Formula Four Performance Urethane is unlike any other. The wheels retained more material, coned less and kept their original shapes and sizes longer than any other wheel. Formula Four Urethane is made using a 100% pure urethane compound. On the hills, in the streets & parks, and in forced flat spot, Formula Four wheels out-performed and resisted flat spots longer with less wear than all other wheels. Formula Four's exclusive combination of High Rebound and Hard Duro produces a faster wheel everywhere. Higher rebound for faster speeds over rough and smooth surfaces. Hard Duro for a harder, faster ride that won't mush out over time. Formula Four's exclusive anti-stick slide gives a fast/consistent, smooth slide all the way through. Slide with confidence start to finish knowing your wheels won't skip or catch mid-slide. Formula Four gives you the highest level of control and consistent grip you can count on.