MOTOR-CYCLE RADIAL TYRE

Abstract: A motor-cycle tyre (1) comprising a ground contacting tread (2) reinforced between its edges (3, 4) by a breaker assembly and having in its normally inflated fitted condition a camber value C/L of between 0.5 and 0.7, a reinforcing carcass ply (14) extending radially inside the breaker assembly and between two bead regions (10, 11) and wrapped in each bead region around an annular bead core (12, 13) from the axial inside to the outside to form carcass ply turn-ups (15, 16) and between the tread edges (3, 4) and bead regions (10, 11), tyre sidewalls (8, 9) wherein the breaker assembly comprises two breaker plies (5, 7) comprising reinforcing cords oppositely inclined with respect to the circumferential direction of the tyre characterised in that the tread comprises two different rubber compounds, the first rubber compound extending in a continuous first layer between the tread edges (3, 4) and the second rubber compound being disposed in a second layer radially outwardly of the layer of the first rubber compound to form the tread running surface in the central portion of the tread.

Description: MOTOR-CYCLE RADIAL TYRE This invention relates to radial motor-cycle tyres and m particular but not exclusively to high performance or race motor-cycle tyres . Such tyres utilise very wide treads which in transverse cross-section are sharply curved to provide gooα contact witn the roaα surface when the motor-cycle is steeply ban eα in cornering. Maintenance of a consistent ground contact area or 'tyre footprint' under all conditions is a major problem m determining general venicle handling. Of particular importance in race motor-cycle tyres of raαial construction is the provision of high cornering power with the good stability to maximise cornering speeds under race conditions. Present radial motor-cycle race tyres have short sidewalls which extend to tne tread edges raαially ana axially outwardly from the tyre beads. The Deads proviαe engagement to the wheelrim on tapereα oeaα seats. The siαewalls are reinforced oy radιa_. carcass plies wnich wnen tensioneα by tne inflation pressure act together with sidewall geometry to provide location of the curved tread regions to withstand cornering forces . The sharply curved tread region of the tyre is specially reinforced by a reinforcing breaker to give the required structural rigidity to allow for banking over of the motorcycle when cornering whilst giving sufficient flexibility to allow localised tread flattening in the ground contact patch for good road grip. Such tyres however, due to their uniform tread structures, do not provide fully optimum performance with regard to tread durability. It tnerefore an ooject of the present invention is to improve tne properties of such tyres. According to one aspect of the present invention a motor-cycle tyre comprises a ground contacting treaα reinforced between its edges by a breaker assembly and having m its normally inflated fitted condition a camber value C/L of between 0.5 and 0. " , a reinforcing carcass ply extending radially inside the breaker assembly and between two bead regions and wrapped in each bead region around an annular bead core from the axial inside to the outside to form carcass ply turn-ups and between the tread edges and bead regions, tyre sidewalls wherein the breaker assembly comprises two breaker plies comprising reinforcing cords oppositely inclined with respect to the circumferential direction of the tyre characterised in that the tread comprises two different rubber compounds, the first rubber compound extending in a continuous first layer between the tread edges and the second rubber compound being disposed in a second layer radially outwardly of the layer of the first rubber compound to form the tread running surface in the central portion of the tread. By camber value is meant the ratio C/L between the radial distance C from the centre to the edge of the tyre tread and the axial distance L between the centre and edαe of the tread. Preferably the tyre comprises an mterfacial fabric layer disposed at the boundary between the first and second rubber layers. Further aspects of the present invention will become apparent from the description of the following embodiments m conjunction with the attached αiagrammatic drawing in which: - Figure 1 shows m cross-section a 170/60 R17 radial motor-cycle tyre intended for hign speed racing . The tyre i of Figure 1 comprises a pair of sidewalls 8 and 9 terminating in bead regions 10 and 11. Eacn bead region is reinforced by an mextensible annular bead core 12 and 13. Extending oetween each oeaα region is a tyre carcass reinforcement ply 14 nicn is anchored in each Dead region by being turneα around tne respective bead core 12,13 laterally from the msiαe to tne outside to form a ply turn-up 15,16. The carcass reinforcement ply 14 comprises a single ply of tyre fabric laid with nylon corαs suostantially radially. Eacn beaα region 10,11 further comprises a hard rubber apex member 17,18 which is anchored to each respective bead core 12,13 and extends tapeπngly radially outwardly. The carcass ply fabric of the present tyre may also comprise polyester, rayon or aramid cords. Further whilst a single ply carcass of cords at substantially 90° may be particularly advantageous m the case of tyres for the rear wheel of the motorcycle, for the front wheel a tyre w th two plies of cords crossed at an angle of 70°-88° may oe advantageous . The tyre 1 has a camber value of 0.6 and comprises a convex tread region 2, having treaα eαges 3,4, reinforced by a breaker assembly. The width T of the tread is 220mm measured along the outer surface. The breaker assembly comprises two oreaker plies 6 and 7 eac^ of wnich comprises Kevlar (Registereα Trade Mark) aramid cord tyre fabric each of 2/165 TEX. The cords ι n eacn of the breaker plies 6 and n are oppositely inclined to eacn other at an angle of 25° to the circumferential direction of the tyre. The raαially inner breaker piy 7 has a widtn E of 200mm and is narrower than tne radxally outer breaker ply 5 which has a width Bo of 220mm. The breaker plies may also comprise steel cords. As evident from Figure 1 the tread of the tyre comprises two distinct layers of rubber. The first rubber layer RLl extends continuously between the tread edges 3 and 4. In the central tread portion a second rubber layer RL2 is disposed radially outward of the first rubber layer RLl and centred on the tyre circumferential centreline C/L. The tread ground contacting surface comprises in the centre the rubber compound of the second rubber layer and to either side in the lateral regions a different rubber compound of the first rubber layer RLl. The portion of the first rubber layer RLl extending radially inward of the second rubber layer has a thickness of 2mm. At the boundary between the first and second rubber layer is disposed an interfacial fabric layer which comprises in this embodiment a rubberised cut fabric ply. This ply comprises nylon cords disposed in mutually parallel configuration and at an angle of ■ between 18°-30° preferably 25° to the tyre circumferential direction. In accordance with the invention the interfacial fabric may comprise other textile materials common in the art. The second layer of rubber RL2 has a width S which is 40% of the tread width TW. According to the invention this width may be in the range of 30%-50%. If the second rubber layer width exceeds 50% of the tread width then the second rubber compound extends too far into the lateral regions of the tread and the cornering performance of the tyre deteriorates. The compound properties of the rubber of the first layer RLl are such that the material provides good grip on cornering whilst those of the rubber of the second layer RL2 are to give low temperature generation in straight running. Preferably the properties of the rubber layer of RLl are characterised by a hardness value at 100°C of between 40-49 Shore 'A' and a tensile modulus at 100°C and 300% extension of less than 5.0 MPa. In contrast the properties of the second rubber layer RL2 are preferably a hardness value at 100°C of not less than 50 Shore 'A' and a tensile modulus at 100 ϋ C and 300% extension of not less than 5.0 MPa Example formulations of rubber compounds suitable for the invention are shown Table 1. The formulation A is a compounα suitable for the softer first rubber layer RLl wnilst compound B is suitable for the harder second rubber layer RL2. The polymer type can be emulsion or solution polymerised styrene butadiene (SBR) ana may contain 20-50% styrene, preferably 25-45%. The reinforcing filler may be either carDon black as shown or silica or a blend of both. The total amount of filler present may be from 15 to 160 parts by weight per hundreα parts by weight of styrene- butadiene rubber. PreferaDly tne filler is present an amount from 30 to 120 parts of tne rubber. If silica is used, then this may be in conjunction with a coupling agent, preferably a silane coupling agent, e.g. bis 1 , 3-triethoxy-silyl propyl tetrasulphide . Silica may have a surface area 60- 300m 2 /g, preferably 80-250 m 2 /g and is preferably precipitated silica. The coupling agent may be used in the amount from 2-18.5% by weight of silica filler, preferably 5-12% by weight. The carbon black may be a high surface area carbon black of SAF or ISAF type, having a surface area 80- 300 m 2 /g and be present at 15 to 160 and preferably 30 to 120 parts by weight per 100 parts by weight of styrene-butadiene rubber. The oil in the composition is preferably an aromatic oil and may be present from 10 to 180 parts by weight per hundred rubber, preferably 15 to 120. Suitable aromatic oils are well known to a man skilled in the art. Preferably they have a specific gravity from 0.95-1.0. The rubber compounds may contain conventional additives, e.g. accelerators, activators, extenders and anti-degradants as desired. The vulcanisation agent is preferably sulphur or a sulphur-contammg compound. The resultant tyres have been found to have good precision under the slower speed involved in cornering and due to the lower temperature generation in the second rubber compound the tyre also has improved durability at high speeα running. Whilst the presence of the mterfacial faoric is preferred most of the advantages of tne present invention can be obtained if it is omitted. TABLE 1

Claims: CLAIMS 1. A motor-cycle tyre (1) comprising a ground contacting tread (2) reinforced between its edges (3,4) by a breaker assembly and having in its normally inflated fitted condition a camber value C/L of between 0.5 and 0.7, a reinforcing carcass ply (14) extending radially inside the breaker assembly and between two bead regions (10,11) and wrapped in each bead region around an annular bead core (12,13) from the axial inside to the outside to form carcass ply turn-ups (15,16) and between the tread edges (3,4) and bead regions (10,11), tyre sidewalls (8,9) wherein the breaker assembly comprises two breaker plies (5,7) comprising reinforcing cords oppositely inclined with respect to the circum erential direction of the tyre characterised in that the tread comprises two different rubber compounds, the first rubber compound extending in a continuous first layer between the tread edges (3,4) and the second rubber compound being disposed in a second layer radially outwardly of the layer of the first rubber compound to form the tread running surface in the central portion of the tread. 2. A tyre according to claim 1, characterised that the second rubber compound layer is centred on the tyre axial centreline (C/L) and has a width (S) of between 30% and 50% of the tread width (TW) , the widths being measured along the arc of the tread surface . 3. A tyre according to claim 1 or 2, characterised by an mterfacial fabric layer disposed at the boundary oetween the first and second rubber layers . 4. A tyre according to claim 3, cnaracterised in that the terfacial fabric layer comprises nylon cords . 5. A tyre according to claim 4, characterised in that the nylon cords are laiα parallel to each other and disposed at an angle of 18°-30° to the tread circumferential αirection. 6. A tyre according to any of claims 1 to 5, cnaracterised m that the central portion of the tread radial thickness of the seconα layer of ruober is between 50% and 80% of tne total radial thickness of tne tread. 7. A tyre according to any of claims 1 to 6, characterised in that the radial thickness (t) of the portion of first rubber layer radially inward of the second layer is not less than 2mm. 8. A tyre according to any of claims 1 to 7, characterised in that the hardness of the rubber of the first rubber layer (RLl) at 100°C lies in range 40-49 Shore 'A' . 9. A tyre according to any of claims 1 to 8, characterised in that the first rubber layer (RLl) has a tensile modulus at 300% extension at 100°C of less than 5.0 MPa. 10. A tyre according to any of claims 1 to 9, characterised in that the rubber of the second rubber layer (RL2) has a hardness at 100°C of not less than 50° Shore 'A' . 11. A tyre according to any of claims 1 to 10, characterised in that the rubber of the second rubber layer (RL2) has a tensile modulus at 300% extension at 100°C of not less than 5.0 MPa.

Inventors: BARRETT GARY TERENCE, WATKINS DAVID ROBERT, BARRETT, GARY, TERENCE, WATKINS, DAVID, ROBERT
Applicants: BARRETT GARY TERENCE, DUNLOP TYRES LTD, WATKINS DAVID ROBERT, BARRETT, GARY, TERENCE, DUNLOP TYRES LTD., WATKINS, DAVID, ROBERT
Application year: 2000
Main classification: B60C11
IPC codes: B60C9, B60C11