Like all moving parts, bearings do eventually wear out. Dirt, dust and water can penetrate the seals and damage the bearings, making them crunchy and inefficient. This saps energy from your ride and in the long term does more damage than good. What you need is a full bearing replacement kit and this product right here has everything you need to revitalise your Hope Pro 2 Evo hubs. Hope part number: HUB3P2ER Features: 5x Stainless Steel Bearings: 2x 6903 2x 6803 1x 17287