The wheels in this catalogue are for manual applications only. When choosing a wheel the load to be carried and the rolling resistance of the wheel are both factors to be taken into account. Rubber or Polyurethane tyred wheels provide impact absorbing and quiet running qualities, but suffer from higher rolling resistance due to the deforming nature of these materials as the wheel rotates. Polypropylene or Nylon wheels do not provide great impact absorbing qualities, but are very strong and are resistant to deformation, so have a relatively low rolling resistance. The rolling resistance can become quite significant with high loads and result in a trolley needing several men to move it. The higher the load expected to be carried the higher the deformation of the wheel, therefore the tyred wheels are more suitable for smaller loads whereas the polypropylene and nylon wheels are suitable for high loads. Larger diameter wheels should be chosen not only for higher load capacity, but also to allow the wheel to comfortably pass over any obstructions, gaps or ridges in the floor. All quoted load ratings in this catalogue assume normal manual usage on solid flat floors. Shock loading is outside the load rating parameters. Uses outside these conditions may call for a wheel of much higher specification.