Unequal load zones
Reactions, clearance, preload, and housing deformation change rolling-element load.
Engineering
Bearing Efficiency Calculator
Estimate bearing-set friction torque and power loss from load, effective coefficient, mean diameter, count, speed, and transmitted torque.
BEARING EFFICIENCY
Convert an explicit friction assumption into loss at speed
Bearing efficiency is not a universal percentage. The calculator makes the assumed friction coefficient and contact diameter visible before converting drag torque to heat and delivered power.
Bearing-set friction torque (N*m)-
Bearing loss power (kW)-
Transmitted input power (kW)-
Power after bearing loss (kW)-
Simplified bearing efficiency-
ENGINEERING DECISION VIEW
Link bearing load and contact diameter to heat
Use the output to compare documented conditions or estimate heat. Improve coefficient evidence before changing equipment or lubrication.
| Balance item | Load / torque | Diameter / speed | Power or torque | Meaning |
|---|
LIVE CALCULATION PROCESS
Formula, substitution, and reconciliation
Tfriction = mu*F*dm/2*count; Ploss = Tfriction*2*pi*N/60,000; efficiency = (Pin-Ploss)/Pin
One entered effective coefficient is applied to each identical represented bearing. This transparent screen does not replace a manufacturer loss model for rolling, sliding, seal, and lubricant drag.
HOW TO USE
Create a visible bearing-loss estimate
- Enter load per represented bearing; do not assume equal sharing without reaction analysis.
- Enter coefficient and mean diameter for the actual bearing and condition.
- Enter speed, transmitted torque, and bearing count.
- Review friction torque before accepting efficiency.
- Retain bearing designation, reaction basis, coefficient provenance, preload, lubrication, and temperature so the loss estimate can be replaced by a detailed manufacturer model.
SUBJECT FUNDAMENTALS
What controls bearing efficiency
- Rolling friction
- Resistance from contact deformation, microslip, and lubricant behavior.
- Mean diameter
- Representative radius basis for friction torque.
- Effective coefficient
- Single fitted assumption summarizing multiple mechanisms.
- Preload
- Internal force that can raise stiffness and loss.
- Lubricant drag
- Resistance sensitive to viscosity, quantity, and speed.
- Bearing-set loss
- Loss for only the bearings inside the selected boundary.
CALCULATION METHOD
Expose the coefficient instead of hiding a fixed percentage
Tfriction = mu*F*dm/2*count; Ploss = Tfriction*2*pi*N/60,000; efficiency = (Pin-Ploss)/Pin
One entered effective coefficient is applied to each identical represented bearing. This transparent screen does not replace a manufacturer loss model for rolling, sliding, seal, and lubricant drag.
DEFAULT CASE AUDIT TRAIL
Symbols, units, substitution, and independent check
| Symbol | Meaning | Unit |
|---|---|---|
| F | Radial load represented per bearing | N |
| mu | Effective friction coefficient | dimensionless |
| dm | Mean bearing diameter | mm |
| z | Identically represented bearing count | whole number |
| Tf | Bearing-set friction torque | N*m |
| N | Rotational speed | rpm |
Default values
- F = 12,500 N, mu = 0.0018, and dm = 85 mm.
- z = 2, N = 3,000 rpm, and transmitted torque = 420 N*m.
Unit conversion
- Mean radius = 85 / 2,000 = 0.0425 m.
- Angular speed = 2 x pi x 3,000 / 60 = 314.159 rad/s.
Numerical substitution
- Friction torque per bearing = 0.0018 x 12,500 x 0.0425 = 0.95625 N*m.
- Bearing-set friction torque = 0.95625 x 2 = 1.9125 N*m.
- Loss power = 1.9125 x 314.159 / 1,000 = about 0.601 kW.
- Transmitted input power = 420 x 314.159 / 1,000 = about 131.947 kW.
Named intermediate results
- Mean contact radius: 0.0425 m.
- Bearing-set friction torque: 1.9125 N*m.
- Delivered power after the simplified loss: about 131.346 kW.
Independent check:Delivered power plus bearing loss returns transmitted input power, and the torque-domain ratio 1 - 1.9125/420 gives the same simplified efficiency as the power-domain ratio.
DEEPER ANALYSIS
Why detailed loss methods need more inputs
Viscosity shifts
Cold oil or excess grease can greatly raise drag.
Seal dominance
Contact seals can exceed rolling-contact loss in small bearings.
WORKED DECISION CASES
Two efficiency decisions
Lubricant comparison
Documented coefficients at the same condition are converted to cooler heat load.
Arrangement review
A paired support estimate is retained while unequal reactions are verified separately.
Bearing efficiency terminology
- Equivalent load
- Simplified load with the same modeled effect as the actual combination.
- Internal clearance
- Relative movement available before mounting and thermal effects.
- Preload
- Controlled internal load.
- Friction torque
- Moment resisting bearing rotation.
- Churning loss
- Power used moving lubricant.
- Thermal equilibrium
- Generated heat equals rejected heat.
EVIDENCE AND DATA LINEAGE
Retain coefficient source and bearing condition
Keep bearing designation, reactions, preload, clearance, fits, lubricant, temperature, speed, torque, seal inclusion, coefficient source, count, and unrounded balance.
LIMITS AND EXCLUSIONS
What the coefficient model excludes
- No manufacturer friction decomposition, thermal network, starvation, skidding, or misalignment analysis is included.
- Identical load and condition are assumed for the entered count.
- Efficiency does not establish life, static safety, speed capability, or temperature.
RELIABLE SOURCES
References for the method and its boundaries
FREQUENTLY ASKED QUESTIONS
Questions about bearing efficiency
Is 0.0018 universal?
No; replace the illustrative default with bearing-specific evidence.
Why load per bearing?
The model multiplies one bearing estimate by count; unequal reactions need separate runs.
Are seals included?
Only if the coefficient explicitly includes them.
Why does efficiency depend on transmitted torque?
A similar loss is a larger fraction of low transmitted power.
Can starting torque be used?
Only for a start-up decision, not stabilized running efficiency.
Does the page select a bearing?
No; life, static safety, speed, lubrication, fit, and clearance remain.
RELATED CALCULATORS
Continue the engineering review
Bearing Safety Factor Calculator
Check dynamic rating life and static safety as separate selection gates.
Shaft Loss Calculator
Place bearing loss inside a broader shaft, seal, and windage balance.
IMPORTANT NOTE
Use a bearing-specific method for final thermal design
Final decisions should use current manufacturer methods or validated tests for the complete bearing arrangement.