These are rubber tire inserts designed to fit 24mm wheels with 24mm width rubber tires. They come in pairs and the black color easily identifies the insert as a hard firmness.
★These hard molded tire inserts come into their own in high track surface temperatures, or on high-speed circuits.
Note: The firmer the insert the less traction your tire will yield. The softer the insert the more traction you will get out of your tires, but they will also wear out faster. | 
