacturing method and tool for extending the knife groove, the central portion is arranged so that when moving along the extended knife groove in the central portion from a first dimension point defining the slender direction of the extended knife groove to a second dimension point defining the slender direction of the extended knife groove, the movement direction does not change relative to the slender direction of the extended knife groove.

[0073] In an embodiment using a simple manufacturing method and tool for extending the knife groove, the extension portion or each extension portion is arranged so that when the extended knife groove in the extension portion is moved from the dimension point defining the slender direction of the extended knife groove to the nearest blind end by moving along the extended knife groove, the movement direction does not change relative to the slender direction of the extended knife groove.

[0074] In an embodiment where the extended sipe comprises a first extended portion and a second extended portion:

[0075] - the first extension portion is preferably arranged such that when moving along the extended sipe in the first extension portion from a first dimension point defining the elongate direction of the extended sipe to the first blind end portion, the moving direction relative to the elongate direction of the extended sipe does not change; and / or

[0076] The second elongated portion is preferably arranged such that when moving along the elongated sipe in the second elongated portion from a second dimension point defining the elongated sipe's elongated direction to the second blind end, the moving direction does not change relative to the elongated sipe's elongated direction.

[0077] In a favorable but optional embodiment, the extension portion or each extension portion extends in an extension direction, and the extension direction of the extension portion or each extension portion forms an angle less than or equal to 80° with the slenderness direction of the extended knife groove, preferably in the range of 30° to 70°, and more preferably in the range of 30° to 50°.

[0078] Thus, edges are created in significantly different directions, which can improve the transmission of forces and enhance the handling properties of the tire both on a straight line and on a curve, regardless of the orientation of the tread blocks in which the extended sipes are arranged.

[0079] Each extension direction is a straight line connecting a blind end portion of an extension portion and a dimension point closest to the blind end portion when moving along the extension sipe from the or each extension portion to the central portion.

[0080] In an advantageous but optional embodiment, the average slenderness direction of the tread blocks forms an angle with the slenderness direction of the extended sipes less than or equal to 45°, preferably 30°, more preferably 15°, even more preferably 5°.

[0081] Therefore, the transmission of force and the driving performance of the tire are improved to the greatest extent. In fact, the more the direction of the force is parallel to the slenderness direction of the tread block, the better the transmission of force and the driving performance of the tire. However, when the tread block is too large in the direction of the force, the tire tends to lose grip with the ground. By providing an extended sipe so that the slenderness direction of the sipe is as close as possible to the slenderness direction of the tread block, the probability of the ground encountering the edge of the sipe when the tire rolls is increased, and thus the probability of losing grip between the tread block and the ground is reduced.

[0082] If the tread block is elongated in the circumferential direction, the slenderness line of the tread block is a straight line or curve connecting the two leading and trailing edges and equidistant from the side edges connecting the leading and trailing edges. If the tread block is elongated in the transverse direction, the slenderness line of the tread block is a straight line or curve connecting the side edges and equidistant from the leading and trailing edges, the side edges connecting the leading and trailing edges. In order to determine whether the tread block is elongated in the circumferential direction or elongated in the transverse direction, the tread block is inscribed in a quadrilateral, two sides of which are parallel to the axial direction and the other two sides are parallel to the circumferential direction. If the two sides parallel to the axial direction are greater than the two sides parallel to the circumferential direction, the tread block is considered to be elongated in the transverse direction. If the two sides parallel to the axial direction are less than the two sides parallel to the circumferential direction, the tread block is considered to be elongated in the circumferential direction.

[0083] If the tread blocks are elongated in the circumferential direction, the average slenderness direction is a straight line passing through the intersection points between the straight slenderness line or the curvilinear slenderness line and the two leading and trailing edges intersecting therewith. If the tread blocks are elongated in the lateral direction, the average slenderness direction is a straight line passing through the intersection points between the straight slenderness line or the curvilinear slenderness line and the two side edges intersecting therewith.

[0084] In an advantageous but optional embodiment,

[0085] - a distance between a first dimension point and a second dimension point of an extended sipe in the slender direction of the extended sipe in the average slender direction of the tread block; and

[0086] - the distance between a first dimension point and a second dimension point of the tread block in the direction of the average slenderness of the tread block,

[0087] The ratio is greater than or equal to 0.5, preferably 0.7.

[0088] Thus, the extended sipe (particularly the central portion) extends over a significant portion of the tread block, which, for the reasons mentioned above, can maximize the improvement of force transmission and tire handling performance in the slender direction of the tread block.

[0089] The first and second dimension points of the tread block in the slender direction are such that the tread block is inscribed between first and second straight lines that are substantially parallel to each other and pass through the first and second dimension points, respectively, wherein the first and second straight lines are perpendicular to the slender direction of the tread block.

[0090] In an advantageous but optional embodiment,

[0091] - a distance between a first dimension point and a second dimension point of the extended sipe in a direction perpendicular to the average slenderness direction of the tread block; and

[0092] - the distance between a first dimension point and a second dimension point of the tread block in a direction perpendicular to the direction of the average slenderness of the tread block,

[0093] The ratio is greater than or equal to 0.3, preferably 0.5.

[0094] Thus, the extended sipes (particularly the extended portions) extend over a significant portion of the tread blocks, which for the reasons mentioned above can maximally improve the transmission of forces and the handling properties of the tire in a direction perpendicular to the slenderness of the tread blocks.

[0095] The first and second dimension points of the sipe in a direction perpendicular to the average slenderness direction of the tread block are such that the sipe is inscribed between first and second straight lines that are substantially parallel to each other and pass through the first and second dimension points, respectively, wherein these first and second straight lines are parallel to the slenderness direction of the tread block.

[0096] Similarly, the first and second dimension points of the tread block in a direction perpendicular to the average slenderness direction of the tread block are such that the tread block is inscribed between first and second straight lines that are substantially parallel to each other and pass through the first and second dimension points, respectively, wherein these first and second straight lines are parallel to the slenderness direction of the tread block.

[0097] In an advantageous but optional embodiment,

[0098] - the length of the curve of the or each extension; and

[0099] - the length of the curve in the central part,

[0100] The ratio is greater than or equal to 0.1, preferably 0.2, and more preferably in the range of 0.2 to 0.5.

[0101] This therefore ensures that the or each blind end portion does not come too close to the edge of the tread block and in turn risk causing any cracks.

[0102] Preferably, in order to reduce the risk of cracking and chipping, the or each tread block comprises a single sipe, wherein said single sipe is an extended sipe.

[0103] Thus, the tread blocks do not include any sipes other than the extended sipes (which may or may not be extended sipes).

[0104] In order to reduce the sensitivity of a large number of tread blocks to the occurrence of cracks and chipping, at least 20%, preferably at least 30% of the number of tread blocks comprise extended sipes. A person skilled in the art will know how to determine the tread blocks most worthy of implementing the invention by performing successive tests.

[0105] Advantageously, at least 50%, preferably 75%, more preferably 100% by number of the tread blocks having circumferential slenderness comprise extended sipes.

[0106] Advantageously, the or each extended sipe has a depth greater than or equal to 50%, preferably 70%, more preferably 90% of the height of the or each tread block in which it is arranged.

[0107] Advantageously, the depth of the or each extended sipe is greater than or equal to 9 mm, preferably in the range of 10 mm to 14 mm. In some variants, the depth is substantially constant. In other variants, the depth is variable, more preferably, the depth of the or each extended portion is less than the depth of the central portion.

[0108] Advantageously, the or each extended sipe has a width less than or equal to 2.0 mm, preferably in the range 0.5 mm to 2.0 mm.

[0109] The above characteristics characterize the tire when new.

[0110] Another object of the invention is the use of a tyre as defined above for racing, preferably for rallying, more preferably for rallying at least on rocky and / or gravel and / or muddy ground, very preferably for rallying on rocky ground. BRIEF DESCRIPTION OF THE DRAWINGS

[0111] The invention will be better understood by reading the following description, which is provided by way of non-limiting example only and with reference to the accompanying drawings, in which:

[0112] - Figure 1 is a tire of the prior art (i.e. MICHELIN LATITUDE ) is a schematic top view of a tread;

[0113] - Figure 2 is a top view of a tire according to the present invention;

[0114] - Figure 3 is a top view of a pair of first and second tires according to the present invention;

[0115] - Figures 4 to 8 for Figure 2 a detailed view of the same tread block of the tread of the tire; and

[0116] - Figures 9 to 12 Detailed views of tread blocks according to various embodiments. DETAILED DESCRIPTION

[0117] The drawings show X, Y, Z reference systems corresponding to the general axial direction (Y), radial direction (Z), and circumferential direction (X) of the tire, respectively.

[0118] Figure 2 A tyre according to the invention is shown, indicated with the general reference numeral 10. The tyre 10 has a generally annular shape about an axis of rotation R substantially parallel to the axial direction Y. The tyre 10 has a size of 17 / 65R15 and is intended for competition use, in this case for rallying, more preferably for rallying at least on rocky and / or gravelly and / or muddy ground, very preferably for rallying on rocky ground. The value "17" relates to the theoretical width of the tread (in this case 17 cm), the value "65" relates to the theoretical diameter of the tyre (in this case 65 cm), and the value "R15" characterizes a radial tyre designed to be mounted on a 15-inch rim. In the various figures, the tyre 10 is shown in a brand new state, i.e. when it has not yet been driven.

[0119] The tire 10 comprises a crown 12 comprising a tread 14 intended to come into contact with the ground through a tread surface 16 when the tire is running. The tread 14 comprises and is delimited by first and second axial edges 16A and 16B, which define an axial width L of the tread surface 16. In this case, L=178 mm. The tire 10 has an inner side INT and an outer side EXT defined when the tire 10 is mounted on a vehicle. The first axial edge 16A is arranged at the inner side INT and the second axial edge 16B is arranged at the outer side EXT.

[0120] The tire 10 comprises two sidewalls 18 extending radially inwardly the crown 12. The tire 10 also comprises two beads (not shown) radially inside the sidewalls 18 and intended to attach the tire 10 to a mounting support, such as a rim. Each sidewall 18 connects each bead to the crown 12.

[0121] The tread 14 includes a plurality of tread blocks 20 and a plurality of cutouts 50 defining the plurality of tread blocks 20. The plurality of cutouts 50 include a plurality of grooves 60 and a plurality of sipes 80.

[0122] The plurality of grooves 60 include first, second and third circumferential grooves 62, 64, 66 arranged so that there is at least one first, second and third substantially circumferential line 63, 65, 67 that passes through each of the first, second and third substantially circumferential grooves 62, 64, 66, respectively, and extends continuously around the circumference of the tire without intersecting any of the plurality of tread blocks 20. The axial width Lc of each of the first, second and third substantially circumferential lines 63, 65, 67 is greater than or equal to 2 mm, preferably greater than or equal to 5 mm, and in this case greater than or equal to 7 mm.

[0123] The first circumferential groove 62 is the circumferential groove that is axially arranged closest to the first axial edge 16A among the first circumferential grooves, the second circumferential grooves, and the third circumferential grooves 62, 64, 66. The third circumferential groove 66 is the circumferential groove that is axially arranged closest to the second axial edge 16B among the first circumferential grooves, the second circumferential grooves, and the third circumferential grooves 62, 64, 66. The second circumferential groove 64 is axially arranged between the first circumferential groove 62 and the third circumferential groove 66.

[0124] The first, second and third circumferential grooves 62 , 64 , 66 are each arranged in an axial portion having an axial width P equal to at most 75%, preferably at most 70%, of the axial width L of the tread 14 and extending from the first axial edge 16A.

[0125] More specifically, the first circumferential groove 62 is axially arranged in a first axial portion P1 extending axially from the first axial edge 16A between axial limits arranged at 3% and 25%, preferably 5% and 20%, of the axial width L of the tread 14. The second circumferential groove 64 is axially arranged in a second axial portion P2 extending axially from the first axial edge 16A between axial limits arranged at 19% and 42%, preferably 23% and 39%, of the axial width L of the tread 14. The third circumferential groove 66 is axially arranged in a third axial portion P3 extending axially from the first axial edge 16A between axial limits arranged at 42% and 70%, preferably 46% and 66%, of the axial width L of the tread 14.

[0126] The plurality of grooves 60 further include transverse grooves 72 extending continuously from the first axial edge 16A to the second axial edge 16B of the tread 14. The transverse grooves 72 extend substantially parallel to each other. Each transverse groove 72 extends axially in an axially variable main direction. Each transverse groove 72 intersects the first circumferential groove, the second circumferential groove, and the third circumferential groove 62, 64, 66, respectively.

[0127] The angle formed by the main direction of each transverse groove 72 and the circumferential direction X is constant over the axial portion extending axially from the first axial edge 16A and the first circumferential line 63, and exhibits a non-zero monotonic variation (strictly decreasing in this case) over an additional axial portion extending axially from the first circumferential line 63 and the second axial edge 16B. Furthermore, the angle DA formed by the main direction DR of each transverse groove 72 and the circumferential direction X of the tire at the first axial edge 16A is greater than the angle DB formed by the main direction DR of each transverse groove 72 and the circumferential direction X at the second axial edge 16B. The angle DA ranges between 70° and 90°, being substantially equal to 90° in this case. The angle DB ranges between 30° and 60°, being substantially equal to 50° in this case.

[0128] The plurality of tread blocks 20 include first, second, third and fourth circumferential rows of tread blocks 20 (represented by reference numerals 22, 24, 28, 26, respectively) of the plurality of tread blocks 20 and first and second additional circumferential rows 30, 32 of tread blocks 20 of the plurality of tread blocks 20. The first and second additional circumferential rows 30, 32 of tread blocks 20 are separated from the first, second, third and fourth circumferential rows 22, 24, 28, 26 of tread blocks 20. The additional circumferential rows 30, 32 are axially closer to the second axial edge than the first, second and third circumferential rows 22, 24, 28, 26, respectively. The first circumferential row 22 of the tread blocks 20 is the row of tread blocks axially arranged closest to the first axial edge 16A among the first, second, and third circumferential rows 22, 24, and 26 of the tread blocks. The third circumferential row 28 is the row of tread blocks axially arranged closest to the second axial edge 16B among the first, second, third, and fourth circumferential rows 22, 24, 28, and 26 of the tread blocks. The second circumferential row 24 is axially arranged between the first circumferential row 22 and the third circumferential row 28. The fourth circumferential row 26 is axially arranged between the second circumferential row 24 and the third circumferential row 28.

[0129] Each tread block 20 of the first circumferential row 22 is axially bounded by the first circumferential groove 62 and the first axial edge 16A. Each tread block 20 of the second circumferential row 24 is axially bounded by the first and second circumferential grooves 62, 64. Each tread block 20 of the third circumferential row 28 is axially bounded at least in part by the third circumferential row 66. Each tread block 20 of the fourth circumferential row 26 is axially bounded by the second and third circumferential grooves 64, 66.

[0130] The first and second circumferential rows 22, 24 each include a single tread block 20 between two circumferentially consecutive transverse grooves 72. The third and fourth circumferential rows 28, 26 each include at least two tread blocks 20, preferably only two tread blocks 20, between two circumferentially consecutive transverse grooves 72.

[0131] The first and second additional circumferential rows 30, 32 of tread blocks 20 are each arranged axially outward of the third circumferential row 28. The second additional circumferential row 32 is arranged axially outward of the first additional circumferential row 30.

[0132] Each tread block 20 of the first additional circumferential row 30 is axially delimited by two inclined grooves 68, 70 intersecting two circumferentially continuous transverse grooves 72. Each tread block 20 of the second additional circumferential row 32 of tread blocks is axially delimited by an inclined groove 70 intersecting two circumferentially continuous transverse grooves 72 and a second axial edge 16B.

[0133] Figure 2 Two circumferential lines 69, 71 are shown passing through the oblique grooves 68, 70, respectively. Each of these circumferential lines 69, 71 must intersect the tread blocks 20 of the first and second additional circumferential rows, 30, 32, respectively, respectively. Thus, more generally, each tread block 20 of the first and second additional circumferential rows, 30, 32, respectively, is arranged such that no substantially circumferential line extends continuously around the circumference of the tire and passes through each oblique groove 68, 70 of each tread block of the first and second additional circumferential rows, 30, 32, respectively, without intersecting the tread blocks 20 of the first and second additional circumferential rows, 30, 32, respectively.

[0134] The first and second additional circumferential rows 30 , 32 each comprise a single tread block 20 between two circumferentially consecutive transverse grooves 72 .

[0135] Each tread block 20 of the plurality of tread blocks 20 comprises a plurality of edges defining a profile, in this case a substantially polygonal profile. Each tread block 20 of each of the first, second, third and fourth circumferential rows 22, 24, 28, 26 and each of the first and second additional circumferential rows 30, 32 comprises a leading edge 202, a trailing edge 204 and side edges 206, 208.

[0136] The angles D1, D2, D3, D4 formed by the average direction of the leading edge 202 of each tread block 20 of the first circumferential row, the second circumferential row, the third circumferential row and the fourth circumferential row 22, 24, 28, 26 and the circumferential direction X are strictly greater than the angles A1, A2 formed by the average direction of the leading edge 202 of each tread block 20 of the first additional circumferential row and the second additional circumferential row 30, 32 and the circumferential direction X.

[0137] An angle D1, D2, D4, D3, A1, A2 formed by the average direction of the leading edge 202 of each tread block 20 of each circumferential row 22, 24, 26, 28, 30, 32 and the circumferential direction X is strictly greater than the angle D2, D4, D3, A1, A2 formed by the average direction of the leading edge 202 of each tread block 20 of the circumferential row 24, 26, 28, 30, 32 axially adjacent thereto and the circumferential direction X, wherein each row 24, 26, 28, 30, 32 axially adjacent to a given circumferential row 22, 24, 26, 28, 30, 32 is closer to the outer side EXT than each corresponding given circumferential row 22, 24, 26, 28, 30, 32.

[0138] 100% of the leading edges 202 of the tread blocks 20 of the third and fourth circumferential rows 28 , 26 respectively have a curvilinear length that is strictly greater than the curvilinear length of each side edge 206 , 208 of said tread blocks 20 .

[0139] Each angle D1, D2, D3, D4 is greater than or equal to 50°, preferably greater than or equal to 60°. Angle D1 is greater than or equal to angle D2. Angle D2 is strictly greater than angle D3. Angle D4 is strictly greater than angle D3. In this particular case, each angle D1, D2 ranges from 70° to 90°, angle D3 ranges from 50° to 70°, and angle D4 ranges from 65° to 85°. D1 = 90°, D2 = 85°, D3 = 60° and D4 = 75°.

[0140] Each angle A1 , A2 is less than or equal to 60°, preferably less than or equal to 50°. Angle A1 is strictly greater than angle A2. In this particular case, each angle A1 , A2 ranges from 30° to 60°. A1 = 45° and A2 = 40°.

[0141] The width of each of the first, second and third circumferential grooves 62, 64, 66 is greater than or equal to 2 mm, preferably ranging from 5 mm to 15 mm, more preferably ranging from 7 mm to 12 mm, in this case equal to 9.7 mm, 8.7 mm and 9.7 mm, respectively. The width of each transverse groove 72 is greater than or equal to 2 mm, preferably ranging from 5 mm to 15 mm, more preferably ranging from 7 mm to 12 mm, in this case equal to 9.6 mm. The width of each oblique groove 68, 70 is greater than or equal to 2 mm, preferably ranging from 5 mm to 15 mm, more preferably ranging from 7 mm to 12 mm, in this case equal to 10 mm.

[0142] The area void ratio of the tread 14 associated with grooves having a width greater than or equal to 2 mm, preferably 4 mm (in this case associated with the circumferential grooves 62, 64, 66, the transverse grooves 72 and the oblique grooves 68, 70) ranges from 35% to 55%, preferably from 40% to 50%, in this case equal to 44%. The volume void ratio of the tread associated with grooves having a width greater than or equal to 2 mm, preferably 4 mm (in this case associated with the circumferential grooves 62, 64, 66, the transverse grooves 72 and the oblique grooves 68, 70) ranges from 30% to 45%, preferably from 35% to 45%, in this case equal to 39%.

[0143] The tread pattern height is greater than or equal to 7 mm, preferably ranging from 9 mm to 16 mm, and in this case equal to 12 mm.

[0144] refer to Figure 3 , shows a pair 100 of first and second tires 10, 10', both tires being tires according to the invention. The tread 14 of the first tire 10 is symmetrical to the tread 14' of the second tire 10' relative to a symmetry plane S substantially perpendicular to the common rotation axis R of the first and second tires 10, 10'. Figure 3 In the example of the present invention, the first tire 10 is intended to be mounted on the right side of the vehicle, while the second tire 10' is intended to be mounted on the left side of the vehicle, so that the inner sides INT of the first and second tires 10, 10' respectively face the wheel arches of the vehicle and so that the outer sides EXT of the first and second tires 10, 10' respectively are fully visible from the outside of the vehicle when the tires are mounted on the vehicle.

[0145] refer to Figure 2 , each tread block 20 of the tread 14 comprises a single sipe 80. Each tread block 20 of each of the first and second circumferential rows 22, 24 and the additional circumferential row 30 comprises a sipe 82 referred to as an extended sipe, in this case a single extended sipe 82.

[0146] Now refer to Figure 4 and Figure 5 A detailed description of the tread blocks 20 of the second circumferential row 24 of tread blocks and the extended sipes 82 disposed therein is provided.

[0147] refer to Figure 4 , each tread block 20 of the second circumferential row 24 is elongated in the circumferential direction X. In fact, each tread block 20 of the second circumferential row 24 is inscribed in a rectangle RE, two sides of which are parallel to the axial direction Y and the other two sides are parallel to the circumferential direction X. Since the two sides parallel to the axial direction Y are smaller than the two sides parallel to the circumferential direction X, each tread block 20 of the second circumferential row 24 is elongated in the circumferential direction X. The slenderness line LE of each tread block 20 of the second circumferential row 24 is a curve connecting the two leading edge 202 and the trailing edge 204, and is equidistant from the side edges 206, 208 connecting the leading edge 202 and the trailing edge 204. The average slenderness direction Ep is a straight line passing through the intersection between the curved slenderness line and the two leading edge 202 and the trailing edge 204 intersecting it.

[0148] The circumferential length of each tread block 20 of the second circumferential row 24 (i.e. the length of the two sides parallel to the circumferential direction X in this case) is equal to 40 mm. The width of each tread block 20 of the second circumferential row 24 (i.e. the length of the two sides parallel to the axial direction Y in this case) is equal to 22 mm.

[0149] The depth of each extended sipe 82 is greater than or equal to 9 mm, preferably ranging from 10 mm to 14 mm, in this case equal to 12 mm. This depth is greater than or equal to 50%, preferably 70%, more preferably 90% of the height of the tread block 20 in which said extended sipe 82 is arranged. In this case, the height of each tread block 20 of the second circumferential row 24 is substantially equal to 12 mm. The width of each extended sipe 82 is less than or equal to 2.0 mm, preferably ranging from 0.5 mm to 2.0 mm, in this case equal to 1.0 mm.

[0150] Each extended slit 82 includes a central portion 84 and first and second extended portions 86, 88, wherein the first and second extended portions 86, 88 are each connected to the central portion 84. Each extended slit 82 also includes first and second blind end portions 90, 92 and first and second dimension points 94, 96, which are arranged to define, on the one hand, the central portion 84 disposed between the first and second dimension points 94, 96, and, on the other hand, define each first and second extended portion 86, 88 disposed between each first and second dimension points 94, 96 and each first and second blind end portion 90, 92, respectively. Each first and second dimension point 94, 96 is separated from each first and second blind end portion 90, 92, respectively.

[0151] The curve length of each of the first and second extensions 86, 88 (i.e. the curve length between each first and second dimension point 94, 96 and each first and second blind end 90, 92, respectively) is equal to 8 mm in this case. The curve length of the central portion 84 (i.e. the curve length between each first and second dimension point 94, 96) is equal to 30 mm in this case. Therefore, the ratio between the curve length of each of the first and second extensions 86, 88 and the curve length of the central portion 84 is strictly less than 1.0, preferably less than or equal to 0.7, preferably 0.5 and greater than or equal to 0.1, preferably 0.2, more preferably in the range of 0.2 to 0.5, in this case equal to 0.27.

[0152] refer to Figure 5 , the first and second dimension points 94, 96 define the slenderness direction Ei of the extended slit 82, the maximum dimension Lmax of the extended slit 82 in the slenderness direction Ei of the extended slit 82, and the maximum dimension Imax of the extended slit 82 in the direction Epi perpendicular to the slenderness direction Ei. Generally, it should be noted that the slenderness direction Ei of the extended slit 82 coincides with the slenderness direction of the central portion 84. The first and second extended portions 86, 88 extend in the extension directions Ea1, Ea2, respectively. In this case, Lmax=31 mm, lmax=10 mm, so that the slenderness of the extended slit 82 is greater than or equal to 1.5, preferably 1.7, more preferably 2.0, and in this case is equal to 3.1.

[0153] The angle formed by the extension directions Ea1 and Ea2 of the first and second extension parts 86 and 88 and the slenderness direction Ei of the extended sipe 82 is less than or equal to 80°, preferably in the range of 30° to 70°, more preferably in the range of 30° to 50°, which is equal to 37° in this case.

[0154] refer to Figure 6 The average slenderness direction Ep of the tread block 20 forms an angle less than or equal to 45°, preferably 30°, more preferably 15°, and even more preferably 5° with the slenderness direction Ei of the extended sipe 82 .

[0155] refer to Figure 7 , in the average slenderness direction Ep of the tread block 20, the distance Li between the first dimension point and the second dimension point 94, 96 of the extended sipe 82 is equal to 31 mm in this case, and the distance Lp between the first dimension point and the second dimension point 98, 100 of the tread block 20 is equal to 41 mm in this case in the average slenderness direction Ep of the tread block 20. The ratio of Li to Lp is greater than or equal to 0.5, preferably 0.7, and is equal to 0.76 in this case.

[0156] refer to Figure 8 , the extended sipe 82 has a first dimension point and a second dimension point of the extended sipe 82 in a direction Epp perpendicular to the average slenderness direction Ep of the tread block 20. In this case, each first dimension point and second dimension point of the extended sipe 82 in the direction Epp coincides with each first and second blind end 90, 92, respectively. In the direction Epp, the distance li between the first dimension point and the second dimension point 90, 92 of the extended sipe 82 is equal to 11 mm. The tread block 20 has a first dimension point and a second dimension point 102, 104 of the tread block 20 in the direction Epp. In the direction Epp, the distance lp between the first dimension point and the second dimension point 102, 104 of the tread block 20 is equal to 22 mm. The ratio of li to lp is greater than or equal to 0.3, preferably 0.5, and in this case is equal to 0.5.

[0157] refer to Figure 5 The central part 84 and the first and second extended parts 86, 88 are respectively arranged so that when moving from the first and second extended parts 86, 88 to the central part 84 along the extended knife groove 82, respectively, when passing through the first and second dimension points 94, 96 of the extended knife groove 82, respectively, there is a change in the movement direction relative to the slenderness direction Ei of the extended knife groove 82.

[0158] The central portion 84 is arranged such that when moving along the extended sipe 82 in the central portion 84 from the first dimension point 94 to the second dimension point 96 , the moving direction does not change relative to the elongation direction Ei of the extended sipe 82 .

[0159] The first extension portion 86 is arranged such that the direction of movement relative to the slenderness direction Ei does not change when moving from the first dimension point 94 to the first blind end portion 90 along the extension slit 82 in the first extension portion 86. Similarly, the second extension portion 88 is arranged such that the direction of movement relative to the slenderness direction Ei does not change when moving from the second dimension point 96 defining the slenderness direction Ei to the second blind end portion 92 along the extension slit 82 in the second extension portion 88.

[0160] Further references Figure 2 , it can be seen that at least 20%, preferably at least 30% (in this case 50%) by number of the tread blocks of the tread comprise extended sipes 82, in this case the tread blocks 20 of the circumferential rows 22, 24 and 30. At least 50%, preferably 75% by number of the tread blocks have a circumferential slenderness, i.e. in this case at least 50%, preferably 75% by number of the tread blocks 20 of the circumferential rows 22, 24, 30 and 32 comprise extended sipes 82.

[0161] Figures 9 to 12 Tread blocks including extended sipes 82 according to other embodiments are shown.

[0162] Different from the extended knife groove 82 described with reference to the previous figures, Fig. 9 and Fig.10 The extended slit 82 in the central portion 84 is not linear. However, for the extended slit 82 described with reference to the previous figures, when moving from the first dimension point 94 defining the slenderness direction Ei to the second dimension point 96 along the extended slit 82 in the central portion 84, the moving direction does not change relative to the slenderness direction Ei.

[0163] Unlike the extended sipe 82 described with reference to the previous figures, the first and second extended portions 86, 88 are bent in the same direction.

[0164] Different from the extended knife groove 82 described with reference to the previous figures, Fig.12 The extended knife groove 82 in FIG. 8 includes a single extended portion 86 .

[0165] The present invention is not limited to the above-described embodiments.

Claims

1. A tire (10), comprising a tread (14), the tread (14) comprising a plurality of tread blocks (20), the tread blocks (20) being defined by a plurality of cutouts (62, 64, 66, 68, 70, 72), at least one of the plurality of tread blocks (20) comprising a sipe (82) referred to as an extended sipe, wherein the extended sipe (82) is arranged in the tread block (20), the extended sipe (82) comprising: - a first blind end portion and a second blind end portion (90, 92); - a first dimension point and a second dimension point (94, 96), the first dimension point and the second dimension point (94, 96) defining the slenderness direction (Ei) of the extended slit (82) and the maximum dimension (Lmax) of the extended slit (82) in the slenderness direction (Ei) of the extended slit (82), the first dimension point and the second dimension point (94, 96) being respectively different from the first blind end portion and the second blind end portion (90, 92); The first and second blind end portions (90, 92) and the first and second dimension points (94, 96) are arranged to define: - a central portion (84) of the extended sipe (82), the central portion (84) being arranged between a first dimension point and a second dimension point (94, 96) defining the elongate direction (Ei) of the extended sipe (82); - at least one extension (86, 88) of the extended slit (82), the extension (86, 88) being arranged between one of the first and second dimension points (94, 96) defining the elongate direction (Ei) of the extended slit (82) and one of the first and second blind end portions (90, 92), wherein the or each extension (86, 88) is connected to the central portion (84); The central portion (84) and the or each extension portion (86, 88) are arranged such that when moving along the extended slit (82) from the or each extension portion (86, 88) towards the central portion (84), the direction of movement changes relative to the slenderness direction (Ei) of the extended slit (82) when passing through the dimension point (94, 96) of the extended slit (82) defining the slenderness direction (Ei) of the extended slit (82); - the length of the curve of the or each extension (86, 88); and - the length of the curve of the central portion (84), the ratio of which is strictly less than 1.

0.

2. Tyre (10) according to the preceding claim, wherein: The first and second blind end portions (90, 92) and the first and second dimension points (94, 96) defining the slender length direction (Ei) of the extended knife groove (82) are arranged to define the first and second extension portions (86, 88), and the first and second extension portions (86, 88) are arranged respectively between each first and second dimension point (94, 96) defining the slender length direction (Ei) of the extended knife groove (82) and each first and second blind end portion, The central portion (84) and each of the first and second extension portions (86, 88) are arranged such that when moving along the extended slit (82) from each of the first and second extension portions (86, 88) toward the central portion (84), when passing through each of the first and second dimension points (94, 96) defining the slenderness direction (Ei) of the extended slit (82), respectively, the moving direction changes relative to the slenderness direction (Ei) of the extended slit (82); - the length of the curve of the first extension and the second extension (86, 88), respectively; and - the length of the curve of the central portion (84), the ratio of which is strictly less than 1.

0.

3. The tire (10) according to any of the preceding claims, which is used for racing, preferably for rallying, more preferably for rallying at least on rocky and / or gravel and / or muddy ground, very preferably for rallying on rocky ground.

4. Tyre (10) according to any one of the preceding claims, wherein: The central portion (84) is arranged so that when moving along the extended knife groove (82) in the central portion (84) from a first dimension point (94) defining the slender direction of the extended knife groove (82) to a second dimension point (96) defining the slender direction (Ei) of the extended knife groove (82), the moving direction does not change relative to the slender direction (Ei) of the extended knife groove (82).

5. Tyre (10) according to any one of the preceding claims, wherein: The extension portion (86, 88) or each extension portion (86, 88) is arranged so that when the extended knife groove (82) in the extension portion (86, 88) is moved from the dimension point (94, 96) defining the slender direction (Ei) of the extended knife groove (82) to the closest blind end (90, 92) by moving along the extended knife groove (82), the movement direction relative to the slender direction (Ei) of the extended knife groove (82) does not change.

6. Tyre (10) according to any one of the preceding claims, wherein: The extension portion (86, 88) or each extension portion (86, 88) extends in an extension direction (Ea1, Ea2), and the angle formed by the extension direction (Ea1, Ea2) of the extension portion (86, 88) or each extension portion (86, 88) and the slenderness direction (Ei) of the extended knife groove (82) is less than or equal to 80°, preferably in the range of 30° to 70°, and more preferably in the range of 30° to 50°.

7. Tyre (10) according to any one of the preceding claims, wherein: The angle formed by the average length direction (Ep) of the tread blocks (20) and the length direction (Ei) of the extended sipes (82) is less than or equal to 45°, preferably 30°, more preferably 15°, and even more preferably 5°.

8. Tyre (10) according to any one of the preceding claims, wherein: - a distance (Li) between a first dimension point (94, 96) of the extended sipe (82) defining the slenderness direction (Ei) of the extended sipe (82) in the average slenderness direction (Ep) of the tread block (20); and - In the average slenderness direction (Ep) of the tread block (20), the ratio of the distance (Lp) between the first dimension point and the second dimension point (98, 100) of the tread block (20) is greater than or equal to 0.5, preferably 0.

7.

9. Tyre (10) according to any one of the preceding claims, wherein: - a distance (li) between a first dimension point and a second dimension point (90, 92) of the extended sipe (82) in a direction (Epp) perpendicular to the average slenderness direction (Ep) of the tread block (20); and - In a direction (Epp) perpendicular to the average slenderness direction (Ep) of the tread block (20), the ratio of the distance (lp) between a first dimension point and a second dimension point (102, 104) of the tread block (20) in a direction (Epp) perpendicular to the average slenderness direction (Ep) of the tread block (20) is greater than or equal to 0.3, preferably 0.

5.

10. Tyre (10) according to any one of the preceding claims, wherein: - the length of the curve of the or each extension (86, 88); and - the curvilinear length of the central portion (84), the ratio being greater than or equal to 0.1, preferably 0.2, more preferably ranging from 0.2 to 0.

5.

11. Tyre (10) according to any one of the preceding claims, wherein: The or each tread block (20) comprises a single sipe (82) which is an extended sipe (82).

12. Use of a tyre (10) according to any of the preceding claims in competitions, preferably in rallies, more preferably at least in rallies on rocky and / or gravelly and / or muddy ground, very preferably in rallies on rocky ground.

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