Bearings & Power Transmission

Bearing L10 Life and Replacement Cost: Plan the Swap Before Failure

Bearing L10 life = (C/P)^p x 10^6 revolutions, where C is dynamic load rating and P is equivalent load. Here is how to calculate it and size bearings for your application.

Bearing L10 Life = (C/P)^p x 10^6 revolutions. C = basic dynamic load rating (from bearing catalog, in Newtons or kN). P = equivalent dynamic load (actual load applied to the bearing). p = 3.0 for ball bearings, 10/3 for roller bearings. For a deep groove ball bearing with C = 25,200 N carrying P = 5,000 N: L10 = (25,200/5,000)^3 x 10^6 = (5.04)^3 x 10^6 = 128 x 10^6 revolutions. At 1,500 RPM: L10 life = 128 x 10^6 / (1,500 x 60) = 1,422 hours.

Equivalent dynamic load P = X x Fr + Y x Fa, where Fr = radial load, Fa = axial load, X and Y are factors from the bearing catalog (dependent on bearing type and Fa/Fr ratio). For purely radial loads: P = Fr. For combined loading, the axial component reduces bearing life. Deep groove ball bearings can handle both radial and moderate axial loads. Angular contact bearings are optimized for combined loading. Always check the catalog for X and Y values at your actual Fa/Fr ratio.

Life adjustment factors modify the basic L10 calculation for reliability level, lubrication adequacy, and contamination. Reliability factor a1: L10 reliability (90% survival) = 1.0, L5 (95% survival) = 0.62, L1 (99% survival) = 0.21. Lubrication factor a23 varies with viscosity ratio (actual oil viscosity / required oil viscosity). At viscosity ratio 2.0 (well-lubricated): a23 = 2-3. At 0.5 (under-lubricated): a23 = 0.1-0.2. Poor lubrication reduces actual bearing life by 5-10x versus catalog L10 life.

In practice, most premature bearing failures are not due to overloading but due to contamination, inadequate lubrication, or improper installation. Contamination factor accounts for particle size and hardness in the lubricant. For clean conditions (filtered oil, well-sealed bearing): contamination factor near 1.0. For light to normal contamination: 0.5-0.8. Severe contamination: 0.1-0.3. A bearing sized for 20,000 hours catalog L10 life will often fail in 2,000-5,000 hours if contamination or lubrication is not controlled.

Bearing preload affects both life and precision. Angular contact and tapered roller bearings are often used in pairs with controlled preload. Light preload increases rigidity, reduces runout, and improves fatigue life by distributing load more evenly. Excessive preload increases heat generation, viscous drag, and fatigue stress, shortening life. Preload magnitude is determined by fit selection (interference fits add preload) and adjustment nut settings. Follow manufacturer recommendations for preload class (light, medium, heavy) based on application stiffness requirements.

Published 2026-05-28.