My dad is a retired big truck/dozer mechanic, and in all fairness, one of the best ( and that comes from several people around KY and IND.) and he judges mine by the miles I put on it, but He keeps it greased very well ( My boat stays in his garage since my divorce) and yes, change races everytime you do bearings. He said bearings last a long time wheb properly greased but why take chances on an easy and cheap job, change them every 2-3 k on a boat trailer. Timex bearings and races, CP seals(if still being made)