Universal caster material soft hard choice
The hard tread of the caster is suitable for running on soft or smooth ground, while the soft tread rolls flexibly on hard or rough surfaces, including most outdoor surfaces.
When selecting wheels, take into account all special ground conditions such as bumps, sinks, thresholds, and dock slats. The bigger the wheel, the softer it is, the easier it is to roll in orbit or similar ground conditions. Rubber wheels, especially high modulus rubber wheels, do not produce noise to protect the ground to the maximum extent, while carbon steel wheels are the hardest. In general, the universal angular wheel is a folding option, with a moderate degree of ground protection that can withstand greater weight.
The above introduction is the universal caster material soft hard choice, hope to help you.