Bearing Preload

Preload removes internal clearance so a bearing runs stiffer and quieter with better shaft location — but it is extra load, and bearing life falls with the cube of load. This shows the trade.

The preload is treated as the bearing's axial load, so P = max(Fr, X·Fr + Y·Fa) with the catalogue X and Y for Fa/Fr above e. Single-row angular contact ball, 40°: X 0.35, Y 0.57, e 1.14 (the defaults). Deep-groove ball: X 0.56, with Y read from the catalogue against f₀Fa/C₀. Below e a light preload leaves P, and the rated life, unchanged. Light preload is usually 2–5% of dynamic capacity. Remember thermal growth adds preload in service — a joint preloaded cold can be badly overloaded hot.