This is a three-position training wheel system, with tool-less installation and removal, so you&';re always the hero without so much as a screwdriver. Reinforcing this, the tubular steel arms are built to take a beating, while the foam tires will never go flat Closed-cell foam tires. Tubular steel arms. Compatible with 2013 and newer models of the Hotrock or Riprock 20-inch Coaster models.