Free Engineering Tool #047
Bearing Minimum Load Calculator
Calculate the minimum radial load required to prevent roller/ball skidding. Enter bearing dimensions, speed, and lubrication type.
Results
Minimum Load Formula (Simplified)
The minimum radial load to prevent skidding is estimated as:
- kr — minimum load factor from the manufacturer’s product table (typically ≈ 0.025 for deep groove ball bearings; higher equivalent values for roller bearings — see table below)
- ν — kinematic viscosity at operating temperature (mm²/s)
- n — rotational speed (RPM)
- dm — mean bearing diameter = (d + D) / 2 (mm)
- For grease lubrication this calculator additionally multiplies the result by a conservative factor of 1.5, since grease-lubricated bearings need a higher minimum load
Mean Diameter
Typical kr Values
| Bearing Type | kr |
|---|---|
| Deep groove ball bearing | ≈ 0.025 |
| Angular contact ball bearing | ≈ 0.03 |
| Cylindrical roller bearing | ≈ 0.25 |
| Tapered roller bearing | ≈ 0.25 |
| Spherical roller bearing | ≈ 0.3 |
Ball-bearing kr values are typical of manufacturer product tables (e.g. SKF lists kr per bearing, roughly 0.02–0.06 for deep groove ball bearings). For roller bearings manufacturers use dedicated minimum-load relations (e.g. Frm ≈ 0.02 × C0 or speed-based formulas); the roller factors above are approximate equivalents so that this simplified formula reproduces the same order of magnitude. Always check the exact value in the bearing product table.
Practical Example
Given: d = 40 mm, D = 80 mm, n = 3000 RPM, ν = 20 mm²/s, kr = 0.025, oil lubrication
dm = (40 + 80) / 2 = 60 mm
Fmin = 0.025 × (20 × 3000 / 1000)2/3 × (60 / 100)²
= 0.025 × 15.33 × 0.36 = 0.14 kN (≈ 140 N)
Cross-check with the simple rule Fmin ≈ 0.01 × C0: for a 6208 bearing (C0 ≈ 17.8 kN) it gives ≈ 0.18 kN — the same order of magnitude.
⚠️ Note: This is a simplified estimation. For critical applications, consult the bearing manufacturer’s specific minimum load guidelines. Actual minimum load depends on internal clearance, cage type, and lubricant properties.
Rolling bearings need a minimum load to ensure proper rolling contact. Without sufficient load, balls or rollers may slide (skid) instead of roll, causing smearing damage, increased heat, and premature failure.
Skidding occurs when the friction force is insufficient to maintain rolling contact. This happens at high speeds with light loads, especially with grease lubrication. The rolling elements accelerate in the unloaded zone and decelerate in the loaded zone, causing sliding.
The factor kr is listed in the bearing manufacturer product tables. Typical values are about 0.025 for deep groove ball bearings and 0.03 for angular contact ball bearings. Roller bearings need proportionally higher minimum loads (manufacturers often quote Frm ≈ 0.02 C0), so this calculator uses higher equivalent factors of about 0.25–0.3 for roller types.
Yes. Grease-lubricated bearings generally require higher minimum loads (factor ≈ 1.5×) than oil-lubricated ones because grease has higher viscous drag, especially at startup and low temperatures.
If actual load is below the minimum, consider: applying a preload (axial spring), using a heavier bearing arrangement, increasing the load path, or switching to a bearing type with lower minimum load requirements. Spring-loaded washers are common on vertical shafts.
The procedures described on this page were developed and field-tested by the Vibromera team using the Balanset-1A, a portable dual-channel balancer and vibration analyzer for on-site rotor balancing.
Professional field balancing instruments and vibration analyzers. Used in 50+ countries.
