GB2303590A

GB2303590A - Tyre tread wear indication

Info

Publication number: GB2303590A
Application number: GB9515152A
Authority: GB
Inventors: Martin Thomas Amerena; Garry Martin Lewis
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-07-24
Filing date: 1995-07-24
Publication date: 1997-02-26
Also published as: GB9515152D0

Abstract

A vehicle tyre has bands (A,B) of different coloured material at different depths beneath the surface of the tyre. As the surface (12) of the tyre wears away through contact with the road, the bands (A,B) become exposed to indicate the amount of wear that has occurred and how much safe use there is left in the tyre. The coloured bands can reveal uneven wear across the width of the tyre and the depth of tread (14) remaining.

Description

AN IMPROVED TYRB This invention relates to a vehicle tyre, particularly but not exclusively to tyres of the kind used for road and off-road vehicles and for aircraft.

Tyres for road vehicles are well known and typically consist of layers of material to form the structure of the tyre and generally having an outer layer made of a rubber compound for its flexibility and frictional properties, and its impermeability to air in a pneumatic tyre. The layer of rubber around the peripheral surface of the tyre that comes into contact with the road usually has a pattern of grooves in it known as the tread which improves the grip of the tyre particularly in wet conditions. The surface of the rubber becomes worn away through contact with the road and this decreases the depth of the tread. Shallow tread can present a potential hazard caused by loss of grip, particularly on a wet road surface. In many countries there are laws specifying the minimum permitted tread depth for safety.

Devices are available for measuring the tread depth of a tyre. Typically these devices consist of a probe that is inserted to contact the floor of a groove and another portion that remains flush with the surface of the tread alongside that groove. However, these devices can be inconvenient, time consuming to use and also imprecise. If the wear of the tyre is uneven then this may not be noticed if the tread depth is only measured at one point on the tyre, thus compromising safety. Uneven wear may be indicative of another fault such as incorrect tyre inflation or vehicle tracking misalignment. Alternatively, if care is taken to measure the tread depth at several places on the tyre, then this is even more time consuming and inconvenient. These devices also require the tyre to be stationary.This makes it difficult for law enforcement officers to detect from a distance whether moving vehicles have illegal tyres.

In other circumstances, tyres having no tread pattern are used, for example, on vehicles used in motor sport in dry conditions. In this case it may be very difficult to determine by inspection how much the rubber has worn and also whether the wear is uneven. If the rubber has worn excessively then there may be an increased risk of skidding or of a puncture. If the wear is uneven then some mechanical adjustment may be required.

It is an aim of the present invention to alleviate, at least partially, one or more of the above mentioned problems.

Accordingly the present invention provides a tyre having a surface layer for engaging a road, the surface layer having an initial thickness; and, radially inward of the surface layer, a band of material of a different colour to the surface layer that becomes exposed when the surface layer is worn away, to indicate the state of wear of the tyre.

Specific embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows in perspective a cut away of a tyre according to the invention; and Figures 2, 3 and 4 show partial cross-sections of tyres according to the invention.

Referring to Figure 1, the tyre comprises a well known structure including layers or plies 10 which can be radial-ply or cross-ply, and tread bracing layers 11 thereover. The surface layer of the tyre 12 is composed of rubber and includes a road-engaging central band, in this case having a tread 14 composed of a pattern of grooves and channels. Incorporated into the surface layer 12 are coloured bands labelled A and B. These bands although shown in cross-section go round the entire circumference of the tyre. The bands can be inserted either when first manufacturing the tyre or when remoulding the tread. The bands can be made of a rubber material into which different coloured filler materials have been mixed to distinguish the bands from the rubber layer 12, and to distinguish between bands A and B.The coloured filler used in the composition of the bands does not adversely effect their physical properties, for example of grip and flexibility.

Figure 2 shows one possible arrangement of the bands A and B. The upper surfaces of bands A are a distance d1 above the floor of the tread grooves and the upper surface of band B is a distance d2 above the bottom of the tread grooves. Distance dz is set to correspond to the minimum legal tread depth (in the United Kingdom 1.6 mm). d1 is greater than d2 and the difference between d1 and d2 is set to correspond to the amount of tyre wear caused by a predetermined usage of the tyre, for example 1,000 miles, during which the band is intended to be visible as a warning of tyre wear. As the tyre is used, the rubber layer 12 in contact with the road surface wears away until the bands A are exposed. This is evident because the material of each band A is a different colour to the layer 12.This indicates that there is then at most only a certain mileage left in the tyre, e.g. 1,000 miles, before the tread depth falls below the legal minimum. It is possible that the band A at one side of the tyre becomes exposed a significant time before the band A at the other side of the tyre. This gives an indication that the vehicle wheel tracking needs adjustment.

If further use of the tyre continues, then eventually coloured band B becomes exposed indicating that the depth of tread is below the legal minimum or some other predetermined minimum safety value.

Figure 3 shows an alternative arrangement of the bands A and B. In this case bands A are directly on top of bands B in a sandwich construction. Clearly the bands A and B must be of different colour in this arrangement. The depths d1 and d2 and the functions of the bands A and B may otherwise be the same as in the arrangement shown in Figure 2. Having a single coloured band A which extends over the middle of the tyre road-engaging portion as well as each edge, or several bands A of which one is in the middle of the road-engaging portion, serves to indicate uneven wear caused for example by incorrect inflation of the tyre as well as tracking misalignment.

Referring to Fig. 4, an alternative arrangement is to have bands A and B that extend across the complete width of the road-engaging portion of the tyre. In the case of an untreaded or slick tyre these bands form a single continuous layer beneath the surface layer 12. In a treaded tyre the bands are intersected by the tread grooves, as shown in Fig. 4, but otherwise are continuous in all parts of the tyre beneath the road-engaging surface layer.

Claims

CLAIPIEI

1. A tyre having a surface layer for engaging a road, the surface layer having an initial thickness; and, radially inward of the surface layer, a band of material of a different colour to the surface layer that becomes exposed when the surface layer is worn away, to indicate the state of wear of the tyre.

2. A tyre according to claim 1, comprising a plurality of said bands of material.

3. A tyre according to claim 2, wherein at least one of said bands is at a different depth below the initial surface of the tyre.

4. A tyre according to claim 3, wherein the colour of a band is indicative of the original depth of the surface layer.

5. A tyre according to any one of claims 2 to 4, wherein the centre of at least one of said bands is not at the same position across the width of the tyre as the centre of another band.

6. A tyre according to any one of the preceding claims, wherein said band or bands extend around the complete circumference of the tyre.

7. A tyre according to any one of the preceding claims, wherein said band or bands span the width of the roadengaging surface layer of the tyre.

8. A tyre according to any one of the preceding claims, wherein said band or bands are continuous in all parts of the tyre beneath the road-engaging surface layer.

9. A tyre according to any one of the preceding claims, wherein the surface layer includes at least one further band of a different colour than the first mentioned band and than the rest of the tyre.

10. A tyre according to any one of the preceding claims, wherein the tyre is treaded and exposure of a band occurs when a predetermined depth of tread remains.

11. A tyre substantially as described herein with reference to and as illustrated in the accompanying drawings.