A PNEUMATIC TYRE AND WHEELRIM FOR A MOTORCYCLE

Abstract: A pneumatic tyre and wheelrim assembly for a motorcycle wherein the tyre comprises a pair of axially spaced wheelrim engaging bead regions (6), a torroidal air pressure retaining carcass (2) reinforced by a ply (7) extending from one bead region (6) to the other bead region (6), a ground contacting tread (1) which is substantially curved in radial cross-section of the tyre and which terminates adjacent to each bead region (6) in a shoulder (3) of the tread (1) characterised by the said shoulder having a radially inwardly facing shoulder formation (4) and the wheelrim comprises a pair of axially spaced bead seats (1) one for each bead region (6) of the tyre and adjacent each bead seat (11) and axially outwards thereof a radially projecting engagement position (13) complementary to the shoulder formation (4) so that in the assembled tyre and wheelrim the tread (11) is easily located directly by the inter-­ engagement of the shoulder formations (4) and the engage­ ment portions (13).

Description: This invention relates to motorcycle tyres and in particular to tyres for high performance and racing motorcycles. When considered in cross section such tyres have sharply curved tread regions which are specially reinforced to provide the necessary tread stability for vehicle stability and steering response Conventionally the edges or shoulders of the tread region are connected to the wheelrim by reinforced sidewalls and wheelengaging bead regions and these regions too have direct influence on the vehicle characteristics. An assembly according to the preamble is known, e.g. from US-A-2477754. An object of the present invention is to still further improve tread stability so that the tyres may provide even better handling characteristics for the vehicle. This object is achieved by the features of claim 1. The present invention provides a pneumatic tyre and wheelrim assembly for a motorcycle wherein the tyre comprises a pair of axially spaced wheelrim engaging bead regions, a torroidal air pressure retaining carcass reinforced by a reinforcing ply extending from one bead region to the other bead region, a ground contacting tread which is substantially curved in radial cross-section of the tyre and which terminates adjacent to each bead region in a shoulder of the tread the said shoulder having a radially inwardly facing shoulder formation and the wheelrim comprises a pair of axially spaced bead seats, one for each bead region of the tyre and adjacent each beadseat and axially outwards thereof a radially projecting engagement portion complementary to the shoulder formation so that in the assembled tyre and wheelrim the tread is radially located directly by the interengagement of the shoulder formations and the engagement portions. This tyre thus has no sidewalls in the conventional sense and the tread is directly located by the wheelrim. The shoulder formation also faces axially outwardly of the tyre and the complimentary engagement portion faces axially inwards so that increased axial location of the tread on the wheelrim is provided. The tyre, which is preferably a radial ply or substantially radial ply tyre, has a tread reinforcing breaker in the tread. The breaker extends parallel to the ground contacting surface of the tread and into both shoulders such that the breaker in the shoulders is substantially perpendicular to the interengaging surfaces and the location thus also acts directly on the breaker. The carcass reinforcing ply may also approach the shoulders substantially perpendicularly and then bend sharply axially and radially inwards towards the bead region. The invention further provides a tyre and wheelrim assembly in which the reinforcement ply may be wrapped around an anular bead reinforcement loop in each bead region. The carcass may have one, two or more reinforcement plies and may have the cords of the plies at 70° - 90° to the circumferential direction to provide a basic radial tyre type of carcass. Preferably the breaker ply or plies extends right into the shoulder regions. Further aspects of the present invention will be apparent from the following description, by way of example only, of one embodiment of the invention in conjunction with the attached diagramatic drawing which is a part transverse cross section of a tyre and wheel rim. The tyre is a radial ply racing motorcycle tyre of the slick or tread patternless type and is mounted on a wheelrim which has a conventional fitting well, not shown. The tyre comprises a tread region which has a markedly convex cross section to provide for banking over of the machine and a torroidal carcass 2 which together with the wheelrim forms the air containing chamber for the assembly. The tread region 1 terminates at either side in a shoulder 3 which has a radially inwardly and axially outwardly facing concave abutment face or shoulder formation 4. The abutment face 4 provides effectively the tread edge. The carcass 2 comprises a carcass crown 5 which extends beneath the tread 1 from the centreline of the tyre C to each side at the points A1. Beginning at the points A the carcass has a pair of bead regions 6 each of which is adopted to fit the wheelrim and provide an air seal and a mechanical engagement in the conventional manner. The carcass 2 is reinforced by a single ply 7 of tyre cord fabric (shown by a continuous line) which extends from one bead to the other around the carcass and which is, in each bead region 6, wrapped around a steel cord bead reinforcement hoop 8. The reinforcing ply 7 comprises rayon cords laid at an angle of 88° to the circumferential direction to provide a radial ply of reinforcement. The carcass 2 also includes two plies of tread reinforcement or breaker layers 9 and 10 (both shown by broken lines). These breaker plies 9 and 10 comprise steelcord tyre breaker fabric and the cords of each ply are laid in opposing senses at an angle of 21° to the centreline of the tread around the tyre. Most importantly both breakers 9 and 10 extend to the tread edges 3 and thus terminate close to the abutment face 4. The wheelrim comprises a pair of axially spaced apart tapered bead seats 11 and radially outwardly projecting flanges 12 but the flanges 12 continue radially outwardly and curve axially outwardly to provide substantial curved abutment faces 13 adjacent to the tread edge faces 4. In the normal unloaded inflated condition the abutment faces 4 at the tread edges are in contact with the abutment faces 13 on the wheelrim thus in use the tread of the tyre together with its reinforcement or breaker package is positively located by the mechanical engagement of the wheelrim. The resultant assembly, in having no sidewalls to provide a flexible connection between the wheelrim and tyre bead, provides greatly improved steering response and handling in a motorcycle. Many different carcass constructions may be used including monoply reinforcements and cross ply carcass constructions. The tyre may have different breaker constructions. Ply and breaker fabric materials may be any of those known in the art dependent on the particular tyre structural properties required. Furthermore the tyre tread may be patterned as well as smooth. The tyre beads may be of different constructions and use alternative reinforcement hoops and it is believed that the direct tread support system, in removing the need for the bead to be constructed to give support to the sidewalls, allows simpler beads to be utilised than hitherto. It is considered that the most important properties of the tyre are that the torroidal air retaining chamber is substantially separate from the tread locating features and thus both may be optimised.

Claims: A pneumatic tyre and wheelrim assembly for a motorcycle wherein the tyre comprises a pair of axially spaced wheelrim engaging bead regions (6), a toroidal air pressure retaining carcass (2) reinforced by a reinforcing ply (7) extending from one bead region (6) to the other bead region (6), a ground contacting tread (1) which is substantially curved in radial cross-section of the tyre and which terminates adjacent to each bead region (6) in a shoulder (3) of the tread (1) and a tread reinforcing breaker (9, 10) disposed radially outside the carcass (2) and extending parallel to the ground contacting surface of the tread, said wheelrim comprising a pair of axially spaced bead seats (11) one for each bead region (6) of the tyre and adjacent each bead seat (11) and axially outwards thereof a radially and axially projecting wheel rim engagement portion (13), the shoulder (3) having a shoulder formation (4) facing radially inwardly and axially outwardly such that the surface of the wheel rim engagement portion (13) contacts the tyre face axially inwardly and radially outwards complementary to the shoulder formation (4), characterized in that the tread (1), the breaker (9,10) and the radially outer end of the wheelrim engagement portion (13) extend to a position of substantially the same radial height, so that in the assembled tyre and wheelrim the tread (1) is at any time readily located directly by the interengagement of the shoulder formations (4) and the wheel rim engagement portions (13) over the entire area of all parts of the surface of the wheelrim engagement portions (13) under all conditions and that all reaction forces are directed inwardly on to the edges of the breaker (9,10). A pneumatic tyre and wheelrim assembly according to claim 1 characterised by the carcass (2) being substantially radial reinforced by cords at 70° to 90° to the circumferential direction of the tyre and the tread reinforcing breaker (9,10) extending into both shoulders (3) such that the breaker (9,10) is substantially perpendicular to the interengaging faces of the tyre and the wheel rim. A pneumatic tyre and wheelrim assembly according to claims 1 or 2 characterised in that the reinforcing ply (7) beneath the tread (1) extends substantially parallel to the ground contacting surface of the tread (1) into both shoulders (3) of the tread such that the reinforcing ply (7) is substantially perpendicular to the interengaging faces of the tyre and the wheel rim and the location acts on the reinforcing ply (7). A pneumatic tyre and wheel rim assembly according to claim 3 characterised in that the reinforcing ply (7) in the shoulder (3) bends sharply axially and radially inwards towards the bead region (6). A pneumatic tyre and wheelrim assembly according to any one of claims 1-4 wherein the reinforcing ply (7) is wrapped around an annular bead reinforcement hoop (8) in each bead region (6). A pneumatic tyre and wheel rim assembly according to claim 5 characterised in that the reinforcing ply (7) comprises two plies.

Inventors: GRIFFITHS, GERALD ANTHONY, INGLEY, PETER, WATKINS, DAVID ROBERT
Applicants: SP TYRES UK LIMITED
Application year: 1986
Main classification: B60C15
IPC codes: B60C9, B60C15, B60C11, B60C3