These large (120mm-diameter) wheels from Dagu Electronics can be used for custom robots that need to traverse complex, rugged terrain. The black tyres are made of soft, spiked rubber for increased traction, and the plastic hubs are chrome (silver) in colour.
The included adapters let you easily mount the wheels to motors with 4mm output shafts.
These wheels are sold in in pairs: you get two wheels and two 4mm adapters.
120mm Off Road Wheel with 25D Motor + Gearbox