Grippy, bouncy, indoor/outdoor Urethane wheels with speedy Silver-5 bearings ensure a smooth, quiet and confident ride. Designed to expand with growing feet, the Stryde adjust up to four full sizes at the push of a button. Size small adjusts from children's shoe sizes 11J-1 and has 64mm wheels. Size medium adjusts from children's shoe size 2-5 and has 72mm wheels.