The grease between the ball bearings in your bicycle wheels allow the wheel to roll efficiently when you push on the pedals. Without them, pedaling would result in a grinding of metal-on-metal contact between the hub and axle, and great difficulty in doing so at all. All wheels come greased from the factory, but over time riding in the rain and other inclement weather will wear down and make dirty this grease. Re-grease the bearings in your bike wheel to make your bike roll like new again.
3. Slide the axle out of the hub body carefully. Make certain none of the bearings fall out of the hub when the axle is removed. Apply a liberal amount of bicycle bearing grease to the bearings that are visible now that the axle has been removed.