Motorcycle tyre

Abstract: A motorcycle tyre having in its normally inflated condition a camber value C/L of between 0.5 and 0.7 and having maximum axial width between the edge (3,4) of the ground contacting tread (2) characterised in that in axial cross-section the tread comprises two tread rubber components (2L,2R) of different rubber compounds joined by a scarf joint (24), the scarf joint (24) having a width (JW) less than the tread width (TW) and having an intertread ply (23) comprising reinforcing cords interposed between the two tread components (2L,2R).

Description: This invention relates to a pneumatic tyre for a motorcycle and in particular but not exclusively to a high performance tyre for a race motorcycle. Motorcycle tyres having in its normally inflated condition a camber value of between 0,5 and 0,7 and having the maximum axial width between the edges of the ground contacting tread are generally known in the art. Such tyres have 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. The treads of such motorcycle tyres are required to be both resistant to wear and damage such that the tyres do not disintegrate under the typically high temperatures and severe conditions of racing but also to have high levels of grip to allow cornering at very high speed. Since these twin requirements demand largely conflicting properties of rubber the compositions of these tread rubbers are a compromise giving a best balance of properties. The configuration of a motorcycle race circuit is a unique combination of curves, corners and straights. Thus on many race circuits the motorcycle is subject to continual changes in direction requiring banking the motorcycle from left to right punctuated by short periods of upright running. Accordingly on these race circuits the tyres run substantially evenly on all parts of the tread during each lap of the circuit. Under these conditions the entire tread reaches a substantially uniform temperature and thus exhibits consistent road contacting characteristics over the whole tread area enabling the rider to race with control and confidence. However certain race tracks have configurations which are not conducive to the development of uniform characteristics over the whole of the tyre tread. Such tracks for example may comprise a succession of long bends and curves in the same direction covering a substantial proportion of the circuit with just a few sharp bends in the opposite direction constituting the remaining minor portion of the circuit. Thus on such circuits the tyres are subjected to relatively long periods of running on one shoulder, which accordingly reaches a very high temperature, only to be suddenly banked over on to the opposite shoulder which in comparison in much cooler and therefore has substantially different road contacting characteristics which are manifest as reduced grip. The problem for the motorcycle rider on such difficult circuits is aggravated by the necessity for the tyre tread rubber to be optimised for wear and damage resistance at the expense of grip in order for the tyres to survive such sustained high temperature running on one shoulder. Thus the rider has to negotiate sharp corners on treads having inherently inferior grip in addition to suffering from poor grip due to low temperature. It is an object of the present invention to provide a motorcycle tyre having improved performance under such circumstances as described above. According to the present invention a motorcycle tyre has in its normally inflated condition a camber value of between 0.5 and 0.7 and has a maximum axial width between the edge of the ground contacting tread characterised in that in axial cross-section the tread comprises two tread rubber components of different rubber compounds joined by a scarf joint, the scarf joint having a width less than the tread width and having an intertread ply comprising reinforcing cords interposed between the two tread components. 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. Further aspects of the invention will become apparent from the following description by way of example only, of one embodiment in conjunction with the following drawing in which: Figure 1 shows a schematic cross-sectional view of a motorcycle tyre of the invention. The tyre of Figure 1 comprises a pair of sidewall regions 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 carcass reinforced ply 14 which is anchored in each bead region by being turned outwardly around the respective bead core 12,13 to form a ply turn-up 15,16. Between the carcass ply and ply turn-up are hard rubber apex members 17,18 which are anchored to each respective bead core 12,13 and extend taperingly radially outwardly. The carcass reinforced ply comprises a single ply of nylon tyre fabric laid with the cords substantially radially. The tyre further comprises a convex tread region 1 extending between tread edges 3,4 and having a camber C/L of 0.6. The tread region 1 has a reinforcing breaker 5 disposed radially outward of the carcass ply comprising two breaker plies 6 and 7 each of which comprises aramid cord tyre fabric. The cords of the breaker plies 6 and 7 are oppositely inclined with respect to each other at an angle of substantially 25° to the tyre circumferential direction. Radially outward of the breaker is a ground contacting tread rubber 2 comprising a left and right tread component 2L and 2R respectively. The two tread components 2L and 2R are joined by a tapering overlap or scarf joint 24 centred substantially on the circumferential centreline CL of the tyre. The scarf joint 24 has a width JW of 50mm which is 22% of the tread width TW measured along the arc of the tread surface. Preferably the scarf joint 24 has a width in the range of 10 to 40% of the tread width. The scarf jcint 24 also includes a circumferentially extending intertread ply 23 lying on the interface between the two tread components 2L and 2R. The intertread ply 23 comprises rubber coated nylon cords of 2/94 TEX lying mutually parallel at 100 cords per decimetre and disposed at substantially 26° to the tyre circumferential direction. The cords of the intertread ply are crossed with respect to the cords of the outermost breaker ply 6. Preferably the cords of the intertread fabric lie at between 15° to 40° to the tyre circumferential direction arid are laid at between 70 and 130 cords per decimetre. The width FW of the intertread ply 23 is 45mm and it extends from the radially inner end of the joint to within 5mm cf the radially outer end of the joint on the tread surface. Preferably the width intertread ply is greater than 50% of the joint width. The rubber compounds of the two tread components are optimised for different characteristics consistent with the configuration of the race circuit on which it is intended to use the tyre. Accordingly for this tyre, which is designed specifically for a circuit with long slow left-hand curves and a few sharp right-hand corners, the left-hand tread component 2L is formulated for wear and damage resistance in prolonged high temperature running whilst the right-hand tread component 2R is formulated for high grip at relative low temperature. Tyres according to the above described embodiment have been fitted to racing motorcycles and shown to give improved performance on difficult race circuits as previously defined.

Claims: A motorcycle tyre having in its normally inflated condition a camber value C/L of between 0.5 and 0.7 and having the maximum axial width between the edges (3,4) of the ground contacting tread (2) characterised in that in axial cross-section the tread comprises two tread rubber components (2L,2R) of different rubber compounds joined by a scarf joint (24), the scarf joint (24) having a width (JW) less than the tread width (TW) and having an intertread ply (23) comprising reinforcing cords interposed between the two tread components (2L,2R). A tyre according to claim 1, characterised in that the scarf joint (24) has a width (JW) between 10 and 40% of the tread width (TW). A tyre according to either of claims 1 or 2, characterised in that the intertread ply (23) has a width (FW) of greater than 50% of the joint width (JW). A tyre according to any of claims 1 to 3, characterised in that the scarf joint (24) is centred substantially on the circumferential centreline (CL) of the tyre. A tyre according to any of claims 1 to 4, characterised in that the reinforcing cords of the intertread ply (23) are organic fibre cords. A tyre according to claim 5, characterised in that the cords of the intertread ply (23) are polyamide cords. A tyre according to any of claims 1 to 6, characterised in that the cords of the intertread ply (23) are laid mutually parallel. A tyre according to claim 7, characterised in that the cords are inclined with respect to the tyre circumferential direction. A tyre according to claim 8, characterised in that the cords are inclined at 15°-40° to the tyre circumferential direction. A tyre according to claim 8, characterised in that the cords are inclined at substantially 26°. A tyre according to any of claims 7 to 10, characterised in that the intertread ply (23) has cords laid at between 70 and 130 cords per decimetre. A tyre according to any of claims 7 to 10, characterised in that the intertread ply has cords laid at 100 cords per decimetre. A tyre according to any of claims 1 to 12, characterised in that the intertread ply (23) comprises rubber coated cords.

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: 1996
Main classification: B60C11
IPC codes: B60C9, B60C1, B60C3, B60C11