1. When the hub and brake drum (disc) are machined, the axial center is not positioned correctly, the machining error is large, the casting surface of the non-machined surface is large, the heat treatment is deformed, and the deformation or wear is uneven during use;
2. The quality of the hub bolts is not equal, the hub mass distribution is uneven or the radial circle is beating, and the end face rounding is too large;
3. Uneven tire quality distribution, large size or shape error, uneven deformation or wear during use, use of retreaded tires or mats, tire repair;
4. The inflatable nozzles of the twin tires are not separated by 180 degrees, and the inflation nozzles of the single tires are not installed 180 apart from the unbalanced dot marks;
5. When the hub, brake drum, tire bolt, rim, inner tube, lining belt, tire, etc. are disassembled and reassembled into tires, the accumulated unbalanced mass or shape deviation is too large, which destroys the original balance.