TYRE SIDEWALLS

Abstract: A tyre having a sidewall (1) with at least one letter or number presented thereon characterised by the letter or number being delineated by means of a series of closely spaced, parallel, shallow grooves (6) formed in the sidewall surface, which extend in a substantially radial direction and all said grooves (6) lie outside the said letter or number which is itself not grooved. Preferably the grooves are in areas of apparent depth only which areas are effectively shadow like areas. Tyres marked in this way have particularly visible letters or numbers.

Description: This invention relates to tyre sidewalls and to a means of improving the legibility of sidewall numbers or letters. Tyre sidewalls are subjected to constant flexure and sidewall materials are specially designed to with stand this without cracking and consequent failure. Any pattern or shape moulded into the surface inevitably provides sources of potential cracks and so efforts have been made to provide increased clarity of sidewall markings by specially shaped grooves of shallow depth. A typical system is shown in UK Patent Publication number 2010755 where special cross sections for the grooves are disclosed to improve the contrast available for markings. Such a system is effective but has limitations as much grooving is often required which provides very many potential crack initiation points although they are of course very shallow. The object of this invention is to improve the legibility of sidewall letters or numbers whilst reducing the amount of grooving and thus to reduce the potential failure sites on the sidewall. According to one aspect of the present invention a tyre sidewall is provided having a sidewall with at least one letter or number presented there on wherein the letter or number is delineated by means of a series of closely-spaced, parallel, shallow grooves formed on the sidewall surface and which extends in a substantially radial direction of the tyre sidewall and all said grooves lie outside the said letter or numeral. By grooves is meant grooves formed into the sidewall or ribs formed to provide grooves there between. The grooves may be provided all around said letter or number but more preferably the grooves extend only throughout an apparent depth zone of the letter or number. By aparent depth zone is meant the area which appears beneath it when the letter or number is lifted substantially from the sidewall surface and the sidewall is viewed at an angle. Said zone is similar to the shadow zone of the letter or numeral if lit from a point directly above the letter. Preferably, the apparent depth zone is substantially equal to the width of the line forming the letter or numeral to provide the smallest possible grooved area whilst giving effective delineation of the letter. The letter or number may also be delineated by a single raised rib having a height from the sidewall of not more than 1mm and a width of not more than 3.0mm. All the grooves are preferably less than 1mm in depth and preferably between 0.8 and 0.5mm in depth. The grooves may be of various cross sectional shapes but a prefered cross section is a triangular section with an apex of said triangle at the deepest point of the groove. Further aspects of the present invention will be apparent from the following description, by way of example only, of one embodiment in conjunction with the attached diagramatic drawings in which: Fig.1 shows a side view of a sector of a tyre sidewall with the letters SP thereon. Fig.2. is a cross section of part of one of the letters on the sidewall of Fig.1. The letters SP shown in Fig.1. are delineated from the basic tyre sidewall 1 by shaded areas 2 to 5. The shaded areas 2-8 are positioned to give the visual appearance that the letters themselves are raised above the tyre sidewall surface by a substantial distance. In fact the shaded areas cover the area that would be in shadow if the letters were raised from the sidewall, illuminated perpendicularly to their own surface and then raised from a side angle or perspective viewpoint. This shadow area is referred to herein as the apparent depth zone. The shaded areas each comprise a closely spaced set of parallel grooves 6 which are formed in the tyre sidewall as shown in Fig.2. Each groove 6 has a triangular cross-section, a depth D1 of only 0.5mm and a width D2 at the tread surface of 1.5mm. Thus the grooves are very shallow compared with the normal groove depth for standard markings. An important feature is the direction of the grooves 6 which is the radial direction of the tyre. Fig.1 shows a sector of a tyre and this has a central axis at the point A. Each letter 5 and P then has its grooves 6 lying in the radial direction. For a satisfactory appearance and clarity of letters or numerals the inventors have found the grooves should be within 10 degrees of the radial direction. In addition the groove length L is substantially equal to or less than the width X of the line forming the letters. This shading means gives letters or numbers which are particularly clear and distinctive to the human eye but secondary means of delineation may additionally be used. The secondary means comprises a 0.8mm high and 0.8mm wide rib of sidewall material 7 around the edge of each letter. This shallow rib above does not make the letters distinct but when added to the unexpectedly clear picture by the radial grooves give an enchanced clarity for the letters or numerals. The invention is particularly useful for large sidewall markings such as Trade Marks or Trade Names. It allows very large characters to be used whilst providing the very small area of only very shallow grooves and thus gives clearly marked tyres without incurring sidewall weakening features. It is particularly effective for normal black tyre sidewalls as the narrow grooves provide good reflectivity and contrast. Nevertheless, its use is not limited to only black sidewalls nor indeed is the groove section limited to triangular.

Claims: 1. A tyre having a sidewall (1) with at least one letter or number presented thereon characterised by the letter or number bneing delineated by means of a series of closely-spaced, parallel, shallow grooves (6) formed in the sidewall surface, which extend in a substantially radial direction of the tyre sidewall (1) and all said grooves (6) lie outside the said letter or number which is itself not grooved. 2. A tyre according to claim 1 characterised in that the series of radially extending grooves (6) extends only throughout an apparent depth zone (2,5) of the said letter or numeral as herein defined. 3. A tyre according to claim 1 or 2 characterised in that the grooves (6) are of similar length to the width of the line being delineated for said letter or numeral. 4. A tyre according to claim 1, 2 or 3 characterised in that the said letter or number is further delineated by a single raised rib (7) having a height from the sidewall surface of less than 1.0mm and a width nor more than 3.0mm. 5. A tyre according to any one of claims 1-4 characterised in that the grooves are less than 1.0mm in depth. 6. A tyre according to claim 5 characterised in that the grooves (6) are between 0.5 and 0.8mm in depth. 7. A tyre according to claim 5 or 6 characterised in that the grooves (6) are triangular in cross section with an apex at the defined part of the groove.

Inventors: BLAKE, ANDREW MARK, SIMPSON, MATHEW
Applicants: SP TYRES UK LIMITED
Application year: 1987
Main classification: B60C13
IPC codes: B60C13