Tyre for bicycle wheels

Abstract

The present invention refers to a tyre for bicycle wheels comprising a tread band containing an anti-puncture system capable of having high resistance to the penetration of foreign bodies, simultaneously ensuring optimal handling performances. In particular the present invention regards a tyre for bicycle wheels comprising: a carcass structure; and—a tread band arranged in radially outer position with respect to the carcass structure; wherein said tread band is made by means of vulcanisation of a cross-linkable elastomeric composition comprising a reinforcement system constituted by modified silicate fibres of nanometric size and fibrillated polymer fibres of micrometric size.

Claims

1. A tyre for bicycle wheels comprising: a carcass structure; and a tread band arranged in radially outer position with respect to said carcass structure; wherein said tread band is made by vulcanisation of cross-linkable elastomeric composition comprising a reinforcement system comprising modified silicate fibres of nanometric size and fibrillated polymer fibres of micrometric size, wherein said fibrillated polymer fibres are made of polymer material with a melting temperature of at least 170° C., and wherein the tyre for bicycle wheels has a weight lower than, or equal to, 2 kg.

2. The tyre according to claim 1, wherein said modified silicate fibres have a diameter between 1 nm and 100 nm and a length lower than 10 um.

3. The tyre according to claim 1, wherein said modified silicate fibres show an aspect ratio between the length and the diameter of at least 2:1.

4. The tyre according to claim 1, wherein said modified silicate fibres are derived from silicate fibres selected from the group consisting of sepiolite fibres, palygorskite or attapulgite fibres, halloysite fibres, wollastonite fibres, organically modified thereof, and mixtures thereof.

5. The tyre according to claim 4, wherein said modified silicate fibres are derived from silicate fibres selected from the group consisting of sepiolite fibres, organically modified thereof, and mixtures thereof.

6. The tyre according to claim 5, wherein said modified silicate fibres comprise from 3.8% to 12% by weight of magnesium with respect to the weight of the fibres themselves.

7. The tyre according to claim 5, wherein said modified silicate fibres comprise amorphous silica deposited on the surface of the fibres themselves.

8. The tyre according to claim 1, wherein said fibrillated polymer fibres are selected from the group consisting of aramid fibres, polyester fibres, acrylic fibres, microfibrillated cellulose fibres, and plant fibres.

9. The tyre according to claim 1, wherein said fibrillated polymer fibres have a diameter between 5 um and 30 um and a length between about 0.05 mm and about 8 mm.

10. The tyre according to claim 1, wherein said fibrillated polymer fibres show an aspect ration between the length and the diameter higher than 30:1.

11. The tyre according to claim 1, wherein said fibrillated polymer fibres show a surface area ranging from about 0.5 m2/g to about 60 m2/g.

12. The tyre according to claim 1, wherein said crosslinkable elastomeric composition comprises: (a) 100 phr of at least one diene elastomeric polymer; (b) from 1 to 60 phr of said modified silicate fibres, (c) from 0.1 phr to 20 phr of said fibrillated polymer fibres, and (d) from 1 to 120 phr of a standard reinforcement filler.

13. The tyre according to claim 12, wherein said modified silicate fibres are present in said elastomeric composition in a quantity ranging from 3 phr to 40 phr.

14. The tyre according to claim 12, wherein said polymer fibres are present in said elastomeric composition in a quantity ranging from 0.5 phr to 10 phr.

15. The tyre according to claim 1, wherein said carcass structure comprises a carcass ply chosen from one carcass ply and multiple carcass plies.

16. The tyre according to claim 15, wherein said carcass ply comprises a plurality of reinforcement cords and the plurality of reinforcement cords are tilted, with respect to an equatorial plane of the tyre, by a first angle comprised between about 30° and about 60°, ends included.

17. The tyre according to claim 1, further comprising one or more reinforcement layers arranged in a radially inner position with respect to said tread band.

18. The tyre according to claim 17, wherein said one or more reinforcement layers are axially extended for a width section between 10% and 90% of the width of said tyre.

19. The tyre according to claim 1, wherein the carcass structure comprises a crown structure, and at the crown structure, a belt layer associated with and in radially outer position with respect to said carcass structure.

20. The tyre according to claim 1, wherein the carcass structure comprises a back-folded end flap of a carcass ply at each bead, and at each bead, a reinforced belt-like element associated with and in a radially outer position with respect to said carcass structure.

Description

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(1) Further characteristics and advantages of the tyre of the present invention will be clearer from the following detailed description of several preferred embodiments thereof, made with reference to the enclosed drawings. In such drawings:

(2) FIG. 1 is a schematic view in radial section of a tyre for racing bicycle wheel in accordance with a first embodiment of the present invention;

(3) FIGS. 2-7 show possible schematic structural schemes representative of embodiments of tyres according to the invention;

(4) FIG. 8 illustrates the graph obtained as described in example 2, which reports the progression of the puncture force with the increase of the deformation of the material for the specimens of example 1.

(5) In FIG. 1, reference number 100 overall indicates a tyre for bicycle wheels according to the present invention. The tyre can be intended to be mounted on the wheels of a racing bicycle, or off-road bicycle (mountain bike or MTB) or city bicycle (urban bike or city bike).

(6) The tyre 100 of FIG. 1 comprises a carcass structure 2 comprising a crown portion 2a preferably symmetrically arranged with respect to the equatorial plane X-X and opposite lateral portions 2b arranged on axially opposite side of the crown portion 2a.

(7) In the embodiment illustrated in the enclosed drawings, the carcass structure 2 comprises only one carcass ply 3 (single-ply tyre), but other embodiments are provided (such as those schematised in FIGS. 6 and 7) in which the carcass structure 2 comprises multiple carcass plies, preferably two (dual-ply tyre).

(8) That described below with reference to the carcass ply illustrated in the drawings is applied both to the single carcass ply of the single-ply tyre and to each carcass ply of the dual-ply tyre, except where explicitly stated otherwise.

(9) The carcass ply 3 is axially extended from a lateral portion 2b of the carcass structure 2 to the opposite lateral portion 2b.

(10) The carcass ply 3 is engaged, at its axially opposite respective end flaps 3a, with respective anchoring annular structures 4, typically termed “bead cores”.

(11) Each end flap 3a of the carcass ply 3 is back folded around a respective bead core 4.

(12) In an alternative embodiment, not illustrated, the carcass ply has its axially opposite end flaps associated without back-fold with the anchoring 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. The second annular insert is instead arranged in an axially outer position with respect to the end of the carcass layer. 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 production of the anchoring annular structure.

(13) The bead cores 4 are preferably made of textile fibres with high elastic modulus, such as aramid fibres (common name for aromatic polyamide fibres) or they are made of metal wires, such as steel wires.

(14) On the outer perimeter edge of the bead cores 4, a tapered elastomeric filler can be applied that occupies the space defined between the carcass ply 3 and the respective back-folded end flap 3a.

(15) The zone of the tyre comprising the bead core 4 and the possible elastomeric filler forms the so-called “bead”, indicated overall in FIG. 1 with 5, intended for anchoring, by means of elastically forced fitting, the tyre on a corresponding mounting rim, not illustrated.

(16) In the back-folded end flap 3a of the carcass ply 3, at each bead 5, a reinforced belt-like element 10 can be applied. Such reinforced belt-like element 10 is situated interposed between the carcass ply 3 and the rim of the wheel when the tyre is mounted on such rim.

(17) In place of the reinforced belt-like element 10, a single reinforcement cord can be used, deposited possibly upon tackifying treatment.

(18) With reference to the tyre of FIG. 1, the two flaps of the up-turns of carcass 3a are each extended to cover the crown portion 2a, being superimposed to form, with a first radially internal carcass layer, three carcass layers in the crown portion 2a.

(19) With reference to FIGS. 2-7, a reinforcement layer 6 is illustrated associated with the carcass structure 2 at the crown portion 2a, which can possibly be present in the tyre as a further anti-puncture protection thereof.

(20) In radially outer position with respect to the carcass structure 2 and, if present, with respect to the reinforcement layer 6, a tread band 7 is provided by means of which the contact of the tyre 100 with the road surface occurs.

(21) The tyre 100—if intended for racing bicycle wheels—typically has an axial size (also indicated herein as “axial extension” or “width”) preferably comprised between about 19 mm and about 38 mm, more preferably between about 19 mm and about 32 mm, still more preferably between about 23 mm and about 28 mm, ends included. The tyre 100 intended for various types of bicycles has an outer diameter (which according to the English name is expressed in inches) preferably comprised between about 24 inches and about 29 inches, more preferably comprised between about 26 inches and about 29 inches, ends included. Correspondingly, the shrinking diameter according to the ISO or E.T.R.T.O. convention is preferably equal to about 559 mm (which corresponds to an outer diameter of 26 inches for off-road bicycles (MTB), or equal to about 571 mm (which corresponds to an outer diameter of 26 inches for road racing bicycles), or equal to about 584 mm (which corresponds to an outer diameter of 27.5 inches for off-road bicycles), or equal to about 622 mm (which corresponds to an outer diameter of 28 inches for road racing bicycles or to an outer diameter of 29 inches for off-road bicycles) or equal to about 630 mm (which corresponds to a particular outer diameter of 27 inches for road racing bicycles).

(22) For example, a first embodiment of the tyre 100 of FIG. 1 has an outer diameter equal to 26 inches, a second embodiment has an outer diameter equal to 28 inches, and a third embodiment has an outer diameter equal to 29 inches.

(23) In case of tyre intended for wheels of off-road bicycles (MTB), the tyre 100 has an axial size preferably comprised between about 37 mm and about 120 mm, ends included.

(24) The tyre 100 intended for city bicycle wheels typically has an axial size preferably comprised between about 32 mm and 62 mm ends included.

(25) The tyre 100 for off-road or city bicycles has an outer diameter preferably comprised between about 26 inches and about 29 inches, ends included. Correspondingly, the shrinking diameter according to the ISO or E.T.R.T.O. convention is preferably comprised between about 559 mm and about 622 mm.

(26) For example, a first embodiment of the tyre 100 of FIG. 1 has an outer diameter equal to 26 inches (shrinking diameter equal to 559 mm), a second embodiment has an outer diameter equal to 27.5 inches (shrinking diameter equal to 584 mm) and a third embodiment has an outer diameter equal to 29 inches (shrinking diameter equal to 622 mm).

(27) The carcass ply 3 of the tyre 100 is preferably made of elastomeric material and comprises a plurality of reinforcement cords 30 arranged substantially parallel to each other. In FIGS. 2-7, the reference number 30 is associated with the set of reinforcement cords.

(28) The reinforcement cords 30 are preferably made of a textile material selected from among Nylon, Rayon, PET, PEN, Lyocell, Aramid, or combinations thereof, in one or more plies, preferably 1 or 2 plies.

(29) The reinforcement cords 30 have a diameter preferably comprised between about 0.10 mm and about 0.55 mm, more preferably between about 0.12 mm and about 0.35 mm, ends included, e.g. equal to about 0.13 mm.

(30) The reinforcement cords 30 have a linear density comprised between about 110 dtex and about 1300 dtex, more preferably between about 230 dtex and about 940 dtex, ends included, e.g. equal to about 470 dtex.

(31) Specific examples of textile materials usable for the aforesaid reinforcement cords 30 are the following:

(32) Nylon 930 dtex/1

(33) Nylon 470 dtex/1

(34) Nylon 230 dtex/1

(35) Aramid 470/1

(36) wherein the number 1 after dtex indicates the number of plies.

(37) The reinforcement cords 30 can nevertheless be made of steel, and in such case they have a diameter preferably comprised between 0.10 mm and 0.175 mm, ends included.

(38) The reinforcement cords 30 are tilted, with respect to the equatorial plane of the tyre 100, by an angle comprised between about 30° and about 60°, ends included.

(39) Preferably, in the case of single-ply tyre, the aforesaid angle is about 45°, and in such case the back-fold flaps can have tilts in the crown portion that are parallel to each other and counter-tilted in proximity to the equatorial plane with respect to the tilt of the reinforcement elements of the first carcass layer (radially more internal). In the case instead of dual-ply tyre, a first carcass ply includes a plurality of reinforcement cords tilted, with respect to the equatorial plane of the tyre, by an angle preferably comprised between about 30° and about 60°, ends included, and a second carcass ply, arranged in radially outer position with respect to the first carcass ply, includes a second plurality of reinforcement cords tilted by the same angle, with respect to said equatorial plane, on opposite sides with respect to the reinforcement cords of the first carcass ply. In this latter case, the reinforcement cords lie on respective planes tilted with respect to the rotation axis Z, thus defining a cross carcass structure.

(40) The carcass ply 3 of the tyre 100 for racing or city bicycle wheels preferably has a density comprised between about 15 TPI and about 360 TPI, more preferably between about 30 TPI, and about 300 TPI, ends included, e.g. equal to about 240 TPI.

(41) Preferably, in the case of dual-ply tyre, each carcass ply has a density comprised between about 15 TPI and about 200 TPI, more preferably between about 30 TPI and about 180 TPI, ends included, e.g. equal to about 120 TPI.

(42) The carcass ply 3 of the tyre 100 for off-road bicycle wheels (MTB) preferably has a density comprised between about 15 TPI and about 120 TPI, more preferably between about 30 TPI and about 90 TPI.

(43) Preferably, in the case of dual-ply tyre or with more than two carcass plies, each carcass ply has a density comprised between about 15 TPI and about 120 TPI, more preferably between about 30 TPI and about 90 TPI.

(44) The tyre 100 illustrated in FIG. 1 does not comprise reinforcement layers, but different embodiments can be provided comprising a reinforcement layer as in the structures illustrated in FIGS. 2-7 or comprising more than one reinforcement layer.

(45) The reinforcement layer 6 is axially extended on the crown portion 2a of the carcass structure 2 for a predetermined width section.

(46) Preferably, such width is lower than the width of the tyre 100. More preferably, in the tyre 100 of FIG. 1 such width is comprised between 20% and 80% of the width of the tyre 100, still more preferably between 30% and 70% of the width of the tyre 100, still more preferably between 40% and 65% of the width of the tyre 100, ends included, while in the tyre for off-road bicycles (MTB) such width is comprised between 30% and 90% of the width of the tyre 100, still more preferably between 40% and 80% of the width of the tyre 100, still more preferably between 60% and 70% of the width of the tyre 100, ends included.

(47) For example, in a tyre 100 for racing bicycle wheels having axial size comprised between 19 and 38 mm, the width of the reinforcement layer 6 is equal to at least 8 mm. Preferably, such width is lower than 24 mm.

(48) For example, in a tyre 100 for off-road bicycle wheels (MTB) having axial size comprised between 50 mm and 70 mm, the width of the reinforcement layer 6 is equal to at least 20 mm. Preferably, such width is lower than 60 mm.

(49) The tread band 7 is made with a cross-linkable elastomeric composition comprising a reinforcement system constituted by modified silicate fibres of nanometric size and fibrillated polymer fibres of micrometric size as previously described.

(50) The tread band 7 is extended axially and in radially outer position with respect to the crown structure 2a and, if present, with respect to the reinforcement layer 6 for a width section which can be lower than or equal to that of the crown structure 2a or of the reinforcement layer 6.

(51) The weight of the tyre 100 for racing bicycle wheels is lower than about 350 g, preferably lower than, or equal to, about 250 g.

(52) The weight of the tyre 100 for city bicycle wheels is higher than about 250 g, preferably higher than, or equal to, about 350 g.

(53) The weight of the tyre 100 for off-road bicycle wheels is higher than, or equal to, about 300 g, more preferably higher than, or equal to, about 350 g.

(54) In a tyre intended for a wheel for off-road bicycle, the tread band 7 comprises a plurality of blocks.

(55) The reinforcement layer 6 is made of elastomeric compound which can be reinforced with the reinforcement system as described for the tread band or typical reinforcement fillers like carbon black and/or silicates, known to the man skilled in the art.

(56) Preferably, the building of the tyre 100 occurs according to processes known to the man skilled in the art.

(57) FIGS. 2-7 illustrate different tyre structure schemes.

(58) In the structural scheme of FIG. 2, the end flaps 3a of the carcass ply 3 are axially spaced from each other and are situated in axial positions different from that of the reinforcement layer 6. In the specific example of FIG. 2, on the back-folded end flap 3a of the carcass ply 3, the reinforced belt-like element 10 is applied—which however does not have to be present.

(59) FIGS. 3-5 schematically show possible embodiments of a single-ply tyre in accordance with the present invention.

(60) Such embodiments differ from that of FIG. 2 due to the fact that the end flaps 3a are partially superimposed on each other at the tread 7, and due to whether or not they comprise the reinforcement layer 6.

(61) In the embodiments of FIGS. 2-5, in proximity to the beads 5 and on the back-folded end flap 3a of the carcass ply 3, the reinforced belt-like element 10 is applied—which however does not have to be present.

(62) FIGS. 6 and 7 schematically show possible embodiments of a dual-ply tyre in accordance with the present invention.

(63) In the embodiment of FIGS. 6 and 7, both the carcass plies 300, 301 have the respective opposite end flaps 300a, 301a back-folded around the bead cores 4, axially spaced from each other and in axial positions different from that of the tread 7.

(64) The embodiments of FIGS. 6 and 7 differ from each other due to whether or not they comprise the reinforcement layer 6.

(65) The present invention has been described with reference to several preferred embodiments. Various modifications can be made to the above-described embodiments, remaining however within the protective scope of the invention as defined by the following claims.

(66) In an alternative embodiment (not illustrated), the tyre for bicycle wheels can comprise a carcass structure 2 of radial type with reinforcement elements arranged tilted with respect to the equatorial plane in proximity to the same equatorial plane, by an angle higher than 65°, preferably comprised between 70° and 90°, said tyre being provided with a structure or belt layer radially external with respect to the so-called zero degree carcass structure comprising reinforcement elements with substantially circumferential orientation, i.e. arranged with tilt lower than 30°, preferably lower than 20° with respect to the circumferential direction perpendicular to the rolling axis of the tyre.

(67) In such structure, the belt layer is formed by helically winding, in axial direction and with preferably constant winding pitch, a single reinforcement cord on the crown portion 2a of the carcass structure 2 according to a winding direction oriented, with respect to the equatorial plane X-X, at an angle comprised between about 0° and about 30°, ends included.

(68) The present invention will be further illustrated hereinbelow by means of a number of examples, which are merely provided for exemplifying purposes and without any limitation of this invention.

EXAMPLE 1—PREPARATION TEST

(69) The elastomeric compositions for tread band NP (normal production), 1(c) and 2(c) (comparison) and 3(i) (invention), which comprise the different reinforcement fillers in the quantities indicated in table 1, were prepared as follows (the quantities of the various components are provided in phr).

(70) All the components, except for sulfur, retardant and accelerant (CBS), were mixed together in an internal mixer (Pomini PL 1.6 model) for about 5 minutes (first step). As soon as the temperature has reached 145+5° C., the elastomeric composition was unloaded. The sulfur, the retardant and the accelerant (CBS) were then added and the mixing was executed in an open roller mixer (second step).

(71) TABLE-US-00001 TABLE 1 NP 1(c) 2(c) 3(i) Natural rubber 50.00 50.00 50.00 50.00 Synthetic rubber 68.75 68.75 68.75 68.75 Fibrillated polymer fibres — 3.00 — 3.00 Modified silicate fibres — — 15.00 15.00 Silica 50.00 50.00 35.00 35.00 Hydrocarbon resin 3.00 3.00 3.00 3.00 Stearic acid 2.00 2.00 2.00 2.00 TESPT 4.50 4.50 4.50 4.50 Zinc oxide 2.50 2.50 2.50 2.50 Wax 2.00 2.00 2.00 2.00 6PPD 3.00 3.00 3.00 3.00 TBBS 2.50 2.50 2.50 2.50 Sulfur 1.20 1.20 1.20 1.20 Natural rubber: STR 20 P 93, SRI Trang Agroindustry; Synthetic rubber: S-SBR - SLR 4630 Styron Sprintan ®polymer extended with 37.5 phr of oil for each 100 phr of dry elastomeric polymer (68.75 phr of S-SBR extended oil equals 50 phr of Styrene Butadiene elastomer) Fibrillated polymer fibres: Kevlar ® Pulp, DuPont ® Modified silicate fibres: Pangel S9 modified as described in example 9 of the Italian patent application No. 102016000108318 filed on 26 Oct. 2016; Silica: precipitated synthetic amorphous silica Zeosil ® 1165 MP; Hydrocarbon Resin: Novares ® TT30; Stearic Acid: Sogis; TESPT: bis[3-(triethoxysilyl)propyl]tetrasulfide; Zinc Oxide: Zincol Ossidi; Wax: Antilux ® 654 microcrystalline wax; 6PPD: N-(1,3-dimethylbutyl)-N′-phenyl-phenylene-diamine; TBBS: N-tertbutyl-2-benzothiazyl sulfenamide (Vulkacit ® NZ); Sulfur: Redball Superfine, International Sulphur Inc.

EXAMPLE 2—ANTI-PUNCTURE TEST

(72) By using the compounds of table 1, rubber specimens were attained with dimensions 200×200×2 mm thickness; such specimens were vulcanised at 170° C. for 10 minutes, and subjected to a puncture test according to the standard DIN EN 14477, adapted in the test conditions, as expressed hereinbelow.

(73) Such test allows evaluating the resistance to perforation of a material by subjecting it to the action of a penetrator (a needle with 0.8 mm diameter), which penetrates the specimen at constant speed. The test is carried out with the aid of a dynamometer capable of adjusting the applied force (measured in N at different penetration depths) and the elastic deformation of the material (measured in mm).

(74) Said applied force is therefore indicative of the resistance of the material to the penetration of a foreign body (the material is more resistant the higher the value of the force); and said elastic deformation is an expression of the capacity of the material to absorb the penetration of a foreign body (the material is more elastic the higher the value of said deformation given the same force).

(75) The tests were executed in climate-controlled environment at a controlled temperature of 23°±2° C. The specimens were climate-controlled for 48 hours before the test.

(76) The following test conditions were used: test speed=50 mm/minute; initial distance between the tip of the penetrator and the specimen-holder=10 mm; applied pre-load=0.5 N.

(77) Tests were carried out on 5 specimens and the average values obtained are reported in the following Table 2.

(78) TABLE-US-00002 TABLE 2 Specimen Force (N) @2 mm Force (N) @3 mm NP 4.07 6.24 1(c) 7.02 12.04 2(c) 3.61 5.98 3(i) 5.90 10.84

(79) The data reported in Table 2 show for specimen 2(c) a behaviour that does not differ—if not for the worse—from that of the reference specimen NP. The puncture force values for specimen 2(c), both at 2 and at 3 mm, are in fact lower than those of the reference specimen NP. On the contrary, specimen 1(c) showed much higher puncture force values, indicative of a high resistance of the material to puncture.

(80) Surprisingly, the specimen 3(i) of the present invention showed a behaviour very similar to that of specimen 1(c) even if the presence of modified silicate fibres would make one assume that a worsened behaviour would be encountered. Therefore, it can be assumed that small quantities of fibrillated micrometric polymeric fibres are sufficient for ensuring high anti-puncture performances.

(81) The graph shown in FIG. 8 reports the progression of the puncture force with the increase of material deformation. The graph, in accordance with the data reported in Table 2, shows very close curves for the specimens NP (curve A) and 2(c) (curve C) and for specimens 1(c) (curve B) and 3(i) (curve D).

(82) The obtained results demonstrate a greater resistance to perforation encountered in the specimens containing Kevlar® Pulp, 1(c) and 3(i), which undergo deformations decidedly lower than those of the specimens NP and 2(c), simultaneously requiring a greater puncture force in order to cause the same deformation.

EXAMPLE 3—STATIC AND DYNAMIC MECHANICAL PROPERTIES

(83) The static mechanical properties (CR rupture load, AR elongation at break) according to the standard UNI 6065 were measured on the specimens of the elastomeric materials described in example 2.

(84) The dynamic mechanical properties E′ and Tan delta were measured, on the same specimens, by using a dynamic Instron model 1341 device in traction-compression mode according to the following methods. A test piece of crosslinked material (170° C. for 10 minutes)—having cylindrical shape (length=25 mm; diameter=14 mm), preloaded to compression up to a longitudinal deformation of 25% with respect to the initial length and maintained at the predetermined temperature (0° C., 23° C. or 40° C.) for the entire duration of the test—was subjected to a dynamic sinusoidal stress having an amplitude of ±3.5% with respect to the pre-load length, with a frequency of 100 Hz.

(85) The dynamic mechanical properties are expressed in terms of values of dynamic elastic modulus (E′) and Tan delta (loss factor). The Tan delta value was calculated as ratio between the viscous dynamic modulus (E″) and the elastic dynamic modulus (E′).

(86) The Tan delta values at 0° C. are predictive of the behaviour of the tyre in wet road surface conditions, those at 23° C. of the behaviour in normal conditions on dry road surface, and those at 40° C. of the behaviour in extreme handling conditions (e.g. fast descents). The Tan delta value at ambient temperature is also able to provide indications with regard to the rolling resistance of the tyre.

(87) The results obtained from the aforesaid determinations are reported in the following Table 3, with values referred to those obtained on the reference specimen NP, normalised to 100.

(88) TABLE-US-00003 TABLE 3 NP 1(c) 2(c) 3(i) STATIC MECHANICAL PROPERTIES CR [MPa] 100 116 100 102 AR [%] 100 128 91 111 DYNAMIC MECHANICAL PROPERTIES E′ 0° C. [Mpa] 100 103 100 98 Tan Delta 0° C. 100 94 89 87 E′ 23° C. [Mpa] 100 102 102 100 Tan Delta 23° C. 100 100 84 84 E′ 40° C. [Mpa] 100 103 100 103 Tan Delta 40° C. 100 104 82 85

(89) The results relative to the static mechanical properties demonstrated a clearly greater resistance of the compound containing fibrillated polymer fibres (specimen 1(c)), with respect to that of normal production NP. The specimen 2(c), containing modified silicate fibres, instead showed increased fragility, even with respect to the specimen NP. Finally, the compound containing the reinforcement system of the present invention showed intermediate resistance, improved with respect to the compound of normal production.

(90) The laboratory tests on the dynamic properties showed discouraging hysteresis values for specimen 1(c) containing Kevlar® Pulp. In fact, with respect to specimen NP, specimen 1(c) showed an increase of the Tan delta values at high temperatures and simultaneously a decrease of the values at 0° C. This suggests high rolling resistance and an overall worsening of the handling of tyres comprising a tread band containing compounds of type 1(c), which have also shown the highest anti-puncture performances among the tested specimens.

(91) The hysteresis values obtained for specimen 2(c), containing modified sepiolite, were clearly lower than those of the specimen NP, at all the tested temperatures. Surprisingly, the hysteresis values obtained for specimen 3(i), containing the reinforcement system of the present invention, resulted very similar to those of specimen 2(c) notwithstanding the presence of fibrillated polymer fibres (Kevlar® Pulp) in the compound.

(92) Although the values at 23° C. suggested for both specimens 2(c) and 3(i) an improved rolling resistance with respect to specimen NP, the Tan delta values at 0° C. for such specimens, and in particular for specimen 3(i), were predictive of an overall worsened handling for tyres comprising a tread band containing such compounds with respect to those of normal production, above all on wet surface.

EXAMPLE 4—HANDLING TEST

(93) Even if the results of the tests on the dynamic mechanical properties predicted worsened handling for all the tested compounds with respect to those of normal production, the Applicant in any case decided to carry out handling tests on tyres comprising a tread band containing compounds of type 3(i). The material containing the reinforcement system of the present invention, constituted by modified silicate fibres and fibrillated polymer fibres, in fact showed improved anti-puncture and rolling resistance properties, with respect to that of normal production.

(94) Racing tyres for bicycles were therefore prepared, with dimensions 622 mm×25c, according to the structure illustrated in FIG. 4 comprising a tread band of elastomeric material according to the compounds NP (reference) and 3(i) (invention) described in example 1.

(95) The carcass structure provided for a rubber-covered carcass ply of 0.3 mm total thickness made of nylon 125 TPI—235 Dtex, equipped with a belt layer made of a square anti-puncture fabric (nylon 20 TPI weft/aramid 40 TPI 470 warp), aramid bead cores and two anti-abrasive square rubber-covered fabrics at the edges. The tyres provided with tread band containing compound NP and 3(i) had average weight of 223 g.

(96) The racing tyres thus formed were mounted on a Cannondale Caad12 Disk racing bicycle and the riding tests were carried out in dry road surface conditions at an average temperature of 31° C., and wet road surface conditions at an average temperature of 14° C. The obtained results are reported in Tables 4 and 5, respectively.

(97) For the purpose of evaluating the behaviour of the tyre, the tester simulated several characteristic manoeuvres and then evaluated the behaviour of the tyre, and assigned a score as a function of the performance of the tyre during said manoeuvre.

(98) Tables 4 and 5 summarise the tester scores sheet for the controllability of the tyres. The results of these tests are expressed by means of an evaluation scale that represents the subjective opinion expressed by the tester, by means of a score system. The values reproduced in the following table represent an average value from among those obtained in several test session (5-6 tests, for example). The results are reported for comparison with those recorded for the tyres provided with tread band containing compound NP.

(99) −−=definitely worsened; −=worsened; 0=equal; +=improved; ++=definitely improved.

(100) TABLE-US-00004 TABLE 4 TESTS IN DRY ROAD SURFACE CONDITIONS RIDING Straight stability 0 Curve stability ++ Precision ++ Contact sensation ++ Safety sensation ++ Controllability ++ Entering a curve while braking ++ Homogeneity/progressivity + Centring in a curve + Predictability at the limit (atl) ++ COMFORT Absorption/responsiveness on 0 bumpy road Handling recovery + PERFORMANCES Combined adherence + Average +

(101) TABLE-US-00005 TABLE 5 TESTS IN WET ROAD SURFACE CONDITIONS RIDING Heating 0 Draining 0 Contact sensation + Safety sensation + Controllability + Homogeneity/progressivity 0 COMFORT Absorption 0 PERFORMANCES Perceived chemical adherence 0 ADHERENCE Traction during braking 0 Traction during acceleration 0 Average 0/+

(102) Surprisingly, the tyres comprising a tread band containing the compound 3(i) of the present invention have shown improved handling in the tests on dry road surface, and comparable if not improved handling on wet road surface with respect to the tyres of normal production.