Differences between some wheels and others
How to keep wheels in good condition
Bearings are the part of the wheel that can be damaged by dust, sand or water. That is why they should be kept in a closed place.
Dirt can develop between the nut and the axle. This causes that you can not remove even the nut, and I do not recommend it. Pour 3-in-1s from time to time to the bearings.
Clean on sheets
If you see that the wheels have a lot of dirt on the surface, you can clean it by moving your finger from side to side on a sheet of paper.