ISO 76 guide
Static Bearing Load Rating and Safety Factor
Use the basic static load rating, equivalent static load, and static safety factor to assess permanent-deformation risk.
What the basic static load rating describes
The basic static load rating C0 is associated with a defined amount of permanent deformation at the most heavily loaded rolling-element contact. For conventional steel bearings, this total permanent deformation of the rolling element and raceway is approximately 0.0001 times the rolling-element diameter. The rating is used when a bearing is stationary, oscillates slowly, rotates at very low speed, or experiences high peak or shock loads. It is different from the dynamic rating C used in fatigue-life calculations.
Equivalent static load and safety factor
For many radial bearings, the catalogue requires the larger of the radial load and a combined-load expression. This common form illustrates that check; the selected bearing's catalogue remains authoritative.
The factors X0 and Y0 and the comparison rule are specific to the bearing type. The required minimum S0 depends on noise sensitivity, shock severity, rotational accuracy, and the consequences of permanent deformation.
Worked example
A selected bearing has a catalogue static load rating C0 = 28 kN. The applicable bearing-specific equation gives an equivalent static load P0 = 12 kN.
The next step is to compare 2.33 with the minimum recommended by the bearing manufacturer for the actual operating conditions. A positive margin alone does not establish that the bearing is suitable.
Loads that should be checked
- Maximum steady load while stationary or turning slowly
- Startup, shutdown, emergency-stop, and process peak loads
- Shock loads transmitted through gears, belts, or couplings
- Preload and assembly loads in addition to external loads
- The most heavily loaded bearing when load sharing is unequal
A bearing can have adequate calculated fatigue life and still be damaged by a short peak load. It can also pass the static check but have inadequate fatigue life in continuous operation.
Standards and further reading
- ISO 76:2006 — Static load ratings
- ISO 76:2006/Amd 1:2017 — Amendment 1
- ISO 17956:2025 — Effective static safety factor for universally loaded rolling bearings
- Use the selected bearing manufacturer's current catalogue for static load factors and application-specific minimum safety factors.
This educational guide does not reproduce the standards. Its equations and examples have been checked against the cited public references, but the guide has not been independently certified or reviewed for your application. Use the current standard, manufacturer data, and an appropriate engineering review for final bearing selection.
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