Why do bearings need a minimum load?

Rolling bearings need a minimum load to ensure proper rolling contact between the rolling elements and raceways. Without sufficient load, the balls or rollers may slide (skid) instead of roll, causing smearing damage, increased heat, and premature failure.

What causes bearing skidding?

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.

How is the minimum load factor kr determined?

The minimum load factor kr is a bearing-specific value listed in the manufacturer's product tables. For deep groove ball bearings it is typically about 0.025. Roller bearings require proportionally higher minimum loads (manufacturers often quote Frm of roughly 0.02 C0), so this calculator uses higher equivalent factors of about 0.25 to 0.3 for roller types.

Does lubrication type affect minimum load?

Yes. Grease-lubricated bearings generally require higher minimum loads than oil-lubricated ones because grease has higher viscous drag, especially at startup. The kinematic viscosity used in the formula should reflect the actual lubricant at operating temperature.

What if my actual load is below the minimum?

If the actual load is below the minimum, you can: apply a preload (axial spring), use a heavier bearing arrangement, increase the load path, or switch to a bearing type with lower minimum load requirements. For vertical shafts, adding a spring-loaded washer is common.

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.

Skidding Prevention Grease / Oil Ball & Roller

Bearing Bore d (mm)

Bearing OD D (mm)

Speed (RPM)

Kinematic Viscosity ν (mm²/s at operating temp)

Bearing Type

Lubrication Type

Quick presets

Results

Minimum Radial Load F_min

—

Mean Diameter dm

—

Factor kr

—

ν × n Product

—

Minimum Load Formula (Simplified)

The minimum radial load to prevent skidding is estimated as:

k_r — 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)
d_m — 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	k_r
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 k_r values are typical of manufacturer product tables (e.g. SKF lists k_r per bearing, roughly 0.02–0.06 for deep groove ball bearings). For roller bearings manufacturers use dedicated minimum-load relations (e.g. F_rm ≈ 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

Example — 6208 Deep Groove Ball Bearing

Given: d = 40 mm, D = 80 mm, n = 3000 RPM, ν = 20 mm²/s, k_r = 0.025, oil lubrication

d_m = (40 + 80) / 2 = 60 mm

F_min = 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 F_min ≈ 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.