RADIAL MOTORCYCLE TYRE

Abstract: A radial motorcycle tyre comprising a ground contacting tread region reinforced between its edges by a breaker structure and having a substantially curved profile in radial cross-section of the tyre, a pair of tyre beads each reinforced by a substantially inextensible bead reinforcement hoop and between each tread edge and bead region a tyre sidewall wherein each sidewall is reinforced by not more than two mutually contacting layers of carcass ply reinforcement for at least 80% of the length of the sidewall from tread edge to bead hoop and no other reinforcement fabric component such that the said 80% or more of the sidewall is substantially flexible. The sidewall preferably contains virtually no apex strip and is also short, i.e. less than 35% of the tyre sectional height (H).

Description: This invention relates to radial motorcycle tyres both for high speed road use and racing use. When considered in cross-section radial motorcycle tyres have sharply curved tread regions reinforced to provide for tread stability and interconnected at each edge to bead regions by flexibly tyre sidewalls which are replaced by radially extending reinforcement cores. The reinforcement cords are anchored in the bead regions by wrapping them around bead reinforcement cords or hoops and hard rubber apex members are positioned on the bead cores projecting radially outwards to provide bead and lower sidewall stiffness. High performance radial motorcycle tyres have begun to use additional sidewall stiffening components in both the shoulder and lower sidewall areas to enhance the stability of the tyre section and provide for good vehicle handling. A tyre according to the preamble of claim 1 is known, e.g. from FR-A-2177884. The inventors of the present invention has found, however, that an opposite approach when carried out in a particular way can give good stability and handling but provide an addition and most unexpected improvement in tyre to road grip. According to the present invention a motorcycle tyre is provided comprising a ground contacting tread region reinforced between its edges by a breaker structure and having a substantially curved profile in radial cross-section of the tyre, a pair of tyre beads each reinforced by a substantially inextensible bead reinforcement hoop and a tyre sidewal between each tread edge and bead region each sidewall being reinforced by not more than two mutually contacting layers of carcass ply reinforcement for at least 80% of the length of the sidewall from the tread edge to bead hoop such that the said 80% or more of the sidewall is substantially flexible wherein the carcass is a radial carcass, the tyre sidewalls each extends entirely radially and axially inwardly of the tread edges, and the length of the tyre sidewalls is less than 35% of the tyre sectional height. Preferably the sidewall includes not more than two inwardly contacting layers of carcass ply reinforcement for at least 90% of the length of the sidewall to further extend the length of the sidewall which is flexible. The carcass ply reinforcements are mutually in contact so that maximum flexibility is obtained and it should be noted that the lack of an apex strip of the bead core gives this mutual contact and full flexibility right down to the bead reinforcement itself. Preferably for at least 50% of the sidewall length from the tread edge towards the bead there is only one layer of carcass ply reinforcement by means of the ply overlap being short. The preferred tyre carcass has only a single ply of reinforcement material without ply overlap. The length of the tyre sidewalls is preferably less than 25%, of the tyre sectional height. Further aspects of the present invention will be apparent from the following description, by way of example only, of one embodiment of the invention which relates to a 375/700 18 inch motocycle race tyre of the slick or patternless type. The tyre comprises a tread region at which has a convex ground engaging surface (2) to allow for banking over of the machine and a toroidal carcass which together with the wheel rim (not shown) forms the air chamber for the tyre. The carcass comprises sidewall (3) and bead regions (4) reinforced by bead reinforcement hoops (5). The tread region (1) is reinforced by two fabric breaker reinforcement plies (6, 7) each comprising conventional weftless tyre fabric and these breaker plies (6, 7) extend into the tread edge regions (8). The sidewalls (3) which extend radially and axially inw ards of the tread edge regions (8) are shorter than any conventional tyres and approximately 30% of the sectional height of the tyre H. The length of the sidewalls (3) being measured from the extremity (9) of the tread edge to the nearest surface position l0 of the bead reinforcement (5) and this length is marked L in the drawing. The carcass of the tyre is reinforced by a single radial carcass reinforcement ply (ll) which comprises substantially weftless textile tyre fabric arranged with the cord at 0° to the radial plane. It should be appreciated, however, that small angles may still be used of this ply in the conventional manner for radial tyres. The carcass ply (ll) is anchored to the bead reinforcement (5) by being wrapped around it and extending radially outwards for a ply overlap region (l2). The ply overlap extends for an outstanding of L over 2 from the surface portion (l0) of the bead reinforcement (5). In the ply overlap region (l2) the reinforcement material of the overlap is adjacent to the main reinforcement and any conventional bead apex member is provided. The resultant sidewall reinforcement is substantially shorter than previous tyres of this type provides a tyre structure which is stable, gives good vehicle handling and yet provides a lighter tyre than hitherto. Most importantly, however, an unexpected advantage is obtained in that the tyre when considered in the banked over construction of the motorcycle has been found to have an increased contact area when compared to a identical tyre with standard sidewalls lengths and constructions including apex strips. This most unexpected advantage is particularly valuable in providing increased cornering power for race machines. A tyre shown also includes a bead chafer strip (l3) extending around the bead region but this has no effect on the present invention. Whilst so far the invention has been found to be particularly useful for motorcycle race tyres the invention is not so limited and applies also to motorcycle tyres for other purposes whether the high degrees of tyre stability provided and high grip are required.

Claims: A motorcycle tyre comprising a ground contacting tread region (2) reinforced between its edges (8) by a breaker structure (6,7) and having a substantially curved profile in radial cross-section of the tyre, a pair of tyre beads (4) each reinforced by a substantially inextensible bead reinforcement hoop (5) and a tyre sidewall (3) between each tread edge (8) and bead region (4), each sidewall (3) being reinforced by not more than two mutually contacting layers (11) of carcass ply reinforcement for at least 80% of the length(L) of the sidewall (3) from the tread edge (8) to bead hoop (5) such that the said 80% or more of the sidewall (3) is substantially flexible characterised in that the carcass is a radial carcass, the tyre sidewalls (3) each extends entirely radially and axially inwardly of the tread edges (8), and the length (L) of the tyre sidewalls (3) is less than 35% of the tyre sectional height (H). A tyre according to claim 1 characterised in that the length of the tyre sidewalls (3) is less than 25% of the tyre section height (H). A tyre according to claim 1 or 2 characterised in that for at least 90% of the length of the sidewall (3) the sidewall (3) includes not more than two mutually contacting layers (11,12) of carcass ply reinforcement. A tyre according to any of claims 1 to 3 characterised in that for at least S0% of the sidewall length (L) from the tread edge (8) towards the bead (4) there is only one layer (11) of carcass ply reinforcement. A tyre according to any one of claims 1-4 characterised in that the bead region (4) has no bead apex strip or other component of hard rubber extending radially outwards of the bead reinforcement hoop (5). A tyre according to claim 5 characterised in that the tyre sidewall (3) includes only one ply (11) of carcass reinforcement material and there is no ply overlap (11) the ply being anchored only at the bead hoop.

Inventors: GRIFFITHS, GERALD ANTHONY, INGLEY, PETER, WATKINS, DAVID ROBERT
Applicants: SP TYRES UK LIMITED
Application year: 1986
Main classification: B60C9
IPC codes: B60C15, B60C9, B60C3