This is the Inner Foam Inserts for 26mm Tires from HPI|
Foam tire inserts.
Helps increase grip and stability of tires.
Prevents tires from caving in during high speed & cornering.
Two foam inserts (dark grey, medium rating)
Width: 21mm (13/16")
Outside Diameter: 60mm (2-3/8")
Inside Diameter: 46mm (1-13/16")
This is installed between the tire and wheel.