Motorcycle tyre

Abstract

A motorcycle tyre comprises a tread band (8) having a plurality of main grooves (20; 60) arranged on opposite sides with respect to an equatorial plane (X-X) of the tyre and a void to solid ratio greater than 10%. Each of said main grooves (20; 60) comprises a first rectilinear portion (21; 61) inclined with respect to the equatorial plane (X-X) by a first angle (α) less than 45° and having an end (21a; 61a) proximal to the equatorial plane (X-X) and an end (21b; 61b) distal from the equatorial plane (X-X). Each of said main grooves (20; 60) further comprises a second rectilinear portion (22; 62) inclined with respect to said first rectilinear portion (21; 61) by a second angle (β) comprised between 90° and 160° and having an end (22a; 62a) proximal to the equatorial plane (X-X) and an end (22b; 62b) distal from the equatorial plane (X-X). Said second rectilinear portion (22; 62) is shorter than said first rectilinear portion (21; 61).

Description

[0001] Motorcycle tyre

[0002] DESCRIPTION

[0003] The present invention relates to a motorcycle tyre.

[0004] The tyre of the invention is intended to be mounted on the front and rear wheels of motorcycles of the "big enduro" (or "big adventuring" or "dual purpose") type, which as known are motorcycles with high piston displacement, power and mass, which are designed to be driven both on asphalt roads and off-road. Such motorcycles generally have a piston displacement equal to or higher than 1000 cm3, power equal to or higher than 100 hp, maximum torque equal to or higher than 100 Nm and mass equal to or higher than 180 Kg.

[0005] Some examples of "big enduro" motorcycles are: BMW GS 1300, KTM 1290 Super Adventure R and Honda CRF1100L Africa Twin.

[0006] The "big enduro" motorcycles have a very wide spectrum of use, ranging from a purely road use, comparable to sport touring with tendencies also towards supersport, to an off-road use that is even more severe than on simple paved roads, such as for example driving on all- terrain circuits, the so-called dirt tracks, or paths comprising river beds, soft ground, mud, sand and rough terrain of various kinds and difficulties.

[0007] In order to satisfy all these types of use, different types of "big enduro" tyres are provided on the market, each focused on a well-defined type of use, such as for example: road sport driving, road touring driving, road journey combined with dirt road, road driving combined with easy off-road, severe off-road combined with road driving.

[0008] Typically, the "big enduro" motorcycle tyres intended mainly for road journey combined with dirt road are approved to reach maximum speeds at least equal to 210 km / h (ETRTO speed index: H). Such tyres generally have a radial section maximum width comprised between 90 mm and 170 mm (e.g., between 90 mm and 120 mm for the front tyres and between 130 mm and 170 mm for the rear tyres) and are mounted on wheel rims having fitting diameters typically comprised between about 17 inches and about 21 inches (e.g., between 19 inches and 21 inches for the front tyres and between 17 inches and 18 inches for the rear tyres).

[0009] The tyre of the present invention is intended to equip "big enduro" motorcycles approved for road journey combined with dirt road. This tyre is therefore used mainly on road surfaces under different set-up conditions (with the rider alone, with the rider and luggage, with the rider and a passenger, with the rider, a passenger and luggage) and different climatic conditions (dry or wet road surface) and sporadically on dirt roads.

[0010] PRIOR ART

[0011] The "big enduro" motorcycle tyres typically comprise a tread band having a tread pattern defined by a plurality of grooves having different shapes and orientation. Examples of such tyres are described in EP2760682B1 and EP2307207B1 to the same Applicant.

[0012] SUMMARY OF THE INVENTION

[0013] Throughout this description and in the following claims, when reference is made to determined values of certain angles, they are deemed to be absolute values, i.e. both positive values and negative values with respect to a plane or a direction of reference, unless specified otherwise.

[0014] 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 range, unless expressly stated to the contrary.

[0015] Moreover, all of the ranges include any combination of the described minimum and maximum values and 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.

[0016] Hereinafter, the following definitions apply.

[0017] The term "motorcycle tyres" is used to indicate a tyre having a high curvature ratio (typically greater than 0.20) and capable of reaching high camber angles when cornering.

[0018] The term "curvature ratio" is used to indicate the ratio of the distance comprised between the radially highest point of the tread band and the maximum cord of the tyre (this distance being also identified as "arrow"), and the maximum cord of the tyre itself, in a cross section of the tyre.

[0019] The term "maximum cord" or "radial section maximum width" is used to indicate the maximum width of the tyre profile, i.e. the length of the segment having as its ends the two axially outermost points of the tread band.

[0020] The term "footprint area" of the tyre is used to indicate the portion of the tyre in contact with the ground or road surface when the tyre is mounted on a wheel rim and a predetermined vertical load is exerted on the tyre.

[0021] 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 symmetrically equal parts.

[0022] The term "tread pattern" is used to indicate the representation of all the points of the tread band (including the grooves) on a plane perpendicular to the equatorial plane of the tyre and tangent to the maximum diameter of the tyre. This representation corresponds to the plan development of the outermost profile of the tread band.

[0023] The measurements of linear quantities (distances, widths, lengths, axial and circumferential extensions, etc.) and / or angles are to be understood as referred to the tread pattern as defined above.

[0024] The term "circumferential development" of the tyre, or of the tread band or of portions or segments thereof, is used to indicate the plan development of the radially outermost surface of the tyre, or of the tread band or of portions or segments thereof, on a plane tangent to the tyre.

[0025] The term "void to solid ratio" is used to indicate the ratio of the overall surface of the grooves of a determined annular portion of the tread band or of a determined portion of the tread pattern of the tyre (possibly of the entire tread band or of the entire tread pattern) and the surface of the determined annular portion of the tread band or of the determined portion of tread pattern (possibly of the entire tread band or of the entire tread pattern).

[0026] The term "annular portion" of a tread band is used to indicate a portion of tread band extending circumferentially along the whole tread band and having a predetermined axial extension, said axial extension being measured on a plane orthogonal to the equatorial plane.

[0027] 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.

[0028] The terms "circumferential" and "circumferentially" are used with reference to the direction of circumferential development 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.

[0029] 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°.

[0030] The expressions "axially innermost" and "axially outermost" indicate a position closer to, and farther from, the equatorial plane with respect to a reference element, respectively. Thus, for example, a first groove portion is axially innermost with respect to a second groove portion when the axial distance of the first groove portion from the equatorial plane is less than that of the second groove portion. Similarly, a first groove portion is axially outermost with respect to a second groove portion when the axial distance of the first groove portion from the equatorial plane is greater than that of the second groove portion.

[0031] The term "position proximal" to the equatorial plane is used to indicate a position closer to the equatorial plane than a "position distal" from the equatorial plane.

[0032] The term "width" of a groove, or of a portion or segment thereof, is used to indicate a dimension measured along a direction orthogonal to the trajectory along which the groove, or the portion or segment thereof, extends.

[0033] The term "length" of a groove, or of a portion or segment thereof, is used to indicate the length of the groove, or of the portion or segment thereof, measured along the trajectory along which the groove, or the portion or segment thereof, extends.

[0034] The term "axial extension" of a groove, or of a portion or segment thereof, is used to indicate the length of the projection of the groove, or of the portion or segment thereof, on a plane orthogonal to the equatorial plane.

[0035] The term "circumferential extension" of a groove, or of a portion or segment thereof, is used to indicate the length of the projection of the groove, or of the portion or segment thereof, on a plane parallel to the equatorial plane. Hereinafter, a groove, or a portion or segment thereof, is considered "circumferentially offset" with respect to another groove, or to a portion or segment thereof, when the circumferentially central points of the two grooves, or of the respective portions or segments, do not lie on a same plane perpendicular to the equatorial plane of the tyre.

[0036] A groove, or a portion or segment thereof, is instead considered "superimposed in the axial direction" on another groove, or on a portion or segment thereof, when the projections on the equatorial plane of the two grooves, or of the respective portions or segments, are at least in part superimposed on each other. In such a case, the projection on the equatorial plane of at least a segment of each of the two grooves is identical to that of at least a segment of the other groove.

[0037] With reference to the angle of the grooves, or of groove portions or segments, of the tread band with respect to the equatorial plane of the tyre, this angle is to be understood, for each point of the groove or of the groove portion or segment, as the angle, in absolute value, formed by performing a rotation which, starting from the direction defined in the tread pattern by the equatorial plane, proceeds up to the direction tangent to the groove or to the groove portion or segment of groove passing through said point. In the case of a tyre intended to be mounted on a rear wheel of a motorcycle, the aforementioned rotation is to be understood as performed by a vector oriented in the opposite direction to the direction of rotation of the tyre, while in the case of a tyre intended to be mounted on a front wheel of a motorcycle, the aforementioned rotation is to be understood as performed by a vector oriented in the direction of rotation of the tyre.

[0038] With reference to the angle of groove portions or segments with respect to a portion or segment of the same groove (hereinafter referred to as the reference portion or segment), this angle is to be understood, for each point of the groove portion or segment, as the angle, in absolute value comprised between 0° and 180°, formed by performing a rotation that, starting from the direction defined in the tread pattern by the reference portion or segment, proceeds up to the direction tangent to the groove portion or segment passing through that point.

[0039] The Applicant has considered a motorcycle segment, that of the "big enduro" motorcycles, which has a very broad spectrum of use, as already mentioned.

[0040] The Applicant has observed that in order to optimally cover the entire spectrum of use of the "big enduro" motorcycles, they should be equipped with tyres suitable to allow high performance both on the road (mainly traction, braking, stability at high speeds, grip on dry and wet surface, handling) and off-road (mainly traction, controllability and directionality), together with the ability to travel many kilometres.

[0041] However, the Applicant has found that considering the current and increasingly common tendency to obtain extreme road performance on the one hand and extreme off-road performance on the other hand, the aforementioned performance characteristics are at least partially in contrast to each other.

[0042] The Applicant has indeed noted that tyres that allow high performance on the road usually have performance limits in severe offroad and vice versa.

[0043] The Applicant has also noted that tyres that balance road and offroad use with good compromise solutions do not allow to reach extreme performance in either area (road and off-road).

[0044] The Applicant has observed that, in accordance with customer demands, the market has recently moved towards more specialised solutions, providing for more segments of tyres for "big enduro" motorcycle, each of which focused on a particular use of the motorcycle. Consistently, the Applicant has proposed tyres for "big enduro" motorcycles suitable for mainly road use and tyres for "big enduro" motorcycles suitable for mainly off-road use.

[0045] The tyres for mainly road use are designed to maximise performance in terms of stability and controllability at high speeds, both during a travel in a straight line and when cornering, handling (or ease of driving), mileage, traction and braking, comfort and wear regularity when travelling on asphalt road surfaces. Moreover, these tyres, being often used throughout the year and under any weather condition, must allow the aforementioned performance to be reached both on dry road surfaces and on road surfaces with low grip, such as in particular wet road surfaces.

[0046] The tyres for mainly off-road use, even severe, are instead designed to maximise performance in terms of controllability and directionality on uneven, slippery and / or inconsistent terrains (e.g. sand, mud, gravel). These tyres must also allow the aforementioned performance to be reached on wet terrains.

[0047] The Applicant has focused his attention on the segment of "big enduro" motorcycle tyres for mainly road use, in particular for road journey combined with dirt road, hereinafter referred to, for simplicity, with the term "big enduro road tyres".

[0048] The Applicant has considered that these tyres are chosen by users who seek performance on road surfaces and also foresee an off-road use, albeit not extreme / severe.

[0049] The Applicant has at first observed that in order to be able to ensure the desired off-road behaviour, it is advisable for the tread band to have a void to solid ratio not less than 10%, therefore greater than that typically provided in road tyres intended for a road use only, such as for example those belonging to the "supersport" category.

[0050] The Applicant has thought about how to improve the performance of the big enduro road tyres compared to those offered by the tyres of the same segment currently on the market (hereinafter referred to as "reference tyres") in terms of traction (in the case of rear tyres) and braking (in the case of both front and rear tyres) on dry or wet road surfaces, without however penalising the off-road performance, i.e. keeping the latter at least equal to those offered by the reference tyres.

[0051] The Applicant has observed that, whatever the segment to which the tyre belongs, its performance on dry or wet road surfaces improve as the tyre's capacity to adhere to the road surface during acceleration and braking increases, this capacity being the greater the lower the void to solid ratio of the tyre. In particular, the Applicant has observed that the adhesion capacity of the tyre to the road surface is the greater the smaller the number and / or the dimensions of the grooves in the footprint area while the tyre is travelling in a rectilinear line and is bending.

[0052] Therefore, according to the Applicant, one way to improve the performance in terms of traction and braking of a big enduro road tyre would be to reduce the number and / or the dimensions of the voids defined by the grooves which are in the footprint area, while still leaving a sufficient number of voids to allow the evacuation of water from the footprint area in the case of wet road surfaces.

[0053] However, the Applicant has observed that a reduction in the number of voids in the footprint area would result in a worsening of the off-road performance of the tyre, a circumstance that would be in contrast with the desire to have an off-road performance at least equal to that of the reference tyres.

[0054] With regard to the off-road performance, the Applicant has observed that in the big enduro road tyres the performance is typically achieved by providing in the footprint area grooves which are long and slightly inclined with respect to the equatorial plane. In fact, these grooves allow to effectively counteract the lateral forces to which the tread band is subjected in off-road both during skids and when driving on wet terrains, guaranteeing the necessary and desired controllability and directionality.

[0055] The Applicant has therefore thought that, in order not to worsen the off-road performance of a big enduro road tyre with respect to that of the reference tyres, it is advisable to continue to provide in the footprint area grooves which are long and slightly inclined with respect to the equatorial plane.

[0056] The Applicant has however observed that such grooves typically comprise portions (hereinafter referred to as "first portions") oriented in such a way as to be particularly suitable for counteracting the aforementioned lateral forces, and other portions (hereinafter referred to as "second portions") oriented in such a way as not to offer any counteraction to the aforementioned lateral forces.

[0057] The Applicant has also observed that, as a result of their orientation, the aforementioned second portions are subject to early wear due to the sliding of the edges of said second portions with the ground during skids, and during acceleration and braking when the tyre is used in the off-road tracks or on asphalt road surfaces, whether they are dry or wet.

[0058] Therefore, wishing to achieve the objective of not worsening the performance in the off-road tracks with respect to that of the reference tyres and at the same time wishing to reduce the number and / or the dimensions of the voids in the footprint area in order to improve the road grip, and thus the performance on the road in terms of traction and braking, the Applicant has thought of reducing the dimensions of the aforementioned second portions, while keeping instead the aforementioned first portions sufficiently extended. According to the Applicant, by dong so an advantageous reduction of the overall wear to which the edges of the aforementioned grooves are subject is also obtained.

[0059] The present invention therefore relates to a tyre comprising a tread band.

[0060] Preferably, the tread band comprises a plurality of main grooves.

[0061] Preferably, the tread band has a void to solid ratio greater than 10%.

[0062] Preferably, said main grooves are arranged on opposite sides with respect to an equatorial plane of the tyre.

[0063] Preferably, each of said main grooves comprises a first rectilinear portion.

[0064] Preferably, said first rectilinear portion is inclined with respect to the equatorial plane by a first angle.

[0065] Preferably, said first angle is less than 45°.

[0066] Preferably, said first rectilinear portion has a first end proximal to the equatorial plane.

[0067] Preferably, said first rectilinear portion has a second end distal from the equatorial plane.

[0068] Preferably, each of said main grooves comprises a second rectilinear portion.

[0069] Preferably, said second rectilinear portion is inclined with respect to said first rectilinear portion by a second angle.

[0070] Preferably, said second angle is greater than 90°.

[0071] Preferably, said second angle is less than 160°.

[0072] In preferred embodiments, said second angle is comprised between 90° and 160°.

[0073] Preferably, said second rectilinear portion has a third end proximal to the equatorial plane.

[0074] Preferably, said second rectilinear portion has a fourth end distal from the equatorial plane.

[0075] Preferably, said second rectilinear portion is shorter than said first rectilinear portion.

[0076] The Applicant has found that a big enduro road tyre whose tread band has the aforementioned void to solid ratio and comprises grooves as described above allows to combine the off-road performance expected by the customers with improved performance in terms of acceleration and braking on dry and wet roads.

[0077] The improved performance on the road is achieved thanks to the greater grip of the tyre caused by the reduction in the dimensions of the aforementioned second rectilinear portions.

[0078] The desired off-road performance is obtained thanks to the provision of a void to solid ratio greater than 10% and to the length and inclination of the first rectilinear portion of the aforementioned grooves.

[0079] The reduced length and the particular inclination of the second rectilinear portion allows to reduce the wear of the edges of the aforementioned grooves.

[0080] The present invention may have at least one of the preferred features described hereinbelow.

[0081] Preferably, the void to solid ratio is greater than 10.5%, more preferably greater than 11%, even more preferably greater than 12%.

[0082] Preferably, the void to solid ratio is less than 22%, more preferably less than 21%, even more preferably less than 20%.

[0083] In preferred embodiments, the void to solid ratio is comprised between 10.5% and 22%, preferably between 11% and 21%, even more preferably between 12% and 20%, for example equal to 14.5% in rear tyres whose size is 170 / 60 / R.17 and equal to 16.5% in front tyres whose size is 120 / 70 / R19.

[0084] The Applicant believes that the provision of the void to solid ratio values described above makes it possible to reach the desired road performance while maintaining the same off-road performance.

[0085] The greater value of the void to solid ratio of the front tyres with respect to that of the rear tyres is due both to the need to maximise the counteraction to the lateral forces to which a front tyre is subjected during the skid of the rear tyre, and to the fact that the front tyres, typically having smaller dimensions and curvature radius than those of the rear tyres, have a narrower and longer footprint area than that of the latter. This implies that any lateral grooves of the tyre are not in the footprint area in some driving conditions, which causes the need to provide a greater number of grooves at the footprint area in order to reach the desired off-road and wet performance.

[0086] The Applicant believes that this greater value of the void to solid ratio of the front tyres, however, does not affect the road performance of these tyres since, at high speeds (such as those that the users of this motorcycle segment wish to reach), the front tyre tends to rise from the road surface, with a consequent reduction in the dimension of the footprint area and thus in the number of voids in the footprint area.

[0087] Preferably, the first angle is less than 40°, more preferably less than 35°, even more preferably less than 30°.

[0088] Preferably, the second angle is greater than 95°, more preferably greater than 100°.

[0089] Preferably, the second angle is less than 150°, more preferably less than 145°, even more preferably less than 140°.

[0090] In preferred embodiments, said second angle is comprised between 95° and 150°, preferably between 100° and 145°, more preferably between 100° and 140°.

[0091] The Applicant believes that the provision of the angle values described above makes it possible to improve both the road performance and the off-road performance of the tyre, while containing the wear of the edges of the aforementioned grooves.

[0092] Preferably, said second rectilinear portion has a length shorter than half, more preferably one third, of the length of said first rectilinear portion.

[0093] It is the Applicant's opinion that this provision also allows to maximize both the road performance and the off-road performance of the tyre.

[0094] Preferably, said first rectilinear portion has a width that progressively increases moving from said first end up to said second end.

[0095] This ensures an effective evacuation of water from the footprint area when driving on wet. A further improvement in the performance of the tyre on dry road surfaces is also reached thanks to the fact that, following high acceleration and braking, such as those typically made by the users of the big enduro road tyres, the groove tends to close at the portion thereof with lower width, causing a reduction in the void to solid ratio in the footprint area and, therefore, an increase in the adhesion capacity of the tyre to the road surface. The Applicant believes that this fact does not negatively impact the ability to evacuate water from the footprint area when driving on wet road surfaces. In this case, in fact, the loads to which the tyre is subjected during acceleration and braking are lower than those to which the tyre can be subjected while driving on dry road surfaces, and in any case such as not to lead to the closure of the aforementioned portions with lower width.

[0096] Preferably, said first end is arranged at a respective distance from the equatorial plane less than 12%, more preferably less than 10%, of the radial section maximum width of the tread band. This provision contributes to obtaining an effective evacuation of water from the footprint area when the tyre travels on wet road surfaces.

[0097] Preferably, said distance is greater than 3%, more preferably greater than 5%, of the radial section maximum width of the tread band.

[0098] In preferred embodiments, said first end is arranged at a respective distance from the equatorial plane comprised between 3% and 12%, more preferably between 5% and 10%, of the radial section maximum width of the tread band.

[0099] Preferably, said third end is arranged at a respective distance from the equatorial plane less than 12%, more preferably less than 10%, of the radial section maximum width of the tread band.

[0100] Preferably, said distance is greater than 3%, more preferably greater than 5%, of the radial section maximum width of the tread band.

[0101] In preferred embodiments, said third end is arranged at a respective distance from the equatorial plane comprised between 3% and 12%, more preferably between 5% and 10%, of the radial section maximum width of the tread band.

[0102] Accordingly, the tyre has, at the equatorial plane, an annular portion of tread band with a sufficiently reduced void to solid ratio, to the benefit of the grip on the road surface and, therefore, of the performance on the dry and wet road surfaces.

[0103] In some embodiments, the distance from the equatorial plane of said first end is equal to that of said third end.

[0104] Preferably, said second end is arranged at a distance from the equatorial plane less than 30%, more preferably less than 25%, of the radial section maximum width of the tread band.

[0105] Preferably, said distance is greater than 10%, more preferably greater than 15%, of the radial section maximum width of the tread band.

[0106] In preferred embodiments, said second end is arranged at a distance from the equatorial plane comprised between 10% and 30%, preferably between 15% and 25%, of the radial section maximum width of the tread band.

[0107] This provision contributes to achieving the desired off-road behaviour of the tyre and ensures that the first rectilinear portion of the main grooves is in the footprint area even when the tyre travels slightly bent, contributing to ensuring the evacuation of water from the footprint area even under such driving conditions on wet road surfaces.

[0108] Preferably, said fourth end is arranged at a distance from the equatorial plane less than 30%, more preferably less than 25%, of the radial section maximum width of the tread band.

[0109] Preferably, said distance is greater than 10%, more preferably greater than 15%, of the radial section maximum width of the tread band.

[0110] In preferred embodiments, said fourth end is arranged at a distance from the equatorial plane comprised between 10% and 30%, preferably between 15% and 25%, of the radial section maximum width of the tread band.

[0111] This provision contributes to achieving the desired off-road behaviour of the tyre and ensures that also the second rectilinear portion of the main grooves is in the footprint area when the tyre travels slightly bent.

[0112] Preferably, the first rectilinear portions of all the main grooves are parallel to each other.

[0113] Preferably, the first rectilinear portions of all the main grooves have the same length.

[0114] Preferably, the second rectilinear portions of all the main grooves are parallel to each other.

[0115] Preferably, the second rectilinear portions of all the main grooves have the same length.

[0116] Preferably, said plurality of main grooves comprises a first series of circumferentially consecutive main grooves arranged on one side with respect to the equatorial plane.

[0117] Preferably, all the main grooves of the first series of main grooves are identical to each other.

[0118] Preferably, said plurality of main grooves comprises a second series of circumferentially consecutive main grooves arranged on the other side of the equatorial plane.

[0119] Preferably, all the main grooves of the second series of main grooves are identical to each other.

[0120] Preferably, the main grooves of the second series of main grooves have a shape specular to that of the main grooves of the first series of main grooves.

[0121] Preferably, said second series of main grooves is circumferentially offset with respect to said first series of main grooves.

[0122] Preferably, in the case of a rear tyre, each main groove of the second series of main grooves is partially superimposed in the axial direction on a respective main groove of the first series of main grooves at respective groove parts having a circumferential extension less than 22%, more preferably less than 20%, even more preferably less than 17%, of the circumferential extension of each main groove.

[0123] The Applicant has found that a partial superposition in the axial direction as the one described above allows to obtain an advantageous regularity of behaviour of the rear tyre during rolling in terms of stiffness / deformation, noise, vibrations and wear. This because there are no axial portions of tread band without main grooves interposed to the axial portions of tread band with main grooves, and because the axial portions of tread band with two opposing main grooves, that for this reason would be subject to a greater deformation than that of the axial portions with only one main groove, have a reduced circumferential extension.

[0124] Preferably, in the case of a front tyre, each main groove of the second series of main grooves is partially superimposed in the axial direction on a respective main groove of the first series of main grooves at respective groove parts having a circumferential extension less than or equal to 55% of the circumferential extension of each main groove.

[0125] Preferably, said circumferential extension is higher than 20%, more preferably higher than 30%, of the circumferential extension of each main groove.

[0126] In preferred embodiments of front tyres, the aforementioned circumferential extension is comprised between 20% and 55%, preferably between 30% and 55% of the circumferential extension of each main groove.

[0127] The Applicant has found that a partial superimposition in the axial direction such as the one described above allows achieving the aforementioned performance with reference to the rear tyre even in a front tyre, irrespective of the fact that in the front tyre the partial superposition in the axial direction of the main grooves is greater than that in the rear tyre. The Applicant has in fact found that the front tyre, being smaller than the rear one, is typically stiffer than the rear one and is subjected to vertical loads lower than those to which the latter is subjected, with a consequent lower risk of suffering excessive deformations.

[0128] Preferably, in all the preferred embodiments of the tyre of the invention, said tread band comprises a plurality of secondary grooves.

[0129] Preferably, said secondary grooves have a circumferential extension shorter than that of said main grooves, so as not to increase the void to solid ratio in the footprint area.

[0130] Preferably, the circumferential extension of each secondary groove is shorter than 50%, more preferably shorter than 40°, than that of the main grooves.

[0131] More preferably, in the case of a rear tyre, the circumferential extension of each groove is shorter than 30% of the circumferential extension of each main groove.

[0132] Preferably, each secondary groove is arranged between two circumferentially consecutive main grooves. In this way, it is avoided that, in the footprint area, between two main grooves there is an axial portion sufficiently extended in the circumferential direction where there are no grooves, a circumstance that would create undesired irregularities in terms of stiffness / deformation and wear, as well as noise and vibrations.

[0133] Preferably, each secondary groove comprises a first segment that extends towards the equatorial plane. This first segment allows the evacuation of water from the central area of the footprint area when the tyre travels on wet road surfaces.

[0134] Preferably, each secondary groove comprises a second segment that extends from the respective first segment towards an end edge of the tread band. This second segment cooperates with the aforementioned first segment and with the first rectilinear portions of the main grooves in evacuating the water from the footprint area.

[0135] Preferably, said second segment does not reach the end edge of the tread band, so as to maintain the void to solid ratio of the entire tread band on values suitable to guarantee the desired road performance.

[0136] Preferably, said first segment is inclined with respect to the equatorial plane by a third angle greater than 90°, more preferably greater than 100°, even more preferably greater than 110°, even more preferably greater than 120°.

[0137] Preferably, said third angle is less than 180°, more preferably less than 170°, even more preferably less than 160°, even more preferably less than 140°.

[0138] In preferred embodiments, said third angle is comprised between 90° and 180°, more preferably between 100° and 170°, even more preferably between 110° and 160°, even more preferably between 120° and 140°.

[0139] Preferably, said second segment is inclined with respect to said first segment by a fourth angle less than 180°, more preferably less than 140°, even more preferably less than 130°, even more preferably less than 120°.

[0140] Preferably, said fourth angle is greater than 40°, more preferably greater than 50°, more preferably greater than 60°.

[0141] In preferred embodiments, said fourth angle is comprised between 40° and 180°, preferably between 40° and 140°, more preferably between 50° and 130°, even more preferably between 60° and 120°, even more preferably between 70° and 110°, even more preferably between 80° and 100°.

[0142] The aforementioned angle values are considered by the Applicant particularly suitable for achieving a distribution of the voids in the footprint area optimised to obtain the desired road behaviour on wet surface and the desired behaviour in the off-road. In particular, the inclination of the first segment is chosen to maximize the off-road performance in combination with the first rectilinear portions of the main grooves, while the inclination of the second segment is chosen to achieve an optimal compromise with reference to the wear problems and to the need to have an effective evacuation of water from the footprint area.

[0143] Preferably, said first segment is shorter than said second segment.

[0144] The Applicant believes that this fact allows to contain the wear of the aforementioned first segments due to the sliding of the edges of said first segments on the ground during skids and during acceleration and braking when the tyre is used on asphalt road surfaces, whether they are dry or wet.

[0145] Preferably, said first segment is shorter than said first rectilinear portion.

[0146] Preferably, said second segment is shorter than said first rectilinear portion.

[0147] Preferably, said second segment is longer than said second rectilinear portion.

[0148] Preferably, the first segments of all the secondary grooves are parallel to each other.

[0149] Preferably, the first segments of all the secondary grooves have the same length.

[0150] Preferably, the second segments of all the secondary grooves are parallel to each other. Preferably, the second segments of all the secondary grooves have the same length.

[0151] Preferably, said plurality of secondary grooves comprises a first series of circumferentially consecutive secondary grooves arranged at least in part on one side with respect to the equatorial plane.

[0152] Preferably, all secondary grooves of the first series of secondary grooves are identical to each other.

[0153] Preferably, said plurality of secondary grooves comprises a second series of circumferentially consecutive secondary grooves arranged at least in part on the other side with respect to the equatorial plane.

[0154] Preferably, all the secondary grooves of the second series of secondary grooves are identical to each other.

[0155] Preferably, the secondary grooves of the second series of secondary grooves have a shape specular to that of the secondary grooves of the first series of secondary grooves.

[0156] Preferably, said second series of secondary grooves is circumferentially offset with respect to said first series of secondary grooves. This offset allows preventing unwanted noise phenomena while the tyre is rolling.

[0157] Preferably, each secondary groove of said first series of secondary grooves is axially adjacent to a respective main groove of said second series of main grooves.

[0158] Preferably, each secondary groove of said second series of secondary grooves is axially adjacent to a respective main groove of said first series of main grooves.

[0159] Preferably, each of the first segments of the secondary grooves of said second series of secondary grooves extends along a respective direction that intersect the second rectilinear portion of the axially adjacent main groove.

[0160] Preferably, the second segments of the secondary grooves of the second series of secondary grooves are substantially parallel to the second portions of the main grooves of the first series of main grooves.

[0161] Preferably, the second segments of the secondary grooves of the second series of secondary grooves are substantially parallel to the first segments of the secondary grooves of the first series of secondary grooves.

[0162] The aforementioned reciprocal arrangement of the main and secondary grooves is such that the first segments of the secondary grooves of the second series of secondary grooves cooperate with the first portions of the main grooves of the first series of main grooves in achieving both the desired off-road behaviour (with particular reference to the counteraction to lateral forces) of a front or rear tyre when the rear tyre skids on one side, and the desired on-road behaviour (with particular reference to the evacuation of water from the footprint area) when the tyre travels on a wet road surface slightly bent on the aforementioned side. Similarly, the first segments of the secondary grooves of the first series of secondary grooves cooperate with the first portions of the main grooves of the second series of main grooves in achieving both the aforementioned desired off-road behaviour of a front or rear tyre when the rear tyre skids on the other side, and the aforementioned desired onroad behaviour when the tyre travels on a wet road surface slightly bent on the aforementioned other side.

[0163] In first preferred embodiments, all the first segments of the secondary grooves extend until they reach the equatorial plane without crossing it. The Applicant believes that the tyres made in accordance with these first preferred embodiments are particularly suitable for being used as rear tyres of big enduro road motorcycles.

[0164] Preferably, in such first preferred embodiments all the first segments of the secondary grooves extend along respective directions that intersect the second rectilinear portion of the axially adjacent main groove.

[0165] In second preferred embodiments, all the first segments of the secondary grooves cross the equatorial plane. The Applicant believes that the tyres made in accordance with these second preferred embodiments are particularly suitable for being used as front tyres of big enduro road motorcycles. In fact, the latter must ensure the evacuation of water from the footprint area so that the rear tyre can travel on a drier road surface segment. The provision of groove segments that cross the equatorial plane is particularly beneficial to this purpose.

[0166] Preferably, in the aforementioned second preferred embodiments all the first segments of the secondary grooves are entirely arranged inside an axially inner annular portion of the tread band that is arranged astride of the equatorial plane.

[0167] Preferably, said axially inner annular portion has an axial extension less than 20%, more preferably less than 15%, even more preferably less than 10%, of the radial section maximum width of the tread band.

[0168] Thanks to the provision of groove segments that cross the equatorial plane, the aforementioned axially inner annular portion has a deformability such as to allow the front tyre to absorb any roughness of the road surface, such as for example road disconnections, bridge connections, etc.

[0169] Preferably, said axially inner annular portion does not comprise groove segments or portions other than the first segments of the secondary grooves.

[0170] In some preferred embodiments, which preferably coincide with the aforementioned second preferred embodiments, each of the first segments of the secondary grooves of said first series of secondary grooves extends along a respective direction that intersect the first rectilinear portion of the axially adjacent main groove. Preferably, the tread band further comprises a plurality of lateral grooves inclined with respect to the equatorial plane by a fifth angle.

[0171] Preferably, said fifth angle is less than 90°, more preferably less than 80°, even more preferably less than 70°, even more preferably less than 65°.

[0172] Preferably, said fifth angle is greater than 20°, more preferably greater than 30°, even more preferably greater than 35°.

[0173] In preferred embodiments, said fifth angle is comprised between 20° and 90°, preferably between 20° and 80°, more preferably between 30° and 70°, even more preferably between 35° and 65°.

[0174] Preferably, a first series of lateral grooves of said plurality of lateral grooves extends from an end edge of the tread band towards the equatorial plane.

[0175] Preferably, the lateral grooves of said first series of lateral grooves are substantially parallel to each other.

[0176] Preferably, a second series of lateral grooves of said plurality of lateral grooves extends from the opposite end edge of the tread band towards the equatorial plane.

[0177] Preferably, the lateral grooves of said second series of lateral grooves are substantially parallel to each other.

[0178] Preferably, first lateral grooves of said first series of lateral grooves extend along respective directions that intersect the second rectilinear portions of respective main grooves.

[0179] Preferably, first lateral grooves of said second series of lateral grooves extend along respective directions that intersect the second rectilinear portions of respective main grooves.

[0180] Preferably, second lateral grooves circumferentially consecutive to said first lateral grooves extend along respective directions that intersect the first rectilinear portions of said respective main grooves.

[0181] Preferably, third lateral grooves circumferentially consecutive to said second lateral grooves extend along respective directions that coincide with the directions along which the second segments of the secondary grooves that are circumferentially arranged between two circumferentially consecutive main grooves extend.

[0182] Preferably, said first lateral grooves have a length equal to that of said second lateral grooves.

[0183] Preferably, said third lateral grooves are shorter than said first lateral grooves.

[0184] Preferably, said third lateral grooves are shorter than said second lateral grooves.

[0185] DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0186] Further characteristics and advantages of the present invention will be more evident from the following description of some preferred embodiments thereof made with reference to the appended drawings. In such drawings:

[0187] - figure 1 is a schematic view of a radial section of a rear tyre in accordance with the present invention, where for simplicity of illustration the tread band is shown without grooves;

[0188] - figure 2 is a front view of a rear tyre in accordance with the present invention;

[0189] - figure 3 is an enlargement of a portion of the tyre of figure 2;

[0190] - figure 4 is a front view of a front tyre in accordance with the present invention;

[0191] - figure 5 is an enlargement of a portion of the tyre of figure 4.

[0192] With reference to figure 1, a motorcycle tyre in accordance with the present invention is labelled with numeral reference 1.

[0193] What is described hereinbelow with reference to figure 1 finds identical application in the case of the rear tyre (shown in figures 2-3 and discussed in more detail in the remainder of this description) and the front tyre (shown in figures 4-5 and discussed in more detail in the remainder of this description).

[0194] The tyre 1 is a tyre for "big enduro" motorcycles with high piston displacement (for example equal to 1000 cm3) and high power (for example equal to 100 hp), with a mass in driving conditions for example equal to 200 Kg or higher.

[0195] The tyre 1 is intended to be mounted on wheel rims having fitting diameters comprised between about 17 inches and about 21 inches (e.g. between 19 inches and 21 inches in the case of a front tyre and between 17 inches and 18 inches in the case of a rear tyre).

[0196] In the tyre 1, an equatorial plane X-X and a rotation axis (not shown) are defined. A circumferential direction arranged according to the direction of rotation R. of the tyre 1 (figures 2-5) 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 are also defined.

[0197] The tyre 1 comprises a carcass structure 2 formed by at least one carcass ply 3 consisting of a sheet of elastomeric material incorporating a plurality of reinforcing cords (not shown) in fibrous textile material.

[0198] In the tyre of figure 1, the carcass structure 2 is of the radial type, i.e. the reinforcing cords of said at least one carcass ply 3 are arranged, in a crown portion of the tyre 1, substantially parallel to each other according to an angle comprised between 70° and 110°, more preferably between 80° and 100°, for example equal to 90°, with respect to the circumferential direction.

[0199] In an embodiment not shown, the carcass structure comprises at least two carcass plies radially superimposed on each other. In this case, the reinforcing cords are essentially parallel to each other in each carcass ply and are oriented according to inclined directions with respect to the equatorial plane of the tyre in each carcass ply and according to opposite directions with respect to the reinforcing cords of the radially adjacent carcass ply 3 (cross-ply carcass). The carcass structure 2 is typically covered, on the inner walls thereof, by a sealing layer 100, so-called "liner", essentially consisting of a layer of air-impermeable elastomeric material, adapted to guarantee the hermetic seal of the tyre 1 itself once inflated.

[0200] The (or each) carcass ply 3 is shaped according to a substantially toroidal configuration and has its axially opposite lateral edges 3a turned up on respective annular reinforcing structures 4 intended to retain the tyre 1 on a corresponding mounting rim (not shown). The annular reinforcing structures 4 are typically referred to as "bead cores".

[0201] On the outer perimeter edge of the bead cores 4 a tapered elastomeric filler 5 is applied which occupies the space defined between the respective carcass ply 3 and the corresponding turned up lateral edge 3a of the carcass ply 3.

[0202] The zone of the tyre 1 comprising the bead core 4 and the elastomeric filler 5 forms the so-called bead 9, which is intended for anchoring the tyre 1 on the rim.

[0203] Preferably, a carcass reinforcing structure may be provided in a radially outer position with respect to the carcass structure (whether radial or cross-ply). Said carcass reinforcing structure comprises a crown ply arranged in a radially outer position with respect to the radially outermost carcass ply and at least at a crown portion of the latter. The crown ply comprises reinforcing elements arranged parallel to each other. The crown ply is arranged on the radially outermost carcass ply so that the reinforcing elements of the crown ply have, with respect to the equatorial plane, an angle opposite to that of the reinforcing cords of the radially outermost carcass ply. Optionally, the carcass reinforcing structure also comprises two plies arranged on opposite sides with respect to the crown ply and not associated with the respective beads.

[0204] In one embodiment thereof, the (or each) carcass ply 3 is made by juxtaposing a plurality of strips of elastomeric material reinforced by the aforementioned reinforcing cords.

[0205] A belt structure 6 is circumferentially applied on the carcass structure 2, in a radially outer position with respect to the latter. The belt structure 6 comprises at least one belt layer 6a typically formed by textile or metallic reinforcing cords embedded in a layer of elastomeric material.

[0206] Preferably, the belt structure 6 is of the zero-degree type, i.e. the belt layer 6a is made by reinforcing cords arranged substantially parallel and side by side so as to form a plurality of coils. These coils are substantially oriented according to the circumferential direction (typically with an angle comprised between 0° and 5°), this direction being usually defined as "at zero degrees" with reference to its lying with respect to the circumferential direction of the tyre 1.

[0207] The belt layer 6a, typically defined as at "zero degrees", may comprise axially juxtaposed windings of a single reinforcing cord or of a rubberized strip-like element comprising axially flanked reinforcing cords.

[0208] The reinforcing cords of the zero-degree belt layer 6a are typically metallic, made by wires of steel with a high carbon content, i.e. wires of steel with a carbon content of at least 0.6% - 0.7%. Preferably, said metal reinforcing cords have a high elongation (HE).

[0209] Optionally, in some tyres, as the one shown in figure 1, an adhesion layer 7 of elastomeric material is arranged between the belt structure 6 and the carcass structure 2 in order to improve the adhesion between the aforementioned structures.

[0210] In a different embodiment, the belt structure comprises two or more radially superimposed belt layers, each layer consisting of elastomeric material incorporating reinforcing cords that are arranged parallel to each other. The belt layers are arranged in such a way that the reinforcing cords of a first belt layer are oriented obliquely with respect to the equatorial plane of the tyre, while the reinforcing cords of the radially adjacent belt layer also have an oblique but crossed orientation with respect to the reinforcing cords of the first layer, so as to form the so-called "cross belt". The same applies to possible additional belt layers, if any. The cross belt typically comprises textile reinforcing cords.

[0211] A tread band 8 is circumferentially superimposed on the belt structure 6, in a radially outer position with respect to the latter.

[0212] Upon a moulding operation carried out in conjunction with a vulcanisation step of the tyre 1, a plurality of grooves oriented as discussed in the remainder of the present description are obtained on the tread band 8, so as to define a particular tread pattern. As already mentioned, for simplicity of illustration in figure 1 the aforementioned grooves are not depicted.

[0213] The tread band 8 (as well as further tyre components not described / illustrated as they are conventional) is made of an elastomeric material.

[0214] The tyre 1 of figure 1 further comprises a pair of sidewalls 10 applied laterally on opposite sides to the carcass structure 2 and also made of elastomeric material.

[0215] 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.

[0216] The tyre 1 also has a radial section maximum width C defined, with reference to figure 1, 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 L 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 may be formed with an edge.

[0217] The tyre 1 preferably has a radial section maximum width C comprised between 90 mm and 170 mm, more preferably between 90 mm and 120 mm in the case of a front tyre and between 130 mm and 170 mm in the case of a rear tyre.

[0218] The tyre 1 has a curvature ratio f / C, defined by the ratio between the arrow f and the aforementioned radial section maximum width C, and a ratio of arrow over total height (f / H) defined by the ratio between the arrow f and the section height H.

[0219] In the case where the tyre 1 is a rear tyre, as the one of figures 2 and 3, the arrow f is preferably comprised between about 40 mm and about 60 mm, the curvature ratio f / C is preferably comprised between about 0.25 and about 0.35, for example equal to about 0.26, while the arrow height ratio on total f / H is preferably comprised between about 0.40 and about 0.60, for example equal to about 0.43.

[0220] In the case where the tyre 1 is a front tyre, such as the one of figures 4 and 5, the arrow f is preferably comprised between about 35 mm and about 60 mm, the curvature ratio f / C is preferably comprised between about 0.30 and about 0.40, for example equal to 0.38 and the ratio of arrow over total height f / H is preferably comprised between about 0.40 and about 0.60, for example equal to about 0.53.

[0221] With reference to figures 2 and 3, the tread pattern of the tread band 8 of a preferred embodiment of a rear tyre 1 made in accordance with the present invention is described hereinbelow.

[0222] The tread band 8 has a void to solid ratio greater than 10%, preferably comprised between 10.5% and 22%, more preferably between 11% and 21%, even more preferably between 12% and 20%, for example equal to 14.5% in the case of a rear tyre whose size is 170 / 60 / R.17 (such as for example the tyre shown in figures 2 and 3) and equal to 16.5% in the case of a front tyre whose size is 120 / 70 / R.19 (such as for example the tyre shown in figures 4 and 5).

[0223] As shown in figure 2, the tread band 8 comprises a first series of circumferentially consecutive main grooves 20 arranged on one side with respect to the equatorial plane X-X and a second series of circumferentially consecutive main grooves 60 arranged on the opposite side with respect to the equatorial plane X-X and circumferentially offset with respect to the main grooves 20.

[0224] The main grooves 20 are identical to each other.

[0225] The main grooves 60 are identical to each other and have a shape specular to that of the main grooves 20.

[0226] The tread band 8 further comprises a first series of circumferentially consecutive secondary grooves 30 arranged on one side with respect to the equatorial plane X-X, in particular on the same side as the main grooves 20, and a second series of circumferentially consecutive secondary grooves 70 arranged on the opposite side with respect to the equatorial plane X-X and, therefore, on the same side as the main grooves 60, and circumferentially offset with respect to the secondary grooves 30.

[0227] Each secondary groove 30 is arranged between two circumferentially consecutive main grooves 20 and is axially adjacent to a respective main groove 60. Similarly, each secondary groove 70 is arranged between two circumferentially consecutive main grooves 60 and is axially adjacent to a respective main groove 20.

[0228] The secondary grooves 30 are identical to each other.

[0229] The secondary grooves 70 are identical to each other and have a shape specular to that of the secondary grooves 30.

[0230] The tread band 8 also comprises a plurality of circumferentially consecutive lateral grooves 41, 42, 43 arranged on one side with respect to the equatorial plane X-X, in particular on the same side as the main grooves 20 and the secondary grooves 30, and a plurality of circumferentially consecutive lateral grooves 81, 82, 83 arranged on the opposite side with respect to the equatorial plane X-X, and therefore on the same side as the main grooves 60 and the secondary grooves 70. The lateral grooves 81, 82, 83 are circumferentially offset with respect to the lateral grooves 41, 42, 43.

[0231] As shown in figure 3, each main groove 20, 60 comprises a respective first rectilinear portion 21, 61 having a respective end 21a, 61a proximal to the equatorial plane X-X and an opposite end 21b, 61b distal from the equatorial plane X-X.

[0232] The first rectilinear portion 21, 61 of each main groove 20, 60 has a width LI that progressively increases moving from the end 21a, 61a up to the opposite end 21b, 61b.

[0233] The end 21a, 61a of the first rectilinear portion 21, 61 of each main groove 20, 60 is arranged at a distance DI from the equatorial plane X-X comprised between 3% and 12%, preferably between 5% and 10%, of the radial section maximum width C of the tread band 8.

[0234] The end 21b, 61b of the first rectilinear portion 21, 61 of each main groove 20, 60 is arranged at a distance D2 from the equatorial plane X-X comprised between 10% and 30%, preferably between 15% and 25%, of the radial section maximum width C of the tread band 8.

[0235] The first rectilinear portion 21, 61 of each main groove 20, 60 is inclined with respect to the equatorial plane by an angle a which, in particularly preferred embodiments of the tyre 1, is less than 45°, preferably less than 35°, even more preferably less than 30°.

[0236] In preferred embodiments of the tyre 1, as for example the one shown in figures 2 and 3, the first rectilinear portions 21 of all the main grooves 20 are substantially parallel to each other. Similarly, the first rectilinear portions 61 of all the main grooves 60 are substantially parallel to each other.

[0237] Each main groove 20, 60 further comprises a respective second rectilinear portion 22, 62 that extends from the end 21b, 61b of the respective first rectilinear portion 21, 61 towards the equatorial plane X- X and is inclined with respect to the first rectilinear portion 21, 61 of the respective main groove 20, 60 by an angle 0 which, in particularly preferred embodiments of the tyre 1, is comprised between 90° and 160°, preferably between 95° and 150°, more preferably between 100° and 145°, even more preferably between 100° and 140°.

[0238] In preferred embodiments of the tyre 1, as for example the one shown in figures 2 and 3, the second rectilinear portions 22 of all the main grooves 20 are substantially parallel to each other. Similarly, the second rectilinear portions 62 of all the main grooves 60 are substantially parallel to each other.

[0239] Each second rectilinear portion 22, 62 has a respective end 22a, 62a proximal to the equatorial plane X-X and an opposite end 22b, 62b distal from the equatorial plane X-X and connected to, or coinciding with, the end 21b, 61b of the respective first rectilinear portion 21, 61.

[0240] The end 22a, 62a of the second rectilinear portion 22, 62 of each main groove 20, 60 is arranged at a distance from the equatorial plane X-X comprised between 3% and 12%, preferably between 5% and 10%, of the radial section maximum width C of the tread band 8.

[0241] Preferably, as in the example shown in figures 2 and 3, this distance is equal to the distance DI described above.

[0242] The second rectilinear portions 22, 62 of the main grooves 20, 60 are shorter than the first rectilinear portions 21, 61. In particularly preferred embodiments of the tyre 1, the second rectilinear portions 22, 62 have a length less than half, preferably less than or equal to one third, of the length of the first rectilinear portions 21, 61.

[0243] Each main groove 20 comprises a marginal portion defined at the end 21a which is superimposed in the axial direction on a marginal portion defined at the end 62a of a respective main groove 60.

[0244] Each main groove 20 further comprises a marginal portion defined at the end 22a which is superimposed in the axial direction on a marginal portion defined at the end 61a of a respective main groove 60. The marginal portions at which the main grooves 20 and the main grooves 60 are superimposed in the axial direction preferably have a circumferential extension less than 20%, more preferably less than 15%, of the circumferential extension of the main grooves 20, 60.

[0245] The secondary grooves 30, 70 have a circumferential extension less than that of the main grooves 20, 60.

[0246] In preferred embodiments of the tyre 1, the circumferential extension of the secondary grooves 30, 70 is less than 50%, more preferably less than 40%, even more preferably less than 30%, of that of the main grooves 20, 60.

[0247] Each secondary groove 30, 70 comprises a first segment 31, 71, preferably rectilinear, and a second segment 32, 72, also preferably rectilinear, which extends from the first segment 31, 71 towards the respective end edge 8a, 8b of the tread band 8, without reaching it.

[0248] Each secondary groove 30, 70 has a substantially V shape, with the first segment 31, 71 that defines an arm of the V, the second segment 32, 73 that defines the other arm of the V and the vertex of the V oriented with respect to the first arm 31, 71 and to the second arm 32, 72 consistently with the direction of rotation of the tyre 1.

[0249] The vertex of the secondary grooves 30 is placed at a distance from the equatorial plane X-X comprised between DI and D2, i.e. it is in an axially outermost position with respect to the ends 21a, 22a of the main grooves 20 and in an axially innermost position with respect to the ends 21b, 22b of the latter. Similarly, the vertex of the secondary grooves 70 is placed at a distance from the equatorial plane X-X comprised between DI and D2, i.e. it is in an axially outermost position with respect to the ends 61a, 62a of the main grooves 60 and in an axially innermost position with respect to the ends 61b, 62b of the latter.

[0250] The first segments 31, 71 are shorter than the second segments 32, 72 and extend towards the equatorial plane X-X until they reach it but without passing beyond it.

[0251] The first segments 31, 71 have a length greater than half the length of the second segments 32, 72.

[0252] The first segments 31, 71 and the second segments 32, 72 are shorter than the first rectilinear portions 21, 61.

[0253] The second segments 32, 72 are longer than the second rectilinear portions 22, 62.

[0254] The first segment 31, 71 of each secondary groove 30, 70 is inclined with respect to the equatorial plane X-X by an angle y comprised between 90° and 180°, more preferably between 100° and 170°, even more preferably between 110° and 160°, even more preferably between 120° and 140°.

[0255] The second segment 32, 72 of each secondary groove 30, 70 is inclined with respect to the first segment 31, 71 of the respective secondary groove 30, 70 by an angle 6 comprised between 40° and 180°, preferably between 40° and 140°, more preferably between 50° and 130°, even more preferably between 60° and 120°, even more preferably between 70° and 110°, even more preferably between 80° and 100°.

[0256] In preferred embodiments of the tyre 1, as for example the one shown in figures 2 and 3, the first segments 31 of all the secondary grooves 30 are substantially parallel to each other. They are also substantially parallel to the second rectilinear portions 22 of the main grooves 20 and to the second segments 72 of the secondary grooves 70. Similarly, the first segments 71 of all the secondary grooves 70 are substantially parallel to each other. They are also substantially parallel to the second rectilinear portions 62 of the main grooves 60 and to the second segments 32 of the secondary grooves 30.

[0257] The second segments 32 of all the secondary grooves 30 are substantially parallel to each other. They are also substantially parallel to the second rectilinear portions 62 of the main grooves 60 and to the first segments 71 of the secondary grooves 70. Similarly, the second segments 72 of all the secondary grooves 70 are substantially parallel to each other and substantially parallel to the second rectilinear portions 22 of the main grooves 20 and to the first segments 31 of the secondary grooves 30.

[0258] Each of the first segments 31 of the secondary grooves 30 extends along a respective direction that intersect the second rectilinear portion 62 of the axially adjacent main groove 60. Similarly, each of the first segments 71 of the secondary grooves 70 extends along a respective direction that intersect the second rectilinear portion 22 of the axially adjacent main groove 20.

[0259] The lateral grooves 41, 42, 43 are substantially parallel to each other and extend from an end edge 8a of the tread band 8 towards the equatorial plane X-X.

[0260] The lateral grooves 81, 82, 83 are substantially parallel to each other and extend from the opposite end edge 8b of the tread band 8 towards the equatorial plane X-X.

[0261] The lateral grooves 41, 42, 43 and the lateral grooves 81, 82, 83 are inclined with respect to the equatorial plane X-X by an angle 0 comprised between 20° and 90°, preferably between 20° and 80°, more preferably between 30° and 70°, even more preferably between 35° and 65°.

[0262] The lateral grooves 41 extend along respective directions that intersect the second rectilinear portions 22 of respective main grooves 20. Similarly, the lateral grooves 81 extend along respective directions that intersect the second rectilinear portions 62 of respective main grooves 60.

[0263] Each lateral groove 42 is circumferentially consecutive to a respective lateral groove 41 and extends along a direction that intersects the first rectilinear portion 21 of a respective main groove 20. Similarly, each lateral groove 82 is circumferentially consecutive to a respective lateral groove 81 and extends along a direction that intersects the first rectilinear portion 61 of a respective main groove 60.

[0264] Each lateral groove 41 and the circumferentially consecutive lateral groove 42 intersect the same main groove 20. Similarly, each lateral groove 81 and the circumferentially consecutive lateral groove 82 intersect the same main groove 60.

[0265] Each lateral groove 43 is circumferentially consecutive to a respective lateral groove 42 and extends along a direction that coincides with the direction along which the second segment 32 of a secondary groove 30 circumferentially consecutive to the main groove 20 discussed above extends. Similarly, each lateral groove 83 is circumferentially consecutive to a respective lateral groove 82 and extends along a direction that coincides with the direction along which the second segment 72 of a secondary groove 70 circumferentially consecutive to the main groove 60 discussed above extends.

[0266] The lateral grooves 41, 42, 81, 82 have substantially the same length, while the lateral grooves 43, 83 are shorter than the lateral grooves 41, 42, 81, 82.

[0267] The lateral grooves 41 and 42 extend partially in an annular portion of tread band 8 that comprises also the second segments 32 of the secondary grooves 30. Similarly, the lateral grooves 81 and 82 extend partially in an annular portion of the tread band 8 that comprises also the second segments 72 of the secondary grooves 70. These annular portions are defined at a distance from the equatorial plane X-X that is greater than D2.

[0268] With reference to figures 4 and 5, the tread pattern of the tread band 8 of a preferred embodiment of a front tyre 1 made in accordance with the present invention is described hereinbelow.

[0269] The description of this tread pattern is identical to that made above with reference to figures 2 and 3 except for what is described hereinbelow. It is therefore avoided repeating the identical part of description, for which reference can be made to the above description. Below only the characteristics that differentiate the tyre 1 of figures 4 and 5 from that of figures 2 and 3 are described.

[0270] In the tread band 8 of the tyre 1 of figures 4 and 5, the main grooves 20 and 60 are superimposed in the axial direction at respective parts having circumferential extension comprised between 10% and 50%, more preferably between 20% and 50%, even more preferably between 30% and 50% of the circumferential extension of each main groove 20, 60.

[0271] In the tread band 8 of the tyre 1 of figures 4 and 5 the first segments 31, 71 of the secondary grooves 30, 70 cross the equatorial plane X-X and are all entirely arranged inside an axially inner annular portion 80 of the tread band 8.

[0272] This axially inner annular portion 80 is defined astride of the equatorial plane X-X and has an axial extension A less than 20%, preferably less than 15%, of the radial section maximum width C of the tread band 8.

[0273] The axially inner annular portion 80 does not comprise segments or portions of grooves other than the aforementioned first segments 31, 71.

[0274] In the tread band 8 of the tyre 1 of figures 4 and 5 the first segments 31, 71 have a length less than or equal to half the length of the second segments 32, 72.

[0275] In the tread band 8 of the tyre 1 of figures 4 and 5 the vertex of the V formed by each secondary groove 30, 70 is oriented, with respect to the first arm 31, 71 and to the second arm 32, 72, in the opposite direction with respect to the direction of rotation of the tyre 1 and is arranged in an axially innermost position with respect to the ends 22a, 62a of the main grooves 20, 60.

[0276] In the tread band 8 of the tyre 1 of figures 4 and 5, the first segment 31 of each secondary groove 30 extends along a direction that intersects the first rectilinear portion 61 of the axially adjacent main groove 60.

[0277] In the tread band 8 of the tyre 1 of figures 4 and 5, the second segments 32 of the secondary grooves 30 and the lateral grooves 41, 42 extend at distinct annular portions of the tread band 8. Similarly, the second segments 72 of the secondary grooves 70 and the lateral grooves 81, 82 extend at distinct annular portions of the tread band 8.

[0278] COMPARATIVE TESTS

[0279] The Applicant has made a sample of a rear tyre 1 in accordance with an embodiment of the present invention and having in particular the tread pattern shown in figures 2 and 3. This tyre hereinbelow is indicated with INV.

[0280] The tyre INV had a structure and dimensions identical to those of a big enduro rear tyre of the Applicant (hereinafter referred to as Ref) currently sold on the market and approved for road journey combined with dirt road, therefore belonging to the same market segment as the tyre INV.

[0281] Outdoor comparison tests were carried out with the tyre Ref, appreciated by the customers for its excellent behaviour on dry and wet road surfaces and for an absolutely satisfactory off-road behaviour.

[0282] The tests were carried out by mounting the tyres INV and Ref (inflated with the same inflation pressure) on the rear wheel of a BMW R1250GS motorcycle, with an identical tyre mounted on the front wheel and under substantially identical environmental conditions.

[0283] The behaviour of the two tyres INV and Ref was evaluated both on the road (dry and wet) and off-road, asking the rider for his opinion. In particular, the items listed in table 1 reported hereinbelow were evaluated, where the opinion expressed by the rider is also reported.

[0284] The road tests were performed by driving on a route with rectilinear parts and bends, with both dry and wet road.

[0285] The off-road tests were carried out by driving several times along a rectilinear route having a fixed length prepared with muddy and sandy terrain that replicated possible conditions that can be found in the natural environment, keeping the terrain as homogeneous as possible after each test. On the rectilinear route, two sensors were installed to determine the time of entry and exit of the motorcycle and the latter was equipped with suitable tools (GPS sensor, engine throttle valve opening sensor and speed sensors in both wheels).

[0286] Table 1

[0287] In Table 1, "=" indicates the positive opinion obtained with the tyre Ref and "+" indicates an improvement with respect to the tyre Ref.

[0288] Table 1 shows that the tyre INV offered improved performance on road surfaces compared to those of the tyre Ref in relation to line holding and grip (and therefore to acceleration and braking), showing a behaviour in line with that of the tyre Ref with regard to all the other items evaluated, including the light off-road. The Applicant thus had confirmation of the fact that the particular tread pattern adopted in the tyre of the invention actually allows to effectively obtain the sought improvement of performance on dry and wet road surface in terms of acceleration and braking, while keeping the same good off-road performance of the tyre Ref.

[0289] Of course, a person skilled in the art can make further modifications and changes to the tyre of the invention described above in order to satisfy specific and contingent application needs, such modifications and changes in any case falling within the scope of protection defined by the following claims.

Claims

CLAIMS1. Motorcycle tyre (1), comprising a tread band (8) having a plurality of main grooves (20; 60) arranged on opposite sides with respect to an equatorial plane (X-X) of the tyre (1) and a void to solid ratio greater than 10%, wherein each of said main grooves (20; 60) comprises:- a first rectilinear portion (21; 61) inclined with respect to the equatorial plane (X-X) by a first angle (a) less than 45° and having a first end (21a; 61a) proximal to the equatorial plane (X-X) and a second end (21b; 61b) distal from the equatorial plane (X-X);- a second rectilinear portion (22; 62) inclined with respect to said first rectilinear portion (21; 61) by a second angle (0) comprised between 90° and 160° and having a third end (22a; 62a) proximal to the equatorial plane (X-X) and a fourth end (22b; 62b) distal from the equatorial plane (X-X); wherein said second rectilinear portion (22; 62) is shorter than said first rectilinear portion (21; 61).

2. Motorcycle tyre (1) according to claim 1, wherein said second rectilinear portion (22; 62) has a length shorter than half the length of said first rectilinear portion (21; 61).

3. Motorcycle tyre (1) according to claim 1 or 2, wherein said first rectilinear portion (21; 61) has a width that progressively increases moving from said first end (21a; 61a) up to said second end (21b; 61b).

4. Motorcycle tyre (1) according to any one of the previous claims, wherein said first end (21a; 61a) and said third end (22a; 62a) are arranged at respective distances (DI) from the equatorial plane (X-X) that are less than 12% of a radial section maximum width (C) of the tread band (8).

5. Motorcycle tyre (1) according to any one of the previous claims, wherein said tread band (8) comprises a plurality of secondary grooves(30; 70) having a circumferential extension shorter than that of said main grooves (20; 60), wherein each of said secondary grooves (30; 70) is arranged between two circumferentially consecutive main grooves (20; 60) and comprises a first segment (31; 71) that extends towards the equatorial plane (X-X) and a second segment (32; 72) that extends from said first segment (31; 71) towards an end edge (8a; 8b) of the tread band (8) without reaching the end edge (8a; 8b).

6. Motorcycle tyre (1) according to claim 5, wherein said first segment (31; 71) is inclined with respect to the equatorial plane (X-X) by a third angle (y) comprised between 90° and 180° and said second segment (32; 72) is inclined with respect to said first segment (31; 71) by a fourth angle (6) less than 180°.

7. Motorcycle tyre (1) according to claim 5 or 6, wherein: said plurality of main grooves (20; 60) comprises a first series of circumferentially consecutive main grooves (20) arranged on one side with respect to the equatorial plane (X-X) and a second series of circumferentially consecutive main grooves (60) arranged on the other side with respect to the equatorial plane (X-X); said plurality of secondary grooves (30; 70) comprises a first series of circumferentially consecutive secondary grooves (30) arranged at least in part on one side with respect to the equatorial plane (X-X) and a second series of circumferentially consecutive secondary grooves (70) arranged at least in part on the other side with respect to the equatorial plane (X-X); wherein each secondary groove (30) of said first series of secondary grooves (30) is axially adjacent to a respective main groove (60) of said second series of main grooves (60) and each secondary groove (70) of said second series of secondary grooves (70) is axially adjacent to a respective main groove (20) of said first series of main grooves (20).

8. Motorcycle tyre (1) according to any one of claims 5 to 7, wherein all the first segments (31; 71) of the secondary grooves (30; 70) extend until they reach the equatorial plane (X-X) without crossing it.

9. Motorcycle tyre (1) according to any one of claims 5 to 7, wherein all the first segments (31; 71) of the secondary grooves (30; 70) cross the equatorial plane (X-X).

10. Motorcycle tyre (1) according to claim 9, wherein all the first segments (31; 71) of the secondary grooves (30; 70) are entirely arranged inside an axially inner annular portion (80) of the tread band (8) that is arranged astride of the equatorial plane (X-X) and has an axial extension (A) less than 20% of a radial section maximum width (C) of the tread band (8).

11. Motorcycle tyre (1) according to claim 9 or 10 when depending on claim 7, wherein the first segments (31) of the secondary grooves (30) of said first series of secondary grooves (30) extend along respective directions that intersect the first rectilinear portion (61) of the axially adjacent main groove (60) and the first segments (71) of the secondary grooves (70) of said second series of secondary grooves (70) extend along respective directions that intersect the second rectilinear portion (22) of the axially adjacent main groove (20).

12. Motorcycle tyre (1) according to any one of the previous claims, wherein the tread band (8) further comprises a plurality of lateral grooves (41, 42, 43; 81, 82, 83) inclined with respect to the equatorial plane (X- X) by a fifth angle (0) less than 90°, wherein a first series of lateral grooves (41, 42, 43) of said plurality of lateral grooves (41, 42, 43; 81, 82, 83) extends from an end edge (8a) of the tread band (8) towards the equatorial plane (X-X) and a second series of lateral grooves (81, 82, 83) of said plurality of lateral grooves (41, 42, 43; 81, 82, 83) extends from an opposite end edge (8b) of the tread band (8) towards the equatorial plane (X-X).

13. Motorcycle tyre (1) according to claim 12 when depending on any one of claims 5 to 11, wherein first lateral grooves (41; 81) of said first series of lateral grooves (41, 42, 43) or second series of lateral grooves (81, 82, 83) extend along respective directions that intersect the second rectilinear portions (22; 62) of respective main grooves (20; 60), second lateral grooves (42; 82) circumferentially consecutive to said first lateral grooves (41; 81) extend along respective directions that intersect the first rectilinear portions (21; 61) of said respective main grooves (20; 60) and third lateral grooves (43; 83) circumferentially consecutive to said second lateral grooves (42; 82) extend along respective directions that coincide with the directions along which the second segments (32; 72) of the secondary grooves (30; 70) that are circumferentially arranged between two circumferentially consecutive main grooves (20; 60) extend.

14. Motorcycle tyre (1) according to claim 13, wherein said first lateral grooves (41; 81) have a length equal to that of said second lateral grooves (42; 82).

15. Motorcycle tyre (1) according to claim 13 or 14, wherein said third lateral grooves (43; 83) are shorter than said first lateral grooves (41; 81) and said second lateral grooves (42; 82).

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