Ceramic Lightning Yellow Seal Bicycle Bearing Kits are specially designed for Off Road and excessively dirty riding environments. These bearings are maintenance free and lubed for life. The heavy duty rubber seal provides extra protection against the harshest elements. These bearings have ceramic balls, with stainless steel races and a C3 fit. Ceramic hybrids are lighter, capable of achieving higher RPM’s and sustaining higher operating temperatures than traditional bearings. Bearings that are packed in grease will require a short break in period to loosen up.