RICTA SPEEDRINGS SLIM 99A 51MMRicta Wheel Dynamics 51mm Speedrings Slim 99a. Ricta Speedrings' give you the feel of a traditional wheel with the speed and reduced rolling resistance of a cored wheel. The unique core design puts urethane around the bearing bore like a non cored wheel and the inner core design helps maintain shape integrity when landing tricks for quick rollaway.