Tyre for vehicle wheels

Abstract

A tyre (1) for vehicle wheels comprises a tread band (2) on which a first main groove (10) and a second main groove (20) are defined, as well as at least one secondary groove (30; 40) which extends between the first main groove (10) and the second main groove (20). The secondary groove (30; 40) comprises a central region (33; 43), having a depth less than a depth of the first main groove (10) and the second main groove (20), and a first end region (34; 44) which extends between the central region (33; 43) and the first main groove (10), having an increasing depth from the central region (33; 43) towards the first end (31; 41).

Description

[0001] TYRE FOR VEHICLE WHEELS

[0002] DESCRIPTION

[0003] The present invention concerns a tyre for vehicle wheels, in particular a winter tyre. A tyre generally comprises a carcass structure shaped toroidally around a rotation axis and including at least one carcass ply having end flaps which are engaged in respective annular anchoring structures, called bead cores.

[0004] In a position radially external to the carcass structure, a belt structure is provided comprising, in the case of car tyres, at least two radially superimposed strips of rubberised fabric provided with reinforcing cords, usually metallic, arranged in each strip parallel to each other but crossed with respect to the cords of the adjacent strip, preferably symmetrically with respect to the equatorial plane of the tyre.

[0005] Preferably, the belt structure further comprises in a radially external position, at least on the ends of the underlying belt strips, also a third layer of textile or metallic cords, arranged circumferentially (at 0 degrees). In tubeless type tyres, there is also a radially internal layer, called "liner", which has waterproofing characteristics to allow air sealing to the tyre itself.

[0006] In a position radially external to the belt structure, a tread band, made of elastomeric material, is applied on which a tread surface intended for contact with the road surface is defined.

[0007] The tyres, in order to obtain adequate grip even on a wet road surface, have a tread band provided with grooves of various shapes and geometry whose main function is to allow the evacuation of the water present between the surface of the tyre and the road surface at the time of mutual contact, preventing the hydrostatic pressure deriving from the impact of the water against the forward travelling tyre from causing the tyre to lift even partially from the road surface and the consequent loss of control of the vehicle (a phenomenon known as "aquaplaning'").

[0008] The grooves formed in the circumferential direction also affect the directionality and travel stability characteristics of the tyre in relation to the ability of the tyre to bear the tangential stresses parallel to the rotation axis of the tyre.

[0009] The grooves formed in the transverse direction, in turn, affect the traction characteristics of the tyre, i.e. the ability to transmit the tangential stresses parallel to the travel direction to the road surface, in particular during the acceleration and braking steps of the vehicle.

[0010] The grooves, overall, define on the tread band a plurality of blocks, each of which comprises a radially external surface intended for contact with the road surface, and which, therefore, forms a portion of the tread surface of the tyre. Each block is furthermore delimited, at least partially, by one or more walls defined by the grooves that surround it.

[0011] In the case of a winter tyre, small notches, called "sipes", which extend from the tread surface of the tyre towards the inside of the block, are usually formed on the blocks of the tread band. The function of the sipes is to offer additional grip elements in the case of driving on a snowy surface and to retain a certain amount of snow, thereby improving grip with the road surface.

[0012] "Circumferential" direction refers to a direction generally oriented according to the rotation direction of the tyre, or, in any case, slightly inclined (at most at 10°) with respect to the rotation direction of the tyre.

[0013] The term "axial" and the expressions "axially internal / external" are used with reference to the axial direction of the tyre, i.e. to a direction parallel to the rotation axis of the same or at most inclined at + / - 5° with respect to it. The axial direction is generally perpendicular to the circumferential direction.

[0014] The term "equatorial plane" of the tyre is intended to mean an axial centre line plane perpendicular to the rotation axis of the tyre.

[0015] The term "transverse" refers to a direction inclined with respect to the circumferential direction of an acute angle greater than at least 10°.

[0016] With "shoulder regions" of the tread band, is intended to mean the portions of tread band that extend circumferentially in a position axially external to the tread band itself.

[0017] Preferably, each shoulder region extends over a width equal to at least 10% of the width of the tread band, more preferably equal to at least 20% of the width of the tread band.

[0018] Preferably, each shoulder region extends over a width less than 30% of the width of the tread band, more preferably less than 25% of the width of the tread band.

[0019] With "equatorial region" of the tread band is intended to mean the portion of the tread band that extend circumferentially in a symmetrical manner around the equatorial plane and delimited on its axially opposed sides by said shoulder regions. The term "groove" is intended to mean a cavity formed in a portion of the tread band, having a width greater than or equal to 1.5 mm, and preferably a depth greater than 3 mm.

[0020] The term "sipe" is intended to mean a cavity formed in a portion of the tread band, having a width less than 1.5 mm, preferably less than or equal to 1 mm. The width of sipes and grooves is intended as measured at a depth greater than or equal to 1 mm, preferably greater than or equal to 1.5 mm.

[0021] With "block" is intended to mean a portion of the tread surface that is delimited by at least one groove, preferably by at least two distinct grooves, on which there is defined, on the radially external surface thereof, a portion of the tread surface intended for contact with the road surface.

[0022] Therefore, both a portion of the tread band with a closed contour, delimited by three or more grooves, and a circumferential rib delimited by a pair of grooves extended circumferentially around the tread band are considered blocks.

[0023] A groove is said to be a "main" groove when it extends transversely from a shoulder region to an equatorial region of the tread band. Preferably, a main groove extends on the tread band so as to cover at least 30% of the width of the tread band, more preferably at least 40% of the width of the tread band.

[0024] Preferably, a main groove is open at an axial end of the tread band.

[0025] Preferably a main groove has a decreasing inclination with respect to an equatorial plane of the tread band from the shoulder region towards the equatorial region. Preferably, a main groove has a depth of at least 5 mm.

[0026] Preferably, a main groove has a width of at least 3 mm, more preferably of at least 5 mm.

[0027] A groove is said to be a "secondary " groove when it extends between a pair of main grooves.

[0028] With "tread pattern" is intended to mean the overall configuration of the tread band as defined by the set of grooves and blocks delimited by them.

[0029] WO 2016\189418, in the name of the same Applicant, describes a winter tyre comprising a plurality of transverse grooves, arranged in succession along the circumferential development of the tyre, wherein a plurality of secondary grooves extend between said transverse grooves defining a plurality of blocks aligned along the direction of the transverse grooves and separated from each other by the secondary grooves.

[0030] The Applicant has preliminarily observed that the tyres intended for driving on wet or snowy road surfaces often have a tread pattern comprising a plurality of main grooves arranged in succession along the circumferential development of the tread band, extending transversely from the opposing shoulder regions towards the equatorial region of the tread band, as well as one or more secondary grooves extending between pairs of successive main grooves. In this way, a plurality of aligned blocks that can have one or more sipes remain defined between each pair of successive main grooves.

[0031] The Applicant has verified that this configuration allows to quickly evacuate significant amounts of water or water mixed with snow slash) that may be present in the ground contacting area.

[0032] Furthermore, the Applicant has observed that the performance of a tyre on a snowy surface depends not only on the quantity and extension of the sipes formed on the blocks, but also on the quantity and configuration of the grooves that delimit the blocks.

[0033] In particular, with reference to the generic tread pattern discussed above, the Applicant has verified that the secondary grooves also contribute to the performance of the tyre on snowy surface.

[0034] The Applicant, however, has verified that the dimensions of these grooves also affect the behaviour of the tyre on dry road.

[0035] In particular, the Applicant has verified that a deep secondary groove can negatively affect the rigidity of the blocks facing on it, all the more so when they are affected by the presence of sipes, thereby decreasing their ability to bear the tangential stresses.

[0036] Due to this weakening, during braking, acceleration or a bend, the block can undergo a strong deformation, resulting in a partial lifting of the block from the road surface with a consequent reduction in the contacting area between block and road surface and, consequently, also in the overall frictional force exerted by the tyre on the road surface.

[0037] In other words, the Applicant has noted that the provision of deep secondary grooves between adjacent blocks if on the one hand it improves behaviour on snowy surface, on the other hand it can penalise performance in terms of grip on both dry and wet road surface.

[0038] The Applicant therefore perceived that in order to meet both needs it could be useful to define sections with differentiated depth in the secondary grooves, so that some sections are able to accommodate a greater amount of snow and other sections keep the blocks facing on the secondary grooves adequately rigid.

[0039] Furthermore, the Applicant has observed that with the same depth and extension, the middle section of the secondary groove is more effective in giving rigidity to the blocks facing on it than to the end sections.

[0040] Finally, the Applicant has found that a tread pattern in which a secondary groove, which extend between a pair of main grooves, and having at least one end region deeper than a central region, allows to increase the snow retention capacity, maintaining, at the same time, a good rigidity of the blocks facing on the secondary groove.

[0041] In particular, in a first aspect thereof, the invention relates to a tyre for vehicle wheels comprising a tread band on which a first main groove and a second main groove are defined.

[0042] Preferably at least one secondary groove which extends between a first end and a second end is defined on said tread band.

[0043] Preferably, said first end opens in said first main groove.

[0044] Preferably, said second end opens in said second main groove.

[0045] Preferably, a plurality of blocks which are delimited at a pair of opposite sides by said first main groove and, respectively, by said second main groove are defined on said tread band.

[0046] Preferably, said blocks are separated from each other by said at least one secondary groove.

[0047] Preferably, said at least one secondary groove comprises a central region and a first end region which extends between said central region and said first end.

[0048] Preferably, said central region has a depth less than a depth of said first main groove. Preferably, said central region has a depth less than a depth of said second main groove.

[0049] Preferably, said first end region has an increasing depth from said central region towards said first end.

[0050] The Applicant considers that thanks to these characteristics, the secondary groove on the one hand keeps the blocks facing on it sufficiently rigid, "tying" them together at a central position, so as to bear the tangential stresses in a balanced manner and, on the other hand, is able to effectively retain the snow at its end region, where it opens in the main groove, synergistically helping to retain the snow also in the main groove.

[0051] This allows, overall, to provide the tread with good behaviour both on a snowy road surface and on a dry or wet road surface.

[0052] The present invention, in the aforesaid aspect, may have at least one of the further preferred features set out below.

[0053] In some embodiments, said first end has a depth less than the depth of said first main groove. In this way, the rigidity of the blocks facing the secondary groove is accentuated also at the end region, improving the grip characteristics on dry or wet surface.

[0054] In some embodiments, wherein said first end has a depth substantially identical to the depth of said first main groove.

[0055] In this way, the snow retention capacity at the end region is accentuated, improving the grip characteristics on snowy surface.

[0056] In some embodiments, said first end region is planar and is preferably inclined, with respect to a tread surface of said tread band, at an angle between 30° and 60°, more preferably of about 45°.

[0057] In other words, the end region of the secondary groove forms a chamfer which connects the central region of the secondary groove with the main groove.

[0058] In some embodiments, said at least one secondary groove comprises a second end region which extends between said central region and said second main groove with an increasing depth from said central region towards said second main groove.

[0059] In this way, also the second end region is able to retain a greater amount of snow, improving performance on snowy surface.

[0060] In some embodiments, said second end region is planar and is preferably inclined, with respect to a tread surface of said tread band, at an angle between 30° and 60°, more preferably of about 45°.

[0061] Preferably, said second end region is symmetrical to said first end region with respect to said central region.

[0062] In this way, the stresses on the blocks facing the secondary groove are more balanced.

[0063] In some embodiments, said at least one secondary groove has a depth, in the region of said central region, greater than 3 mm.

[0064] In some embodiments, said at least one secondary groove has a depth, in the region of said central region, of less than 8 mm.

[0065] In some embodiments, said at least one secondary groove has a width less than 5 mm.

[0066] In some embodiments, said plurality of blocks comprise at least three blocks which are separated from each other by a first secondary groove and by a second secondary groove, each of said secondary grooves having the characteristics of said at least one secondary groove.

[0067] In other words, said plurality of blocks comprises at least three blocks and said at least one secondary groove comprises a first secondary groove and a second secondary groove that separate said at least three blocks from each other.

[0068] In some embodiments, said central region of said first secondary groove has a depth less than a depth of said central region of said second secondary groove.

[0069] In some embodiments, said first end of said first secondary groove has a depth less than the depth of said first primary groove and said first end of said second secondary groove has a depth which is substantially identical to the depth of said first primary groove.

[0070] In this way, the characteristics of rigidity of the blocks and of snow retention can be suitably differentiated between the different secondary grooves, for example as a function of their positioning on the tread band.

[0071] In some embodiments, said first secondary groove has a depth, in the region of said central region, between 3 mm and 5 mm, preferably of about 4 mm.

[0072] In some embodiments, said first secondary groove has a width between 2 mm and 3 mm.

[0073] In some embodiments, said second secondary groove has a depth, in the region of said central region, between 6 mm and 8 mm, preferably of about 7 mm.

[0074] In some embodiments, said second secondary groove has a width between 3 and 4 mm.

[0075] In some embodiments, said second secondary groove has a width greater than a width of said first secondary groove.

[0076] In this way, the snow retention capacity of the second secondary groove is further accentuated.

[0077] In some embodiments, said blocks of said plurality of blocks are aligned in a transverse alignment direction with respect to an equatorial plane of said tread band. Preferably, said first secondary groove is in an axially external position with respect to said second secondary groove.

[0078] In this way, the first secondary groove, which is closer to the axial end of the tread band, is overall less deep than the second secondary groove, which is closer to the equatorial plane, giving greater rigidity to the axially external blocks, while the second secondary groove is mainly intended for snow retention.

[0079] Preferably, the third secondary groove is defined in an axially external position, for delimiting the first shoulder region from the equatorial region.

[0080] Preferably, the second secondary groove is defined in an axially internal position, more preferably the first secondary groove is defined in an intermediate position between the other two secondary grooves. Preferably, said first main groove and said second main groove open at an axial end of said tread band.

[0081] In some embodiments, said first main groove and said second main groove have a width between 3 mm and 11 mm.

[0082] Preferably, said first main groove and said second main groove have a width which decreases from a first end thereof which is defined in said shoulder region to a second end thereof which is defined in said equatorial region.

[0083] In some embodiments, said first main groove and said second main groove have sections with different inclination with respect to an equatorial plane. Preferably the difference in inclination between each section of said first main groove and a corresponding section of said second main groove is less than 20°, more preferably less than 10°, even more preferably less than 5°.

[0084] In some embodiments, said first main groove and said second main groove are formed in alternating succession along the entire circumferential development of said tread band.

[0085] In some embodiments, said first main groove and said second main groove have a depth greater than 5 mm, preferably greater than 7 mm, more preferably of about 9 mm.

[0086] The characteristics and advantages of the invention will be better understood from the detailed description of some of its preferred embodiments, illustrated by way of non-limiting example with reference to the accompanying drawings, in which:

[0087] - figure 1 is a schematic front view of a significant portion of the tread band, extended on a plane, of a tyre for vehicle wheels made in accordance with the present invention,

[0088] - figure 2 is a schematic view on an enlarged scale of a pitch of the tread band of the tyre of figure 1,

[0089] - figure 3 is a perspective and sectional view along the line III-III of figure 2, and

[0090] - figure 4 is a sectional view along the line IV-IV of figure 2,

[0091] - figure 5 is a sectional view along the line V-V of figure 2.

[0092] With reference to the attached figures, 1 globally denotes a tyre for vehicle wheels made in accordance with the present invention.

[0093] The tyre 1 has a conventional generally toroidal shape extended around a rotation axis, defining an axial direction Y of the tyre, and crossed by an equatorial plane X, perpendicular to the rotation axis.

[0094] The tyre 1 comprises a tread band 2 on which a tread surface 3 is defined which is arranged in a position that is radially external to the tread band 2 and intended for contact with a road surface.

[0095] The tread band 2 has a width L and extends axially between a first axial end 2a and an opposite second axial end 2b.

[0096] The tyre 1 has, for example, a nominal section width of about 225 mm with a shoulder diameter of 17 inches.

[0097] An equatorial region 4, which extends circumferentially and symmetrically around the equatorial plane X, as well as a first shoulder region 5 and a second shoulder region 6, which extend respectively at the axially opposite sides of the equatorial region 4, in a position axially external to the same tread band 2 up to the respective axial ends 2a, 2b of the tread band 2, remain defined on the tread band 2.

[0098] The equatorial region 4 extends indicatively over a width equal to about 60% of the width of the tread band 2.

[0099] On the tread band 2, a plurality of grooves of various dimensions and configurations are formed which delimit a plurality of blocks, so as to define, overall, the tread pattern of the tyre 1.

[0100] In particular, the tread pattern has a modular configuration in which a pitch M is identified which is repeated in succession along the circumferential development of the tread band 2.

[0101] Each module M, represented in enlarged scale in figure 2, comprises a first main groove 10 and a second main groove 20, which both extend from the first axial end 2a of the tread band 2 up to the equatorial region 4, crossing the first shoulder region

[0102] 5.

[0103] In particular, the first main groove 10 extends between a first, axially external end 11, which open at the first axial end 2a of the tread band 2, and a second, axially internal end 12, which closes an end section 13 of the first main groove 10 that extends in a zig-zag manner along the equatorial plane X.

[0104] The second main groove 20 extends between a first, axially external end 21, which opens at the first axial end 2a of the tread band 2, and a second, axially internal end 22, which converges into the end section 13 of the first main groove 10.

[0105] Corresponding main grooves 10a and 20a extend from the second axial end 2b of the tread band 2 up to the equatorial region 4, crossing the second shoulder region

[0106] 6.

[0107] The course of the main grooves 10a, 20a is substantially similar to that of the first and second main groove 10, 20, so the following detailed description of the main grooves 10 and 20 may also refer, mutatis mutandis, to the main grooves 10a, 20a. The two pairs of main grooves 10, 20 and 10a, 20a, are in fact substantially symmetrical with respect to the equatorial plane X, apart from a slight circumferential offset and apart from the end section 11 of the first main groove 10, on which the main grooves 10a and 20a also converge.

[0108] The first main groove 10 and the second main groove 20 have a slightly curvilinear course, with an inclination with respect to the equatorial plane X that decreases from the first shoulder region 5 up to the equatorial region 4.

[0109] The first main groove 10 and the second main groove 20 have a depth varying from about 7 mm in the first shoulder region 5 to about 8.8 mm in the equatorial region 4, while they have a width which decreases from a first end 11, 21 thereof, where it is between 7 mm and 11 mm, up to the end section 13 (and to the second end 12) and, respectively, to the second end 22, where it is between 3.5 mm and 5.5 mm.

[0110] A first secondary groove 30, a second secondary groove 40 and a third secondary groove 50 further extend between the first main groove 10 and the second main groove 20, as well as between the second main groove 20 and the first main groove 10 of the next pitch M.

[0111] In particular, the third secondary groove 50 is defined in an axially external position, for delimiting the first shoulder region 5 from the equatorial region 4, the second secondary groove 40 is defined in an axially internal position and the first secondary groove 30 is defined in an intermediate position between the other two secondary grooves.

[0112] The first secondary groove 30 extends substantially straightly between a first end 31, which opens on the first main groove 10, and a second end 32, which opens on the second main groove 20.

[0113] The first secondary groove 30 comprises a central region 33, extended over about 90% of the longitudinal extension of the secondary groove 30, as well as a first end region 34 and a second end region 35, which are longitudinally opposite, respectively including the first end 31 and the second end 32.

[0114] The first secondary groove 30 has a substantially constant width, for example equal to about 2.5 mm, and a variable depth along its longitudinal development.

[0115] In particular, the central region 33 has a substantially constant depth Pl, for example equal to about 4 mm, while the first and second end region 34, 35 have a linearly increasing depth from the central region 33 towards the first end 31 and, respectively, the second end 32, both of which have, for example, a depth of about 5.5 mm, less than the depth of the first main groove 10.

[0116] The first and second end region 34, 35 are preferably formed by respective planes inclined at about 45° with respect to the central region 33.

[0117] The second secondary groove 40 extends substantially straight, substantially parallel to the first secondary groove 30, between a first end 41, which opens on the first main groove 10, and a second end 42, which opens on the second main groove 20.

[0118] The second secondary groove 40 comprises a central region 43, extended over about 90% of the longitudinal extension of the secondary groove 40, as well as a first end region 44 and a second end region 45, which are longitudinally opposite, respectively including the first end 41 and the second end 42.

[0119] The second secondary groove 40 has a substantially constant width, for example equal to about 3.5 mm, greater than the width of the first secondary groove 30.

[0120] The second secondary groove 40 also has a variable depth along its longitudinal development, greater than the depth of the first secondary groove 30.

[0121] In particular, the central region 43 has a substantially constant depth P2, for example equal to about 7.2 mm, while the first and second end region 44, 45 have a linearly increasing depth from the central region 43 towards the first end 41 and, respectively, the second end 42, both of which have a depth for example of about 8.7 mm, almost identical to the depth in that area of the first main groove 10 and of the second main groove 20, respectively.

[0122] The first end region 44 and the second end region 45 are preferably formed by respective planes inclined at about 45° with respect to the central region 43 which connects the central region 43 with the bottom of the first main groove 10 and of the second main groove 20.

[0123] The third secondary groove 50 extends along a curvilinear direction between a first end 51, which opens on the first main groove 10, and a second end 52, which opens on the second main groove 20.

[0124] The third secondary groove 50 has a substantially constant depth and width, for example respectively equal to about 4 mm and about 2.5 mm, substantially identical to the central region 33 of the first secondary groove 30.

[0125] The third secondary groove 50, moreover, is crossed by a sipe 53 which is formed longitudinally on its bottom.

[0126] Between each main groove 10a and the main groove 20a, as well as between the main groove 20a and the main groove 10a of the next pitch M, there are formed corresponding secondary grooves 30a, 40a and 50a which are entirely similar to the first secondary groove 30, to the second secondary groove 40 and to the third secondary groove 50, respectively.

[0127] The first main groove 10 and the second main groove 20 laterally delimit four blocks, all denoted with 60, aligned along an alignment direction which is substantially defined by the longitudinal development of the main grooves 10, 20, and which are separated from each other by the secondary grooves 30, 40 and 50.

[0128] On each block 60 there are also formed one or more sipes 61 which open on the tread surface portion 3 and extend parallel to the alignment direction of the blocks 60. Of course, in embodiment variants not illustrated, the sipes can assume different configurations, for example they can be oriented along an axial direction.

[0129] The sipes 61 have for example a width of about 0.5 mm and a depth of about 7 - 9 mm.

[0130] An incision 62 less than 1 mm deep can also be formed on each block 60, mainly for aesthetic purposes.

[0131] The tests carried out by the Applicant on a tyre made according to the preferred example described above have shown excellent behaviour both on snowy road surfaces and on dry road surfaces and, again, on wet road surfaces.

[0132] As in fact previously reiterated, thanks to the characteristics illustrated above, the secondary grooves on the one hand keep the blocks facing on them sufficiently rigid, "tying" them together at a central position, so as to bear the tangential stresses in a balanced way and, on the other hand, are able to effectively retain snow at their end regions, where they open in the main grooves: for these reasons good behaviour is obtained both on a snowy road surface and on a dry or wet road surface.

[0133] Naturally, those skilled in the art may make further modifications and variants to the above-described invention with the purpose of meeting specific and contingent application needs, variants and modifications in any case falling within the scope of protection as defined by the successive claims.

Claims

CLAIMS1. A tyre (1) for vehicles wheels, comprising a tread band (2) on which there are defined:- a first main groove (10) and a second main groove (20),- at least one secondary groove (30; 40) which extends between a first end (31; 41) which opens in said first main groove (10) and a second end (32;42) which opens in said second main groove (20),- a plurality of blocks (60) which are delimited at a pair of opposite sides by said first main groove (10) and by said second main groove (20), respectively, and which are separated from each other by said at least one secondary groove (30; 40), wherein said at least one secondary groove (30; 40) comprises:- a central region (33; 43) having a depth less than a depth of said first main groove (10) and a depth of said second main groove (20),- a first end region (34; 44) which extends between said central region (33;43) and said first end (31; 41) with an increasing depth from said central region (33; 43) towards said first end (31; 41).

2. A tyre according to claim 1, wherein said first end (31) has a depth less than the depth of said first main groove (10).

3. A tyre according to claim 1, wherein said first end (41) has a depth substantially identical to the depth of said first main groove (10).

4. A tyre according to any one of the preceding claims, wherein said first end region (34; 44) is planar.

5. A tyre according to claim 4, wherein said first end region (34; 44) is inclined with respect to a tread surface (3) of said tread band (2) at an angle between 30° and 60°.

6. A tyre according to any one of the preceding claims, wherein said at least one secondary groove (30; 40) comprises a second end region (35; 45) which extends between said central region (33; 43) and said second main groove (20) with an increasing depth from said central region (33; 43) towards said second main groove (20).

7. A tyre according to claim 6, wherein said second end region (35; 45) is symmetrical to said first end region (34; 44) with respect to said central region (33; 43).

8. A tyre according to any one of the preceding claims, wherein said at least onesecondary groove has a depth, in the region of said central region, less than 8 mm.

9. A tyre according to any one of the preceding claims, wherein said at least one secondary groove has a width less than 5 mm.

10. A tyre according to any one of the preceding claims, wherein said plurality of blocks (60) comprise at least three blocks which are separated from each other by a first secondary groove (30) and by a second secondary groove (40), each of said secondary grooves having the characteristics of said at least one secondary groove.

11. A tyre according to claim 10, wherein said central region (33) of said first secondary groove (30) has a depth less than a depth of said central region (43) of said second secondary groove (40).

12. A tyre according to claim 10 or 11, wherein said first end (31) of said first secondary groove (30) has a depth less than the depth of said first main groove (10) and said first end (41) of said second secondary groove (40) has a depth which is substantially identical to the depth of said first main groove (10).

13. A tyre according to any one of claims 10 to 12, wherein said second secondary groove (40) has a width greater than a width of said first secondary groove (30).

14. A tyre according to any one of claims 10 to 13, wherein said blocks (60) of said plurality of blocks are aligned in a transverse alignment direction with respect to an equatorial plane (X) of said tread band (2) and said first secondary groove (30) is in an axially external position with respect to said second secondary groove (40).

15. A tyre according to any one of the preceding claims, wherein said first main groove (10) and said second main groove (20) have a width which is between 3 mm and 11 mm and which decreases from a first end (11; 21) thereof which is defined in the shoulder region (5) up to a second end (12; 22) thereof which is defined in said equatorial region (4).

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