The present invention relates generally to tire and wheel assemblies suitable for vehicles and other items fitted with wheels.  The preferred embodiments of the invention are particularly useful for earth moving and excavating vehicles with low pressure tires, but the invention is not limited to this application and will have numerous other applications. 
According to one aspect of the present invention a tire and wheel assembly comprises a plurality of chambers for containing pressurised fluid, at least two of the chambers being interconnected by means enabling flow of fluid between one chamber and the other, the connecting means allowing fluid to pass preferentially from the one chamber to the other so providing a shock absorbing effect when the tire passes over an obstruction. 
The pressurised fluid will, in general, be air or other gas or vapour or a mixture of air or gas or vapour or a combination of any of the foregoing with a liquid. 
A non-mechanical shock absorber within the tire enables earth moving and excavating vehicles to retain structural strength for excavating with the facility to travel faster on site roads or public roads.  This reduces cycle times on site and transport times between sites leading to increased productivity. 
By virtue of the fact that fluid passes preferentially from one chamber to the other the tire and wheel assembly of the present invention has a shock absorption facility which is particularly suitable for use on earth moving and excavating vehicles. 
Multi-chamber tires have been proposed hitherto.  Most of them have been devised with safety in mind and as a result the individual chambers are interconnected such that air passes freely from the inner chamber to the outer chamber during inflation and use until a puncture or blow-out when gas or air loss is restricted from the inner chamber. 
The tire and wheel assembly of the preferred embodiment of the present invention has at least one first passage interconnecting outer and inner chambers enabling substantial free flow of air or other gases between the chambers.  In order to ensure that air or other gases flow preferentially from outer to inner chambers at least one second passage may be provided which allows air or other gases to pass from the outer to the inner chambers only.  This may be achieved by using a one-way valve in at least some of the second passages. 
The ratio between the free flow path and the one way flow path and the relative sizes of outer and inner chambers will be determined by experiment and possibly varied according to the particular application for which the tire is designed.  It is presently envisaged that the total one way flow path will have greater cross-sectional area than the two way flow path. 
In one preferred embodiment of the invention a plurality of passages interconnect the outer and inner chambers some of which allow one-way air or gas flow only.  The passages may be identical with the exception that some of them are provided with one way valves.  As noted above in the case of several identical passages it is presently envisaged that there will be more "one-way" passages than "two-way" passages. 
The use of one-way valves is a simple way of ensuring preferential flow of gas from one chamber to another.  Alternatively valve or restrictor designs may be available which themselves define a two-way flow path with preferential flow in one direction.  For example, a plurality of flap valves may be provided, the flap of each valve being formed with a through passage.  With such an arrangement the flap valves will open to allow relatively free flow of fluid in one direction, and the through passages will permit restricted flow in the opposite direction. 
The tire and wheel assembly itself may define a single chamber divided into outer and inner chambers by a dividing wall or walls extending across the single chamber.  The dividing wall may be a sheet secured to or integral with the tire.  Alternatively the inner chambers may be partially or completely surrounded by the outer chamber.  Either way the tire may be designed to sit on a wheel rim with the wheel rim defining one wall of one or more of the chambers.  For example a single inner chamber may be designed as a complete inner tube which is partially or completely enclosed by a tire and wheel assembly defining the outer chamber or the means defining both outer and inner chambers may be the wheel rim with the outer chamber partially surrounding the inner chamber. 
In all the foregoing examples of the invention it may be necessary for inner chambers to be reinforced to prevent collapse under excess pressure in the outer chamber and to encourage air or other gases to flow from the outer chamber to the inner chambers. 
Alternatively the inner chamber may be fabricated to form a single or a series of rigid chambers each assembled and connected radially to form a single rigid construction attached to the wheel rim.