The frictional properties of any plain bearing depend on the lubrication system. Either hydrodynamic or hydrostatic lubrication can provide low friction. Gas bearings have the lowest friction levels.
Friction in hydrodynamic and hydrostatic bearings is a function of lubricant viscosity and shear rate. Shear rate increases with increasing rotational speed and decreasing film thickness. Friction coefficient is generally below 0.001.
Self-lubricated bearings vary widely. It is difficult to predict performance for a given bearing/lubricant system. The range of coefficients of friction is 0.01 to 0.10 for boundary lubrication and 0.01 to 0.3 for self-lubrication.
Caution must be used when applying friction coefficient handbook data. Conditions under which the values were measured should be known and duplicated in the application. Coefficient of friction tends to increase with increasing surface roughness, dryness, and cleanliness of surfaces, and decreasing temperature.
