GB2582626A

GB2582626A - Improvements in and relating to tyres

Info

Publication number: GB2582626A
Application number: GB1904322.3A
Authority: GB
Inventors: Adams Richard
Original assignee: GECKO RUBBER Ltd
Current assignee: GECKO RUBBER Ltd
Priority date: 2019-03-28
Filing date: 2019-03-28
Publication date: 2020-09-30
Anticipated expiration: 2039-03-28
Also published as: GB201904322D0; GB2582626B

Abstract

A tyre 101 comprising an annular expanded rubber body 102 enclosing a concentrically arranged annular cavity 106 containing a fluid (e.g. air), the body 102 having an opening 107 providing fluid communication from outside the tyre body to the cavity 106, and at least one valve 105 for controlling flow of fluid through the opening 107. Preferably, the tyre body comprises a tread surface (103; fig. 2a), a wheel attachment surface (104; fig. 2a), and opposing side wall surfaces, at least the side walls being formed by the expanded rubber body 102. The tread 103 may also be formed by the body 102, or may be a bonded solid rubber part (203; fig. 3a). The body 102 may include a seam (108; fig. 2a) between the cavity 106 and the outer surface of the body, sealed with sealant. There may be an inner tube in the cavity. There may be multiple cavities (e.g. see figures 5-9a, 10a-10b), each including inner tubes. Also disclosed is a wheel assembly comprising a wheel rim and a tyre attached to the wheel rim. The tyre may be suitable for a bicycle (figs 1-4), an automobile (figs 5-9), or a heavy goods vehicle (figs 10a,b).

Description

Intellectual Property Office Application No. GB1904322.3 RTM Date:15 August 2019 The following terms are registered trade marks and should be read as such wherever they occur in this document: Instron (page 4, 10) Schrader (page 14) Dunlop (page 14) Mocon (page 21) Intellectual Property Office is an operating name of the Patent Office www.gov.uk /ipo -1 -Improvements in and relating to tyres

Field of the Invention

The present invention concerns tyres. More particularly, but not exclusively, this invention concerns vehicle tyres and tyre assemblies comprising an expanded rubber body, a cavity containing a fluid, and a valve for regulating flow of fluid into and/or out of the cavity. The invention also concerns kits of parts for such tyre assemblies.

Background of the Invention

A tyre is a ring-shaped component that surrounds the rim of a wheel, typically provided to cushion the wheel from a surface. Vehicle tyres act as points of contact between a vehicle and the ground, thereby transferring a vehicle's load to the ground.

Typically, a wheel assembly comprises a wheel hub for attachment of the wheel to a vehicle, a wheel rim forming a ring surrounding the wheel hub, and a tyre forming a ring surrounding the wheel rim. The tyre may be attached to the wheel rim. The rim may be attached to the hub, for example by one or more supporting members (e.g. in the form of a disc or spokes).

The resistance of a vehicle tyre to deformation during use affects both tyre and vehicle performance, and is an important property. In some instances, it is desirable to be able to modify the resistance of a vehicle tyre against forces that act to deform the tyre, e.g. to suit the environment in which the vehicle is being used. In commonly used pneumatic tyres, the tyre and the wheel together define a ring-shaped air pocket.

Typically, the resistance of the tyre to deformation is adjusted by altering the air pressure within the air pocket. Air pressure in the tyre pocket is commonly referred to as 'tyre pressure'. Variations in tyre pressure typically alter the area of the tyre surface that contacts the ground during use. For example, an increase in tyre pressure typically increases the deformation resistance of the tyre, thereby decreasing the area of contact between the tyre and ground and reducing rolling resistance, while decreasing tyre pressure typically decreases the deformation resistance of the tyre, thereby increasing the area of surface tread in contact with the ground, often improving grip.

A disadvantage of conventional pneumatic tyres is their susceptibility to puncturing. Modern pneumatic tyres are typically a trade-off between puncture resistance, weight, durability, comfort and road grip. For example, durability and puncture resistance may be improved by using a harder and/or tougher material to form the tyre, but often at the cost of comfort and road grip. Alternatively, a thicker layer of softer material may improve puncture resistance, but often at the cost of weight and performance. Continued use of a vehicle with a 'flat' (i.e. deflated) tyre often leads to damage of the tyre and/or the wheel rim. Typically, when a tyre is punctured, the resulting loss of tyre pressure causes the tyre to collapse under the weight of the vehicle. Some tyre manufacturers have developed so-called 'run-flat' tyres, often having reinforced side walls that prevent total collapse of the tyre when pressure is lost from the air pocket. The operating range and performance of such tyres when 'running flat' is often limited, and side wall reinforcement typically increases weight and cost of the tyre.

Unlike pneumatic tyres, solid rubber tyres are not susceptible to puncture and may offer similar road grip as a pneumatic tyre made of the same material. However, solid rubber tyres typically suffer from problems of unacceptably high weight and poor comfort. Puncture proof (i.e. 100% puncture resistant) tyres of similar weight to traditional pneumatic tyres may alternatively be formed from cast foam polyurethane materials. However, polyurethane materials are often unsuitable for use on the outer surface of vehicle tyres because of their inferior grip characteristics as compared to traditional pneumatic tyres usually made from a rubber material. Encasing polyurethane foam inside a rubber tyre shell may improve grip, but complicates manufacture and it has been found that the stiffness of polyurethane materials can result in ride quality and handling considerably inferior to that enjoyed with a traditional rubber pneumatic tyre.

The mechanical properties of solid rubber tyres and cast foam polyurethane tyres, such as resistance to deformation, are dictated at the point of manufacture and cannot later be altered to improve passenger comfort or vehicle performance. Recently, expanded rubber materials have been used to make puncture resistant and/or puncture proof tyres of similar weight and mechanical properties to traditional pneumatic tyres. WO 2015/198040 Al discloses a process for making expanded rubber articles, such as moulded tyres. The two stage manufacturing process disclosed therein enables the shape and size of the expanded rubber article to be precisely controlled. The resultant expanded rubber moulded tyre is lighter than a solid rubber tyre of the same volume and is less susceptible to puncturing than a modern pneumatic tyre. The use of a rubber material (rather than polyurethane, for example) provides grip and handling properties more comparable to those of a conventional rubber pneumatic tyre, while avoiding undue complications in manufacture.

US 2010/0122758 Al discloses a tyre including a foam portion made of rubber or plastic material and foamed integrally to be a ring-shaped foam portion, and a resilient portion received in the foam portion and having a hollow space defined therein. US 2007/0056670 Al discloses a tyre having a core located in a tyre cavity and a cured and foamed elastomeric material located in the tyre cavity adjacent to the core. The core may be made from a solid material, a precured and foamed elastomeric material or a hollow rigid structure. However, the hollow space or cavity of the tyre is inaccessible after manufacture. Tyres having an expanded rubber part and methods for making such tyres are also disclosed in CN101204911; US 4,060,578; US 1,227,791; US 2002/0129883; EP0594072 Al; US 2008/0142136 A1; and WHO1254411.

Expanded rubber materials (also known as foam rubber or sponge rubber materials) are materials formed from a matrix of rubber filled with air in pockets and/or channels. In closed cell expanded rubber materials, the air is contained in discrete pockets, whilst open cell expanded rubber materials comprise interconnected air-filled cells. As used herein, the term "expanded rubber" refers to both open cell and closed cell expanded rubber materials; the term "solid rubber" refers to (at least partially cured) rubber materials that have not been expanded to form an air-filled matrix.

Expanded rubber articles are typically significantly lighter than solid rubber articles of the same volume, and may, for example, be at least 90 % lighter. For example, if a natural rubber (NR) part has a specific gravity (SG) of 1.2, an equivalent expanded rubber part typically has an SG of 0.12 or less. A further advantage of expanded rubber articles is that they commonly consist of less rubber material than an equivalently sized solid rubber article, and so may, for example, be less costly to -4 -produce. In the automotive and aeronautical industries in particular, reducing weight is especially useful for reducing fuel consumption of vehicles and craft.

Another advantage of expanded rubber materials is that they may have a shore hardness as low as 5 shore A, whilst the minimum shore hardness of solid rubber materials is usually around 30 shore A (as measured using an InstronTM hand-held hardness gauge, Shore A type, according to the ASTM D2240 test method). The softer expanded rubber material offers sealing properties not normally found with solid rubber materials because the expanded rubber is more deformable and thus forms better seals around other objects. In particular, an expanded rubber part may deflect at lower loadings than an equivalently sized solid rubber part because the modulus (which typically decreases with increasing 'softness') of expanded rubber is considerably lower than that of solid rubber. The (open/closed) microcellular structure of expanded rubber confers a lower modulus to the bulk material than the solid structure of non-expanded rubber.

In comparison to solid rubber materials, expanded rubber materials may, for example, offer improved vibration isolation and vibration damping, anti-shock and noise insulation. Expanded rubber materials can be formulated to offer a range of vibration/noise isolation and damping properties. For example, the hysteresis properties of the expanded rubber material can be controlled by including in the expandable rubber formulation different rubber polymers, fillers, process aids and curing systems.

It will be appreciated that an expanded rubber tyre should be able to cope with a variety of loads depending on the vehicle type, and provide reliable service over an extended time period and/or distance. For example, a bicycle tyre should be able to cope with loads of up to 100 kg when installed on a bicycle wheel and provide 5 years or more and/or 5000 miles or more service without discernible and/or significant deterioration of its properties including its shape, texture, hardness and grip.

Similarly, an automotive tyre should be able to cope with loads of up to 1000 kg when installed on an automobile wheel and provide 5 years or more and/or 30000 miles or more service without discernible and/or significant deterioration of its properties including its shape, texture, hardness and grip. -5 -

The present invention seeks to mitigate the above-mentioned problems.

Alternatively or additionally, the present invention seeks to provide an improved expanded rubber moulded tyre.

Summary of the Invention

The invention provides a tyre assembly for engagement with a wheel rim, the tyre assembly comprising: a tyre body having a tread surface, a wheel attachment surface, opposing side wall surfaces extending between the wheel attachment surface and the tread surface; a concentrically arranged annular cavity containing a fluid; and at least one valve for controlling flow of fluid from outside the tyre assembly to the at least one cavity, wherein the tyre body includes an expanded rubber body disposed between the cavity and the tread surface and between the cavity and the side wall surfaces. The expanded rubber body is optionally a concentrically arranged annular body. The expanded rubber body optionally encloses the annular cavity and has at least one opening providing fluid communication from outside the tyre assembly to the at least one cavity, wherein the at least one value is disposed in said at least one opening. Alternatively, the at least one cavity is optionally defined between the expanded rubber body and a wheel rim of a wheel with which the tyre body is engaged in a wheel assembly, at least one opening providing fluid communication from outside the tyre assembly to the at least one cavity is provided in the expanded rubber body or the wheel rim and at least one value is disposed in said at least one opening.

The present invention provides, according to a first aspect, a tyre assembly comprising a tyre body comprising an annular expanded rubber body enclosing at least one cavity containing a fluid and having at least one opening providing fluid communication from outside the tyre body to the at least one cavity, and at least one valve for controlling flow of fluid through the opening. Optionally, the at least one cavity is an annular cavity, e.g. arranged concentrically with the annular expanded rubber body. It will be appreciated that the annular expanded rubber body and the annular cavity are concentric when they share the same centre, for example wherein the shared centre lies at the centre of a wheel hub when the tyre assembly is mounted on a wheel. Optionally, the valve is disposed in the at least one opening. -6 -

Alternatively, the valve is located at least partially outside the at least one opening, for example entirely outside the at least one opening (for example, the valve may be joined to an entrance of the at least one opening, option directly or via a conduit). Optionally, the cavity is configured so that when the tyre assembly is attached to a wheel rim, the cavity is disposed circumferentially around the wheel rim. Herein, the term wheel rim refers to the edge of a vehicle wheel that makes contact with the tyre assembly, and which is connected to a wheel hub. Optionally, the number of openings corresponds to the number of cavities, for example wherein the tyre assembly comprises a single opening for each cavity. Optionally, the number of valves corresponds to the number of openings, for example wherein the tyre assembly comprises a single valve for each opening. Alternatively, it may be that the tyre assembly comprises a single valve for controlling flow of fluid through a plurality of openings (for example, the plurality of openings may be in fluid communication with each other and with a valve). It will be appreciated that the at least one cavity is wholly contained within the expanded rubber body, such that the at least one cavity is entirely surrounded by the expanded rubber body except at the at least one opening. Optionally, the fluid is a gas. The gas may be a gas mixture, for example air or a mixture including nitrogen. Preferably, the expanded rubber body is a moulded expanded rubber body.

The present inventor has discovered that many of the benefits of an expanded rubber moulded tyre are provided when only an outer portion of the tyre is formed of expanded rubber. Furthermore, when an expanded rubber moulded tyre is provided with an interior cavity that is in fluid connection with the exterior of the tyre, many of the benefits of a conventional pneumatic tyre can be imparted to a tyre constructed from expanded rubber. Therefore, providing a cavity containing a fluid in the expanded rubber body and a valve for controlling flow of fluid into and/or out of the cavity has been found to provide an advantageous combination of properties of a pneumatic tyre with those of an expanded rubber tyres. For example, having the at least one cavity enclosed by an expanded rubber body may provide effective puncture resistance without unduly increasing tyre weight and/or compromising performance such as grip. Furthermore, having a cavity and valve for controlling flow of fluid into and/or out of the cavity allows fluid pressure within the cavity to be varied, thereby providing convenient replication of the feel of a pneumatic tyre and/or the ability to -7 -vary tyre pressure during use. For example, an annular cavity concentrically arranged with the annular expanded rubber body may allow fluid to move throughout the tyre, thereby providing a consistent cushioning effect as the tyre rotates under load. Optionally, the expanded rubber body is an open cell or closed cell, e.g. closed cell, expanded rubber. Optionally, the expanded rubber body comprises one or more rubber polymers selected from the list consisting of natural rubber (NR), butadiene rubber (BR) and styrene butadiene rubber (SBR). Such rubber polymers have been found to offer high resilience, good tensile strength and tear resistance, and are widely available materials. Additionally, SBR, BR and NR are cost effective elastomeric materials. Optionally, the expanded rubber body is formed from an expandable rubber formulation comprising an elastomeric material. For example, the expanded rubber body may be formed by a curing and expanding an expandable rubber formulation.

As used herein, the term elastomeric material refers to a natural or synthetic material comprising polymers and/or oligomers and, optionally, monomers, wherein the material has elastic properties. Preferably, the elastomeric material is a curable rubber, such as a vulcani sable rubber. 'Curable rubbers' are rubber materials capable of being toughened or hardened by crosslinking of polymer and/or oligomer chains in the rubber material. Optionally, the curable rubber is partially cured. Preferably, the elastomeric material is a sulfur-curable rubber. It may be that an elastomeric material comprising a sulfur-curable rubber provides a tyre having excellent grip, handling and ride comfort when used on a variety of road and/or track surfaces in various conditions. For example the tyre may have particularly good dynamic physical rubber properties as compared to tyres made from a different expanded material, such as polyurethane foam.

Optionally, the expandable rubber formulation used to form the expanded rubber body additionally comprises a curing agent and an expansion agent. The curing agent is preferably a vulcanisation agent. As used herein, the term vulcanisation agent' refers to any substance that promotes crosslinking of elastomeric polymer chains. Preferably, the curing agent is a sulfur-based curing agent.

Preferably, the curing agent comprises sulphur. As used herein, the term 'expansion agent' refers to a substance capable of promoting expansion of the expandable rubber formulation, for example via a foaming process. Preferably, the expansion agent is a -8 -blowing agent, for example a chemical blowing agent. Chemical blowing agents are substances that undergo chemical reactions to produce gaseous products. Preferably, the expansion agent expands the expandable rubber formulation by evolving a gas (e.g. nitrogen), thereby providing a gas-filled rubber matrix in which the gas fills discrete or interconnecting pockets. Preferably, the curing agent and the expansion agent are thermally-activated and are activated by heating the expandable rubber formulation. Advantageously, the curing agent is activated at a temperature of from 120 °C to 170 °C. Preferably, the curing agent comprises sulphur, an accelerator and an activator. For example, the curing agent may comprise an accelerator selected from the list consisting of N-cyclohexyl-2-benzothiazylsulphenamide (CBS), mercaptobenzothiazole (MET) or tetramethylthiuram disulphide (TMTM). A bisphenol cure system may, optionally, be used with FKM, or a peroxide cure system with EPDM. Optionally, the expansion agent comprises a gas-releasing component that decomposes to evolve gas, especially nitrogen gas, when heated and, optionally, an initiator that initiates decomposition of the gas-releasing component at a temperature lower than the normal decomposition temperature of the gas-releasing component. Preferably, the optional gas-releasing component is a chemical blowing agent that evolves useful quantities of gas when heated to vulcanisation temperatures, for example when heated to a temperature of from 120 °C to 170 °C. Preferably, the chemical blowing agent is stable during processing and in the presence of the curing agent, and is easily dispersed during mixing. Optionally, the expansion agent comprises a chemical blowing agent selected from the group consisting of azodicarbonamide (ADC), Dinitrosopentamethylene Tetramine (DNPT), ppoxybi sbenzene sulphonyl hydrazide (OBSH) and benzene sulphonyl hydrazide (BSH).

Preferably, the expansion agent comprises an initiator, or "kicker," to lower the activation temperature of the optional gas-releasing agent. Optionally, the expansion agent comprises a kicker and a chemical blowing agent. The kicker acts as a 'process aid' and may, for example, be selected from the group consisting of acids, bases, organic alcohols and metal compounds. The expanded rubber body, may, for example, be a closed cell expanded rubber comprising one or more rubber polymers selected from the list consisting of natural rubber (NR), butadiene rubber (BR) and styrene butadiene rubber (SBR) together with a curing agent and/or an expansion agent. -9 -

Optionally, the elastomeric material comprises one or more high viscosity unsaturated rubber polymers. Typically, an expandable rubber formulation comprising a rubber elastomeric material, a blowing agent and a curing agent (and any other optional components, such as oils, fillers and/or anti-degradants) has highly viscous, putty-like consistency. The elastomeric material may, for example, comprise one or more rubber polymers, or be a blend of two or more rubber polymers, selected from the group consisting of natural rubber (NR), styrene butadiene rubber (SBR), butadiene rubber (BR), brominated isobutylene-isoprene based rubber (BIIR), acrylonitrile butadiene rubber (NBR), polychloroprene rubber (CR), ethylene propylene diene monomer rubber (EPDM) and fluorinated elastomers (FKM). In particular, the elastomeric material may comprise NR, BR or SBR, or a blend of NR, BR and SBR. For example, the elastomeric material may comprise a blend of SBR, NR, BR and BI IR. It has been found that SBR, BR and NR offer high resilience, good tensile strength and tear resistance, and are widely available materials.

Additionally, it has been found that SBR, BR and NR are cost effective elastomeric materials and are often referred to as 'general purpose' rubbers. Preferably the elastomeric material comprises, for example the elastomeric material consists substantially of, one or more rubber polymers curable by sulfur vulcanisation.

Optionally, the expandable rubber formulation comprises one or more process aids. Suitable process aids include naphthenic or paraffinic process oil and/or cross-linked oil. Process aids have been found to improve network viscosity during the moulded blank formation step, and, for example, during the expansion of the expandable rubber formulation.

Optionally, the expandable rubber formulation comprises a filler. It has been found that a filler may, for example, reinforce the expanded rubber article.

Preferably, the filler is selected from the group consisting of carbon black fillers (such as Super Abrasion Furnace, High Abrasion Furnace, Fast Extrusion Furnace) and other non-black fillers (such as clay, chalk and silica). For example, the expandable rubber formulation may comprise silica and a silane coupling agent. It has been found that the silane coupling agent may, for example, crosslink the filler into the polymer network to improve the physical properties of the vulcanised rubber.

-10 -Further optional additives to the expandable rubber formulation include antidegradants (such as phenylphenylene diamine (DPPD) and/or alkylphenylene diamine (6PPD)).

Optionally, the expanded rubber body has a high modulus. The hardness can, for example, be measured using an Instron hand held Shore A hardness gauge.

Preferably, the expanded rubber body has a hardness of from 40 to 70 Shore A, for example 45 to 65 Shore A. It will be understood that the expanded rubber body may be manufactured with a thin layer of a higher density, harder expanded rubber at its surface (referred to as a 'skin' layer). The thickness of the skin layer can be varied by adjustment of e.g. the rubber composition, moulding temperature, moulding pressure and moulding time. Typically, the expanded rubber body has a skin thickness of up to 1.5 mm, such as up to 1 mm, for example up to 0.5 mm. As used herein, the hardness of the expanded rubber body is the hardness of the expanded rubber body core, that is, excluding the skin layer. Optionally, the skin layer has a hardness around 10 Shore A higher than the hardness of the core of the expanded rubber body. It may be that the modulus of the expanded rubber body varies as between the centre of the body and the skin at a surface of the expanded rubber body. Preferably, the expanded rubber core has a modulus of at least 40 Shore A, for example at least 45 Shore A, at the centre of the body and/or a modulus of no more than 80 Shore A, for example no more than 75 Shore A, at the surface skin of the body. Preferably, the expanded rubber body has a density of from 0.2 to 1 kg/litre, such as 0.4 to 0.8 kg/litre, for example approximately 0.60 kg/litre. It may be that tyre comprising a high modulus, low density expanded rubber body has very good dynamic and physical properties whilst also being light as compared to solid rubber material. It may be that such a tyre is particularly durable.

Optionally, the tyre assembly is a vehicle tyre assembly. Examples of vehicles include a bicycle (e.g. a conventional pedal cycle, commonly referred to as a pushbike), a motorcycle (including, for example, motorised scooters and/or high performance motorcycles), an industrial or agricultural vehicle, an automobile, a light commercial vehicle and/or a large goods vehicle. As used herein, a motorcycle is a motorised, two-or three-wheeled vehicle (also known as a motorbike); a small motorcycle is a motorcycle having a power output of up to 11kW (e.g. having a cylinder capacity of no more than 125 cc in the case of combustion engined motorcycles); a large motorcycle has a power output of up to 35 kW (e.g. above 125 -11 -cc). As used herein, an automobile is any motorised passenger transport vehicle having four or more wheels (including, for example, passenger cars, multi-purpose vehicles, off-road vehicles, roadsters). As used herein, a light commercial vehicle is a commercial vehicle having a gross weight of no more than 3.5 metric tons (including vehicles commonly referred to as vans and/or pickups) As used herein, a large goods vehicle is a commercial vehicle having a gross weight of more than 3.5 metric tons (including vehicles commonly referred to as heavy goods vehicles, lorries and/or trucks). As used herein, industrial and agricultural vehicles are vehicles intended for use in industry and agriculture, respectively, including vehicles licenced for use on public roads. Non-limiting examples of industrial and agricultural vehicles include fork-lift trucks and tractors. Optionally, the tyre assembly comprises a moulded tyre, such as a moulded tyre configured to have a resistance fit with a wheel rim.

Additionally or alternatively, the tyre assembly comprises one or more clips for attachment of the moulded tyre to a wheel rim. Optionally, the tyre assembly comprises a plurality of clips sized and configured to engage with a wheel rim to hold the tyre in place on the wheel. Preferably, each clip is in the form of a staple, for example a metal staple (such as a stainless steel metal staple) or a glass filled nylon staple (such as a glass filled nylon staple comprising approximately 30% glass). Preferably, the clip is at least partially embedded in the tyre body, for example at least partially embedded in the expanded rubber body of the tyre. It will be appreciated that it is particularly important to have an expanded rubber body with a high tear strength when using such embedded clips. Preferably, the tyre comprises at least 10 pairs, for example at least 16 pairs of clips, substantially equally spaced around the inner circumference of each tyre sidewall. Preferably, the plurality of clips is arranged to be pushed into place at least partially under the edge of the rim (for example entirely under the rim in the bead recess) of a wheel, thereby resiliently holding the tyre in place on the wheel. Optionally, the tyre assembly comprising one or more clips is a tyre assembly for use with a bicycle or a motorbike. Preferably, the clips are arranged so that the tyre can be pushed into place inside the rims of the wheel without damaging the tyre, for example by pushing against the clips rather than the rubber surface of the tyre. Optionally, each clip comprises a plurality of prongs extending from an elongated base portion, the prongs being arranged to penetrate the expanded rubber body of the tyre thereby securing the elongated body to a surface of -12 -the tyre. Preferably, the prongs are configured to pass through the expanded rubber body from one side to the other. Optionally, each clip is sized and configured to cooperate with another clip disposed on the opposite side of the tyre, optionally wherein at least two of the prongs of one clip engage with a part of the other clip.

Preferably, the elongated base portion has a curved profile to fit with the circumferential shape of the wheel rim bead recess. It will be understood that a bicycle wheel rim often has a U-shaped cross section, with inwardly depending lips at the open top of the U. Such inwardly depending lips are typically referred to as the clinchers. As used herein, the inter-rim spacing is the gap between opposed sides of the U-shaped rim, and the inter-clincher spacing is the gap between opposed inwardly depending lips, and the clincher overhang is the distance that each inwardly depending lip extends from the inner surface of the side of the U-shaped rim. Preferably, width of the elongated base portion of the clip is about the same as the clincher overhang. Preferably, the length of at least two of the prongs is larger than the inter-clincher spacing and smaller than the inter-rim spacing, optionally about the same as the inter-clincher spacing plus the clincher overhand. Optionally, the prongs have a length of at least about 30 mm, a width of about 3.5 mm, a spacing of about 17 mm, and a material thickness of about 1.5 mm. In use, it may be that the clips allow the tyre to be fitted onto the wheel by stretching the tire around the wheel as one sidewall of the tire and the clips on that sidewall of the tire are placed between the rims of the wheel and then pushing the clips on the other sidewall between the rims to compress the tire into place. It may be that the clips are sized and configured such that they can be conveniently pushed into place using a flat-headed screwdriver, a flat headed tyre lever or a similar tool, or they can be pushed in by the use of a rubber mallet directed on the shoulder of the tyre over the clip. Such clips may, for example, conveniently allow the moulded tyre to be fitted to a conventional wheel rim, such as a wheel rim designed for use with a conventional pneumatic tyre.

Additionally or alternatively, the tyre assembly comprises one or more security bolts for securing the moulded tyre to a wheel rim. Optionally, the one or more security bolts, if present, is configured to pass through a least part of the wheel rim and at least part of the expanded rubber body. For example, the one or more security bolts may be configured to penetrate the wheel rim and the expanded rubber body. -I3_

Optionally, the expanded rubber body comprises one or more moulded through-passages for accommodating a security bolt.

Optionally, the at least one cavity is configured to contain a fluid at a pressure higher than ambient pressure, optionally when the tyre assembly is mounted on a wheel. It will be understood that ambient pressure is the pressure outside the tyre assembly, such as atmospheric pressure. It will be appreciated that the tyre assembly may be configured to cooperate with a wheel (e.g. with the rim of a wheel) so that the wheel and the tyre assembly are together structured to contain the fluid at a pressure higher than ambient pressure. It will be appreciated that suitable tyre pressures vary considerably according to the nature of the vehicle they are designed for and the use that the vehicle is intended for. For example, an agricultural vehicle may have a tyre, pressure as low as 5 psig (0.34 barg), while a high performance road bicycle may have a tyre pressure as high as 110 psig (7.6 barg). As used herein, psig' and barg' are gauge pressures, indicating the amount by which the measured pressure exceeds atmospheric pressure. Optionally, the at least one cavity contains the fluid at a pressure of at least 5 psig (0.34 barg), for example at least 10 psig (0.69 barg), optionally at least 20 psi (1.38 barg), such as at least 30 psig (2.07 barg). Optionally, the at least one cavity contains the fluid at a pressure of from 5 psig (0.34 barg) to 200 psig (13.79 barg), for example from 10 psig (0.69 barg) to 180 psig (12.41 barg), optionally from 20 psi (1.38 barg) to 150 psig (10.34 barg), such as from 30 psig (2.07 barg) to 100 psig (8.27 barg). Optionally, the expanded rubber body is configured such that the cavity is capable of containing the fluid at such pressures, optionally when the tyre assembly is mounted on a wheel. Filling the cavity of the tyre assembly with a fluid (such as gas, e.g. air), results in an increase in pressure within the cavity.

At high pressure, the tyre is less deformable as a result of external forces, resulting in a firmer ride but with lower rolling resistance. An increase in cavity pressure results in less of the surface area of the tyre being in contact with the road surface. This lowers the resistance between the ground and the tyre, decreasing the rolling resistance. On the other hand, a decrease in cavity pressure makes the tyre more susceptible to deformation, and increases the area of tyre surface in contact with the ground, resulting in an increased grip.

It will be appreciated that the at least one valve may be a valve of any suitable type. Having a valve advantageously allows re-inflation of the cavity following a loss -14-of cavity pressure. Optionally, the at least one valve is a two-way valve operable to control flow of fluid both into and out of the cavity. Optionally, the at least one valve is a Schrader valve, a Presta valve, or a Dunlop valve, preferably a Schrader valve or a Presta valve. Having a two-way valve advantageously allows pressure in the cavity to be raised or lowered as desired by the user. For example, a user may wish to adjust tyre pressure to suit driving/riding conditions and/or terrain.

Optionally, the tyre body comprises a tread section, opposing side wall sections and at least one wheel attachment section. The opposing side wall sections extend between the wheel attachment section and the tread section. Addtionally or alternatively, the tyre body comprises a tread surface, opposing side wall surfaces and at least one wheel attachment surface. The opposing side wall surfaces extend between the wheel attachment surface and the tread surface. It will be understood that the tread surface, side wall surfaces and wheel attachment surface may be the outer surface of the corresponding sections. During normal use and when the tyre assembly is mounted on a wheel rim, the tread surface is brought into contact with the ground as the tyre rotates, the side wall surfaces separate the wheel rim from the tread surface and thus from the ground, and the at least one wheel attachment surface is directly or indirectly attached to the wheel. For example, the wheel attachment surface may be directly or indirectly received by the wheel rim. Optionally, the tyre assembly comprises one or more clips or brackets for connecting the tyre assembly to the wheel.

Additionally or alternatively, the tyre attachment surface is optionally shaped to cooperate with a wheel rim, for example shaped to provide an interference fit with a wheel rim. Optionally, the at least one opening extends between the at least one cavity at the wheel attachment surface of the tyre body. It may be that in such an arrangement, the wheel rim protects the opening (and thus the valve controlling fluid flow through the opening) when the tyre assembly is attached to a wheel. It will be understood that the tread surface and the side wall surfaces are exposed to the elements, and thus to debris, when the tyre assembly is mounted on a wheel. Optionally, the tread surface comprises a moulded tread pattern. It will be appreciated that any suitable tread pattern may be utilised, depending for example on the size of the tyre, the type of vehicle and the intended use of the vehicle. Optionally, at least one of the opposing side wall surfaces comprises a moulded information panel, for example indicating parameters such as tyre size, speed, pressure and/or age.

-15 -The expanded rubber body forms at least a part of the tyre body. Optionally, the expanded rubber body forms at least the side surfaces of the tyre body, for example wherein the expanded rubber body is not covered by another rubber-containing material on the outer surfaces of the side walls (which outer surfaces extend between the tread surface and the wheel attachment surface). Additionally or alternatively, the expanded rubber body forms at least the tread surface of the tyre body, for example wherein the expanded rubber body is not covered by another rubber-containing material on the tread surface. Additionally or alternatively, the expanded rubber body forms at least the wheel attachment surface of the tyre body, for example wherein the expanded rubber body is not covered by another rubber-containing material on the wheel attachment surface. Optionally, the tyre body substantially consists of the expanded rubber body. It may be that such configurations are particularly straightforward and cost effective to manufacture. It will be appreciated that any surface of the tyre body may be considered to be formed by the expanded rubber body when said surface is covered or adorned by a non-rubber material, such as an adhesive, a dye or paint, or a grip enhancing material (e.g. studs).

Optionally, the tyre assembly of the first aspect of the invention comprises: a tyre body having a tread section, a wheel attachment section, and opposing side wall sections extending between the wheel attachment section and the tread section; a concentrically arranged annular cavity containing a fluid; and at least one valve, wherein the tyre body includes an annular expanded rubber body that encloses the annular cavity, the expanded rubber body having an opening providing fluid communication from outside the tyre assembly to the at least one cavity and wherein the at least one valve is for controlling flow of fluid through the opening. The expanded rubber body preferably forms at least part of the tread section, sidewall sections and wheel attachment section.

Optionally, the tyre body comprises a solid rubber part in addition to the expanded rubber body. It will be appreciated that a solid rubber part may be formed from a non-expandable, and/or non-expanded, rubber formulation. For example, the solid rubber part may be formed by curing a solid rubber formulation. Optionally, the solid rubber part is bonded to the expanded rubber body, e.g. directly bonded (such as by crosslinking bonds between rubber polymers in the expanded rubber body and rubber polymers in the solid rubber part). Optionally, the solid rubber part, when -16 -present, forms at least part of the tread surface of the tyre body, for example covering the expanded rubber body across the tread surface. Optionally, the solid rubber part, when present, forms at least part of the side wall surfaces of the tyre body, for example covering the expanded rubber body across the side wall surfaces. Optionally, the solid rubber part, when present, forms at least part of the wheel attachment surface of the tyre body, for example covering the expanded rubber body across the wheel attachment surface. Optionally, the solid rubber part substantially, e.g. entirely, surrounds the expanded rubber body. Alternatively, the solid rubber part forms only the tread surface, or only the tread surface and the side wall surfaces of the tyre body.

Optionally, the solid rubber part, when present, has a modulus of from 40 to 80 Shore A, for example approximately 70 Shore A. Optionally, the solid rubber part is comoulded with the expanded rubber part.

As used herein, the axis of rotation of a tyre (or a wheel) is the axis about the tyre (or wheel) rotates when the tyre is in use. As used herein, a plane of a tyre (or a wheel) is a plane perpendicular to the axis of rotation of the tyre (or wheel). Unless otherwise stated, the plane of the tyre (or wheel) is understood to be the plane that lies at the mid-point across the width of the tyre body. As used herein, the width of the tyre body is measured parallel to the axis of rotation of the tyre, and the height of the tyre body is measured parallel to the plane of the tyre (perpendicular to the axis of rotation of the tyre). For example, the width (also referred to as the "section width") may be the distance from one side wall surface to the opposing side wall surface, and/or the height may be the distance from the wheel attachment surface to the tread surface. Unless otherwise stated, width is taken to be maximum width, and height is taken to be maximum height. Typically (disregarding the tread pattern and any other moulded relief on the tyre surface), the width is substantially constant at all points of the tyre body at a given distance from the axis of rotation, and the height is substantially constant at all points of the tyre in a given plane parallel to the plane of the tyre. As used herein, the thickness of the expanded rubber body is the distance between an inner surface and an outer surface of the expanded rubber body; typically it is the distance between the surface of the at least one cavity and the surface of the expanded rubber body that forms or lies underneath the tread surface, a side wall surface or the tyre sidewall surface. Unless otherwise stated, the thickness referred to herein is taken to be the minimum thickness at any point of the expanded rubber body, -17-and unless otherwise stated is measured across the width of the tyre body or along the height of the tyre body. As used herein, the peripheral top thickness of the expanded rubber body is the minimum distance between the at least one cavity and the surface of the expanded rubber body that forms or lies underneath the tread surface of the tyre assembly. As used herein, the peripheral side thickness of the expanded rubber body is the minimum distance between the at least one cavity and the surface of the expanded rubber body that forms or lies underneath one of the side wall surfaces of the tyre assembly. Typically (disregarding the tread pattern and any other moulded relief on the tyre surface), the thickness and/or peripheral thickness is substantially constant at all points of the tyre at a given distance from the axis of rotation and from the plane parallel to the plane of the tyre (i.e. the tyre has rotational symmetry). As used herein, the intercavity width of the expanded rubber body is the minimum distance between adjacent cavities in the expanded rubber body. As used herein, the sum width of the expanded rubber body is the amount of the tyre body width that is made up by the expanded rubber body excluding the amount of the tyre body width that is made up by the at least one cavity and the solid rubber part, if present. As used herein, the sum height of the expanded rubber body is the amount of the tyre body height that is made up by the expanded rubber body excluding the amount of the tyre body height that is made up by the at least one cavity and the solid rubber part, if present. As used herein, the sum cavity width of the expanded rubber body is the amount of the tyre body width that is made up by the cavities. As used herein, the sum cavity height of the expanded rubber body is the amount of the tyre body height that is made up by the cavities. In some parts of the tyre, the sum thickness of the expanded rubber body may be equal to the tyre body height and/or the tyre body width. It will be appreciated that the gas-filled cells within an expanded rubber are considered to form part of the expanded rubber material. Thus, the thickness of an expanded rubber part is the distance between opposing moulded surfaces of the expanded rubber part including the distance across such cells contained within the expanded rubber part.

It has been found that excellent tyre performance is obtained when the cavity or cavities are made as large as possible while providing a sufficient width of expanded rubber material to maintain adequate puncture resistance. Preferably, the width of expanded rubber material is sufficient to maintain adequate dimensional stability -18 -without requiring reinforcement with non-expanded rubber materials. Preferably, the width is sufficient to maintain tyre integrity under normal load when pressure is lost from the cavity or cavities (i.e. the tyre provides 'run-flat' performance). Optionally, the peripheral side thickness of the expanded rubber body is at least 0.2 times, such as at least 0.4 times, for example at least 0.5 times, the width of the adjacent cavity.

Optionally, the peripheral side thickness of the expanded rubber body is 0.2 to 2 times, such as 0.4 to 1.5 times, for example 0.5 to 1 times the width of the adjacent cavity. Optionally, the peripheral top thickness of the expanded rubber body is at least 0.2 times, such as at least 0.4 times, for example at least 0.5 times the height of the adjacent cavity. Optionally, the peripheral top thickness of the expanded rubber body is 0.2 to 2 times, such as 0.4 to 1.5 times, for example 0.5 to 1 times the height of the adjacent cavity. It will be understood that the adjacent cavity is the cavity adjacent the side or top of the tyre body at the position of thickness measurement. Optionally, the intercavity width of the expanded rubber body is at least 0.2 times, such as at least 0.4 times, for example at least 0.5 times the width of the adjacent cavity. Optionally, the intercavity width of the expanded rubber body is 0.2 to 2 times, such as 0.4 to 1.5 times, for example 0.5 to 1 times the width of the adjacent cavity. Optionally, the tyre body has a ratio of expanded rubber body sum width to cavity sum width of from 0.2 to 2, such as from 0.5 to 1.5, for example 0.7 to 1.3, when measured across the width of the tyre at the point of maximum cavity sum width. Optionally, the tyre body has a ratio of expanded rubber body sum height to cavity sum height of from 0.2 to 3, such as from 0.5 to 2, for example 0.7 to 1.5, when measured along the height of the tyre at the point of maximum cavity sum height.

Optionally, the peripheral side thickness of the expanded rubber body is at least 8 mm, such as at least 10 mm, for example at least 15 mm, such as 8 mm to 250 mm, for example 10 mm to 200 mm or 20 mm to 100 mm. Optionally, the peripheral top thickness of the expanded rubber body is at least 10 mm, such as 12 mm to 250 mm, for example 15 mm to 200 mm. Optionally, the or each cavity has a maximum width of at least 15 mm to 400 mm, such as 20 mm to 300 mm, for example 25 mm to 200 mm. Optionally, the solid rubber tread layer (if present) has a thickness of at least 2 mm, such as at least 3 mm, for example at least 4 mm, such as 2 mm to 100 mm, 3 mm to 80 mm or 4 mm to 40 mm. Optionally, when the tyre comprises multiple annular cavities, the minimum intercavity width is at least 8 mm, such as at least 10 -19-mm, for example at least 15 mm. Optionally, the expanded rubber body has at least one of (e.g. at least three of, such as all of): (i) a peripheral side thickness of from 8 mm to 250 mm, such as 10 mm to 200 mm, for example 15 mm to 100 mm; (ii) a peripheral top thickness of 10 mm to 250 mm, such as 15 mm to 200 mm, for example 20 mm to 100 mm; (iii) a solid rubber tread layer (if present) thickness of 2 mm to mm, such as 3 mm to 80 mm, for example 4 mm to 40 mm; (iv) an optional intercavity width (if two or more cavities present) of 5 mm to 250 mm, such as 10 mm to 200 mm, for example 15 mm to 100 mm; and (v) a maximum cavity width of 15 mm to 400 mm, such as 20 mm to 300 mm, for example 25 mm to 150 mm.

It will be appreciated that tyre sizes and capacities vary widely depending on the intended use of the tyre. For example, larger tyres are typically used on larger vehicles. Furthermore, tyre dimensions vary according to desired tyre performance. For example, tyres intended to be used in harsh environments and/or tyres intended to be used in an application where 'run-flat' performance is a priority may be constructed with a greater material thickness separating the tyre cavity or cavities from tyre outer surface. On the other hand, tyres intended to be used with light vehicles and/or where low weight is a priority may be constructed with lesser material thickness separating the tyre cavity or cavities from tyre outer surface. The following non-limiting examples are presented as suitable tyre dimensions for common tyre applications.

Optionally, the tyre is for a bicycle or a small motorcycle and has 1 or 2 annular cavities, e.g. a single annular cavity. Optionally, the tyre is a tyre for a bicycle or small motorcycle, and the expanded rubber body has: (i) a peripheral side thickness of at least 8 mm, such as at least 10 mm, for example at least 15 mm; and, (ii) a peripheral top thickness of at least 10 mm, such as at least 12 mm, for example at least mm. Optionally, the tyre is a tyre for a bicycle or small motorcycle, and the expanded rubber body has at least one of (e.g. at least three of, such as all of): (i) a peripheral side thickness of from 8 mm to 60 mm, such as 10 mm to 50 mm, for example 15 mm to 40 mm; (ii) a peripheral top thickness of 10 mm to 60 mm, such as 12 mm to 50 mm, for example 15 mm to 40 mm; (iii) a solid rubber tread layer (if present) thickness of 2 mm to 20 mm, such as 3 mm to 15 mm, for example 4 mm to 10 mm; (iv) an intercavity width (if two or more cavities present) of 5 mm to 60 mm, such as 8 mm to 50 mm, for example 10 mm to 40 mm; and (v) a maximum cavity -20 -width of 15 mm to 200 mm, such as 20 mm to 150 mm, for example 25 mm to 100 MM.

Optionally, the tyre is for a large motorcycle, an automobile or a light commercial vehicle, and has a plurality of annular cavities, such as 2 to 4, e.g. 2 or 3, annular cavities. Optionally, the tyre is for a large motorcycle, an automobile or a light commercial vehicle, and the expanded rubber body has: (i) a peripheral side thickness of at least 20 mm, such as at least 30 mm, for example at least 40 mm; and, (ii) a peripheral top thickness of at least 20 mm, such as at least 30 mm, for example at least 40 mm. Optionally, the tyre is for a large motorcycle, an automobile or a light commercial vehicle, and the expanded rubber body has at least one of (e.g. at least three of, such as all of): (i) a peripheral side thickness of from 20 mm to 100 mm, such as 30 mm to 80 mm, for example 40 mm to 60 mm; (ii) a peripheral top thickness of from 20 mm to 100 mm, such as 30 mm to 80 mm, for example 40 mm to 60 mm; (iii) a solid rubber tread layer (if present) thickness of 5 mm to 50 mm, such as 10 mm to 40 mm, for example 15 mm to 30 mm; (iv) an intercavity width (if two or more cavities present) of from 20 mm to 100 mm, such as 30 mm to 80 mm, for example 40 mm to 60 mm; and (v) a maximum cavity width of 20 mm to 200 mm, such as 40 mm to 150 mm, for example 50 mm to 100 mm.

Optionally, the tyre is for a large goods vehicle, an industrial vehicle or an agricultural vehicle, and has a plurality of annular cavities, such as 2 to 8, e.g. 3 or 4, annular cavities. Optionally, the tyre is for a large goods vehicle, an industrial vehicle or an agricultural vehicle, and the expanded rubber body has: (i) a peripheral side thickness of at least 50 mm, such as at least 750 mm, for example at least 100 mm; and, (ii) a peripheral top thickness of at least 50 mm, such as at least 75 mm, for example at least 100 mm. Optionally, the tyre is for a large goods vehicle, an industrial vehicle or an agricultural vehicle, and the expanded rubber body has at least one of (e.g. at least three of, such as all of): (i) a peripheral side thickness of from 50 mm to 250 mm, such as 75 mm to 200 mm, for example 100 mm to 150 mm; (ii) a peripheral top thickness of from 50 mm to 250 mm, such as 75 mm to 200 mm, for example 100 mm to 150 mm; (iii) a solid rubber tread layer (if present) thickness of mm to 100 mm, such as 20 mm to 80 mm, for example 30 mm to 60 mm; (iv) an intercavity width (if two or more cavities present) of from 50 mm to 250 mm, such as mm to 200 mm, for example 100 mm to 150 mm; and (v) a maximum cavity width of 50 mm to 400 mm, such as 60 mm to 350 mm, for example 100 mm to 300 mm. Optionally, the expanded rubber body comprises a seam extending between the at least one cavity and an outer surface of the expanded rubber body. Optionally, the tyre assembly comprises a seam extending between the at least one cavity and an outer surface of the tyre body. Optionally, the seam extends between the at least one cavity and the wheel attachment surface. Optionally, the seam is an annular seam, such as an annular seam lying in a plane parallel to the plane of the tyre. Optionally, the seam extends along the entire inner circumferential surface of the expanded rubber body and/or the tyre body. Such a seam may allow for convenient moulding of the at least one cavity during tyre manufacture. Optionally, the seam intersects the at least one opening. Optionally, the number of seams corresponds to the number of cavities, for example wherein each cavity has an associated seam providing access to the cavity from outside the tyre. Optionally, the expanded rubber body and/or the tyre body is configured so that opposing sides of the seam are brought into contact with each other to close the cavity when the tyre assembly is mounted on a wheel. It will be appreciated that a seam may be desirable when the expanded rubber body is formed as a unitary structure during a moulding step, and the cavity is defined by an insert (especially a re-usable insert). However, it will also be appreciated that other manufacturing methods may optionally be utilised, such as a method using a sacrificial insert designed to remain inside the expanded rubber body after manufacture, in which case a seam may not be required.

Optionally, the tyre assembly comprises a gas bather lining at least part of the at least one cavity. Optionally, the tyre assembly comprises a gas barrier for providing a substantially gas-seal around the fluid contained in the cavity. Optionally, the gas barrier has an oxygen permeability of no more than 1 cc-mm/m2-day-mmHg, such as no more than 0.9 cc-mm/m2-day-mmHg, for example no more than 0.8 cc-mm/m2day-mmHg, optionally no more than 0.7 cc-mm/m2-day-mmHg. As used herein, oxygen permeability is measured using a Mocon OX-TRAN 2/61 permeability tester at 60° C. under the principle of R. A. Pasternak et at in Vol. 8 JOURNAL OF POLYMER SCIENCE: PART A-2 467 (1970). Disks of gas barrier material are prepared by compression-molding the material with slow cooling to provide defect free pads using a compression and curing press. Test samples are vulcanized.

-22 -Thickness of a compression-molded pad is around 0.38 mm. Disks with 2" diameter are punched out from molded pads for permeability testing. The disks are conditioned in a vacuum oven at 60° C. overnight prior to the measurement. Disks are mounted on a template and sealed with vacuum grease. A steady flow of oxygen at 10 mL/min is maintained on one side of the disk, while a steady flow of nitrogen at 10 mL/min is maintained on the other side of the disk. Using the oxygen sensor on the nitrogen side, increase in oxygen concentration on the nitrogen side with time can be monitored. The time required for oxygen to permeate through the disk, or for oxygen concentration on the nitrogen side to reach a constant value, is recorded and used to determine the oxygen gas permeability. Data is reported either as an oxygen permeation rate (OPR) in cc*mm/(m2-day) or a permeability coefficient in cc*mm/(m2-day-mmHg) obtained by dividing OPR with the atmospheric pressure. OPR is the transmission rate normalized for sample thickness and is expressed as volume (cc) of gas per unit area of sample (m2) in a discreet unit of time (24 hours).

Optionally, the gas barrier is configured to cooperate with the valve to inhibit or prevent leakage of fluid out of the cavity. Optionally, the gas barrier comprises a butyl rubber material. Optionally, the gas barrier comprises at least 20 wt%, such as at least 40 wt%, for example at least 50 wt%, butyl rubber material, based on the weight of the gas barrier. Optionally, the cavity is lined with a butyl rubber material.

As used herein, a butyl rubber material is a synthetic rubber comprising a copolymer of isobutylene and isoprene, including functionalised butyl rubbers such as halogenated butyl rubber. It will be appreciated that halogenated butyl rubbers include brominated rubber and/or chlorinated rubber. It will be appreciated that butyl rubber compositions are well known for their combination of flexibility as gas impermeability. Any suitable butyl rubber composition may be used. For example, the gas bather may be formed by a sheet of butyl rubber material, such as a sheet of butyl runner material comoulded with the expanded rubber body, and/or by a sprayed or poured coating, such as a coating solution of butyl rubber material applied before, intermediate or after the moulding process in which the expanded rubber body is formed. Optionally, the gas barrier includes a sealant which seals together the opposing sides of the seam, if present, and/or seals with the valve. Optionally, the sealant is in the form of a coating that lines at least part of, such as all of, the inner surface of the expanded rubber body around the cavity. Optionally, the gas barrier is -23 -in the form of an inner tube assembly. Optionally, the tyre assembly comprises at least one inner tube assembly, for example comprising an inner tube disposed in the at least one cavity. It will be appreciated that tyre inner tubes are well known, and that any suitably sized inner tube assembly may be used in the tyre assembly of the present invention. For example, an appropriately sized inner tube assembly intended for use with a conventional pneumatic tyre may be suitable. Optionally, the number of inner tube assemblies corresponds to the number of cavities, optionally such that an inner tube assembly is disposed in each cavity. Optionally, the at least one valve is comprised in the inner tube assembly. The inner tube may be filled, via the valve, with a fluid, such as a gas. It will be appreciated that the tyre assembly need not include a gas barrier separate to the expanded rubber body. For example, during manufacture, the expanded rubber body may be moulded with the valve in-situ, thereby sealing the valve into the at least one opening. Additionally or alternatively, the sides of the seam, if present, and/or the opening and the valve may be sealed together using an adhesive. For example, the adhesive may be a rubber based cement, typically comprising a mixture of solid rubber and a volatile solvent. Appropriate adhesives for securing rubber materials to other rubber materials and/or substrates such as metals are well known. Suitable adhesives include those commonly used with conventional pneumatic tyres. In such an arrangement, it may be that the expanded rubber body itself provides an adequate seal between the cavity and the atmosphere around the tyre, and so there is no need for a gas barrier lining the entire inner surface of the cavity. Optionally, the tyre assembly has a rate of inflation pressure loss from the cavity of no more than 3.5 % per month, such as no more than 3 % by month, for example no more than 2.5 % per month, when measured according to ASTM F1112.

It will be appreciated that inflation pressure loss varies according to the composition of the expanded rubber body, tyre dimensions and composition of the gas barrier (if present). Adjustments to the formulation(s) used to produce tyre bodies and gas barriers in order to reach a specified pressure retention are commonly undertaken by the skilled person.

It will be appreciated that the at least one cavity may be any shape. For example, the at least one cavity may have an angular (e.g. square or triangular) cross-sectional shape, optionally wherein the angular shape has rounded corners. Optionally, the at least one cavity has a circular or elliptical cross-sectional shape.

-24 -Optionally when the at least one cavity has an elliptical shape, optionally wherein the longitudinal axis of the ellipse is parallel to the plane of the tyre or parallel to the axis of rotation of the tyre. Such shapes and/or arrangements may provide a particularly resilient tyre structure.

Optionally, the expanded rubber body encloses a plurality of cavities. Each cavity may include any feature of the at least one cavity disclosed herein. For example, each of the plurality of cavities may optionally have an annular shape, and may optionally be concentrically arranged with the tyre body and/or with each other. The plurality of cavities may optionally be arranged side by side across the width of the tyre body and/or stacked along the height of the tyre body. Optionally, the tyre includes at least three cavities, optionally wherein the at least three cavities are arranged in a staggered layout along the height of the tyre. For example, the height of the expanded rubber body occupied by one cavity may partially overlap with the height of the rubber body occupied by an adjacent cavity. It will be appreciated that the cavities may not necessarily all be the same size.

Conventional pneumatic tyres typically comprise: (i) a casing material (e.g. a textile, such as Rayon or rubberised polyester) for maintaining tyre shape when the tyre is pressurised, and (ii) a strengthening material (e.g. steel cords) for enhancing shape retention and directional stability. Thus, modern tyres include a wide variety of different materials, often making manufacturing a complex process and inhibiting or preventing recycling. Optionally, the tyre body of the tyre assembly of the present invention is substantially free of casing material and/or strengthening material. For example, the tyre body is free from textile and/or steel cord. Alternatively, in certain embodiments, for example large tyres, the tyre body of the tyre assembly of the present invention may comprise a casing material and/or a strengthening material in addition to the expanded rubber material.

The invention further provides a tyre assembly for engagement with a wheel rim, the tyre assembly comprising: a tyre body having a tread surface, a wheel attachment surface, opposing side wall surfaces extending between the wheel attachment surface and the tread surface; a concentrically arranged annular cavity containing a fluid; and at least one valve for controlling flow of fluid from outside the tyre assembly to the at least one cavity, wherein the tyre body includes a concentrically arranged expanded rubber body disposed between the cavity and the -25 -tread surface and between the cavity and the side wall surfaces, wherein the at least one cavity is defined between the expanded rubber body and a wheel rim of a wheel with which the tyre body is engaged in a wheel assembly, and wherein at least one opening providing fluid communication from outside the tyre assembly to the at least one cavity is provided in the expanded rubber body or the wheel rim and at least one value is disposed in said at least one opening. Such a tyre assembly may be incorporated in a wheel assembly of a second aspect of the invention.

According to a second aspect of the invention there is also provided a wheel assembly comprising a wheel rim and a tyre attached to the wheel rim, the tyre having a circumferential tread surface, opposing side wall surfaces extending between the wheel rim and the tread surface, wherein the wheel assembly comprises at least one annular cavity extending around the wheel rim, wherein the tyre comprises an expanded rubber body disposed between each cavity and the tread surface and between each cavity and the side wall surfaces, and wherein the wheel assembly comprises at least one valve for regulating flow of fluid into and/or out of the at least one cavity. Optionally, the expanded rubber body and the wheel rim together define the at least one cavity. For example, it may be that the wheel rim forms a side of the cavity. For example, the at least one cavity is defined only by the wheel rim, the expanded rubber body and the valve (optionally wherein the cavity is lined with a gas barrier). Optionally, the valve is sealingly engaged with the wheel rim. Optionally, the expanded rubber body is sealingly engaged with the wheel rim.

It will be appreciated that the tyre of the wheel assembly of the second aspect of the invention may include any feature described in relation to the tyre assembly of the first aspect of the invention. For example, the wheel assembly may optionally comprise an inner tube assembly as described in relation the tyre assembly of the first aspect of the invention. Optionally, the wheel assembly comprises an inner tube assembly having an inner tube disposed in the at least one cavity and comprising the at least one valve. As a further example, the valve may be arranged as described in relation to the tyre assembly of the first aspect of the invention. Optionally, the valve is disposed in the opening. Alternatively, the valve is disposed at least partially, for example entire, outside of the opening (for example the valve may be connected to an entrance of the opening, e.g. directly or via a conduit). Optionally, the wheel rim -26 -comprises a conduit providing fluid communication from outside the wheel assembly to the at least one cavity, for example wherein the valve is connected to the conduit. Optionally, the wheel rim has a tyre engagement surface and tyre has a corresponding wheel engagement surface, the engagement surfaces being sized and configured to provide an interference fit between the wheel and the tyre. Optionally, the wheel engagement surface comprises a plurality of projections sized and configured to engage with a complementary plurality of recesses provided on the tyre engagement surface of the wheel. Optionally, one or more of the plurality of projections has a flared shape having a width larger at its distal end than at its proximal end. It will be understood that the distal end of a projection is the end further from the body attached to the projection (e.g. the distal end of a projection on the wheel engagement surface of a tyre is the end furthest from the tyre body and thus received by the tyre engagement surface of the wheel rim), whereas the proximal end of the projection is the end at which the projection joins the body attached to the projection (e.g. the proximal end of a projection on the wheel engagement surface of a tyre is the point at which the projection joins the tyre body). Optionally, the wheel engagement surface of the tyre comprises one or more (e.g. a plurality of) projections having a trapezoidal cross-section, optionally wherein the base at the distal end of the projection is larger than the base at the proximal end. Optionally, at least one (optionally a plurality of) the projections is an annular projection extending around the inner circumferential edge of the tyre. Optionally, the wheel assembly comprises at least one, preferably a plurality of, for example four or more, such as six or more, security bolts for securing the tyre to the wheel. Optionally, each security bolt penetrates a portion of the wheel rim and a portion of the tyre. For example, each security bolt extends through a portion of the wheel rim across one or more recesses of the tyre attachment surface and through a portion of the tyre across one or more projections of the tyre attachment surface. Optionally, each security bolt extends across substantially the entire width of the wheel. Preferably, each security bolt has a threaded end that is received in a corresponding threaded cavity in the wheel rim.

Alternatively, each security bolt passes through the entire wheel, for example wherein a nut is screwed onto the threaded end of the bolt to retain the bolt on the wheel. Optionally, each security bolt is accommodated in a moulded through-hole provided in the expanded rubber body of the tyre. Additionally or alternatively, each security -27 -bolt is accommodated in a drilled through-hole, for example wherein the hole is drilled by the bolt itself Optionally, each security bolt is fed through moulded or drilled through-holes in the inner circumference of the tyre, e.g. from the side of the wheel in which the valve is positioned when the valve is positioned on the side, initially through the wheel rim and then intermittently through portions of the wheel rim (either side of the portions of the tyre), and then screwed into a threaded opening on the opposite side of the wheel rim.

Optionally, the tyre body of the tyre assembly of the first aspect of the invention, and/or the tyre of the wheel assembly of the second aspect of the invention is formed by a two-stage moulding process, for example as disclosed in International (PCT) Publication No. W02015/198040A1 (Gecko Rubber Ltd.). Optionally, the tyre is made by a process comprising: (a) a moulded blank formation step, in which an expandable rubber formulation, comprising an elastomeric material, a curing agent and an expansion agent, is heated in a first mould cavity to partially cure the expandable rubber formulation thereby forming a moulded blank, wherein the first mould cavity confines expansion of the expandable rubber formulation; (b) a releasing step, in which the moulded blank is released from the first mould cavity and in which the moulded blank expands to a volume larger than the volume of the first mould cavity thereby forming an expanded moulded blank; and, (c) a further curing step, in which the expanded moulded blank is heated to further cure and expand the expandable rubber formulation thereby forming the expanded rubber tyre; wherein the expanded moulded blank is heated in a second mould cavity in further curing step (c). Optionally, the process of the invention additionally comprises a stabilisation step, in which the expanded moulded blank is left to stabilise for a period sufficient that the volume of the expanded moulded blank is substantially constant. The optional stabilisation step is carried out before the additional curing step. By leaving the expanded moulded blank to stabilise, the expanded moulded blank is allowed to reach a constant volume before it is subjected to the further curing step. For example, the moulded blank may, in a first period, undergo a very rapid initial expansion during the releasing step, and then continue to expand more slowly and/or shrink in a second period to form the expanded moulded blank. It has been found that when the expanded moulded blank is left to stabilise, the consistency of the size of the expanded moulded blank and thus that of the expanded rubber tyre is improved.

-28 -When the tyre comprises a solid rubber part, such as a solid rubber tread layer, the process preferably further comprises contacting the expandable rubber formulation with an additional rubber formulation during the moulded blank formation step, wherein the additional rubber formulation comprises an elastomeric material and a curing agent, and wherein the additional rubber formulation is at least partially cured during the moulded blank formation step to provide a solid rubber part bound to the expanded rubber part.

According to a third aspect, the present invention provides a kit of parts for assembling the tyre assembly of the first aspect of the invention, the kit of parts comprising the expanded rubber body. Optionally, the kit of parts comprises the at least one valve. It will be appreciated that the kit of parts optionally comprises any component of the first aspect of the invention. For example, the kit of parts comprises the inner tube assembly described in relation to the first aspect of the invention. It will be appreciated that the kit of parts may be provided in a disassembled state. For example, when the expanded rubber body comprises a seam, the expanded rubber body may be provided without the opposing sides of the seam sealed or adhered together. Additionally or alternatively, the valve may be provided detached from the expanded rubber body (for example, the kit may be configured to allow insertion of the valve into the opening during assembly of the tyre assembly from the kit of parts.

Additionally or alternatively, when the kit of parts comprises an inner tube assembly, the inner tube assembly may be provided separately from the expanded rubber body (for example, the kit may be configured to allow insertion of the inner tube into the at least one cavity during assembly of the tyre assembly from the kit of parts).

According to a fourth aspect, the present invention provides a kit of parts for assembling the wheel assembly of the second aspect of the invention, the kit of parts comprising the tyre of the first aspect of the invention. Optionally, the kit of parts comprises the at least one valve and/or the wheel rim of the second aspect of the invention. Optionally, the tyre comprises the expanded rubber body of the first aspect of the invention. It will be appreciated that the kit of parts optionally comprises any component of the first or second aspect of the invention. For example, the kit of parts comprises the inner tube assembly described in relation to the second aspect of the invention. It will be appreciated that, as for the kit of parts of the third aspect of the -29 -invention, the kit of parts of the fourth aspect of the invention may be provided in a disassembled state.

According to a fifth aspect, the resent invention comprises a wheel assembly comprising a wheel and a tyre assembly according to the first aspect of the invention, for example wherein the at least one cavity is inflated to a pressure of at least 10 psig (0.69 barg), optionally at least 20 psi (1.38 barg).

It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa.

Description of the Drawings

Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which: Fig. la shows a side view of a tyre assembly; Fig. lb shows a cross-sectional view of the tyre assembly of Fig. 1 a taken across the plane of the tyre; Fig. 2a shows a cross-sectional view of the tyre assembly of Fig. la taken along line A-A; Fig. 2b shows a cross-sectional view of the tyre assembly of Fig. la taken along line B-B; Fig. 3a shows a cross-sectional view of another tyre assembly; Fig. 3b shows a side view of a portion of the tyre assembly of Fig. 3a; Fig. 4 shows a cross-sectional view of another tyre assembly; Fig. 5 shows a cross-sectional view of a wheel assembly of a fourth embodiment of the invention; Fig. 6 shows a cross-sectional view of another wheel assembly; Fig. 7a shows a cross-sectional view of another wheel assembly; Fig. 7b shows another cross-sectional view of the wheel assembly of Fig. 7a; Fig. 8a shows a cross-sectional view of another wheel assembly; Fig. 8b shows another cross-sectional view of the wheel assembly of Fig. 8a; Fig. 9a shows a cross-sectional view of another wheel assembly; -30-Fig. 9b shows a side view of the when assembly o Fig. 9a; and, Fig. 10 shows a cross-sectional view of another wheel assembly.

Detailed Description

It will be understood that all drawings are schematic. The tyre assemblies of Figs. 1-4 are particularly well suited for use as bicycle or small motorcycle tyres, while the wheel assemblies of Figs. 5-9 are particularly well suited for use as automobile, light goods vehicle and large goods vehicle wheels, and the wheel assembly of Figs. 10a and 10b is particularly well suited for use as a large goods vehicle, agricultural vehicle or industrial vehicle wheel. Fig. la shows a side view of a tyre assembly 101 according to a first embodiment of the invention. The tyre assembly 101 comprises an annular expanded rubber body 102. A tread surface 103 of the tyre assembly 101 comprises a moulded tread pattern. A wheel attachment surface 104 allows attachment of the tyre assembly 101 to a wheel rim (not shown in Fig. la). A valve 105 provides fluid communication from outside the tyre assembly 101 to a cavity enclosed by the annular expanded rubber body 102 (not shown in Fig. 1a).

Fig. lb shows a cross-sectional view of the tyre assembly 101, taken across the plane of the tyre. As shown in Fig. lb, the expanded rubber body 102 encloses a concentrically arranged annular cavity 106. An opening 107 extends between the cavity 106 and the wheel attachment surface 104 and accommodates the valve 105 (which controls the flow of fluid through the opening 107 and into and/or out of the cavity 106).

Fig. 2a shows a cross-sectional view of the tyre assembly of Fig. la taken along line B-B. As shown in Fig. 2a, the expanded rubber body 102 forms the tread surface 103, opposing side wall surfaces 109, and the wheel attachment surface 104. The tread surface 103 extends across the outer circumferential edge of the tyre body and partially along its side towards the inner circumferential edge. The wheel attachment surface 104 extends across the inner circumferential edge of the tyre body and partially along its side towards the outer circumferential edge. The opposing side wall surfaces 109 extend between the wheel attachment surface 104 and the tread surface 103. The portion of the wheel attachment surface 104 that extends partially along the side of the tyre body comprises a moulded annular bead 104b (also shown in Fig. la). The bead 104b of the wheel attachment surface 104 provides a resistance fit with a wheel rim, being shaped to cooperate with a typical wheel rim (e.g. a wheel rim having inwardly depending lips around its outer circumferential edges). The expanded rubber body 102 also comprises an annular seam 108 which extends between the cavity 106 and the wheel attachment surface 104. The seam 108 is an annular seam which lies in a plane parallel to the plane of the tyre assembly 101, and extends along the entire inner circumferential surface of the tyre assembly 101. As shown in Fig. 2b, the seam 108 intersects the opening 107. The seam 108 allows removal of a mould insert used during the manufacturing process to shape the cavity 106. The expanded rubber body 102 is configured so that opposing sides of the seam 108 are brought into contact with each other to close the cavity 106 when the tyre assembly 101 is mounted on a wheel rim. In use, the sides of the seam 108 are bonded together by a rubber cement adhesive.

Fig. 2b shows a cross-sectional view of the tyre assembly of Fig. la taken along line A-A. The valve 105 is shown disposed in the opening 107. In use, the expanded rubber body 102 is sealed to the valve by a rubber cement adhesive. The cavity 106 is capable of containing a fluid at pressures of at least 30 psig. An increase in pressure within cavity 106 results in the tyre assembly 101 being less deformable as a result of external forces. An increase in the pressure within cavity 106 also results in a smaller area of the tread surface 103 being in contact with a ground surface. Furthermore, an increase in the pressure within the cavity stretches the tyre shape slightly, pushing the wheel attachment surface into a more intimate arrangement with the wheel rim (not shown in Fig. 2b).

Fig. 3a shows a cross-sectional view of a tyre assembly 201 according to a second embodiment of the invention. The tyre assembly 201 comprises an expanded rubber body 202 which encloses a cavity 206. The tread surface is formed from a solid rubber tread layer 203. The solid rubber tread layer 203 comprises is made from a non-expandable rubber formulation, and is bonded to the expanded rubber body 202 by crosslinking bonds. The tyre body is formed by combining a partially cured and expanded expandable rubber formulation (used to form the expanded rubber body 202) and a partially cured solid rubber formulation in a mould, and then expanding and curing the expandable rubber formulation in the mould simultaneously with -32_ curing the solid rubber formulation, thereby forming cross-linking bonds between the two rubber formulations. The tread surface 203 further comprises a moulded pattern. A wheel attachment surface 204 extends across the inner circumferential edge of the tyre body and partially along its side towards the outer circumferential edge. A seam 208 extends between the cavity 206 to the wheel attachment surface 204. The tyre assembly 201 comprises a plurality of clips 210 configured to engage with a wheel rim hold the tyre in place on the wheel (the clips form a similar shape to the annular bead 104b of the tyre assembly 101 of the first embodiment of the invention). Each clip 210 is in the form of a staple, the prongs of which are partially embedded into the wheel attachment surface 204. The wheel attachment surface 204 of the expanded rubber body 202 has a high tear strength to prevent damage from insertion of clips 210. The clips provide convenient pressure points so that the tyre body can be pushed over the wheel rim without damaging the tyre (e.g. a tool can be pressed against the clip rather than the tyre surface, allowing a force to be applied in order to stretch the tyre without the tool accidentally penetrating the expanded rubber body 202). Fig. 3b shows a side view of a portion of the tyre assembly 202. The clips 210 extend in a ring just inside of the inner circumferential edge of the tyre body. Each clip is slightly curved to allow it to sit comfortably inside the circumferential edge of the wheel rim when the tyre is fitted to a wheel (not shown in Fig. 3b).

Fig. 4 shows a cross-sectional view of a tyre assembly 301 according to a third embodiment of the invention. The tyre assembly 301 comprises an expanded rubber body 302 which encloses a cavity 306. An opening 307 extends between the cavity 306 and the wheel attachment surface 304 accommodating the valve 305 (which controls the flow of fluid through the opening 307 and into and/or out of the cavity 307). The tyre assembly 301 comprises a gas barrier 311 lining the walls of the cavity 306 within the expanded rubber body 302. The gas barrier 311 is an inner tube comprising the valve is 305.

Fig. 5 shows a cross-sectional view of a wheel assembly 401 according to a fourth embodiment of the invention. The wheel assembly 401 comprises a tyre 403 attached to a wheel rim 402 (the rest of the wheel is omitted for clarity). The tyre 403 has an expanded rubber body 407 that forms a tread surface 404 and opposing side wall surfaces 405 extending between the wheel rim 402 and the tread surface 404. The expanded rubber body 407 and the wheel rim 402 together define multiple on annular cavities 406 extending around the wheel rim 402. Each annular cavity 406 has an elliptical cross-sectional shape with the longitudinal axis of the ellipse being parallel to the plane of the wheel. The wheel rim 402 has a tyre engagement surface shaped to cooperate and provide an interference fit with a corresponding wheel engagement surface 408 on the tyre. The wheel engagement surface comprises a plurality of annular projections 409 sized and configured to engage with a complimentary plurality of recesses provided on the tyre engagement surface. The projections 409 each have a trapezoidal shape having a width larger at its distal end than at its proximal end. The wheel rim 402 comprises detachable annular side portions 420 which can be removed to facilitate convenient detachment/attachment of the tyre 403. The side portions 420 help to clamp the tyre 403 in place when the wheel is in use. Increasing fluid pressure inside the cavities 506 helps to push the wheel engagement surface of the tyre 403 into intimate contact with the tyre engagement surface of the wheel rim 402.

Fig. 6 shows a cross-sectional view of a wheel assembly 501 according to a fifth embodiment of the invention. The wheel assembly 501 is similar in structure to the wheel assembly 401 of Fig. 5. The wheel assembly 501 comprises a tyre 503 attached to a wheel rim 502 (the rest of the wheel is omitted for clarity). The tyre 503 comprises an expanded rubber body 507 and a solid rubber layer 504 forming a tread surface (bound together by cross-linking bonds). The expanded rubber body 507 and the wheel rim 502 together define multiple annular cavities 506 extending around the wheel rim 502. Each annular cavity 506 has a circular cross-sectional shape.

Fig. 7a shows a cross-sectional view of a wheel assembly 601 according to a sixth embodiment of the invention. The wheel assembly 601 is similar in structure to the wheel assembly 501 of Fig. 6, comprising a wheel rim 602, tyre 603, multiple annular cavities 606, an expanded rubber body 607, and solid rubber tread layer 603. Unlike the wheel assembly 501 of Fig. 6, the wheel assembly 601 comprises two (rather than three) annular cavities 606. Each annular cavity has a circular cross-sectional shape. The wheel rim 602 defines a conduit 608 extending between the two cavities 606 and outside of the wheel rim 602. The exit of the conduit 608 on the outer surface of the wheel rim 602 is fitted with a valve 615 for regulating flow of fluid into and out of the cavities 606.

Fig. 7b shows another cross-sectional view of the wheel assembly 601 of Fig. 7a. The cross section of Fig. 7b is taken at a different point around the tyre body. The wheel assembly 601 comprises a plurality of security bolts 610 for securing the moulded tyre 603 to the wheel rim 602. Each security bolt 610 passes through the wheel rim and through a projection formed on the wheel attachment surface of the tyre 603 (which projection is accommodated in a corresponding recess on the tyre attachment surface of the wheel rim 602). The security bolts 610 act to reinforce and strengthen the interference fit between the tyre 603 and the wheel rim 602 Each security bolt 610 extends into the wheel assembly from the side and across about a third of the width of the wheel assembly, and is aligned with a corresponding security bolt 610 extending in from the opposite side of the wheel assembly 601.

Fig. 8a shows a cross-sectional view of a wheel assembly 701 according to a seventh embodiment of the invention. The wheel assembly 701 is similar in structure to the wheel assembly 601 of Fig. 7a, comprising a wheel rim 702, tyre 703, two annular cavities 706, an expanded rubber body 707, and solid rubber tread layer 703.

Each annular cavity has a circular cross-sectional shape. The wheel rim 702 defines conduits 708 extending between each of the two cavities 706 and outside of the wheel rim 702. The exit of each conduit 708 on the outer surface of the wheel rim 702 is fitted with a valve 715 for regulating flow of fluid into and out of the cavities 706.

Fig. 8b shows another cross-sectional view of the wheel assembly 701 of Fig. 8a. The cross section of Fig. 8b is taken at a different point around the tyre body. The wheel assembly 701 comprises a plurality of security bolts 710 for securing the moulded tyre 703 to the wheel rim 702. Each security bolt 710 passes through the wheel rim and through projections formed on the wheel attachment surface of the tyre 703 (which projections are accommodated in corresponding recesses on the tyre attachment surface of the wheel rim 702). Each security bolt 710 extends across the full width of the wheel assembly from one side to the other and is accommodated in moulded holes provided in the tyre body. A nut is threaded onto the distal end of the security bolt to hold the bolt in place on the wheel.

Fig. 9a shows a cross-sectional view of a wheel assembly 801 according to an eighth embodiment of the invention. The wheel assembly 801 is similar in structure to the wheel assembly 701 of Fig. 8a, comprising a wheel rim 802, tyre 803, two annular cavities 806, an expanded rubber body 807, and solid rubber tread layer 803. Each annular cavity has a circular cross-sectional shape. The wheel rim 802 defines conduits 808 extending between each of the two cavities 806 and outside of the wheel rim 802. The exit of each conduit 808 on the outer surface of the wheel rim 802 is fitted with a valve 815 for regulating flow of fluid into and out of the cavities 806.

The wheel assembly 801 further comprises a gas barrier 811 lining the walls of the cavity defined by the expanded rubber body 807. The gas barrier 811 is a layer of halobutyl rubber. The wheel rim 802 (being made of impermeable alloy metal) does not require a gas barrier lining.

Fig. 9b shows a side view of the wheel assembly 801 of the eight embodiment of the invention. The wheel assembly 801 is shown complete with a wheel hub 812 attached to the wheel rim 802.

Fig. 10a shows a cross-sectional view of a wheel assembly 1001 according to a ninth embodiment of the invention. The wheel assembly 1001 is similar in structure to the wheel assembly 601 of Fig. 7a, comprising a wheel rim 1002, tyre 1003, multiple annular cavities 1006, an expanded rubber body 1007, and solid rubber tread layer 1003. Unlike the wheel assembly 601 of Fig. 7a, the wheel assembly 1001 comprises four (rather than two) annular cavities 1006 in a stacked arrangement. Two of the annular cavities 1006a are defined partly by the expanded rubber body 1007 and the wheel rim 1002, the other annular cavities 100b6 are defined entirely by the expanded rubber body 1007, and are located further towards the tread surface than the other two cavities 1006b. The annular cavities 1006b are linked to the annular cavities 10a by an opening 1030 extending through the expanded rubber body 1007, thereby providing fluid communication within each stacked pair of cavities. Each annular cavity 1006a, 1006b has a circular cross-sectional shape. The wheel rim 1002 defines a conduit 1008 extending between the four cavities 1006a, 1006b and outside of the wheel rim 1002. The expanded rubber body 1007 additionally comprises annular seams 1031 extending from each upper cavity 1006b to the corresponding lower cavity 1006a in each stacked pair (see Fig. 10b). The seams 1031 intersect the openings 1030. The exit of the conduit 1008 on the outer surface of the wheel rim 1002 is fitted with a valve 1015 for regulating flow of fluid into and out of the cavities 1006.

Fig. 10b shows another cross-sectional view of the wheel assembly 1001 of Fig. 8a. The cross section of Fig. 10b is taken at a different point around the tyre body. The wheel assembly 1001 comprises a plurality of security bolts 1010 for securing the moulded tyre 1003 to the wheel rim 1002. Each security bolt 1010 passes through the wheel rim and through projections formed on the wheel attachment surface of the tyre 1003 (which projections are accommodated in corresponding recesses on the tyre attachment surface of the wheel rim 10702). Each security bolt 1010 extends across substantially the entire width of the wheel assembly from one side to the other, with the distal threaded end being screwed into a threaded hole in the wheel rim on the side opposite to the valve.

Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. For example, the tyre body may incorporate any number of cavities of any shape. Where a cavity is defined partly by the expanded rubber body and partly by the wheel rim, the base of the cavity may be formed by any part of the wheel rim, for example by a projection or recess where projections and/or recesses are present.

Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.