The field of the invention is camera dollies.  More specifically, the application relates to a system for allowing quick change of wheels on a camera dolly.  In motion picture or video filming, cameras are often supported on camera dollies, so that camera lens positions, angles, and elevations may be smoothly and easily achieved without interruption.  Most camera dollies are pushed by “dolly grips” or camera dolly operators.  For use on a relatively smooth and hard surface, such as on a sound stage, or other indoor set, the camera dolly is preferably provided with solid tires having relative high hardness, to reduce rolling friction, and make it easier to push and maneuver the camera dolly. 
For use on more irregular surfaces, for example an indoor surface having small cracks, bumps, etc.,  a softer solid tire is preferred, to absorb shock impulses, albeit with a small increase in rolling friction.  For use on still more irregular surfaces, pneumatic tires are typically used, to provide a higher degree of shock absorption, although with a greater increase in rolling friction.  For use on unpaved surfaces, such as grass, sand, etc.,  or in other applications where a maximum level of smoothness in dolly movement is required, dolly track is laid down, with the dolly wheels rolling on the smooth metal rails of the track.  Having a smooth rolling surface, or a way to absorb the shock impacts created when rolling over an irregular surface, is important, as shock impacts generated via the rolling movement of the camera dolly wheels can cause unacceptable movement of the camera lens during filming, resulting in unsteady recorded images. 
It is frequently necessary to change the wheels on the camera dolly, to compensate for change in the ground conditions.  For example, if a first part of a film sequence takes place indoors, the hard solid wheels may be used.  Then, if the sequence continues outdoors, it may then be necessary to change over to a pneumatic or track wheel.  While a combined track/pneumatic wheel, as described in U.S. Pat.  No.  4,943,101, incorporated herein by reference, has been successfully used in the past, to avoid wheel changeover when switching between track and pneumatic wheels, it remains necessary to change wheels when the harder solid wheels are needed.  In addition, fast wheel changes are assisted by the wheel system described in U.S. Pat.  No.  6,349,994 B1, also incorporated herein by reference. 
However, the dolly must still be lifted up to unweight the wheels, before the wheels can be changed.  A typical unmotorized camera dolly weighs about 300 to 500 pounds.  When loaded with crane arm and accessories, this can increase up to about 1200 pounds.  The usual practice is generally for the dolly operators to simply manually lift and chock up one side of the dolly at a time, to change the wheels.  While this technique works, it risks injury from heavy lifting.  It also requires at least two people.  Manual lifting can also damage the camera dolly if the lifting and chocking is not at a structural hard point of the camera dolly.  Accordingly, there remains a need for designs which allow fast changeover of camera dolly wheels.