What is bearing preload and why is it important?

• A. Preload increases clearance to allow movement
• B. Preload applies a constant axial load to remove internal clearance, improving stiffness and life.
• C. Preload is only for alignment
• D. Preload reduces stiffness

Answer: (B)

Preload is a deliberate axial force you apply to a bearing to take up its internal clearance, so there’s no loose play between the raceways and rolling elements. When that clearance is removed, the elements stay in constant contact under load, which makes the bearing stiffer. This increased stiffness helps the shaft resist deflection, improves load distribution, reduces vibration and wear, and leads to more predictable operation and longer bearing life. Preload is typically established by tightening end caps, using spacers, or employing springs to create a small, controlled axial load at install. It’s important to set preload correctly: too much preload increases friction and heat and can shorten life, while too little leaves unwanted play.