I used Harbor Freight 8" hard rubber casters all with locks,Northern Tool has a good selection as well, it made such a big difference from little 4" casters,moving it with a car attached on smooth floor is a effortless ,also great when loading and unloading on the flatbed , I don't think you'd benefit much from pneumatic casters unless you like to push it around in dirt field or work on your car on the front lawn with plush grass
