"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. Tire Type Pneumatic, Overall Width in. 21, Tire Size H x W in. 10 x 4, Compatible With Northern item# 144323, Height in. 5."