The C-hubs are available in all standard caster angles (0, 2, 4 and 6) and are also available in 4 different hardnesses (Medium, Hard, Graphite and Alu) that are optimized for particular racing conditions. The EU Edition includes medium rigidity (M) C-hubs specially optimized for rubber-tire racing, while the US Edition includes hard rigidity (H) C-hubs specially optimized for foam-tire racing.