The hardness of the wheel material is generally selected according to the purpose. For example, the common wheels are nylon wheels, super polyurethane wheels, high-strength polyurethane wheels, high-strength artificial rubber wheels, iron wheels, pneumatic wheels and so on. Super polyurethane wheels and high-strength polyurethane wheels can meet the control requirements whether driving on indoor or outdoor ground. High-strength synthetic rubber tires can be used in hotels, medical devices, floors, wooden floors, ceramic tile floors and other quiet ground when walking, while nylon wheels and iron wheels are suitable for places with uneven ground or iron chips on the ground. Air pump wheel is suitable for light load and soft and uneven road surface.