A: 

Traditional automobile wheel bearings are composed of two sets of tapered roller bearings or ball bearings.

The hub bearing unit is developed on the basis of standard angular contact ball bearings and tapered roller bearings. It combines two sets of bearings as a whole. It has good assembly performance, can omit clearance adjustment, light weight, compact structure, and load capacity. Large, sealed bearings can be pre-loaded with grease, omit external wheel hub seals, and are free from maintenance. They have been widely used in cars, and there is a trend to gradually expand their applications in trucks.