Motorcycle radial tyre

Abstract: A motorcycle radial tyre comprises a 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) of radially disposed cords 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) characterised in that the breaker assembly comprises two breaker plies (6,7) comprising aromatic polyamide cords oppositely inclined with respect to the circumferential direction of the tyre and a supplementary ply (5,25) disposed radially adjacent to the breaker plies (6,7) and comprising nylon reinforcements laid parallel to each other and disposed at an angle in the range of 75°-90° to the circumferential direction of the tyre.

Description: This invention relates to radial motorcycle tyres and in particular but not exclusively to high performance or race motorcycle tyres. Such tyres utilise very wide treads which in transverse cross-section are sharply curved to provide good contact with the road surface when the motorcycle is steeply banked in cornering. Maintenance of a consistent ground contact area of 'tyre footprint' under all conditions is a major problem in determining general vehicle handling. Of particular importance in race motorcycle tyres of radial construction is the provision of high cornering power with the good stability to maximise cornering speeds under race conditions. Present radial motorcycle race tyres have short sidewalls which extend to the tread edges radially and axially outwardly from the tyre beads. The beads provide engagement to the wheelrim on tapered bead seats. The sidewalls are reinforced by radial carcass plies which when tensioned by the 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. An object of the present invention is to improve the properties of such tyres. According to the present invention a radial motorcycle tyre comprises a tread reinforced between its edges 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 of radially disposed cords 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 characterised in that the breaker assembly comprises two breaker plies comprising aromatic polyamide cords oppositely inclined with respect to the circumferential direction of the tyre and a supplementary ply positioned radially adjacent to the breaker plies and comprising nylon reinforcements laid parallel to each other and disposed at an angle in the range of 75°-90° to the circumferential direction of the tyre. 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 edge of the tread. Preferably the aromatic polyamide cords of the two breaker plies are inclined at between 16 and 30 degrees and most preferably they are inclined at 25 degrees to the circumferential direction of the tyre. The supplementary ply may be disposed radially inside or radially outside the two breaker plies and preferably the plies of the breaker assembly are arranged in order of increasing width in the direction of radial inside to the radial outside. Motorcycle tyres constructed according to the present invention have been found to have improved grip, cornering power and stability under all conditions. Further aspects of the present invention will become apparent from the description of the following embodiments in conjunction with the attached diagrammatic drawings in which:- Figure 1 shows in cross-section first embodiment of the present invention being a 190/55 R17 radial motorcycle tyre intended for high speed racing; and Figure 2 shows in cross-section second embodiment being a 185/55 R17 radial motorcycle tyre also intended for high speed use. The tyres 1 and 20 of Figures 1 and 2 respectively each comprise a pair of sidewalls 8 and 9 terminating in bead regions 10 and 11. Each bead region is reinforced by an inextensible annular bead core 12 and 13. Extending between each bead region is a tyre carcass reinforcement ply 14 which is anchored in each bead region by being turned around the respective bead core 12,13 laterally from the inside to the outside to form a ply turn-up 15,16. The carcass reinforcement ply 14 comprises two plies of tyre fabric comprising rubber covered nylon cords of 2/140 TEX laid with the cords substantially radially. Whilst the present embodiment comprises a carcass reinforcement of two plies it may equally comprise a single carcass ply or multiple carcass plies. Each bead region 10,11 further comprises a hard rubber apex member 17,18 which is anchored to each respective bead core 12,13 and extends taperingly radially outwardly. The tyres have a camber value of 0.6 and comprises a convex tread region 2, having tread edges 3,4 reinforced by a breaker assembly. The breaker assembly comprises two breaker plies 6 and 7 each of which comprises Kevlar (Registered Trade Mark) aramid cord tyre fabric each of 2/165 TEX. The cords in each of the breaker plies 6 and 7 are oppositely inclined to each other at an angle of 25° to the circumferential direction of the tyre. The radially inner breaker ply 6 is narrower than the radially outer breaker ply 7. In the first embodiment, the tyre 1 shown in Figure 1, radially outside and immediately adjacent to the two breaker plies 6 and 7 is an over-breaker ply 5 comprising rubber covered nylon cords of 2/94 TEX. The cords in the over-breaker ply 5 are laid at an angle of substantially 90° to the circumferential direction of the tyre. As shown in Figure 1 the plies 5, 6 and 7 forming the breaker assembly are arranged in order of increasing width in the axial direction of the tyre from the inside radially outwards. The radially outermost over-breaker ply 5 extends substantially to the tread edges. In the second embodiment, the tyre 20 shown in Figure 2, a sub-breaker ply 25 comprising rubber covered nylon cords of 2/140 TEX is disposed radially inside and immediately adjacent to the two breaker plies 6 and 7. The cords in the sub-breaker ply 25 are laid at an angle of 80° to the circumferential direction of the tyre and cross, i.e. are oppositely inclined to, the aromatic polyamide cords of the adjacent breaker ply 6. Again, as in the first embodiment, the plies 25, 6 and 7 forming the breaker assembly of the tyre 20 are arranged in order of increasing width in the axial direction of the tyre from the inside radially outwards. The radially outer breaker ply 7 extends substantially to the tread edges. The resultant tyres according to the present invention have been found to have improved cornering power and stability under all conditions and improved grip. This construction has also been shown to give superior speed under race conditions.

Claims: A radial motorcycle tyre (1) comprising a 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) of radially disposed cords 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) characterised in that the breaker assembly comprises two breaker plies (6,7) comprising aromatic polyamide cords oppositely inclined with respect to the circumferential direction of the tyre and a supplementary ply (5,25) disposed radially adjacent to the breaker plies (6,7) and comprising nylon reinforcements laid parallel to each other and disposed at an angle in the range of 75°-90° to the circumferential direction of the tyre. A radial motorcycle tyre according to claim 1, characterised in that the nylon reinforcements of the supplementary ply (5,25) are cords. A motorcycle radial tyre according to either of claims 1 or 2, characterised in that the aromatic polyamide cords of the two breaker plies (6,7) are inclined at 16 to 30 degrees with respect to the circumferential direction of the tyre. A motorcycle tyre according to any one of claims 1 to 3, characterised in that the aromatic polyamide cords of the two breaker plies (6,7) are inclined at 25° to the circumferential direction of the tyre. A motorcycle radial tyre according to any of claims 1 to 4, characterised in that the radially outermost breaker ply (7) is wider than the adjacent radially inner breaker ply (6). A motorcycle radial tyre according to any of claims 1 to 5, characterised in that the plies of the breaker assembly are disposed in order of increasing width in the direction of the radial inside to the radial outside. A motorcycle radial tyre according to any of claims 1 to 6, characterised in that the supplementary ply (5) is disposed radially outside the breaker plies (6,7). A motorcycle radial tyre according to claim 7, characterised in that the supplementary ply (5) has reinforcements laid at an angle of 80°-90° to the circumferential direction of the tyre. A motorcycle radial tyre according to claim 8, characterised in that the supplementary ply (5) has reinforcements laid at an angle of 85°-90° to the circumferential direction of the tyre. A motorcycle radial tyre according to any of claims 1 to 6, characterised in that the supplementary ply (25) is disposed radially inside the breaker plies (6,7). A motorcycle radial tyre according to claim 10, characterised in that the reinforcements of the supplementary ply are laid at an angle of 75° to 85° to the tyre circumferential direction.

Inventors: JACKSON MICHAEL, NOCK NIGEL GERARD, WATKINS DAVID ROBERT, JACKSON, MICHAEL, NOCK, NIGEL GERARD, WATKINS, DAVID ROBERT
Applicants: SUMITOMO RUBBER IND, SUMITOMO RUBBER INDUSTRIES LTD.
Application year: 1995
Main classification: B60C9
IPC codes: B60C9, B60C3