Motor-cycle radial tyre

Abstract: A radial motor-cycle tyre having improved lateral grip under camber with good stability has tread reinforced by two main breaker plies comprising parallel reinforcing cords oppositely inclined with respect to the tyre circumferential direction and a supplementary breaker ply disposed radially outward of the main breaker plies and comprising a cord reinforced central ply portion and to either side of the central ply portion an outer ply portion comprising rubber having no cord reinforcement.

Description: This invention relates to radial motor-cycle tyres and in 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 good contact with the road surface when the motor-cycle is steeply banked in cornering. Maintenance of a consistent ground contact area or 'tyre footprint' under all conditions is a major problem in determining general vehicle handling. Of particular importance in race motor-cycle tyres of radial 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 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. Another type for motorcycle according the preamble of claim 1 is known from JP-A-61 016 105. Such tyres however, due to their uniform breaker structures, do not provide fully optimum stability and lateral grip particularly under camber. Such tyres also suffer from excessive tread wear under acceleration at high camber angles particularly when the tyre is oversteering. It therefore an object of the present invention is to improve the properties of such tyres. According to one aspect of the present invention a radial motor-cycle 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 wherein the breaker assembly comprises two main breaker plies comprising parallel reinforcing cords oppositely inclined with respect to the circumferential direction of the tyre characterised by a supplementary breaker ply disposed immediately radially outwardly of the two main breaker plies and comprising in the centre a central ply portion comprising cord reinforced rubber fabric and abutting the central portion on either axial edge two outer ply portions comprising rubber having no cord reinforcement. 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 two outer ply portions of the supplementary breaker ply have a thickness in the range 0.75 to 1.0 mm and comprise a blend of 80% natural and 20% emulsion styrene-butadiene rubbers, and preferably have a hardness in the range 70 to 80 Shore A, and modulus at 300% extension in the range of 10 to 15 MPa. Also preferably the central ply portion has a width of between 35% and 65% of the width of the widest of the two main breaker plies. Further aspects of the present invention will become apparent from the description of the following embodiments in conjunction with the attached diagrammatic drawing in which:- Figure 1 shows in cross-section a 170/60 R17 radial motor-cycle tyre intended for high speed racing. The tyre 1 of Figure 1 comprises 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 a single ply of nylon tyre fabric laid with the cords substantially radially. Each read 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 tyre 1 has a camber value of 0.6 and comprises a convex tread region 2, having tread edges 3,4, reinforced by a breaker assembly. The width TW of the tread is 220 mm measured along the outer surface. The breaker assembly comprises two main breaker plies 5 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 5 and 7 are oppositely inclined to each other at an angle of between 16° and 36°, preferably 25°, to the circumferential direction of the tyre in the central crown region of the tyre. The radially inner breaker ply 7 has a width Bi of 200 mm and is narrower than the radially outer breaker ply 5 which has a width Bo of 220 mm. Radially outside and immediately adjacent to the main breaker plies a supplementary breaker ply 6 having width equal to that of the adjacent main breaker ply 5 and comprising in the central region a central ply portion 6c which is flanked in the left and right edge regions by outer ply portions 6L and 6R respectively and which abut the edges of the central ply portion 6c. The central ply portion 6c comprises rubber tyre fabric reinforced by parallel cords of polyamide extending at 30° or less to the circumferential direction of the tyre and crossed with respect to the cords of the radially inwardly adjacent main breaker 5. The width 5 of the central ply portion 6c is 110 mm, i.e. 50% of the width Bo of the widest of the main breaker plies 5. The two outer ply portions which are of equal width comprise rubber compound without cord reinforcement. The rubber compound is a blend of 80% by weight of Natural rubber and 20% by weight of an Emulsion SBR. These outer ply portions have a hardness in the range of 70 to 80 Shore A and specifically 72 Shore A and a modulus at 300% extension in the range of 10 to 15 MPa, specifically 12.8 MPa. The thickness of the two outer ply portions 6L and 6R is substantially the same as that of the central ply portions 6c and is in the range of 0.75 to 1.0 mm. The resultant tyres have been found to have improved cornering power and stability under all conditions and improved grip particularly lateral grip when the tyre is running under camber. This construction has also been shown to give superior tread wear resistance under acceleration at high camber angles when the tyre is oversteering.

Claims: A radial motor-cycle 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) wherein the breaker assembly comprises two main breaker plies (5,7) comprising parallel reinforcing cords oppositely inclined with respect to the circumferential direction of the tyre wherein a supplementary breaker ply (6) is disposed immediately radially outwardly of the two main breaker plies (5,7) and characterized in that said supplementary breaker ply (6) comprising in the centre a central ply portion (6c) comprising cord reinforced rubber fabric and abutting the central portion on either axial edge two outer ply portions (6L,6R) comprising rubber having no cord reinforcement. A radial motor-cycle tyre according to claim 1 wherein the two outer ply portions (6L,6R) of the supplementary breaker ply 6 have a thickness in the radial direction of 0.75-1.0 mm. A radial motor-cycle tyre according to either of claims 1 or 2 characterised in that the two outer ply portions (6L,6R) of the supplementary breaker ply (6) have a rubber hardness in the range of 70 to 80 Shore A. A radial motor-cycle tyre according to claim 3, characterised in that the two outer ply portions (6L,6R) have a rubber hardness of 72 Shore A. A radial motor-cycle tyre according to any of claims 1 to 4, characterised in that the two outer ply portions (6L,6R) of the supplementary breaker ply (6) have a rubber modulus at 300% extension of between 10 and 15 MPa. A radial motor-cycle tyre according to any of claims 1 to 5, characterised in that the outer ply portions (6L,6R) of the supplementary breaker ply (6) have a rubber modulus at 300% extension of 12.8 MPa. A radial motor-cycle tyre according to any of claims 1 to 6, characterised in that the two outer ply portions (6L,6R) of the supplementary breaker ply (6) comprises a blend of 80% by weight of natural rubber and 20% by weight of emulsion SBR rubber. A radial motor-cycle tyre according to any of claims 1 to 7, characterised in that the reinforcing cords of the central ply portion (6c) of the supplementary breaker ply (6) are inclined at an angle of 30° or less to the tyre circumferential direction. A radial motor-cycle tyre according to any of claims 1 to 8, characterised in that the reinforcing cords of the central ply region (6c) of the supplementary breaker ply (6) comprising polyamide cords. A radial motor-cycle tyre in accordance with any of claims 1 to 9, characterised in that the central ply portion (6c) of the supplementary breaker ply (6) has a width (5) in the range 35% to 65% of the width (Bo) the wider of the two main breaker plies (5,7). A radial motor-cycle tyre according to any of claims 1 to 10, characterised in that the supplementary breaker ply (6) has a width equal to the width (Bo) of the widest of the two main breaker plies (5,7). A radial motor-cycle according to any of claims 1 to 5, characterised in that the radially outermost main breaker ply (5) is wider than the inner main breaker ply (7). A radial motor-cycle tyre according to any of claims 1 to 12, characterised in that the reinforcing cords of the two main breaker plies (5,7) are inclined at an angle of between 16° and 36° in the central crown region. A radial motor-cycle tyre according to any of claims 1 to 13, characterised in that the reinforcing cords of the two main breaker plies (5,7) comprise aramid cords.

Inventors: JACKSON MICHAEL, WATKINS DAVID ROBERT, JACKSON, MICHAEL, WATKINS, DAVID ROBERT
Applicants: SUMITOMO RUBBER IND, SUMITOMO RUBBER INDUSTRIES LTD.
Application year: 1998
Main classification: B60C9
IPC codes: B60C9