Motorcycles tyre

Abstract

Motorcycles tyre, comprising: a radial carcass structure (2); a belt structure (6) applied in radially outer position with respect to the radial carcass structure (2); a tread band (8) applied in radially outer position with respect to the belt structure (6). The tyre (1) has a curvature ratio (f/C) greater than or equal to about 0.25. The tread band (8) comprises: a plurality of blocks (14) mutually spaced so as to define a tread pattern with a void/solid ratio (1−Sb/St) comprised between about 25% and about 50%; transverse grooves (11) placed in succession along the circumferential extension of the tyre (1) and each substantially extending over the entire axial width of the tread band (8). Each transverse groove (11) substantially extends along an axial direction. Two successive transverse grooves (11) circumferentially delimit an assembly (12) of blocks (14) placed in succession over the entire axial width of the tread band (8). Circumferential grooves (13) delimit the blocks (14) of an assembly (12). A ratio between a circumferential length (LI) of the blocks (14) and a width (L2) of the transverse grooves (11) is equal to or greater than about 2.

Claims

1. A motorcycle tyre, comprising: a radial carcass structure; a belt structure applied in a radially outer position with respect to the radial carcass structure; and a tread band applied in a radially outer position with respect to the belt structure; the tyre having a curvature ratio (f/C) greater than or equal to about 0.25, wherein the tread band comprises: a plurality of blocks mutually spaced so as to define a tread pattern with a void/solid ratio (1−Sb/St) smaller than 50%; transverse grooves placed in succession along a circumferential extension of the tyre and each extending substantially over an entire axial width of the tread band, wherein each transverse groove substantially extends along an axial direction, wherein two successive transverse grooves circumferentially delimit an assembly of blocks placed in succession over the entire axial width of the tread band; and circumferential grooves delimiting the blocks of the assembly, wherein a ratio of a circumferential length (L1) of the blocks to a circumferential width (L2) of the transverse grooves is equal to or greater than about 2.

2. The motorcycle tyre according to claim 1, wherein the void/solid ratio ranges from about 25% to smaller than 50%.

3. The motorcycle tyre according to claim 1, wherein the ratio of the circumferential length (L1) of the blocks to the circumferential width (L2) of the transverse grooves is equal to or smaller than about 4.5.

4. The motorcycle tyre according to claim 1, wherein the tyre is a front tyre and the circumferential length (L1) of the blocks is greater than or equal to about 25 mm or wherein the tyre is a rear tyre and the circumferential length (L1) is greater than or equal to about 35 mm.

5. The motorcycle tyre according to claim 1, wherein the tyre is a front tyre and the circumferential length (L1) of the blocks is smaller than or equal to about 40 mm or wherein the tyre is a rear tyre and the circumferential length (L1) is smaller than or equal to about 50 mm.

6. The motorcycle tyre according to claim 1, wherein a ratio of a circumferential length (L1) of one of the blocks of the plurality of blocks to a height (h1) of the block is greater than or equal to about 3.

7. The motorcycle tyre according to claim 6, wherein the tyre is a front tyre and the height (h1) of the block is greater than or equal to about 6 mm or wherein the tyre is a rear tyre and the height (h1) of the block is greater than or equal to about 8.5 mm.

8. The motorcycle tyre according to claim 7, wherein the tyre is a front tyre and the height (h1) of the block is smaller than or equal to about 8.5 mm or wherein the tyre is a rear tyre and the height (h1) of the block is smaller than or equal to about 11 mm.

9. The motorcycle tyre according to claim 6, wherein the tyre is a front tyre and the ratio of the circumferential length (L1) of one of the blocks of the plurality of blocks to the height (h1) of the block is smaller than or equal to about 5.5 or wherein the tyre is a rear tyre and the ratio of the circumferential length (L1) of one of the blocks of the plurality of blocks to the height (h1) of the block is smaller than or equal to about 5.

10. The motorcycle tyre according to claim 9, wherein the tyre is a front tyre and the height (h1) of the block is greater than or equal to about 6 mm or wherein the tyre is a rear tyre and the height (h1) of the block is greater than or equal to about 8.5 mm.

11. The motorcycle tyre according to claim 10, wherein the tyre is a front tyre and the height (h1) of the block is smaller than or equal to about 8.5 mm or wherein the tyre is a rear tyre and the height (h1) of the block is smaller than or equal to about 11 mm.

12. The motorcycle tyre according to claim 1, wherein at least some of the circumferential grooves delimiting the blocks of the assembly are at least partially misaligned with respect to their respective circumferentially successive circumferential grooves delimiting the blocks of an adjacent assembly of blocks.

13. The motorcycle tyre according to claim 12, wherein at least some of the circumferentially successive circumferential grooves, at least partially misaligned, have a gap (L5) greater than or equal to about 4 mm.

14. The motorcycle tyre according to claim 12, wherein at least some of the circumferentially successive circumferential grooves, at least partially misaligned, have a gap (L5) smaller than or equal to about 6.5 mm.

15. The motorcycle tyre according to claim 1, wherein the tyre is a rear tyre and has a ratio of curvature height to total height (f/H) greater than or equal to about 0.4 or wherein the tyre is a front tyre and has a ratio of curvature height to total height (f/H) greater than or equal to about 0.4.

16. The motorcycle tyre according to claim 1, wherein the belt structure is at zero degrees.

17. The motorcycle tyre according to claim 1, wherein at least one portion of the tread band comprises a vulcanised elastomeric material obtained by vulcanising an elastomeric blend comprising 100 phr of at least one elastomeric polymer, from 30 to 130 phr of at least one reinforcing filler comprising at least 55% of an inorganic material chosen from silica alumina, silicates, hydrotalcite, calcium carbonate, kaolin, titanium dioxide, and mixtures thereof.

Description

DESCRIPTION OF THE DRAWINGS

(1) Such description will be set forth hereinbelow with reference to the enclosed drawings, provided only for explanatory purposes and hence non-limiting, in which:

(2) FIG. 1 schematically shows a radial section of a rear motorcycles tyre according to the present invention;

(3) FIG. 2 shows a perspective view of a portion of the tread band of the tyre of FIG. 1;

(4) FIG. 3 shows the extension of a wider portion of the tread band of the tyre of FIGS. 1 and 2 on a plane perpendicular to the equatorial plane of the tyre;

(5) FIG. 4 schematically shows a radial section of the tread band according to the line IV-IV of FIG. 3;

(6) FIG. 5 shows a perspective view of a portion of the tread band of a front motorcycles tyre according to the present invention;

(7) FIG. 6 shows the extension of a wider portion of the tread band of the tyre of FIG. 5 on a plane perpendicular to the equatorial plane of the tyre;

(8) FIG. 7 schematically shows a radial section of the tread band according to the line VII-VII of FIG. 6;

(9) FIG. 8 illustrates a comparison radar chart.

DETAILED DESCRIPTION

(10) With reference to FIGS. 1-7, reference number 1 overall indicates a tyre for wheels of motorcycles. The tyre 1 of FIGS. 1-4 is a rear tyre. The tyre 1 of FIGS. 5-7 is a front tyre. The tyres 1 illustrated are motorcycles tyre defined as “big enduro” or “dual purpose” with medium-large engine capacity (e.g. about 600-1200 cm.sup.3 or even greater) and/or medium-high power (e.g. 70 cv or greater) and motorcycle mass in driving position for example about 150 Kg or greater. In association with the tyre 1, an equatorial plane “X-X” and a rotation axis (not shown in the figures) are defined. The following are also defined: a circumferential direction arranged according to the rotation sense of the tyre 1 and an axial direction perpendicular to the equatorial plane “X-X” and/or parallel to the rotation axis.

(11) The tyre 1 comprises a carcass structure 2 formed by at least one carcass layer 3 comprising a plurality of reinforcement elements (cords).

(12) The carcass structure 2 is typically covered on its inner walls by a sealing layer 100, or so-called “liner”, essentially constituted by a layer of air-impermeable elastomeric material, adapted to ensure the hermetic seal of the tyre 1 itself once inflated.

(13) The reinforcement elements, included in the carcass layer 3, preferably comprise textile cords made of fibrous material, not illustrated.

(14) The carcass structure 2 is of radial type, i.e. the cords of said at least one carcass layer 3 are arranged substantially parallel to each other and in radial sense, i.e. according to an angle comprised between 70° and 110°, more preferably between 80° and 100°, with respect to the circumferential direction.

(15) The carcass layer 3 is shaped according to a substantially toroidal configuration and is engaged, by means of opposite circumferential edges 3a thereof, with at least one reinforcement annular structure.

(16) In particular, the opposite circumferential edges 3a of the carcass layer 3 can be turned up around the reinforcement annular structures, each comprising one or more metallic annular bead cores 4 and a tapered elastomeric filler 5 which occupies the space defined between the carcass layer 3 and the corresponding turned-up circumferential edge 3a of the carcass layer 3.

(17) The zone of the tyre 1 comprising the metallic annular bead core 4 and the elastomeric filler 5 forms the so-called bead 9 intended for anchoring the tyre 1 on a corresponding mounting rim, not illustrated.

(18) In one embodiment, the carcass layer 3 is made by means of fitting together a plurality of elastomeric material strips reinforced by the aforesaid cords.

(19) In a non-illustrated embodiment, the carcass layer 3 has its opposite lateral edges associated, without turn-up, with particular reinforcement annular structures provided with two annular inserts. A filler made of elastomeric material can be arranged in axially outer position with respect to the first annular insert. A second annular insert can instead be arranged in axially outer position with respect to the end of the carcass layer 3. Finally, in axially outer position with respect to said second annular insert, and not necessarily in contact therewith, a further filler can be provided that terminates the making of the reinforcement annular structure.

(20) A belt structure 6 is circumferentially applied on the carcass structure 2 in radially outer position, such belt structure 6 comprising at least one belt layer 6a typically formed by textile or metallic rubber-covered cords.

(21) Preferably, the belt structure is of the type at zero degrees, i.e. the belt layer 6a is made by means of cords substantially arranged parallel and side-by-side to form a plurality of coils. Such coils are substantially oriented according to the circumferential direction (typically with an angle between 0° and 5°), such direction normally being termed “at zero degrees” with reference to its lying position with respect to the circumferential direction of the tyre 1.

(22) Preferably, the belt layer 6a typically termed at “zero degrees” can comprise axially adjacent windings of a single cord or of a strip-like element of rubber-covered fabric comprising axially adjacent cords.

(23) The cords of the belt layer 6a at zero degrees are typically metallic cords, made by means of steel wires with high carbon content, i.e. steel wires with a carbon content of at least 0.6-0.7%. Preferably such metallic cords have high elongation (HE).

(24) In a different embodiment, the belt structure provides for two or more radially superimposed belt layers, each layer constituted by elastomeric material reinforced with cords arranged parallel to each other. The layers are arranged in a manner such that the cords of a first belt layer are obliquely oriented with respect to the equatorial plane of the tyre, while the cords of the radially adjacent belt layer also have oblique but cross orientation with respect to the cords of the first layer (the so-called “cross belt”) and the same holds true for possible other belt layers. The cross belt typically provides for textile cords.

(25) For the purpose of improving the adhesion between the belt structure 6 and the carcass structure 2, an adhesion layer 7 made of elastomeric material can be provided, interposed between the two aforesaid structures.

(26) In a non-illustrated embodiment, the belt structure 6 can be constituted by at least two radially superimposed layers. Such layers are arranged in a manner such that the cords of the first belt layer are obliquely oriented with respect to the circumferential direction of the tyre 1, while the cords of the second belt layer also have oblique orientation, but are substantially symmetrically cross with respect to the cords of the first layer. The cords of the first belt layer delimit, with the cords of the second belt layer, an angle equal to or greater than about 20°. The cords of the first belt layer delimit and/or the cords of the second belt layer delimit, with a circumferential direction of the tyre, an angle equal to or greater than about 10°. Such belt structure 6 is termed cross ply and is preferably employed for front tyres 1 (an example of which is illustrated in FIGS. 5-7).

(27) A tread band 8 is circumferentially superimposed on the belt structure 6; on such tread band 8, following a moulding operation executed simultaneously with a step of vulcanisation of the tyre 1, circumferential and transverse grooves are typically obtained, arranged to delimit a plurality of blocks according to geometries detailed in the course of the present description.

(28) According to a preferred embodiment, the tread band 8 (as with other components of the tyre) is made by means of an elastomeric material comprising 100 phr of at least one elastomeric diene polymer.

(29) With “elastomeric polymer” it is intended a natural or synthetic polymer which at ambient temperature can be repeatedly stretched to at least double its original length and which after removal of the traction load returns immediately and with force to its approximately original length (definition according to ASTM, E8 committee, Philadelphia 1976).

(30) With “diene polymer” it is intended a polymer or copolymer which derives from the polymerisation of one or more different monomers, among which at least one of these is a conjugate diene (conjugated diolefin).

(31) The elastomeric composition for tyres according to the present invention comprises at least 10 phr of at least one reinforcing filler.

(32) Preferably, the composition comprises at least 20 phr or 30 or phr 40 phr or 50 phr of at least one reinforcing filler.

(33) Preferably, the composition comprises no more than 150 phr or 140 or phr or 130 phr or 120 phr or 110 phr or 100 phr of at least one reinforcing filler.

(34) Preferably, said reinforcing filler is an inorganic material selected from silica alumina, silicates, hydrotalcite, calcium carbonate, kaolin, titanium dioxide and/or mixtures thereof.

(35) Optionally, the reinforcing filler further comprises carbon black.

(36) Preferably, said reinforcing filler comprises carbon black in the elastomeric composition in a quantity comprised between 1 phr and 50 phr, preferably between about 5 phr and about 40 phr.

(37) Preferably the elastomeric material for tread comprises silica as substantially prevalent filler, preferably in a percentage equal to or greater than 50% of the overall filler, preferably greater than 60%, preferably equal to or smaller than 98%. The elastomeric material for tread, as with other tyre components, can also comprise further ingredients and additives as vulcanising system, compatibilisation plasticisers, anti-oxidants and anti-ozonants and all those ingredients known to the man skilled in the art of blends for tyres.

(38) The tyre 1 can also comprise a pair of sidewalls 10 laterally applied on opposite sides to said carcass structure 2.

(39) 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.

(40) The tyre 1 also has a maximum transverse section width “C”, defined by the distance between the laterally opposite ends “E” of the tread band 8, and a curvature height “f”, defined by the distance of the top of the tread band 8 from a line passing through said laterally opposite ends “E”, measured on the equatorial plane “X-X” of the tyre 1. The laterally opposite ends “E” of the tread band 8 can be formed with an edge.

(41) The tyre 1 has a “curvature ratio” (f/C) defined by the ratio between the curvature height “f” and the aforesaid maximum transverse section width “C”.

(42) The tyre 1 has a ratio of “curvature height to total height” (f/H) given by the ratio between the curvature height “f” and the section height “H”.

(43) The abovementioned references (“H”, “X-X”, “r”, “C”, “f”, “E”) were indicated in FIG. 1 for the rear tyre but are also identical for the front tyre of FIGS. 5-7.

(44) The rear motorcycles tyre 1 of the invention, like that illustrated in FIGS. 1-4, are intended to be mounted on rear wheels having size of the maximum chord “C” substantially comprised between 130 and 190 mm.

(45) Preferably, the curvature height “f” of the rear tyres 1 according to the invention is comprised between about 40 mm and about 60 mm.

(46) The rear tyres 1 according to the invention, have a curvature ratio “f/C” comprised between about 0.25 and about 0.35. For example, the curvature ratio “f/C” of the tyre 1 of FIG. 1 is about 0.26.

(47) The rear tyres 1 according to the invention have a ratio of curvature height to total height “f/H” comprised between about 0.40 and about 0.60. For example, the ratio of curvature height to total height “f/H” of the tyre 1 of FIG. 1 is about 0.43.

(48) The front motorcycles tyre 1 of the invention, like that illustrated in FIGS. 5-7, are intended to be mounted on front wheels having size of the maximum chord “C” substantially comprised between 90 and 130 mm.

(49) Preferably, the curvature height “f” of the front tyres 1 according to the invention is comprised between about 35 mm and about 60 mm.

(50) The front tyres 1 according to the invention have a curvature ratio “f/C” comprised between about 0.30 and about 0.40. For example, the curvature ratio “f/C” of the tyre 1 of FIG. 7 is about 0.38.

(51) The front tyres 1 according to the invention, have a ratio of curvature height to total height “f/H” comprised between about 0.40 and about 0.60. For example, the ratio of curvature height to total height “f/H” of the tyre 1 of FIG. 7 is about 0.53.

(52) As previously mentioned, the tyre 1 according to the invention is of knobbed type, i.e. the transverse and circumferential grooves delimit a plurality of mutually spaced blocks. Such blocks define a tread pattern with a void/solid ratio comprised between about 25% and about 50%, preferably between about 28% and about 40%. Such ratio is the value complementary to one of the ratio between the total of the top surfaces of the blocks “Sb” of a specific portion of the tread pattern of the tyre 1 and the overall surface “St” of the specific portion of tread pattern (1-Sb/St).

(53) As better seen in FIGS. 2, 3, 5 and 6, the tyre 1 according to the invention (front and rear) has a tread band 8 with transverse grooves 11 placed in succession along the circumferential extension of the tyre 1 itself. Each of the transverse grooves 11 substantially extends over the entire axial width of the tread band 8. Two successive transverse grooves 11 circumferentially delimit between them an assembly of blocks 12 placed in succession over the entire axial width of the tread band 8. Preferably, each of the transverse grooves 11 mainly extends axially, in the sense that at least one plane containing the rotation axis of the tyre 1 traverses the groove without intersecting the two assemblies of blocks 12 which delimit it.

(54) Each assembly of blocks 12 is also divided into single blocks 14 by circumferential grooves 13. Such circumferential grooves 13 are interrupted by the transverse grooves 11 or, in other words, they traverse the entire assembly of blocks 12 and open into the two adjacent transverse grooves 11.

(55) As is visible in the enclosed figures, the blocks 14 can have shape and size different from each other but a ratio between a circumferential length “L1” of the blocks 14 and a width “L2” of the transverse grooves 11 is comprised between about 2 and about 4.5, more preferably between about 2.1 and about 4. In order to simplify illustration, in the enclosed FIGS. 3 and 6 the maximum circumferential length “L1” of the blocks 14 and the maximum width “L2” of the transverse grooves 11 have been indicated; preferably however the following definitions are applied.

(56) By “circumferential length of the blocks” it is intended the average size of the extension along a circumferential direction of the blocks 14. Said average size is calculated on the extension of the tread band 8 (on a plane perpendicular to the equatorial plane of the tyre 1 and tangent to the maximum diameter of the tyre 1). Said average size is calculated by dividing the sum of the area of the top surface of the block 14, measured on the extension of the tread band 8 on the aforesaid plane, by the maximum axial length “L3” of said block 14, measured on the extension of the tread band 8 on the aforesaid plane.

(57) By “width of a transverse groove” it is intended the average size of the extension along a circumferential direction of the transverse groove 11. Said average size is calculated on the extension of the tread band 8 on the aforesaid plane. Said average size is calculated by dividing the area of the transverse groove 11, measured on the extension of the tread band 8 on the aforesaid plane, by the axial length “L4” of said transverse groove 11, measured on the extension of the tread band 8 on the aforesaid plane, which coincides with the width of the tread band 8. Preferably, for a rear tyre 1, like that of FIGS. 2, 3 and 4, the circumferential length “L1” of the blocks 14 is comprised between about 35 mm and about 50 mm. Preferably, for a front tyre, like that of FIGS. 5, 6 and 7, the circumferential length “L1” of the blocks 14 is comprised between about 25 mm and about 45 mm. For example, the rear tyre 1 has a circumferential length “L1” of about 45 mm and a transverse width “L2” of about 15 mm (L1/L2=3). For example, the front tyre 1 has a circumferential length “L1” of about 25 mm and a transverse width “L2” of about 10 mm (L1/L2=2.5).

(58) Preferably, a height “h1” of the blocks 14 is measured from a bottom surface of the transverse grooves 11 and perpendicular to the top surface of the blocks 14. The height of the blocks 14 hence coincides with the depth of the transverse grooves 11 (FIGS. 4 and 7).

(59) A ratio between the circumferential length “L1” of one of the blocks 14 and the height “h1” of said block 14 is comprised between about 3 and about 5.5, preferably between about 3.5 and about 5.5. Preferably, said ratio between the circumferential length “L1” of one of the blocks 14 and the height “h1” of said block 14 is smaller than or equal to about 5.5 for the front tyre 1 and about 5 for the rear tyre 1.

(60) Preferably, for a rear tyre 1, like that of FIGS. 2, 3 and 4, the height “h1” of the blocks 14 is comprised between about 8.5 mm and about 11 mm. Preferably, for a front tyre 1, like that of FIGS. 5, 6 and 7, the height “h1” of the blocks 14 is comprised between about 6 mm and about 8.5 mm. For example, the rear tyre 1 has a circumferential length “L1” of about 45 mm and a height “h1” of the blocks 14 of about 10 mm (L1/h1=4.5). For example, the front tyre 1 has a circumferential length “L1” of about 30 mm and a height “h1” of the blocks 14 of about 7 mm (L1/h1=4.3).

(61) In some embodiments, the circumferential grooves 13 have a depth “h2” equal to the depth “h1” of the transverse grooves 11. In other embodiments, the circumferential grooves 13 have a depth “h2” smaller than the depth “h1” of the transverse grooves 11. For example, in a rear tyre 1, like that of FIGS. 2, 3 and 4, the circumferential grooves 13 (see in particular FIGS. 2 and 4) are less deep than the transverse grooves 11. For example, in a front tyre 1, like that of FIGS. 5, 6 and 7, at least some of the circumferential grooves 13 (see in particular FIGS. 5 and 7) are as deep as the transverse grooves 11.

(62) In addition, as better seen in FIGS. 3 and 6, at least some of the circumferential grooves 13 of an assembly 12 of blocks 14 are at least partially misaligned with respect to the respective circumferential grooves 13 of an adjacent assembly 12 of blocks 14. In other words, the circumferential grooves 13 of an assembly 12 of blocks 14 are only partially placed in front of the circumferential grooves 13 of the adjacent assemblies 12 and/or face towards the blocks 14 of the adjacent assemblies 12. The circumferential grooves 13 of assemblies 12 of adjacent blocks 14, partially misaligned, have a gap “L5” (FIG. 3), preferably comprised between about 4 mm and about 6.5 mm.

(63) As is visible in both illustrated embodiments, each block 14 has a substantially quadrilateral peripheral edge, e.g. rectangular, square or trapezoidal, with adjacent sides that delimit an angle between them comprised between about 70° and about 100°. In addition, at least one of the sides of the quadrilateral can be concave and is preferably formed by two segments which define an edge of about 170°.

(64) With specific reference to FIGS. 2, 3 and 4, the tread 8 of the illustrated rear tyre 1 has a first module “A” and a second module “B” (FIG. 3) which are repeated along the circumferential extension of the tyre 1 itself. The sequence of the two modules “A” and “B” along the circumferential extension of the tread band 8 can vary.

(65) Each of the two modules “A” and “B” comprises two circumferentially adjacent assemblies 12 of blocks 14 delimiting a respective transverse groove 11 between them. In FIG. 3, the two modules “A” and “B” are adjacent and in addition are separated from each other by a transverse groove 11. The circumferential length “L1” of the blocks 14 of the second module “B” is greater than the circumferential length “L1” of the blocks 14 of the first module “A” and the width “L2” of the transverse groove 13 of the first module “A” is smaller than the width “L2” of the transverse groove 13 of the second module “B”.

(66) The first module “A” comprises a first assembly 12 formed by three blocks 14. A central block 14 is placed astride the equatorial plane “X-X” of the tyre 1 and has rectangular shape. A lateral block 14 is arranged on each of the two sides of the central block 14, separated by a circumferential groove 13 and has a trapezoidal shape, with a greater base of the trapezoid axially directed towards the equatorial plane “X-X” of the tyre 1.

(67) The first module “A” comprises a second assembly 12 formed by six blocks 14. Two rectangular central blocks 14 are placed at the sides of the equatorial plane “X-X” of the tyre 1 and separated from each other by a circumferential groove 13.

(68) Two lateral blocks 14 are arranged on each of the two sides of the two central blocks 14, separated by respective circumferential grooves 13 and each have a trapezoidal shape, with a greater base of the trapezoid axially directed away from the equatorial plane “X-X” of the tyre 1. Also the two lateral blocks 14 are separated from each other by a circumferential groove 13.

(69) The two central blocks 14 of the second assembly 12 have an overall axial width smaller than an axial width of the single central block 14 of the first assembly 12.

(70) The second module “B” also comprises a first and a second assembly 12 with blocks 14 similar to those described for the first assembly 12 but with different size, as specified above.

(71) It follows that assemblies 12 of blocks 14 comprising three blocks 14 are circumferentially alternated with assemblies 12 of blocks 14 comprising six blocks 14. In addition, assemblies 12 of blocks 14 comprising a single central block 14 are circumferentially alternated with assemblies 12 of blocks 14 comprising two central blocks 14. In addition, assemblies 12 of blocks 14 comprising the lateral blocks 14 with the greater base of the trapezoid axially directed towards the equatorial plane “X-X” are circumferentially alternated with assemblies 12 of blocks 14 comprising the lateral blocks 14 with the greater base of the trapezoid axially directed away from said equatorial plane “X-X”.

(72) The form of the lateral blocks 14 determines a curvature of the transverse grooves 11. The transverse grooves 11 have a wavy or curved middle line “M”, intended as site of the points equidistant from the blocks 14 of the two assemblies 12 which delimit such grooves. As is visible in FIG. 3, the middle lines “M” of two circumferentially successive transverse grooves 11 have curvatures directed towards opposite sides.

(73) Also the tread 8 of the front tyre 1 of FIGS. 4, 5 and 6 has a first module “C” and a second module “D” which are repeated along the circumferential extension of the tyre 1 itself. The sequence of the two modules “C” and “D” along the circumferential extension of the tread band 8 can vary.

(74) Each of the two modules “C” and “D” comprises two assemblies 12 of circumferentially adjacent blocks 14 delimiting a respective transverse groove 11 between them. In FIG. 6, the two modules “C” and “D” are adjacent and also separated from each other by a transverse groove 11. The circumferential length “L1” of the blocks 14 of the second module “D” is greater than the circumferential length “L1” of the blocks 14 of the first module “C” and the width “L2” of the transverse groove 13 of the first module “C” is smaller than the width “L2” of the transverse groove 13 of the second module “D”.

(75) The first module “C” comprises a first assembly 12 formed by four blocks 14. Two trapezoidal central blocks 14 are placed at the sides of the equatorial plane “X-X” of the tyre 1 and separated from each other by a circumferential groove 13. A lateral block 14 is arranged on each of the two sides of the central blocks 14, separated by a circumferential groove 13 and has a substantially rectangular shape.

(76) The first module “C” comprises a second assembly still formed by four blocks 14. Two rectangular central blocks 14 are placed at the sides of the equatorial plane “X-X” of the tyre 1 and separated from each other by a circumferential groove 13. A lateral block 14 is arranged on each of the two sides of the central blocks 14, separated by a circumferential groove 13 and has a trapezoidal shape, with a greater base of the trapezoid axially directed towards the equatorial plane “X-X” of the tyre 1.

(77) The two central blocks 14 of the second assembly have an overall axial width greater than an axial width of the two central blocks 14 of the first assembly.

(78) The second module “D” also comprises a first and a second assembly 12 with blocks 14 similar to those described for the first assembly 12 but with different size, as specified above.

(79) It follows that assemblies 12 of blocks 14 comprising two central blocks 14 having a first overall axial width are circumferentially alternated with assemblies 12 of blocks 14 comprising two central blocks 14 having a second overall axial width that is different from the first overall axial width.

(80) The form of the lateral blocks 14 determines a curvature of the transverse grooves 11. The transverse grooves 11 have a wavy or curved middle line “M”, intended as site of the points equidistant from the blocks 14 of the two assemblies 12 which delimit such grooves.

EXAMPLE

(81) The Applicant has conducted some comparative tests on tyres, as described hereinbelow.

(82) A front tyre and a rear tyre according to the invention were obtained with the characteristics reported in the following Table 1 (Tyre Set A).

(83) TABLE-US-00001 TABLE 1 Set A Set A - Invention Front tyre 120/70 R19 carcass structure Radial belt structure Zero degrees void/solid ratio 1 - Sb/St 35% Ratio: circumferential length of blocks/ 2.20 width of transverse grooves L1/L2 Ratio: circumferential length of blocks/ 3.70 height of blocks L1/h1 Curvature ratio f/C 0.33 Ratio: curvature height to total height f/H 0.57 Tread blend (BR/SBR) polymer filled with 75% by weight of silica Rear tyre 170/60 R17 carcass structure Radial belt structure Zero degrees void/solid ratio 1 - Sb/St 30% Ratio: circumferential length of blocks/ 2.50 width of transverse grooves L1/L2 Ratio: circumferential length of blocks/ 3.82 height of blocks L1/h1 Curvature ratio f/C 0.26 Ratio: curvature of height to total 0.49 height f/H Tread blend (BR/SBR) polymer filled with 76% by weight of silica E.T.R.T.O. speed codes V (up to 240 km/h)

(84) The Applicant, for the purpose of improving performances, took the following tyres as base of the comparative driving test:

(85) Set B—Pirelli for mainly road use;

(86) Set C—Pirelli for mainly off-road use.

(87) TABLE-US-00002 TABLE 2 Sets B and C Set B Set C Front tyre 120/70 R19 carcass structure Radial Radial belt structure Zero degrees Cross belts void/solid ratio 1 - Sb/St 19% 53% Ratio: circumferential NO BLOCKS 1.45 length of blocks/width of transverse grooves L1/L2 Ratio: circumferential NO BLOCKS 3.20 length of blocks/height of blocks L1/h1 curvature ratio f/C 0.33 0.29 Ratio: curvature height to 0.57 0.40 total height f/H Tread blend (BR/SBR) polymer (BR/SBR) polymer filled with 95% by filled with 100% CB weight of silica Rear tyre 170/60 R17 carcass structure Radial Radial belt structure Zero degrees Zero degrees void/solid ratio 1 - Sb/St 18% 53% Ratio: circumferential NO BLOCKS 1.30 length of blocks/width of transverse grooves L1/L2 Ratio: circumferential NO BLOCKS 2.90 length of blocks/height of blocks L1/h1 curvature ratio f/C 0.30 0.24 Ratio: curvature height 0.50 0.39 to total height f/H Tread blend DUAL 100% CB polymer COMPOUND: (BR/ (BR/SBR) SBR) polymer filled with 76% (center)- 95% (shoulder) by weight of silica E.T.R.T.O. speed codes V (up to 240 km/h) T (up to 190 km/h)

(88) Road tests were executed (ON—handling in dry and wet conditions, holding in dry and wet conditions, stability and stability at full load conditions) with a BMW R1200 GS with 2.5 bar front-2.9 bar rear pressures.

(89) Off-road tests were executed (OFF—performance, traction, handling) with a BMW R1200 GS with 1.0 bar front-1.0 bar rear pressures.

(90) The results of such tests are reported in the following comparative table (Table 3) and in the relative radar chart of FIG. 8. The results of these tests are expressed for comparison of Set A and Set B with respect to the reference Set C taken as base. The values reproduced in the following table represent an average value among those obtained in multiple test sessions.

(91) TABLE-US-00003 TABLE 3 comparative Set A Invention Set B Set C ON-Stability 110 120 100 ON-Stability at full load 110 120 100 ON-Handling in dry conditions 110 120 100 ON-Handling in wet conditions 120 140 100 ON-Holding in dry conditions 120 130 100 ON-Holding in wet conditions 120 140 100 OFF-Traction 95 70 100 OFF-Handling 110 80 100

(92) Table 3 shows that the tyres made in accordance with the present invention have on-road (ON ROAD) stability at high speeds, holding in dry conditions and handling only slightly worse than pure road tyres, hence decidedly greater than the performances offered by the known knobbed tyres for off-road use and even greater than the performances offered by the known motorcycles tyre for “big enduro” or “dual purpose” motorcycles, such as those described in the documents WO 2013/046004 and EP 2 307 208.

(93) The tyres made in accordance with the present invention have a holding in wet conditions comparable to the carved road tyres.

(94) The tyres made in accordance with the present invention have traction and handling properties off-road (OFF ROAD) that are decidedly greater than those of the abovementioned known motorcycles tyres for “big enduro” or “dual purpose” motorcycles (like those described in the documents WO 2013/046004 and EP 2 307 208). Surprisingly, the tyres according to the present invention offer a handling off-road greater than the pure knobbed tyres.

(95) The optimal on-road conduct is obtained due to the road carcass and belt structure, as well as due to the high ratio between the circumferential length of the blocks and the circumferential width of the transverse grooves and that, unexpectedly, such optimal on-road conduct is not compromised by the presence of said grooves (which positively contribute to the traction off-road).

(96) The selection of the ratio between the circumferential length of the blocks and the circumferential width of the transverse grooves allows optimising the on-road conduct compatibly with the traction off-road, and optimising the traction off-road compatibly with the on-road conduct, since the width of the grooves is such that said grooves are not stably filled with earth.

(97) The selection of the ratio between the circumferential length of the blocks and the height of the blocks allows limiting the deformation of the blocks with respect to a pure knobbed tyre—hence optimising the on-road conduct and still ensuring the effective traction off-road since the tread clings to the loose terrain.

(98) The aligned circumferential grooves allow the immediate evacuation of the mud in off-road conditions and their partial misalignment reduces the hinge effect on the profile, increasing the rigidity and ensuring the on-road performances of the tyre.