Bearing clearance has a significant impact on bearing service life, temperature rise, noise and other performance indicators. Therefore, it is necessary to select an appropriate clearance according to the working conditions and performance requirements. Bearing clearance is divided into radial clearance and axial clearance, which respectively refer to the displacement of one fixed race relative to the other along the radial and axial directions from one extreme position to the other. The radial clearance of a bearing includes the original clearance in the free state before installation, the assembled clearance after mounting on the spindle and bearing housing, and the operating clearance formed under load during operation. For ball bearings, the optimal operating clearance is close to zero; for roller bearings, a small amount of operating clearance can be maintained. For components requiring high support stiffness, the bearing should be applied with a certain preload. These are the principles for determining the radial clearance of bearings.

Angular contact ball bearings and tapered roller bearings are usually mounted face-to-face or back-to-back, with the internal clearance or preload determined by the axial position of one of the bearing races. Starting from the zero-clearance condition, the specified clearance can be obtained by adjusting the thickness of the shim on the bearing outer race or by loosening/tightening the lock nut on the shaft. There is a fixed relationship between the axial and radial clearances of such bearings, and it is sufficient to meet the requirement of either value.

The following aspects should also be considered when selecting bearing clearance:

1. The working conditions of the bearing, such as load, temperature, speed, etc.;

2. The performance requirements for the bearing, such as rotational accuracy, friction torque, vibration and noise, etc.;

3. Interference fits between the bearing and the shaft/housing bore will result in a reduction in bearing clearance;

4. During bearing operation, the temperature difference between the inner and outer races causes a decrease in bearing clearance;

5. Differences in the thermal expansion coefficients of the shaft and housing materials will lead to a reduction or increase in bearing clearance;

6. A large temperature difference between the inner and outer races of deep groove ball bearings requires them to withstand large axial loads or improve their self-aligning performance, which in turn demands a higher limiting speed and lower bearing friction torque;

When the basic clearance group fails to meet the application requirements, an auxiliary clearance group should be selected. The large-clearance auxiliary group is suitable for interference fits between the bearing, shaft and housing bore, while the small-clearance auxiliary group is applicable to occasions that require high rotational accuracy, strict control of the axial displacement of the housing bore, and reduction of vibration and noise.