Wheel bearings are one of the key parts of the car, its main role is to carry the weight and provide an accurate guide for the rotation of the hub , which requires that it not only can withstand axial load also bear the radial load. Wheel bearing units is the standard angular contact ball bearings and tapered roller bearings developed on the basis of it as one of the two sets of bearings , having a good assembly performance , you can omit clearance adjustment , light weight, compact structure, large load capacity , the can be pre- loaded grease sealed bearings , hub seals and maintenance omitted from the external wheel , etc., have been widely used in cars , the truck also has a tendency to graduallyexpand the application .