的确是这样，在off-road的时候经常要检查

Wheel bearings are lubricated internally and sealed. Lubricants generate pressure when agitated, so the seals are designed to allow this to escape. The drawback is, such a wheel seal is not water tight. When driving on a flooded street, or through high water, moisture can enter the bearing. This quickly emulsifies the lubricant and bearing failure will follow. Water deep enough to reach the lower edge of the wheel can cause damage. Modern bearings are not serviceable, so any contamination means replacement of the bearing.