Preload
Vorspannung
Preload is a deliberately set negative operating clearance: the rolling elements are held under a defined internal force between the raceways even without external load. It is applied by axially adjusting two bearings against each other in O or X arrangement, by springs, or by matched fits and spacer rings; spindle bearings are commonly supplied as factory-matched sets.
Preload increases rigidity, improves shaft guidance accuracy, prevents skidding of unloaded rolling elements and reduces noise and vibration — at the cost of higher friction and heat, with excessive preload drastically shortening life. Typical uses include machine-tool spindles, pinion bearings and servo drives. Always follow the designer's specified preload method when mounting or replacing.