WO2025215519A1 - Off-road motorcycle tyre - Google Patents

Abstract

An off-road motorcycle tyre comprises a tread band having a maximum chord (C). The tread band comprises a central annular portion (M) extending astride of an equatorial plane (X-X) of the tyre (1) and comprising a plurality of circumferentially consecutive first central blocks (15) arranged next to the equatorial plane (X-X) and a plurality of circumferentially consecutive second central blocks (50) arranged next to the equatorial plane (X-X) on the opposite side with respect to the first central blocks (15), each second central block (50) being axially adjacent to a respective first central block (15). An intermediate annular portion (5) without blocks is arranged astride of the equatorial plane (X-X) and extends between the first central blocks (15) and the second central blocks (50). Each first central block (15) and the respective second central block (50) are arranged at a respective minimum mutual distance in the axial direction such that the ratio between said minimum mutual distance and said predetermined maximum chord (C) is greater than, or equal to, 0.15.

Description

Off-road motorcycle tyre

DESCRIPTION

The present invention relates to a tyre for off-road motorcycles, or for motorcycles of the "Motocross" type.

Preferably, the tyre of the invention is intended to be mounted on the front wheel of motorcycles of the "Motocross" type, which, as known, are motorcycles intended to be used off-road. These motorcycles may have medium-large piston displacement (such as 450 cc or more) or lower piston displacement (such as 125 cc or 250 cc).

Motorcycles of the "Motocross" type also comprise the so-called "Minicross" motorcycles, which typically have piston displacement comprised between 65 cc and 85 cc.

Examples of motorcycles of the "Motocross" type of medium-large piston displacement are:

- KTM 450 SX-F, having piston displacement equal to 450 cc, power equal to 63 hp, maximum torque equal to 53 Nm and mass equal to 104 KG;

- Honda CRF450R, having a piston displacement equal to 450 cc, power equal to 52 hp, maximum torque equal to 47 Nm and mass equal to 106 KG.

Examples of some tyres of the type described above and produced by Pirelli Tyre S.p.a. are: MX Extra X, MX 32 MidHard, XC MidHard, MC MidHard, MX32 MidSoft, XC MidSoft, MC360 MidSoft.

The tyre of the present invention is approved for an off-road use, primarily during professional and amateur competitions.

PRIOR ART

Tyres intended for motorcycles of the "Motocross" type are typically used in extreme conditions, with highly differentiated types of terrain other than asphalt: sandy, rocky, compact, etc. In particular, in the case of use during a competition, the conditions of use of these tyres become very harsh, and the tyres must guarantee excellent performance in terms of durability, tear resistance, grip, stability and traction on such differentiated terrains, even at high speeds.

Typically, tyres having a tread pattern defined by a plurality of blocks arranged either on a central annular portion of the tread band and on opposite lateral and/or shoulder annular portions of the tread band are used in this product segment. These blocks are capable of penetrating the terrain (particularly sandy or soft or medium-soft terrain) to ensure traction, particularly during acceleration and braking.

Examples of these tyres are described in US 6651711 B2, US 20082457A1, EP 2374636B1, EP 2529954 Bl, EP 3047981 Bl, US 2015165826 Al, EP 3006232 Bl, EP 3339057 Bl, EP 3501853 Bl, CN 208053001 U, CN 211222917 U.

SUMMARY OF THE INVENTION

Throughout the present description and in the following claims, when reference is made to certain values of certain angles, these values are deemed to be absolute values, i.e. both positive values and negative values with respect to a reference plane or direction, unless specified otherwise.

Moreover, when reference is made to any range of values comprised between a minimum value and a maximum value, the aforementioned minimum and maximum values are deemed to be included in the aforementioned range, unless expressly stated otherwise.

Moreover, all of the ranges include any combination of the described minimum and maximum values and also include any intermediate range, even if not expressly described specifically.

Even if not expressly indicated, any numerical value is deemed to be preceded by the term "about" to also indicate any numerical value that differs slightly from the one described, for example to take into account the dimensional tolerances typical of the field of reference.

Hereinafter, the following definitions apply.

The term "equatorial plane" of the tyre is used to indicate a plane perpendicular to the rotation axis of the tyre and that divides the tyre into two equal parts.

The term "motorcycle tyre" is used to indicate a tyre having a high curvature ratio, typically greater than 0.20.

The term "curvature ratio" is used to indicate the ratio between the distance comprised between the radially highest point of the tread band and the maximum width of radial section of the tyre (such distance also being identified as "arrow"), and the same maximum width of the tyre, in a cross section thereof.

The term "maximum width of radial section", or "maximum chord", is used to indicate the maximum width of the profile of the tyre, i.e. the length of the segment having as its ends the two axially outermost points of the profile of the tread band.

The term "circumferential extension" of the tyre, or of the tread band or of portions thereof, is used to indicate the extension in plan of the outer base surface of the tread band or of portions thereof, on a plane tangent to the tyre. The circumferential extension has a length that can be measured at the equatorial plane.

The term "tread pattern" is used to indicate the representation of all the points of the tread band on a plane perpendicular to the equatorial plane of the tyre and tangent to the maximum diameter of the tyre. The tread pattern is defined by the plurality of blocks, possibly including recesses, and by a plurality of longitudinal and/or transversal cavities, grooves and/or channels that separate the various blocks from each other.

The term "block" is used to indicate a portion of tread band protruding from the outer base surface of the tread band by a height not shorter than 7 mm. The block is delimited, on at least two of its sides, by respective grooves and, on two of its other sides, either by a respective groove or by a respective connecting element. In case the block is positioned on the axially outermost portion of the tread band, it is delimited in the axial direction by the axially outermost face of the tread band and, in the axially innermost position, by at least one groove.

The term "connecting element" is used to indicate a portion of tread band which, projecting from the outer base surface of the tread band, connects two adjacent blocks. This connecting element has a height, from the outer base surface of the tread band, shorter than 50% the height of the blocks, preferably shorter than 40%, more preferably shorter than 30%.

The term "groove" is used to indicate a furrow formed on the tread band and delimiting a block. The base surface of the groove lies on the outer base surface of the tread band. Therefore, the groove has a height equal to the distance in the radial direction between the outer base surface of the tread band and the top surface of at least one of the adjacent blocks.

The term "recess" is used to indicate a furrow formed in a block and having a depth lower than the depth of the block. The recess therefore has a depth lower than the height of the grooves.

The sizes of angles, and/or linear quantities (distances, widths, lengths, etc.) and/or surfaces are deemed as referred to the tread band or to the tread pattern as defined above.

The terms "radial" and "axial" and the expressions "radially inner/outer" and "axially inner/outer" are used with reference to a direction substantially parallel to the equatorial plane of the tyre and to a direction substantially perpendicular to the equatorial plane of the tyre, respectively, i.e. to a direction substantially perpendicular to the rotation axis of the tyre and to a direction substantially parallel to the rotation axis of the tyre, respectively.

The terms "circumferential" and "circumferentially" are used with reference to the direction of circumferential extension of the tyre, i.e. to the rolling direction of the tyre, which corresponds to a direction lying on a plane coinciding with or substantially parallel to the equatorial plane of the tyre.

The expressions "axially inner" and "axially outer" indicate a position respectively closer to, and farther from, the equatorial plane with respect to a reference element. Thus, for example, a first face of a block is axially inner with respect to a second face of the block when the axial distance of the first face from the equatorial plane is shorter than that of the second face. Similarly, a first face of a block is axially outer with respect to a second face of the block when the axial distance of the first face from the equatorial plane is greater than that of the second face.

The term "width" is used to indicate a dimension measured along a direction perpendicular to the equatorial plane, i.e. along an axial direction.

The term "circumferential length" is used to indicate a dimension measured along a direction lying on, or parallel to, the equatorial plane, i.e. along a circumferential direction.

The term "minimum mutual distance" between two blocks is used to indicate the distance measured along a predetermined direction at the points of a block that are closer to the adjacent bock nearest to those points. Therefore, the minimum mutual distance between two blocks is measured at the points on the blocks where the blocks have the maximum axial width.

A block is considered "misaligned" in the axial direction, or "circumferentially offset", from another block when the centres of gravity of the two blocks do not lie on the same plane perpendicular to the equatorial plane of the tyre. Consequently, a block is considered "aligned" to another block in the axial direction when the centres of gravity of the two blocks lie on the same plane perpendicular to the equatorial plane of the tyre and are placed at a mutual distance in the axial direction shorter than 90% of a maximum circumferential length of the block.

Instead, a block is considered "aligned" to another block in the circumferential direction when the centres of gravity of the two blocks lie on a single plane parallel to the equatorial plane of the tyre or on two planes parallel to the equatorial plane of the tyre and placed at a mutual distance in the axial direction shorter than 10% of the maximum chord of the tread band.

The blocks that are aligned in the circumferential direction form a "circumferential row" of blocks.

With reference to the angular arrangement of the blocks or of a face of the block (or of a portion of such a face) with respect to the equatorial plane of the tyre, such an angular arrangement is deemed for each point of the block or of the face of the block (or of a portion of such a face) as referring to the angle, comprised in an absolute value between 0° and 90°, formed by carrying out a rotation that, starting from the direction defined in the tread pattern by the equatorial plane, proceeds up to the direction tangent to the block and passing through such point. In the case the reference plane is not the equatorial plane but a plane perpendicular to the equatorial plane, the values of the angles are complementary to those measured with reference to the equatorial plane.

With reference to the faces of a block, a face of a block is "flat" if all its points lie on the same plane, while it is "concave" towards the inside of the block if the segment joining two opposite edges of the block is not entirely contained within the block. The concavity can be defined by a single curved surface or by at least two rectilinear surfaces inclined with respect to each other.

The expression "substantially parallel" indicates not only a condition of perfect parallelism, but also a condition diverging from the perfect parallelism by an angle not greater than 10°.

The term "void to solid ratio" is used to indicate the ratio between the overall surface of the grooves of a given annular portion of the tread band or tread pattern of the tyre (possibly of the entire tread band or tread pattern) and the surface of the given portion of tread band or tread pattern (possibly of the entire tread band or tread pattern). This ratio coincides with the complement to 1 of the ratio between the sum of the top surfaces of the blocks of a given portion of the tread band (possibly of the entire tread band) and the total area of said given portion of the tread band (possibly of the entire tread band).

The term "footprint area" of the tyre is used to indicate the portion of the tyre in contact with the ground when the tyre is mounted on a wheel rim and a predetermined vertical load is exerted on the tyre.

Hereinafter, it is understood that a flat face, or a portion or part or wall thereof, of a block may also be slightly curved, such curve being interpolate by a plane tangent to the curve at any point or by a plane on which the ends of that curve lie.

The expression "module", when referred to a tread band, and in particular to the tread pattern, is used to indicate a portion of tread pattern repeated identically in succession along the entire circumferential extension of the tread band. The modules, whilst keeping the same pattern configuration, can nevertheless have different circumferential lengths.

The Applicant has taken into consideration motorcycles of the "Motocross" type, which, as already said, are widely used in off-road.

The Applicant observed that in order to optimally cover their entire range of use, these motorcycles should be equipped with tyres capable of ensuring high performance in terms of traction (both in acceleration and braking), lateral grip, driving stability and durability, both on hard and soft terrain.

The Applicant observed that, in accordance with the customer demands, the market has recently been moving towards extremely specialised solutions, with several types of tyres for motorcycles of the "Motocross" type, each of these types being focused on a particular type of terrain.

Consistently, the Applicant proposed some tyres for motorcycles of the "Motocross" type suitable for off-road use on hard terrain, other tyres for motorcycles of the "Motocross" type suitable for off-road use on medium-hard terrain, further tyres for motorcycles of the "Motocross" type suitable for off-road use on medium-soft terrain, other tyres for motorcycles of the "Motocross" type suitable for off-road use on soft terrain.

The Applicant has recently focused its attention on front tyres for motorcycles of the "Motocross" type designed for off-road use on medium-soft terrain.

The Applicant observed that these tyres are required, among other things, to have high driving stability and high lateral grip when the tyre is relatively unloaded (i.e. during acceleration, when most of the load is on the rear tyre). These are in fact performance characteristics that, if not specifically and properly considered, are likely to be heavily penalised by the reduced consistency and compactness of the terrain on which the tyre is intended to be used.

The Applicant reflected on how these performance characteristics could be maximised, while trying not to penalise others.

The Applicant has thought that in order to maximise the driving stability and lateral grip of front tyres intended to be used on medium- soft terrain, each of the blocks provided in the tread band, especially those arranged at or near the equatorial plane, should be capable of penetrating the terrain as much as possible. In this way, according to the Applicant, each block finds sufficient terrain at its side to define an effective restraint and force exchange interface, to the benefit of the stability and repeatability of the relative positioning between tyre and terrain and, consequently, of the driving stability and lateral grip of the tyre during acceleration.

The Applicant has understood that in order to achieve the desired high penetrability of the blocks in the terrain it is advisable that each of them, from the time when it enters the footprint area during tyre rolling and until it leaves the footprint area, is able to move the necessary amount of terrain in the axial direction to allow a complete penetration of the block, without such terrain movement being hindered by axially adjacent blocks.

For this reason, the Applicant has thought to provide the tread band with an annular portion arranged astride of the equatorial plane and without blocks, and with two circumferential rows of blocks (hereinafter referred to as "first central blocks" and "second central blocks") arranged on opposite sides with respect to the aforementioned annular portion, arranging the two circumferential rows of blocks at a mutual distance from each other such that each block of each of said circumferential rows of blocks is sufficiently far in the axial direction from a respective adjacent block of the other circumferential row of blocks.

The Applicant has found that this mutual arrangement of blocks also allows to achieve an unexpected improvement in the tyre off-road braking performance, even on harder terrain.

This improvement is unexpected since, in order to effectively counteract the strains to which the tyre is subjected during braking, it would have been obvious either to arrange some of the blocks astride of the equatorial plane, so as to have gripping edges precisely in the part of the tread band where braking strains are greatest, or to provide circumferential rows of blocks with a reduced distance from each other in the axial direction, so as to increase as much as possible the overall area provided with blocks within the footprint area, this last feature being particularly important especially on hard terrain.

According to the Applicant, the unexpected improvement in terms of braking on medium-soft terrain, but also on harder terrain, is due to the fact that during off-road braking, each block in the ground contacting area is subjected to a series of slippages alternated with moments in which the block grips the terrain. These intermittent slippages make it possible that no portions of the block are more stressed than others. In other words, during off-road braking, each block in the footprint area deforms sufficiently evenly, to the benefit of the braking efficiency and grip.

The present invention relates to an off-road motorcycle tyre comprising a tread band having a predetermined maximum chord.

Preferably, the tread band comprises a central annular portion extending astride of an equatorial plane of the tyre.

Preferably, the tread band comprises two lateral annular portions arranged on opposite sides with respect to the central annular portion.

Preferably, the central annular portion comprises a plurality of circumferentially consecutive first central blocks arranged next to the equatorial plane.

Preferably, the central annular portion comprises a plurality of circumferentially consecutive second central blocks arranged next to the equatorial plane on the opposite side with respect to the plurality of first central blocks.

Preferably, each second central block is axially adjacent to a respective first central block.

Preferably, the central annular portion comprises an intermediate annular portion arranged astride of the equatorial plane and extending between said plurality of first central blocks and said plurality of second central blocks.

Preferably, said intermediate annular portion is without any blocks.

Preferably, each first central block and the respective second central block are arranged at a respective minimum mutual distance in the axial direction such that the ratio between said minimum mutual distance and said predetermined maximum chord is greater than, or equal to, 0.15.

The Applicant has found that a tread pattern made according to what described above allows tyres for motorcycles of the "Motocross" type designed to perform on medium-soft terrain to achieve excellent performance not only in terms of driving stability and lateral grip, but also in terms of braking, even on harder terrain, without at the same time affecting the other performance characteristics typically required to this type of tyre.

The present invention can have at least one of the preferred characteristics described hereinafter.

Preferably, the ratio between said minimum mutual distance and said predetermined maximum chord is less than 0.3.

In preferred embodiments, the ratio between said minimum mutual distance and said predetermined maximum chord is comprised between 0.15 and 0.3.

Preferably, said minimum mutual distance is greater than 12 mm.

Preferably, said minimum mutual distance is shorter than 30 mm.

In preferred embodiments, said minimum mutual distance is comprised between 12 mm and 30 mm.

Preferably, said predetermined maximum chord is greater than 77 mm.

Preferably, said predetermined maximum chord is less than 113 mm.

In preferred embodiments, said predetermined maximum chord is comprised between 77 mm and 113 mm.

Preferably, the tread band has a predetermined circumferential extension and said first central blocks and said second central blocks are arranged at the aforementioned minimum mutual distance along the entire circumferential extension of the tread band.

It is foreseen, however, that said first central blocks and said second central blocks are arranged at the aforementioned minimum mutual distance only at a part of the circumferential extension of the tread band, and in particular at a circumferential section of said central annular portion having a length of not less than 75% of said predetermined circumferential extension.

Preferably, said intermediate annular portion is without any blocks along the entire circumferential extension of the tread band.

However, it is foreseen that said intermediate annular portion is without any blocks only at a part of the circumferential extension of the tread band, and in particular at the aforementioned circumferential section of said central annular portion.

In some preferred embodiments, at least some of said first central blocks are connected to the respective second central blocks by respective connecting elements arranged astride of the equatorial plane.

Preferably, each first block has a predetermined maximum circumferential length and a predetermined maximum axial width.

Preferably, the ratio between said predetermined maximum circumferential length and said predetermined maximum axial width is greater than 1.2.

Preferably, the ratio between said predetermined maximum circumferential length and said predetermined maximum axial width is less than 1.5.

In preferred embodiments, the ratio between said predetermined maximum circumferential length and said predetermined maximum axial width is comprised between 1.2 and 1.5.

The Applicant believes that the provision of blocks with a maximum axial width less than the maximum circumferential length facilitates penetration of the blocks into the terrain, while at the same time offering an effective counteraction to the strains to which the blocks are subjected during braking.

Preferably, said predetermined maximum circumferential length is greater than 13 mm.

Preferably, said predetermined maximum circumferential length is shorter than 15 mm.

In preferred embodiments, said predetermined maximum circumferential length is between 13 mm and 15 mm.

Preferably, said predetermined maximum axial width is less than 10 mm.

Preferably, said predetermined maximum axial width is greater than 5 mm.

In preferred embodiments, said predetermined maximum axial width is comprised between 5 mm and 10 mm.

Preferably, said first central blocks are aligned with each other in the circumferential direction.

Preferably, said second central blocks are aligned with each other in the circumferential direction.

Preferably, each of said first central blocks and/or second central blocks is delimited by an axially inner face and an axially outer face opposite to the axially inner face.

The axially inner and axially outer faces therefore delimit a block on opposite sides along an axial direction.

Preferably, each of said first central blocks and/or second central blocks is delimited by a first transversal face and a second transversal face opposite to the first transversal face. The first transversal face and the second transversal face, therefore, delimit a block on opposite sides along the circumferential direction.

In some preferred embodiments, at least one of the axially inner face, the axially outer face, the first transversal face and the second transversal face is flat.

In other preferred embodiments, at least one of the axially inner face, the axially outer face, the first transversal face and the second transversal face is concave towards the inside of the respective block.

The Applicant observed that the provision of concave faces towards the inside of the block allows, on the one hand, to locally increase the distance between portions of adjacent blocks in the axial and/or circumferential direction, to the benefit of penetrability, and, on the other hand, facilitates the compaction of the terrain next to those faces, to the benefit of lateral grip and driving stability.

In some preferred embodiments, the axially inner face of the first blocks and/or second blocks is substantially parallel to the equatorial plane.

In other preferred embodiments, the axially inner face of the first central blocks and/or second central blocks comprises a first wall extending between an axially inner edge of said first transversal face and a central portion of said axially inner face.

Preferably, said first wall is inclined with respect to a respective first reference plane perpendicular to the equatorial plane by a first angle.

Preferably, the axially inner face of the first central blocks and/or second central blocks comprises a second wall extending between an axially inner edge of said second transversal face and said central portion of said axially inner face.

Preferably, said second wall is inclined with respect to said respective first reference plane on the opposite side with respect to said first wall by a second angle.

Preferably, said first wall and second wall join to each other at a first joining line defined in said central portion of said axially inner face.

Preferably, said first joining line has a distance in the axial direction from the equatorial plane greater than the distance in the axial direction from the equatorial plane of said axially inner edge of said first transversal face.

Preferably, said first joining line has a distance in the axial direction from the equatorial plane greater than the distance in the axial direction from the equatorial plane of said axially inner edge of said second transversal face.

The aforementioned first wall and second wall define in the axially inner face of the first central blocks and/or second central blocks a concavity towards the inside of the block.

Preferably, said first joining line is arranged at a distance in the axial direction from the equatorial plane such that the ratio between said distance and said maximum chord is greater than 0.13.

Preferably, said first joining line is arranged at a distance in the axial direction from the equatorial plane such that the ratio between said distance and said maximum chord is shorter than 0.26.

In preferred embodiments, said first joining line is arranged at a distance in the axial direction from the equatorial plane such that the ratio between said distance and said maximum chord is comprised between 0.13 and 0.26.

Preferably, said first joining line is arranged at a distance in the axial direction from the equatorial plane greater than 7 mm.

Preferably, said first joining line is arranged at a distance in the axial direction from the equatorial plane shorter than 16 mm.

In preferred embodiments, said first joining line is arranged at a distance in the axial direction from the equatorial plane comprised between 7 mm and 16 mm.

Preferably, the distance in the axial direction between said first joining line and said axially inner edge of said first transversal face is equal to the distance in the axial direction between said first joining line and said axially inner edge of said second transversal face.

Preferably, said first angle is greater than 45°, more preferably greater than 55°, even more preferably greater than 65°, even more preferably greater than 75°.

Preferably, said first angle is less than 89°, more preferably less than 88°, even more preferably less than 87°, even more preferably greater than 86°.

In preferred embodiments, said first angle is comprised between 45° and 89°, preferably between 55° and 88°, more preferably between 65° and 87°, even more preferably between 75° and 86°, e.g. equal to 82°.

Preferably, said second angle is greater than 45°, more preferably greater than 55°, even more preferably greater than 65°, even more preferably greater than 75°.

Preferably, said second angle is less than 89°, more preferably less than 88°, even more preferably less than 87°, even more preferably less than 86°.

In preferred embodiments, said second angle is comprised between 45° and 89°, preferably between 55° and 88°, more preferably between 65° and 87°, even more preferably between 75° and 86°, e.g. equal to 82°.

In particularly preferred embodiments, said first angle is equal to said second angle.

In some preferred embodiments, this first transversal face is substantially perpendicular to the equatorial plane.

In other preferred embodiments, said first transversal face comprises a third wall extending between said axially inner edge of said first transversal face and a central portion of said first transversal face.

Preferably said third wall is inclined with respect to a respective second reference plane parallel to said equatorial plane by a third angle.

Preferably, said first transversal face comprises a fourth wall extending between an axially outer edge of said first transversal face and said central portion of said first transversal face.

Preferably, said fourth wall is inclined with respect to said respective second reference plane on the opposite side with respect to said third wall by a fourth angle.

Preferably, said third wall and fourth wall join to each other at a second joining line defined in said central portion of said first transversal face.

Preferably, said second joining line has a distance in the circumferential direction from the circumferentially closest first central block or second central block greater than that of the axially inner edge of said first transversal face.

Preferably, said second joining line has a distance in the circumferential direction from the circumferentially closest first central block or second central block greater than that of the axially outer edge of said first transversal face.

The aforementioned third wall and fourth wall define in the first transversal face of the first central blocks and/or second central blocks a concavity towards the inside of the block.

Preferably, said second joining line is arranged at a distance in the circumferential direction from the circumferentially closest first central block or second central block such that the ratio between said distance and said predetermined circumferential extension is greater than 1.30.

Preferably, said second joining line is arranged at a distance in the circumferential direction from the circumferentially closest first central block or second central block such that the ratio between said distance and said circumferential extension is less than 1.65.

In preferred embodiments, said second joining line is arranged at a distance in the circumferential direction from the circumferentially closest first central block or second central block such that the ratio between said distance and said predetermined circumferential extension is comprised between 1.30 and 1.65.

Preferably, said second joining line is arranged at a distance in the circumferential direction from the circumferentially closest first central block or second central block greater than 30 mm.

Preferably, said second joining line is arranged at a distance in the circumferential direction from the circumferentially closest first central block or second central block shorter than 36 mm.

In preferred embodiments, said second joining line is arranged at a distance in the circumferential direction from the circumferentially closest first central block or second central block comprised between 30 mm and 36 mm, preferably between 32 mm and 35 mm.

Preferably, the distance in the circumferential direction between said second joining line and said axially inner edge of said first transversal face is equal to the distance in the circumferential direction between said second joining line and said axially outer edge of said first transversal face.

Preferably, said third angle is greater than 45°, more preferably greater than 55°, even more preferably greater than 65°, even more preferably greater than 75°.

Preferably, said third angle is less than 89°, more preferably less than 88°.

In preferred embodiments, said third angle is comprised between 45° and 89°, preferably between 55° and 88°, more preferably between 65° and 88°, even more preferably between 75° and 88°, e.g. equal to 87°.

Preferably, said fourth angle is greater than 45°, more preferably greater than 55°, even more preferably greater than 65°, even more preferably greater than 75°.

Preferably, said fourth angle is less than 89°, more preferably less than 88°.

In preferred embodiments, said fourth angle is comprised between 45° and 89°, preferably between 55° and 88°, more preferably between 65° and 88°, even more preferably between 75° and 88°, e.g. equal to 79°.

In particularly preferred embodiments, said third angle is equal to said fourth angle.

Preferably, said axially outer face has a circumferential length shorter than that of said axially inner face.

Preferably, said second transversal face has a length in the axial direction shorter than that of said first transversal face.

Preferably, each of said first central blocks comprises a connecting wall connecting said axially outer face to said second transversal face.

Preferably, each of said second central blocks comprises a connecting wall connecting said axially outer face to said second transversal face.

Preferably, said connecting wall is inclined with respect to said axially outer face by an angle greater than 10°, more preferably greater than 20°, even more preferably greater than 30°.

Preferably, said connecting wall is inclined with respect to said axially outer face by an angle of less than 80°, more preferably less than 70°, even more preferably less than 60°.

In preferred embodiments, the connecting wall is inclined with respect to the axially outer face by an angle comprised between 10° and 80°, preferably between 20° and 70°, more preferably between 30° and 60°.

The provision of the aforementioned inclined connection wall facilitates the penetration of each central block when it enters the footprint area and makes it possible to maintain a certain distance between each central block and a respective block among those that will be referred to below as "lateral blocks" even if the central blocks are sufficiently far from the equatorial plane. This makes it easier for the central blocks to penetrate into the terrain.

Preferably, the circumferential length of said axially outer face is equal to half the circumferential length of said axially inner face.

Preferably, the length of said second transversal face is equal to half the length of said first transversal face.

Preferably, each lateral annular portion of said two lateral annular portions comprises a plurality of respective circumferentially consecutive lateral blocks.

Preferably, said lateral blocks are misaligned in the axial direction with respect to said first central blocks.

Preferably, said lateral blocks are misaligned in the axial direction with respect to said second central blocks.

This misalignment allows, during rolling, the central blocks entering the footprint area to be able to move the necessary amount of terrain in the axially outer direction to allow complete penetration of these blocks even at their axially outer sidewalls, without such terrain movement being hindered by the lateral blocks. A desired distribution of the blocks in the footprint area is also achieved, ensuring as much as possible a continuous and uniform grip with the terrain in the various driving conditions of the tyre as well as an effective transfer of the lateral and longitudinal stresses between the terrain and the footprint area. All this to the benefit of off-road performance.

Preferably, each of said lateral blocks has an axially inner face which is concave towards the inside of the block.

Preferably, each of said lateral blocks is arranged at an oblique distance from the closest first central block or second central block such that the ratio between said oblique distance and said maximum chord is less than 0.23.

Preferably, each of said lateral blocks is arranged at an oblique distance from the closest first central block or second central block such that the ratio between said oblique distance and said maximum chord is greater than 0.15.

In preferred embodiments, each of said lateral blocks is arranged at an oblique distance from the closest first central block or second central block such that the ratio between said oblique distance and said maximum chord is comprised between 0.15 and 0.23.

Preferably, said oblique distance is greater than 15 mm.

Preferably, said oblique distance is shorter than 23 mm.

In preferred embodiments, said oblique distance is comprised between 15 mm and 23 mm.

Preferably, said oblique distance is calculated between said connecting wall and the adjacent edge of the lateral block closest to said connecting wall.

Preferably, said tread band comprises two shoulder annular portions arranged on opposite sides with respect to the central annular portion in an axially outer position with respect the two lateral annular portions.

Preferably, each shoulder annular portion comprises a plurality of circumferentially consecutive shoulder blocks.

Preferably, said shoulder blocks are aligned in the axial direction to said first central blocks.

Preferably, said shoulder blocks are aligned in the axial direction to said second central blocks. Preferably, each of said shoulder blocks has an axially inner face which is concave towards the inside of the block. This concavity contributes to compacting the terrain between a shoulder block and the closest central block, to the benefit of off-road performance.

Preferably, each of said shoulder blocks is arranged at a distance in the axial direction from the closest first central block or second central block such that the ratio between said distance and said maximum chord is less than 0.33.

Preferably, each shoulder block is arranged at a distance in the axial direction from the closest first central block or second central block such that the ratio between that distance and that maximum chord is greater than 0.25.

In preferred embodiments, each shoulder block is arranged at a distance in the axial direction from the closest first central block or second central block such that the ratio between said distance and said maximum chord is comprised between 0.25 and 0.33.

Preferably, said distance is greater than 25 mm.

Preferably, said distance is shorter than 31 mm.

In preferred embodiments, said distance is comprised between 25 mm and 31 mm.

Preferably, said tread band has a void to solid ratio greater than 0.85.

Preferably, said tread band has a void to solid ratio of less than 0.90.

In preferred embodiments, the said tread band has a void to solid ratio comprised between 0.85 and 0.90.

The Applicant found that the aforementioned void to solid ratio values allow to maximise the tyre off-road performance in medium-soft terrain.

Preferably, a pair of blocks formed of a first central block and a second central block, possibly plus a lateral block adjacent to the first central block and a lateral block adjacent to the second central block, possibly plus a shoulder block adjacent to the first central block and a shoulder block adjacent to the second central block, belong to, and define, a module that is repeated along the entire circumferential extension of the tread band.

Preferably, said tyre has a fitting diameter comprised between 10 inches and 22 inches.

Preferably, said tyre is a front tyre.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Further characteristics and advantages of the tyre of the present invention will become clearer from the following detailed description of preferred embodiments thereof, made with reference to the appended drawings. In such drawings:

- Figure 1 is a schematic view of a radial section of a motorcycle tyre according to the present invention;

- Figure 2 is a schematic perspective view of a first preferred embodiment of a front tyre according to the present invention;

- Figure 3 is a schematic front view of a portion of the tyre of Figure 2;

- Figures 4 and 5 schematically show an enlargement of a circumferential section of the portion of Figure 3;

- Figure 6 schematically shows an enlargement of a block shown in the previous figures and of its relative position with respect to a similar circumferentially adjacent block;

- Figure 7 is a schematic front view of a portion of the tread band of a second preferred embodiment of a front tyre according to the present invention.

With reference to Figures 1 and 2, a tyre for motorcycles having a high weight and medium-large piston displacement, so-called "off-road" or of the "Motocross" type, according to a preferred embodiment of the present invention, is indicated with 1.

Tyre 1 is a front tyre, i.e. it is intended to be mounted on the front wheel of the aforementioned motorcycles.

An equatorial plane X-X and a rotation axis R are defined in the tyre 1 (Figure 2). A circumferential direction arranged according to the direction of rotation W of the tyre 1 and therefore parallel to the equatorial plane X-X and an axial direction perpendicular to the equatorial plane X-X and/or parallel to the rotation axis R are also defined.

The tyre 1 comprises a carcass structure 2 formed by at least two carcass plies 3 radially overlapping each other and each consisting of a sheet of elastomeric material incorporating a plurality of reinforcing cords made of fibrous textile material, not shown.

The reinforcing cords are essentially parallel to each other in each carcass ply 3 and are oriented according to directions inclined with respect to the equatorial plane X-X of the tyre 1 in each carcass ply 3 and according to opposite directions with respect to the cords of the radially adjacent carcass ply 3 (carcass with crossed plies).

The carcass structure 2 is typically coated, on the inner walls thereof, by a sealing layer 100, or so-called "liner", essentially consisting of an airtight layer of elastomeric material, adapted to ensure the hermetic seal of the tyre itself 1 once inflated.

Each carcass ply 3 is shaped according to a substantially toroidal configuration.

At least some of the carcass plies 3 have their axially opposite lateral edges 3a turned-up to respective annular reinforcing structures 4 intended to hold the tyre I on a corresponding mounting rim (not shown). The annular reinforcing structures 4 are typically called "bead cores".

In order to increase the structural homogeneity of the tyre 1, the carcass plies 3 have an axial extension different from each other. A tapered elastomeric filler 5 is applied on the outer perimetral edge of the bead cores 4. The elastomeric filler 5 occupies the space defined between the respective carcass ply 3 and the corresponding turned-up lateral edge 3a of the carcass ply 3.

The area of the tyre 1 comprising the bead core 4 and the elastomeric filler 5 forms the so-called bead 9, which is intended to anchor the tyre 1 on the rim, not shown.

In one embodiment thereof, each carcass ply 3 is made by arranging side by side a plurality of strips of elastomeric material reinforced by the aforementioned cords.

A belt structure 6 is applied on the carcass structure 2, in a radially outer position thereof. The belt structure 6 comprises at least one belt layer 6a typically formed from rubber-coated textile or metallic reinforcing cords.

Preferably, the belt structure 6 is of the zero degrees type, i.e. the belt layer 6a is made through reinforcing cords arranged substantially parallel and side-by-side to form a plurality of turns. Such turns are substantially oriented according to the circumferential direction (typically with an angle comprised between 0° and 5°), such a direction usually being called "zero degrees" with reference to how it lies with respect to the circumferential direction of the tyre 1.

Preferably, the typically called "zero degrees" belt layer 6a can comprise windings arranged axially side-by-side of a single reinforcing cord or of a rubber-coated textile band which comprises reinforcing cords arranged axially side-by-side.

The reinforcing cords of the zero degrees belt layer 6a are typically metal cords. They are made of steel wires having high carbon content, i.e. steel wires with a carbon content of at least 0.6 - 0.7%. Preferably such metal reinforcing cords are high elongation (HE) cords.

In order to improve adhesion between the belt structure 6 and the carcass structure 2, an adhesion layer 7 made of elastomeric material is provided between the aforementioned two structures. Such an adhesion layer preferably extends over a surface substantially corresponding to the extension surface of the belt structure 6.

Alternatively, the adhesion layer 6 extends over a surface larger than the extension surface of the belt structure 6.

In a preferred embodiment, the adhesion layer 6 comprises short aramid fibres, e.g. Kevlar®, dispersed in said elastomeric material.

A tread band 8 is provided in a radially outer position with respect to the belt structure 6. The tread band 8 is made of an elastomeric material and, following a moulding operation carried out in conjunction with a vulcanisation step of the tyre 1, a plurality of blocks are typically obtained on the tread band 8, the blocks being separated from each other by longitudinal and/or transversal cavities or grooves to define a desired tread pattern.

The composition of the tread band 8 is such that the tread band 8 has only one compound on its radially outer surface.

In one embodiment, the tread band 8 is made in a cap-and-base mode and comprises a radially outer portion overlapped to an elastomeric substrate (not shown in Figure 1). The substrate is overlapped on the belt structure 6 and preferably extends over a surface substantially corresponding to the extension area of the radially outer portion of the tread band 8. Alternatively, said substrate extends only over a portion of the radially outer extension of the tread band 8, for example over opposite lateral portions of the tread band 8.

The tyre 1 further comprises a pair of sidewalls 10 applied laterally on opposite sides with respect to said carcass structure 2.

With reference to Figure 1, the tyre 1 has a section height "H" measured, on the equatorial plane "X-X", between the top of the tread band 8 and the fitting diameter, identified by a reference line "r" passing through the beads 9 of the tyre 1.

The tyre 1 also has a maximum chord "C", defined by the distance between the laterally opposite ends "E" of the tread band 8, and an arrow "f", defined by the distance of the top of the tread band 8 from a line passing through said laterally opposite ends "E", measured on the equatorial plane "X-X" of the tyre 1. The laterally opposite ends "E" of the tread band 8 can be formed with a joining line.

The tyre 1 has a "curvature ratio" f/C, defined by the ratio between the arrow "f" and the aforementioned maximum chord "C", less than or equal to approximately 0.33, relatively high sidewalls and not particularly high curvature.

Preferably, the tyre 1 has a maximum chord C comprised between 77 mm and 113 mm and is intended to be mounted on wheel rims having fitting diameters comprised between 14 inches and 22 inches.

In the tyre 1, the sidewall height ratio (H-f)/H is equal to at least about 0.3.

Preferably, the tyre 1 has a fitting diameter comprised between 14 inches and 22 inches.

As shown in the figures, the tyre 1 is of the tread block type, i.e. the tread band 8 comprises a base surface 8a (Figures 1-3) from which a plurality of blocks, defined by a plurality of grooves, protrude.

The blocks and grooves define a tread pattern having a void to solid ratio comprised between 0.85 and 0.90, e.g. equal to 0.87.

As shown in the figures, the tread band 8 is symmetrical with respect to the equatorial plane X-X.

The blocks of the embodiment of the tyre shown in Figure 2 are described hereinafter with reference to Figures 3-6.

Figure 3 shows a portion of the tread band 8 of the tyre 1 of Figure 2 in a frontal view thereof, while Figures 4 and 5 show an enlargement of the portion of Figure 3. In particular, Figure 4 shows a module T of pitch P that repeats circumferentially along the entire circumferential extension of the tyre 1. Some particularly interesting dimensions are also shown in Figure 5. Please note that Figures 2-5 are schematic drawings that do not necessarily reflect the exact distances between the various blocks and the mutual arrangement of the blocks.

With reference to Figure 3, the tread band 8 comprises a central annular portion M extending astride of the equatorial plane X-X, two lateral annular portions L arranged on opposite sides with respect to the central annular portion M and two shoulder annular portions S arranged on opposite sides with respect to the central annular portion M in an axially outer position with respect to the two lateral annular portions L.

The central annular portion M comprises a first circumferential row 15* of circumferentially consecutive first central blocks 15 arranged next to the equatorial plane X-X and aligned with each other in a circumferential direction, a second circumferential row 55* of circumferentially consecutive second central blocks 55 arranged next to the equatorial plane X-X on the opposite side with respect to the first central blocks 15 and aligned with each other in the circumferential direction, and an intermediate annular portion 50 arranged astride of the equatorial plane X-X, extending between the first circumferential row 15* and the second circumferential row 55*, and without any blocks.

Each second central block 55 is axially adjacent to a respective first central block 15. In particular, each second central block 55 is aligned in the axial direction to a respective first central block 15.

In one embodiment not shown, each first central block 15 is connected to a respective second central block 55 by a respective connecting element arranged astride of the equatorial plane X-X.

Each of the two lateral annular portions L comprises a respective circumferential row 20*, 60* of circumferentially consecutive lateral blocks 20, 60. Each of the two shoulder annular portions S comprises a respective circumferential row 30*, 70* of circumferentially consecutive shoulder blocks 30, 70.

The lateral blocks 20, 60 are misaligned in the axial direction with respect to the first central blocks 15 and the second central blocks 55.

The shoulder blocks 30, 70 are misaligned in the axial direction with respect to the lateral blocks 20, 60 and aligned in the axial direction to the first central blocks 15 and second central blocks 55.

As shown in Figure 4, in a module T of pitch P there is a first central block 15, the second central block 55 axially aligned to it, a lateral block 20 adjacent to the aforementioned first central block 15, the lateral block 60 axially aligned to said lateral block 20, a shoulder block 30 adjacent to said lateral block 20, the shoulder block 70 adjacent to said lateral block 60 and axially aligned to the aforementioned shoulder block 30.

Preferably, the tyre 1 is defined by a plurality of modules T as described above, which are repeated as such along the entire circumferential extension of the tread band 8. However, alternative embodiments are foreseen in which the aforementioned modules T are repeated as such only over a circumferential section of the tyre 1 of not less than 75% of the circumferential extension of the tread band 8.

Hereinafter, details will be provided about the shape and relative position of the first central blocks 15 and second central blocks 55 with respect to each other and to the lateral blocks 20, 60 and shoulder blocks 30, 70. This description will be made with reference to Figures 3-6. For ease of reading, although reference will be made to both the first central blocks 15, and their relative position with respect also to the lateral blocks 20 and the shoulder blocks 30, and the second central blocks 55, and their relative position with respect also to the lateral blocks 60 and the shoulder blocks 70, in Figures 4 to 6 the numerical references and dimensions will only be associated with the first central blocks 15, the lateral blocks 20 and the shoulder blocks 30, it being understood that these numerical references and dimensions are also intended to be associated with the second central blocks 55, the lateral blocks 60 and the shoulder blocks 70.

As shown in Figure 5, each first central block 15 and the second central block 55 adjacent thereto are placed at a minimum mutual distance D comprised between 12 mm and 30 mm.

This minimum mutual distance D is chosen in such a way that the ratio between the minimum mutual distance D and the maximum chord C of the tread band 8 is comprised between 0.15 and 0.3.

Each first central block 15 and second central block 55 has a predetermined maximum circumferential length Lc and a predetermined maximum axial width La.

Preferably, the maximum circumferential length Lc is comprised between 13 mm and 15 mm, e.g. equal to 14 mm.

Preferably, the maximum axial width La is comprised between 5 mm and 10 mm, e.g. 9 mm.

Preferably, the ratio between the maximum circumferential length Lc and the maximum axial width La is comprised between 1.2 and 1.5, e.g. equal to 1.3.

With reference to Figures 4-6, each of the first central blocks 15 and of the second central blocks 55 is delimited by an axially inner face 15a, an axially outer face 15b opposite to the axially inner face 15a, a first transversal face 15c and a second transversal face 15d opposite to the first transversal face 15c.

The axially outer face 15b has a circumferential length lc shorter than the length of the axially inner face 15a, preferably equal to half the length of the axially inner face 15a, the latter being substantially equal to the maximum circumferential length Lc.

The second transversal face 15d has a length in the axial direction la shorter than the length of the first transversal face 15c, preferably half the length of the first transversal face 15c, the latter being substantially equal to the maximum axial width La.

A connecting wall 190 connects the axially outer face 15b to the second transversal face 15d. This connecting wall 190 is inclined with respect to the equatorial plane X-X by an angle comprised between 10° and 80°, preferably between 20° and 70°, more preferably between 30° and 60°, e.g. equal to 36°.

The axially outer face 15b is flat and parallel to the equatorial plane X-X.

The second transversal face 15d is flat and perpendicular to the equatorial plane X-X.

On the other hand, the axially inner face 15a and the first transversal face 15c are concave, with concavity facing toward the inside of the block.

In particular, as shown in Figure 6, the axially inner face 15a comprises a first wall 150a, extending between an axially inner edge 150 of the first transversal face 15c and a central portion 155 of the axially inner face 15a, and a second wall 160a, extending between an axially inner edge 160 of the second transversal face 15d and the aforementioned central portion 155 of the axially inner face 15a.

The axially inner edge 150 of the first transversal face 15c and the axially inner edge 160 of the second transversal face 15d have the same distance De in the axial direction from the equatorial plane X-X.

The first wall 150a and the second wall 160a are inclined on opposite sides with respect to the equatorial plane X-X by a first angle al and a second angle a2, respectively, such angles being preferably equal to each other and comprised between 45° and 89°, preferably between 55° and 88°, more preferably between 65° and 87°, even more preferably between 75° and 86°, e.g. equal to 82°. The first wall 150a and the second wall 160a join to each other at a first joining line VI defined in the central portion 155 of the axially inner face 15a and having a distance Dvl in the axial direction from the equatorial plane X-X greater than the distance De.

The first joining line VI is far away in the axial direction from the axially inner edge 150 of the first transversal face 150a as it is far away in the axial direction from the axially inner edge 160 of the second transversal face 160a.

The distance Dvl is preferably comprised between 6 mm and 16 mm and is such that the ratio between the distance Dvl and the maximum chord C is preferably comprised between 0.13 and 0.26.

The first transversal face 15c comprises a third wall 170a extending between an axially inner edge 150 of the first transversal face 15c and a central portion 175 of the first transversal face 15c and a fourth wall 180a extending between an axially outer edge 180 of the first transversal face 15c and the aforementioned central portion 175 of the first transversal face 15c.

The axially inner edge 150 and the axially outer edge 180 of the first transversal face 15c have the same distance dx in the circumferential direction from the circumferentially closest central block 15 (or 55).

The third wall 170a and the fourth wall 180a are inclined on opposite sides with respect to a reference plane P2 parallel to the equatorial plane X-X by a third angle 01 and a fourth angle 02, respectively, such angles being preferably equal to each other and comprised between 45° and 89°, preferably between 55° and 88°, more preferably between 65° and 88°, even more preferably between 75° and 88°, e.g. equal to 79°.

The third wall 170a and the fourth wall 180a join to each other at a second joining line V2 defined in the central portion 175 of the first transversal face 15c and having a distance dv2 in the circumferential direction from the circumferentially closest central block 15 (or 55) greater than the distance dx.

The second joining line V2 is far away in the circumferential direction from the axially inner edge 150 of the first transversal face 150a as it is far away in the circumferential direction from the axially outer edge 180 of the first transversal face 150a.

The distance dv2 is preferably comprised between 30 mm and 36 mm, e.g. 34 mm, and is such that the ratio between the distance dv2 and the circumferential extension of the tread band 8 is preferably comprised between 1.3 and 1.65, e.g. equal to 1.5.

In view of the fact that the axially inner face 15a and the first transversal face 15c are not flat, in the tyre 1 described above:

- the minimum mutual distance D is measured in the axial direction between the axially inner edge 150 of a first central block 15 and the axially inner edge of the second central block 55 axially aligned thereto, or between the axially inner edge 160 of a first central block 15 and the axially inner edge of the second central block 55 axially aligned thereto;

- the maximum circumferential length Lc is measured in the circumferential direction between the second transversal face 15d of a central block 15, 55 and the axially inner edge 150 of the first transversal face 15c or the axially outer edge 180 of the first transversal face 15c of the same central block 15, 55;

- the maximum axial width La is measured in the axial direction between the axially inner edge 150 of the first transversal face 15c or the axially inner edge 160 of the second transversal face 15d of a central block 15, 55 and the axially outer face 15b of the same central block 15, 55;

- the circumferential length lc is measured in the circumferential direction between the axially outer edge 180 of the first transversal face 15c of a central block 15, 55 and the point where the axially outer face 15b joins the connecting wall 190 of the same central block 15, 55;

- the length la is measured in the axial direction between the axially inner edge 160 of the second transversal face 15d of a central block 15, 55 and the point where the second transversal face 15d joins the connecting wall 190 of the same central block 15, 55.

Each of the lateral blocks 20, 60 is arranged at an oblique distance do from the closest central block 15 (or 55) comprised between 15 mm and 23 mm, e.g. equal to 20 mm, and such that the ratio between the oblique distance do and the maximum chord C is comprised between 0.15 and 0.23, e.g. equal to 0.20.

As shown in Figure 5, the oblique distance do is measured in the oblique direction between the connecting wall 190 of a central block 15, 55 and the adjacent edge of the lateral block 20, 60 closest to it.

As shown in Figure 4, each lateral block 20, 60 has an axially inner face 20a, 60a which is concave towards the inside of the block. As a result of this concavity, each lateral block 20, 60 has, at its axially inner face 20a, 60a, opposite edges having a distance in the axial direction from the equatorial plane X-X shorter than the distance of a central portion of that face interposed between said edges.

Similarly, each shoulder block 30, 70 has an axially inner face 30a, 70a which is concave towards the inside of the block. As a result of this concavity, each shoulder block 30, 70 has, at its axially inner face 30a, 70a, opposite edges having a distance in the axial direction from the equatorial plane X-X shorter than the distance of a central portion of that face interposed between said edges.

Each of the shoulder blocks 30 is arranged at a distance ds in the axial direction from the first central block 15 axially aligned thereto such that the ratio between the distance ds between the aforementioned shoulder block 30 and the aforementioned first central block 15 and the maximum chord C is comprised between 0.25 and 0.33.

Preferably, the distance ds is comprised between 25 mm and 31 mm, e.g. equal to 28 mm.

The distance ds is measured in the axial direction between any one of the opposite edges of the axially inner face 30a of a shoulder block 30, 70 and the axially outer face 15b of the central block 15, 55 aligned thereto.

Figure 7 shows a portion of the tread band of an embodiment of the tyre of the present invention alternative to the one described above. Only those parts where the tread band 8 differs from that of the tyre 1 described with reference to Figures 2-6 are depicted by a continuous line. Everything else is identical to the above and is depicted by hatching.

The tread band of the tyre of Figure 7 differs from that of the tyre 1 of Figure 2 only in that the first central blocks 15 and the second central blocks 55 have respective axially inner faces 15a that are flat and parallel to the equatorial plane X-X and respective first transversal faces 15c that are flat and perpendicular to the equatorial plane X-X.

COMPARATIVE TESTS

The Applicant has made a sample of a front tyre 1 in accordance with an embodiment of the present invention and in particular having the tread pattern shown in Figure 2. Such a tyre is indicated hereinafter with INV.

The tyre INV had structure and dimensions identical to those of a front tyre of the Applicant for motorcycles intended for off-road use and currently sold on the market. Such a tyre is indicated hereinafter with Ref.

Outdoor comparison tests were carried out with the tyre Ref, the latter being appreciated by customers for its excellent off-road behaviour.

The tests were carried out by mounting both the tyres (inflated with the same inflation pressure) on the front wheel of a Honda CRF 450 motorcycle, with an identical tyre mounted on the rear wheel and in substantially identical environmental conditions.

The front tyres INV and Ref had the following size: 80/100-21.

The rear tyre had the following size: 110/90-19.

The behaviour of the two tyres INV and Ref on the same off-road track was evaluated and the driver was asked to make a judgement. In particular, the items listed in Tables 1 and 2 below were evaluated, where the opinion expressed by the driver is also given.

Table 1 relates to tests on medium-soft terrain.

Table 2 relates to tests on hard and compact terrain.

In the aforementioned tables, "=" indicates the positive opinion obtained by the tyre Ref and "+" indicates an improvement with respect to the tyre Ref.

Table 1

Table 2

Tables 1 and 2 show that the tyre INV generally performed better than the tyre Ref on both medium-soft and hard and compact terrain, in particular with reference to the three items listed in the tables, showing a behaviour in line with that of the tyre Ref with regard to all the other items evaluated and not reported herein for ease of discussion.

The Applicant thus had a confirmation that the particular tread pattern adopted in the tyre of the invention effectively achieves the sought improvement in off-road performance in terms of driving stability and lateral grip, with an unexpected improvement in braking performance on both medium-soft and hard and compact terrain. This improvement in braking was neither expected nor desired, as the Applicant's objective was to improve performance on medium-soft terrain in terms of driving stability and lateral grip.

Of course, a person skilled in the art can make further modifications and changes to the tyre described above in order to satisfy specific and contingent application requirements, these modifications and changes being in any case within the scope of protection as defined by the following claims.

Claims

1. Off-road motorcycle tyre (1), comprising a tread band (8) having a predetermined maximum chord (C), said tread band (8) comprising a central annular portion (M) extending astride of an equatorial plane (X-X) of the tyre (1) and two lateral annular portions (L) arranged on opposite sides with respect to the central annular portion (M), wherein the central annular portion (M) comprises:

- a plurality of circumferentially consecutive first central blocks (15) arranged next to the equatorial plane (X-X);

- a plurality of circumferentially consecutive second central blocks (55) arranged next to the equatorial plane (X-X) on the opposite side with respect to the plurality of first central blocks (15), each second central block (55) being axially adjacent to a respective first central block (15);

- an intermediate annular portion (50) arranged astride of the equatorial plane (X-X) and extending between said plurality of first central blocks (15) and said plurality of second central blocks (55), said intermediate annular portion (50) being without any blocks; wherein each first central block (15) and the respective second central block (55) are arranged at a respective minimum mutual distance (D) in the axial direction such that the ratio between said minimum mutual distance (D) and said predetermined maximum chord (C) is greater than, or equal to, 0.15.

2. Off-road motorcycle tyre (1) according to claim 1, wherein each first central block (15) and second central block (55) has a predetermined maximum circumferential length (Lc) and a predetermined maximum axial width (La), wherein the ratio between said predetermined maximum circumferential length (Lc) and said predetermined maximum axial width (La) is greater than 1.2.

3. Off-road motorcycle tyre (1) according to claim 1 or 2, wherein said first central blocks (15) are aligned to each other in the circumferential direction and said second central blocks (55) are aligned to each other in the circumferential direction.

4. Off-road motorcycle tyre (1) according to any one of the previous claims, wherein each of said first central blocks (15) and second central blocks (55) is delimited by an axially inner face (15a), an axially outer face (15b) opposite to the axially inner face (15a), a first transversal face (15c) and a second transversal face (15d) opposite to the first transversal face (15c), wherein at least one of the axially inner face (15a), the axially outer face (15b), the first transversal face (15c) and the second transversal face (15d) is flat or concave towards the inside of the respective block.

5. Off-road motorcycle tyre (1) according to claim 4, wherein the axially inner face (15a) is substantially parallel to the equatorial plane (X- X) or comprises:

- a first wall (150a) extending between an axially inner edge (150) of said first transversal face (15c) and a central portion (155) of said axially inner face (15a) and inclined with respect to a respective first reference plane (Pl) perpendicular to the equatorial plane (X-X) by a first angle (al);

- a second wall (160a) extending between an axially inner edge (160) of said second transversal face (15d) and said central portion (155) of said axially inner face (15a) and inclined with respect to said respective first reference plane (Pl) on the opposite side with respect to said first wall (150a) by a second angle (a2); wherein said first wall (150a) and second wall (160a) join to each other at a first joining line (VI) defined in said central portion (155) of said axially inner face (15a) and having a distance (Dvl) from the equatorial plane (X-X) in the axial direction greater than the distance (De) from the equatorial plane (X-X) in the axial direction of said axially inner edge (150) of said first transversal face (15c) and of said axially inner edge (160) of said second transversal face (15d).

6. Off-road motorcycle tyre (1) according to claim 5, wherein said first angle (al) and second angle (a2) are comprised between 45° and 89°.

7. Off-road motorcycle tyre (1) according to any one of claims 3 to 6, wherein said first transversal face (15c) is substantially perpendicular to the equatorial plane (X-X) or comprises:

- a third wall (170a) extending between said axially inner edge (150) of said first transversal face (15c) and a central portion (175) of said first transversal face (15c) and inclined with respect to a respective second reference plane (P2) parallel to said equatorial plane (X-X) by a third angle (01);

- a fourth wall (180a) extending between an axially outer edge (180) of said first transversal face (15c) and said central portion (175) of said first transversal face (15c) and inclined with respect to said respective second reference plane (P2) on the opposite side with respect to said third wall (170a) by a fourth angle (02); wherein said third wall (170a) and fourth wall (180a) join to each other at a second joining line (V2) defined in said central portion (175) of said first transversal face (15c) and having a distance (dv2) in the circumferential direction from the circumferentially closest first central block (15) or second central block (55) greater than the distance (dx) in the circumferential direction of the axially inner edge (150) and of the axially outer edge (180) of said first transversal face (15c) from the first central block (15) or second central block (55).

8. Off-road motorcycle tyre (1) according to any one of claims 3 to 7, wherein:

- said axially outer face (15b) has a circumferential length (Ic) shorter than that of said axially inner face (15a); - said second transversal face (15d) has a length (la) in the axial direction shorter than that of said first transversal face (15c); and wherein each of said first central blocks (15) and second central blocks (55) comprises a connecting wall (190) that connects said axially outer face (15b) to said second transversal face (15d).

9. Off-road motorcycle tyre (1) according to any one of the previous claims, wherein each lateral annular portion (L) of said two lateral annular portions (L) comprises a plurality of respective circumferentially consecutive lateral blocks (20, 60), wherein said lateral blocks (20, 60) are misaligned in the axial direction with respect to said first central blocks (15) and second central blocks (55) and each of said lateral blocks (20, 60) is arranged at an oblique distance (do) from the closest first central block (15) or second central block (55) such that the ratio between said oblique distance (do) and said predetermined maximum chord (C) is less than 0.23.

10. Off-road motorcycle tyre (1) according to claim 9, wherein said tread band (8) comprises two shoulder annular portions (S) arranged on opposite sides with respect to the central annular portion (M) in an axially outer position with respect to the two lateral annular portions (L), wherein each shoulder annular portion (S) comprises a plurality of circumferentially consecutive shoulder blocks (30, 70), wherein said shoulder blocks (30, 70) are aligned in the axial direction with said first central blocks (15) and second central blocks (55) and wherein each of said shoulder blocks (30, 70) is arranged at a distance (ds) in the axial direction from the closest first central block (15) or second central block (55) such that the ratio between said distance (ds) in the axial direction and said predetermined maximum chord (C) is comprised between 0.25 and 0.33.

11. Off-road motorcycle tyre (1) according to any one of the previous claims, wherein said tread band (8) has a void to solid ratio comprised between 0.85 and 0.90.

12. Off-road motorcycle tyre (1) according to any one of the previous claims, wherein said tyre (1) has a fitting diameter comprised between 14 inches and 22 inches and a maximum chord (C) comprised between 77 mm and 113 mm.

13. Off-road motorcycle tyre (1) according to any one of the previous claims, wherein said tyre (1) is a front tyre.