MOTORCYCLE RADIAL TYRE

Abstract: A motorcycle tyre comprises a radial carcass ply (1), the carcass in each bead region being turned axially outward around a bead hoop (7) to form a turnup ply portion (8), the tyre having a camber value C/L in the range 0.5 to 0.7 characterised in that the tread (6) is provided with a bandage ply (2) disposed radially outward of the carcass ply (1) and comprising cords disposed parallel to the circumferential direction and in the tread central portion the bandage ply (2) is adjacent to the carcass ply (1) and in the axial edge portions of the tread the bandage ply (2) is spaced apart from the carcass ply (1) by a reinforcing strip (3) comprising at least one reinforcing ply comprising textile reinforcing elements disposed at an angle to the tyre circumferential direction, the radially outer edge (10) of each turnup portion is separated from the adjacent edge of the reinforcing strip (3) by a distance of at least 5mm.

Description: MOTORCYCLE RADIAL TYRE TECHNICAL FIELD This invention relates to radial motorcycle tyres Such tyres utilise very wide treads which m transverse cross-section are snarply curved to provide good contact with the road surface when the motorcycle is steeply banked m cornering. Maintenance of a consistent ground conract area or 'ryre footprint' under all conditions is a major problem m determining general vehicle handling. BACKGROUND ART Present radial motorcycle tyres have short sidewalls which extend to the tread edges radially and axially outwardly from the tyre beads. The beads provide engagement to the wheelnm on tapered bead seats. The sidewalls are reinforced by radial carcass plies whicn when tensioned by the inflation pressure act togetner with sidewall geometry to orovide location of the curved tread regions to withstand cornering forces . The sharply curved tread region of the conventional motorcycle tyre is specially reinforced by a reinforcing belt or brea er to give the requireo structural rigidity to allow for banκιng over of the motorcycle when cornering wnilst giving sufficient flexibility to allow localised tread flattening m the ground contact pater for good road grip. Conventionally such a belt comprises two plies of tyre fabric each being reinforced by parallel corαs disposed at an angle to the tyre circumferential direction with the cords crossed with respect to the adjacent ply. Such tyres however, due to their uniform breaker structures, do not provide fully optimum stability and lateral grip. A motorcycle tyre having in the treaα region a bandage ply and in eacn tread edge ^ region an additional reinforcing ply is known from EP-B-0 628 435. However m this known tyre the ply turnup edge extends full\ radially outwarα to overlap the additional pl . However m such a structure the sidewall stiffness is increased which decreases riαmg comfort . It therefore an object of the present invention is to improve the properties of such tyres. DISCLOSURE OF THE INVENTION According to one aspect of the present invention a pneumatic motorcycle tyre comprising a reinforcing carcass ply of radially disposed cords extending m a main ply portion between two bead regions through siαewall regions and a ground contacting tread region, the carcass in eacn Dead region being turned axially outward around an mextensible bead hoop and thereafter extended radially outward to form a turnup ply portion, the tyre having a camber value C/L m the range 0.5 to C.7 characterised m that the tread region is provided with a bandage ply disposed radially outward of the carcass ply extending substantially between the axial edges of the tread and comprising reinforcing cords disposed suostantially parallel tc tne tyre circumferential direction and m the tread central portion the bandage ply is immediately adjacent to the carcass ply and m each of the axial edge portions of the tread the bandage ply is spaced apart from the carcass ply by a reinforcing strip comprising at least one reinforcing ply comprising textile reinforcing elements disposed at an angle to the tyre circumferential direction, the radially outer edge of each turnup ply portion is separatee from the adjacent edge of the reinforcing strip oy at least 5 mm. 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 reinforcing elements of the two reinforcing strips are cords disposed at an angle of between 20" to 70 c to the tyre circumferential direction . The reinforcing elements of the reinforcing strip may comprises polyamide, rayon, polyester or aramiα cord, polyethylene naphthalate (PEN) cr steel. BRIEF DESCRIPTION OF THE DRAWINGS Further aspects of the present invention will become apparent from the description of tne following embodiments in conjunction with the attached diagrammatic drawing m which: - Figure 1 shows m cross-section a 170/60 R17 radial motorcycle tyre according to a first emoodiment of the invent on; Figure 2 shows an enlarged detail view of the shoulder region of the tyre of Figure 1 ; Figure 3 shows another configuration of the reinforcing strip according to the invention; Figure 4 shows a schematic plan diagram of the symmetrical arrangement of the reinforcing elements about the central equatorial axis of the tyre of Figure 1; and Figures 5A-5C show schematic diagrams of other reinforcing strip conf gurations according to the invention . MODE FOR CARRYING OUT THE INVENTION The tyre of Figure 1 comprises a ground contacting tread region 6 a pair of sidewalls 4 terminating IΓ oead regions 5. Each bead region is reinforced by an mextensible annular beao core 7. Extending between each bead region is a tyre carcass reinforcement ply 1 which is anchored each bead region by being turned around the respective bead core 7 laterally from the inside to the outside to form a ply turnup portion 8 having a radially outer edge 10. Tne carcass reinforcement ply 1 comprises a single ply tyre fabric laid with the cords substantially radially. Each read region further comprises a hard rubber apex member 9 which ±s anchored to each respective bead core and extends tapeπngly radially outwardly . The tyre has a camber value of 0.6 and comprises a convex tread region 6, having tread shoulder edges TS. The width of the tread __.s 220 mm measured along the arc of outer surface, _ . e . the arc lengtr of half tread width S betweer the tread centre TC on the tyre circumferential central axis X and the tread should edge TS is 110 mm. By camber value is mea^t tne ratio C/L of respectively the radial distance C and the axial distance L between the pc t cf maximum tyre diameter at the tread centre TC and the tread should edge TS . Disposed in the tread region 6 and radially outward of the ply 1 is a bandage ply 2. The width of the bandage ply taken along the arc of the tread is 100 mm such that the bandage ply 2 extends substantially under the entire ground contacting surface of the tread. The bandage ply 2 is formed as a 'jointless bandage' and comprises a narrow tape having a plurality of reinforcing elements running longitudinally embedded in rubber, the tape being spirally wound around the circumference of the tyre such that the reinforcing elements lie substantially at 0 C or at least a very small angle ' of less than 5 L to the tyre circumferential direction. The reinforcing elements of the narrow tape comprise aramid ccrds but may also ccmprise ccrds or filaments of other textile materials such as nylon, polyester, rayon or glass. As shown in Figure i, in the central region of the tread the bandage 2 is disposed immediately adjacent td, i.e. contacting, the ply 1. However each of the two axial parts of the tread the bandage 2 is spaced radially apart from tne ply by a circumferentially extending reinforcing strip 3 wnich is interposed between them. Eacr reinforcing strip comprises a single reinforcing ply comprising plural reinforcing elements embedded rubber and disposed m parallel configuration and inclined at an angle of 45 c to the tread circumferential direction . In accordance with the invention the axially outer edge 3e of each of the reinforcing strips is spaced apart from the radially outer edge 10 of the adjacent ply turnup by a distance S which is not less than 5 mm. By this the laterally outer portions of tne tread are reinforced whilst the radιali\ outer portion of the sidewall has sufficient flexibility to give good nee comfort. Whilst the above embodiment nas a s_nσle ply the carcass ply max comprise a plurality of plies. In this embodiment the reinforcing elements of the reinforcing ply are nylon (polya ide) cord of 940 dtex . Other reinforcing elements which have proved effective the invention include polyamide of 2100 dtex, rayon of 1840 dtex and aramid. The reinforcing strips are preferably arranged symmetrically about the central circumferential axis X so that the reinforcing elements 3R of one strip 3 are inclined the opposite direction to those of the other strip as shown the schematic diagram of Figure 4. In accordance with the invention the reinforcing elements of the reinforcing strip may comprise cords or filaments of tyre materials sucn as textile materials such as polyamide, polyester, rayon or aramid or polyethylene naphthalate or they may comprise steel cords. Further tr- reinforcing elements may be inclined at an ang_e of between 20° and 70 r or preferably 45 to 60° to the tyre circumferential direction. Each of the reinforcing plies of the reinforcing strips 3 has a thickness m the radial direction of 0.7 mm and a width I m the axial direction measured parallel to the arc of the tread of 40 mm which is 36% of the length of the tread arc S which is one half of the tread width. In accordance with the invention the width / of eac^ reinforcing strip may be between 25% and 50% of the arc length S and its thickness the radial direction may be the range 0.5 mm to 3.0 mm. In tnis embodiment, as evidert from Figure 2 which shows an enlarged detail of the should part circled as B Figure 1, the axially outer edge 3Ξ of the reinforcing strip 3 is positioned axially inward of the outer edge 2E of the banoage ply 2 and is remote from it by a distance a wnich this embodiment is 5% of the width £ of the reinforcing strip 3. In accordance witn the present invention, the separation a between the outer edges of the reinforcing strip 3 and the bandage 2 may be up to 25% of the width L of the reinforcing strip. Furthermore the axially outer edge 3E of the reinforcing strip may alternatively be disposed axially outward beyond the edge of the bandage ply 2, as shown Figure 3, when again the distance a may lie the range of 0 to 25% of the reinforcing strip width . However no evert does the strip extend to lie between the ply turnup 8 and the ply ma portion 1. In other embodiments of the invention each of the reinforcing strips 3 may comprise two reinforcing plies, eacn comprising parallel reinforcing elements inclined at an angle of between 20°-70° to the tyre circumferential or equatorial direction X. The two reinforcing plies cf the reinforcing strip may be disposed side-by-side or preferably overlap at least partially. In a preferred arrangement one of the plies completely underlies or overlies the other ply. The two reinforcing plies cf tne reinforcing strip may be of the same axial width or they may be different widths with the wider of the two plies being either the radially inner ply as shown m Figure 5A or the radially outer ply as shown Figure 5B. the reinforcing plies may underlie or overlies each other completely as shown Figure 5A and Figure 5B or partially as shown m Figure 5C. Further the reinforcing elements of each reinforcing ply may be inclined m the same direction as shown m Figure 5A or m opposite directions as shown in Figure 5B. Furthermore the reinforcing elements of each reinforcing play may be inclined at the same angle or at different angles αl , θ and αo,β as shown m Figures 5A and 5B. Tyres prepared accordance with the invention have demonstrated improved handling characteristics. In particular the tyres have demonstrated improved stiffness and grip at maximum lean angle giving improved stability cornering together- with good straight line stability.

Claims: CLAIMS 1. A pneumatic motorcycle tyre comprising a reinforcing carcass ply of radially disposed cords extending in a mam ply portion between two bead regions through sidewall regions and a ground contacting tread region, the carcass each bead region being turned axially outward around an mextensible bead hoop ano thereafter extended radially eutward to form a turnup ply portion having a radially outer end (10), the tyre having a camber value C/L m the range 0.5 to 0.7 characterised m that the tread region is provided with a bandage ply disposed radially outward of the carcass ply extending substantially between the axial edges of the tread and comprising reinforcing cords disposed substantially parallel to the tyre circumferential direction and m the tread central portion the bandage ply is immediately adjacent to the carcass ply and in each of the axial edge portions of the tread tne bandage ply is spaced apart from the carcass ply by a reinforcing strip ( 3) comprising at least one reinforcing ply comprising textile reinforcing elements disposed at an angle to the tyre circumferential direction, the radially outer edge (10) of each turnup portion is separated from the adjacent edge of the reinforcing strip (3) by a distance of at least 5 mm. 2. A tyre according to claim 1, characterised that the reinforcing elements of the at least one ply are disposed at an angle m the range of 20° to 70°. 3. A tyre according to either of claims 1 or 2, characterised that the reinforcing elements are cords . 4. A tyre according to any of claims 1 to 3, characterised m that the reinforcing elements of the strip comprise polyamide, one or more materials selected from polyethylene naphthalate (PEN) rayon, polyester or aramid material or steel. 5. A tyre according to of claims 1 to 4, characterised that each reinforcing strip (3) has a width (*0 measured along the arc of .the tread between 25% and 50% of tne arc length (S) of the tread between the tread centre (TC) and the tread snoulder (TS ) . 6. A tyre according to any of claims 1 to 5, characterised m that the reinforcing strip (3) comprises two reinforcing plies (3A,3B;. 7. A tyre according to claim 6, characterised m that the two reinforcing plies of the reinforcing strip overlies each other at least m part. 8. A tyre according to claim 7, characterised in that one of the two reinforcing plies is disposed completely within the edges of the other reinforcing ply. 9. A tyre according to any of claims 1 to 8, characterised that the axially outer edge of each of the reinforcing strips (3) is disposed within a distance (a) measured along the carcass ply (1) from the adjacent edge of the bandage ply (2) of not more than 25% of the strip width {() . 10. A tyre according to any, of claims 1 to 9, characterised m that the axially outer edge of each of the strips (3) is disposed radially Outward of the radially outer edge of tne ply turnup portion. 11. A tyre according to any of claims 1 to 10, characterised that each reinforcing strip has a thickness m the radial direction of 0.5 mm to 3.0 mm. 12. A tyre according to any of claims 1 to 8, characterised m that each reinforcing strip has a thickness m tne radial direction of 0.7 mm.

Inventors: FAURE JEAN-LUC, MONTCEAU JEAN-PAUL, FAURE, JEAN-LUC, MONTCEAU, JEAN-PAUL
Applicants: DUNLOP SA, FAURE JEAN LUC, MONTCEAU JEAN PAUL, DUNLOP FRANCE, FAURE, JEAN-LUC, MONTCEAU, JEAN-PAUL
Application year: 2000
Main classification: B60C9
IPC codes: B60C9, B60C15