RADIAL TYRE FOR VEHICLES

Abstract: A radial tyre for a vehicle, preferably a motorcycle, comprising a carcass reinforced by a ply (13) of radially disposed cords wrapped in each of two piece regions (9,10) round an annular bead core (11,12) to provide a ply turn up (17), a tread (1) reinforced by a breaker assembly (4) and between the tread edges and bead regions (9, 10) tyre sidewalls (7, 8) characterised in that each sidewall (7, 8) includes immediately adjacent to and axially outwards of the carcass ply (13) a rubber sidewall member (14) having a modulus in the range of 10-20 MPa and having an upper edge (16) positioned at the edge of the breaker assembly (4) and a lower edge (15) radially inwards of the carcass ply turn up edge (17). The lower edge of the rubber sidewall member (14) is preferably positioned at the bead core so that the rubber sidewall member is continuous from the bead core to the edge of the breaker assembly.

Description: This invention relates to radial motorcycle tyres and in particular to tyres for high speed use including racing. High speed radial tyres are prone to breaker edge looseness which leads to premature tyre failure. Breaker edge looseness occurs due to fatigue in the band between the breaker cords in the edge regions where the breaker joins the sidewall, which is a point in a radial tyre where deformations tend to be concentrated. Prior tyre constructions which attempt to reinforce the tyre sidewall and breaker edge regions include the example DE-A-3242323 (corresponding to the preamble of claim 1). One object of the present invention is to substantially improve resistance to breaker edge looseness. Another object particularly of value in motorcycle tyres is to improve the vehicle handling properties by means of providing an improved total sidewall construction having consistent stiffness properties with minimum sidewall length. Such improvements allow the use of very short sidewall lengths to give lower aspect ratio tyres which gives tyres still better properties of grip, durability and vehicle handling. The present invention provides a radial motorcycle tyre comprising a carcass reinforced by a ply of radially disposed cords wrapped in each of two bead regions around an annular bead core to provide a ply turn up, a tread reinforced by a breaker assembly, said tread and breaker assembly being substantially curved in transverse cross-section of the tyre and, between the tread edges and bead regions, tyre sidewalls, each sidewall including immediately adjacent to and axially outwards of the carcass ply a continuous sidewall member comprising only rubber compound having a substantially constant thickness, and having an upper edge interconnected to a breaker assembly which comprises at least a ply reinforcement fabric, said ply overlying the upper edge of the rubber sidewall member, and a lower edge of the sidewall member which is positioned at the bead core radially inwards of the carcass ply turn-up edge, characterised in that the ply turn-up has a length less than 60% of the sidewall length, the rubber compound of the sidewall member has a modulus in the range of 10 to 20 MPa, and the breaker assembly comprises two or more plies of reinforcement fabric, the outer one overlying the upper edge of the rubber sidewall member. Preferably the outer breaker ply overlies the upper edge of the rubber sidewall member by between 5 and 10 mm to interconnect the rubber sidewall member and the breaker assembly. The rubber sidewall member is preferably of constant thickness before tyre shaping. One embodiment of the present invention will now be described, by way of example only, in conjunction with the attached diagrammatic drawing showing in cross-section a 325/550-18 radial motorcycle tyre intended for high speed motorcycle racing. The tyre comprises a convex tread region 1 having tread edges 2,3 and reinforced by a tread reinforcing breaker assembly 4. The breaker assembly 4 comprises two tyre fabric breaker plies 5 and 6 each of which comprises weftless Kevlar (Registered Trade Mark) cord tyre fabric laid with the cords at 25° to the circumferential direction with the cords of ply 5 crossing the cords of ply 6. Ply 5, the outer ply, extends into each tread edge 2 and 3 whereas ply 6 is 5mm short of ply 5 at each side for a reason to be explained. The tyre further comprises a pair of sidewalls 7 and 8 terminating in bead regions 9 and 10. Said bead region is reinforced by an annular bead core 11,12. A tyre carcass reinforcement ply 13 which comprises a single ply of rayon tyre fabric laid with the cords substantially radial extends around the tyre and is anchored in each bead 9 and 10 by being wrapped around its respective bead core 11 or 12. It should be especially noted that no tapered bead apex is provided. Instead a rubber sidewall member 14 is provided in each sidewall. The sidewall members 14 comprise rubber compound having a modulus of 13 MPa (the hardness may be in the range of 10-20 MPa), and including adhesion prompting agents to give high adhesion to the adjacent components in the tyre. The sidewall members 14 are of substantially constant thickness being 1mm thick when assembly of the tyre carcass is carried out and extend through the whole sidewall length such that the radially inner edge 15 is substantially in contact with the bead core 11 or 12 and the radially outer edge 16 abuts the edge of the inner breaker ply 6. Thus the sidewall member outer edge 16 is overlaid by the outer breaker ply 5 and securely anchored into the breaker/tread assembly. The hard sidewall member 14 is immediately adjacent to the carcass ply 13 and bonded thereto along its full length. Finally the carcass ply 13, after wrapping around the bead core 11 or 12 is turned-up on the outside of the tyre to a radial height of 15mm to provide a carcass turn up 17 and the bead includes a cross-woven fabric chafer 18. The resultant tyre has sidewalls 7, 8 each formed by a single radial ply and a rubber reinforcement member 14 anchored to both head cores 11, 12 and breaker edge. The overlap of the outer breaker ply over the edge of the rubber reinforcement member is particularly important. The sidewall rubber member 14 after tyre shaping has its thickness still within 60% of the original thickness along its full length and so provides a substantial rubber reinforcement member. The resultant tyre has been found to have greatly improved resistance to breaker edge looseness caused by fatigue on high speed test. The mechanism of this is not yet fully understood but is believed to be due to the hardness of the rubber sidewall member and its continuity through the full length of the sidewall. It has been found that the sidewall member may have a modulus in the range of 10 - 20 MPa, more preferably 12 - 15 MPa. Suitable rubber sidewall member dimensions for a 18″ motorcycle tyre are in the ranges of 0.30 to 1.00mm for thickness and 30 to 80mm for length. The carcass ply overlap height is not very critical and may fact be reduced to zero. In the case of the two breaker ply motorcycle race tyre described, however, this height is preferably in the size of 15% to 60% of the sidewall length.

Claims: 1. A radial motorcycle tyre comprising a carcass reinforced by a ply (13) of radially disposed cords wrapped in each of two bead regions (9,10) around an annular bead core (11,12) to provide a ply turn up (17), a tread (1) reinforced by a breaker assembly (4), said tread (1) and breaker assembly (4) being substantially curved in transverse cross-section of the tyre and, between the tread edges and bead regions (9,10), tyre sidewalls (7,8), each sidewall (7,8) including immediately adjacent to and axially outwards of the carcass ply (13) a continuous sidewall member (14) comprising only rubber compound having a substantially constant thickness, and having an upper edge (16) interconnected to a breaker assembly (4) which comprises at least a ply reinforcement fabric, said ply overlying the upper edge of the rubber sidewall member (14), and a lower edge (15) of the sidewall member (14) which is positioned at the bead core (11,12) radially inwards of the carcass ply turn-up edge (17), characterised in that the ply turn-up (17) has a length less than 60% of the sidewall length, the rubber compound of the sidewall member (14) has a modulus in the range of 10 to 20 MPa, and the breaker assembly comprises two or more plies (5,6) of reinforcement fabric, the outer one (5) overlying the upper edge of the rubber sidewall member (14). 2. A tyre according to claim 1 characterised in that the outer breaker ply (5) overlies the rubber sidewall member (14) by between 3 and 10 mm. 3. A tyre according to claim 2 characterised in that the carcass ply turn up (17) is in the range of 15% to 60% of the sidewall length. 4. A tyre according to claim 3 characterised in that the rubber sidewall member (14) has a substantially constant thickness before tyre shaping and that following shaping its thickness in the upper edge region is not less than 60% of its thickness in the lower edge region. 5. A tyre according to any of claims 1 to 4 characterised in that the tyre sidewall (7,8) has no additional rubber compound component axially outwards of the rubber sidewall member (10).

Inventors: GRIFFITHS, GERALD ANTHONY, INGLEY, PETER, WATKINS, DAVID ROBERT
Applicants: SP TYRES UK LIMITED
Application year: 1987
Main classification: B60C13
IPC codes: B60C15, B60C13, B60C9, B60C3