A roller bearing supports relative rotation through rollers positioned between raceways. The animation shows a cylindrical roller bearing with a rotating inner ring, fixed outer ring and rollers carried around by a cage. Its calculator compares two assumed equivalent friction coefficients; it does not select a bearing or calculate fatigue life.
Anti-friction Roller Bearing Interactive Calculator
Compare assumed sliding and rolling equivalent friction coefficients at the same load and effective radius.
Equation Used
This ideal comparison assumes equal load, effective radius and speed. Entering 0.10 and 0.001 gives a coefficient ratio of 100, with the rolling case at 1% of the sliding reference. It does not calculate a real bearing’s total friction torque or heat generation.
- Normal load and speed are held constant.
- This compares friction coefficient only, not full bearing fatigue life.
- The rolling-coefficient control spans 0.001 to 0.005; this illustrative range is not a specification for all roller bearings.
Friction, fatigue life and installation condition are different engineering questions. The two-coefficient comparison below answers only the first in an idealized form.
Rollers, rings and cage
Load passes from the shaft through the inner ring and loaded rollers into the outer ring and housing. As the inner ring turns, each roller spins and its center travels around the bearing. The cage separates and guides the rollers; it does not carry the shaft load in place of the raceways.
The cutaway exposes the length of the cylindrical rollers. Their nominal line contact becomes a finite contact area under load. Tapered and spherical roller bearings use different raceway and roller geometry; they are not represented by merely changing these friction sliders.
Real roller bearings include rolling and sliding contact, lubricant motion and, where fitted, seal friction. The equivalent coefficient is a simplified way to compare two assumed cases, not a complete contact or thermal model.
Parts shown
- Inner ring: turns with the shaft in this illustration.
- Outer ring: stays fixed in its support.
- Cylindrical rollers: transmit load between the raceways.
- Cage: keeps the rollers separated as they orbit.
Mounting fits, internal clearance, lubrication and permitted misalignment depend on the specific bearing and installation. No universal fit or clearance can be inferred from this cutaway.
Applications and bearing geometry
Roller-bearing arrangements support shafts in machinery such as gearboxes, rolls, conveyor pulleys and wheel assemblies. The appropriate construction depends on radial and axial loads, shaft location, speed, available space and alignment.
Cylindrical rollers suit arrangements needing radial support; axial capability depends on their flange design. Tapered rollers can support combined loads when arranged and adjusted appropriately. Spherical roller geometry allows a specified amount of self-alignment. Those distinctions require actual product data, not a friction coefficient alone.
What the friction calculator computes
Let μs be Sliding mu and μr be Rolling mu. Reduction = μs/μr. Rolling Loss = 100μr/μs%. Friction Cut = 100(1 − μr/μs)%. Coeff Drop = μs − μr.
Rolling Loss is the rolling case as a percentage of the sliding reference. It is not a percentage of motor input power, and Friction Cut is not bearing efficiency. The model supplies neither load, speed nor effective radius, so it cannot output force, torque or watts.
If both comparisons used an assumed equivalent torque expression T = μFr with identical F and r, the torque ratio would equal the coefficient ratio. Equal speed would then give the same ratio of frictional power. Real bearing friction requires more detailed data and is not necessarily proportional to one constant coefficient.
Fatigue life is a separate calculation. Basic roller-bearing L10h = (C/P)^(10/3) × 10⁶/(60n), using catalog dynamic rating C, equivalent load P and rpm n. It is a statistical rating, not a service guarantee. These quantities are not inputs to this calculator.
Worked example: interpreting the four outputs
Set Sliding mu to 0.100 and Rolling mu to 0.001. Reduction is 100.0×, Rolling Loss is 1.0%, Friction Cut is 99.0%, and Coeff Drop is 0.099.
Keep Sliding mu at 0.100 and change Rolling mu to 0.005. Reduction becomes 20.0×, Rolling Loss 5.0%, Friction Cut 95.0%, and Coeff Drop 0.095. The second coefficient is five times the first rolling assumption, so its relative loss is also five times larger in this model.
At the opposite control extremes, μs = 0.020 and μr = 0.005 give Reduction 4.0×, Rolling Loss 25.0%, Friction Cut 75.0%, and Coeff Drop 0.015. These results compare entered numbers; they do not establish the performance of any particular bearing or bushing.
Choosing a shaft support
| Support | Relevant design questions |
|---|---|
| Roller bearing | Roller geometry, loads, speed, alignment, clearance and lubrication. |
| Ball bearing | Contact geometry, radial and axial capability, speed and stiffness. |
| Plain bushing | Sliding surfaces, lubricant, pressure, velocity and wear. |
| Fluid-film support | Film formation, supply, stiffness and starting conditions. |
A generic ranking of price, friction, service life or speed by bearing type would conceal the conditions that determine performance. Compare actual components at the required operating conditions.
Condition and damage
Raceway fatigue, contamination, corrosion, lubricant problems, mounting damage and electrical damage are possible concerns in a bearing installation. More than one may contribute to a failure.
Noise, temperature or a polished contact mark alone cannot establish the cause. Preserve operating history and inspect according to the equipment and bearing manufacturer’s diagnostic guidance. This coefficient calculator contains no fault-diagnosis or remaining-life model.
Installation information to check
Use the specified bearing designation, fits, clearance or preload, lubrication and mounting procedure. Apply mounting forces through the ring being fitted, avoiding a load path through the rolling elements.
Commissioning limits and monitoring intervals belong to the actual assembly. This illustration supplies no universal heating temperature, allowed misalignment, run-in time or acceptable temperature rise. Extra cooling or a cage substitution does not, by itself, authorize operation above a catalog limit.
Roller-bearing questions
No. Its two inputs are equivalent friction coefficients. It calculates their ratio, relative loss, percentage reduction and difference.
No. It is 100μr/μs, the rolling assumption relative to the sliding reference. No motor input power is entered.
No. Rotation speed is illustrative. The sliders change the numerical coefficient comparison rather than a driven-shaft dynamics model.
Do not infer that from this calculator. Permissible speed depends on the specific bearing and operating conditions, including more than temperature alone. Obtain applicable manufacturer guidance.
No. Noise alone cannot identify a unique damage mechanism or establish safe continued use. Diagnose the actual assembly and its operating history.
No. It denotes an internal-clearance class, not a universal capacity or life upgrade. Select clearance for the installation.
No. Their load support, axial setting and alignment behavior differ. The complete shaft arrangement determines which construction is appropriate.
No. Those depend on the actual bearing, ring materials, dimensions and assembly procedure. Use the component’s instructions rather than a generic value.
References and further reading
SKF: Using a friction model as an engineering tool separates rolling, sliding, seal and drag contributions. Consult the bearing manufacturer’s current catalog and mounting guidance for actual component selection.
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