Internal Bearing Load Distribution Relevant to ISO 16281

Why internal load distribution matters

External force is not divided equally among a bearing's rolling elements. Internal clearance, preload, contact angle, ring displacement, elastic deformation, and misalignment determine which elements are loaded and by how much. The most heavily loaded contact often governs stress and rating life.

ISO 16281:2025 covers modified reference rating life for universally loaded rolling bearings and includes effects beyond the basic ISO 281 calculation. It replaced the previous ISO/TS 16281:2008 technical specification. The standard includes operating clearance, tilt or misalignment, and internal rolling-element load distribution in the life calculation.

The calculation model

For each rolling element j, the relative ring displacement and local geometry produce a normal approach δ_j. An element carries load only when that approach closes the available clearance and establishes contact.

In simplified Hertzian relationships, the exponent is commonly 3/2 for ball or point contact and 10/9 for roller or line contact. A complete model uses bearing geometry, slice or contact models where applicable, and the method specified for the bearing type.

Force and moment equilibrium

The unknown ring translations and tilts are adjusted until the vector sum of all rolling-element contact forces and moments balances the applied radial force, axial force, and overturning moments. Because contact load depends nonlinearly on displacement—and contacts can open or close—the solution is normally iterative.

1. PositionLocate each rolling element around the bearing pitch circle.
2. DeflectCalculate local approach from translations, tilt, clearance, and geometry.
3. LoadConvert positive contact approaches into rolling-element loads.
4. BalanceIterate until internal forces and moments equal the applied load system.

Worked calculation setup

Consider a radial roller bearing with 12 rollers under a 20 kN radial load. Dividing 20 kN by 12 would incorrectly predict 1.67 kN per roller. Instead, the solver starts with ring displacement in the load direction. Rollers opposite the load direction may retain clearance and carry no load, while rollers inside the load zone carry different loads according to their angular position and local deflection.

The displacement is iterated until the resolved roller forces sum to 20 kN. If a moment or misalignment is added, the load can also vary along each roller and the two raceway contacts. BearingSolve performs this numerical equilibrium step and exposes the resulting rolling-element load and stress distributions.