"The Wesco Superwheel Attachment for the StairKing Battery-Powered Appliance Truck sold separately offers better mobility over rough surfaces. Installs in seconds and is equipped with 10in. x 4in. 4-ply pneumatic tires. Provides 4-wheel support and eases transport over rough surfaces. U.S.A. Product Type Accessory, Height in. 5, Tire Type Pneumatic, Tire Size in. 10, Overall Width in. 21."