4 Types of Bearing Loads: Powerful Guide to Radial, Axial, Combined & Moment Loads

Selecting the correct bearing is not simply a matter of matching the shaft diameter with the bearing bore. One of the most important steps in bearing selection is to determine the type, direction, magnitude and operating condition of the load acting on the bearing.

A bearing can experience a radial load, axial load, combined radial-and-axial load, or a moment load. The wrong interpretation of the load can lead to excessive heat, vibration, premature wear, raceway damage, lubrication problems and ultimately bearing failure.

For example, a cylindrical roller bearing designed primarily for radial loading is not automatically the best choice for a large axial load. Similarly, a thrust bearing designed for axial loading may not be suitable when substantial radial loading is present. SKF Company notes that roller bearings generally accommodate heavier bearing loads than similarly sized ball bearings, while bearing type selection also depends strongly on load direction and magnitude.

This guide explains how to determine the bearing load type step by step and how to use that information when selecting a bearing.

1. What Is Bearing Load?

Bearing load is the force transmitted between the shaft, bearing rolling elements and housing during machine operation.

The load may come from:

• Shaft weight
• Pulley tension
• Gear forces
• Belt forces
• Chain forces
• Motor torque
• Machine vibration
• External mechanical forces
• Thrust generated by gears or pumps
• Misalignment or eccentric loading

The first task is to determine where the force is acting and in which direction.

A useful approach is to draw a free-body diagram of the shaft and identify all external forces before selecting the bearing.

2. Main Types of Bearing Loads

There are four important load categories:

1. Radial load
2. Axial load
3. Combined radial and axial load
4. Moment or tilting load

SKF identifies radial, axial, combined and moment loading as important load-direction categories for bearing selection.

Radial Load

A radial load acts approximately perpendicular to the shaft axis.

For example, if a pulley mounted on a rotating shaft is pulling downward because of belt tension, the resulting force can create a radial load on the bearing.

Typical applications include:

• Electric motors
• Conveyor rollers
• Fans
• Pumps
• Gearboxes
• Rollers
• Machine tools

Cylindrical roller bearings, needle roller bearings and many deep-groove ball bearings are commonly associated with radial loading. SKF notes that some cylindrical and needle roller bearing designs are intended for pure radial loads, while other bearing designs can also accommodate axial components.

Axial Load

An axial load acts parallel to the shaft axis.

It is also commonly called a thrust load.

Examples include:

• Screw mechanisms
• Thrust generated by gears
• Pump shaft thrust
• Propeller systems
• Vertical shafts
• Machine-tool spindle forces

Thrust ball bearings are designed for axial loading. Depending on the bearing design, axial load may be supported in one direction or both directions.

Combined Load

A combined load occurs when radial and axial forces act simultaneously.

This is extremely common in industrial machinery.

For example, a shaft carrying a helical gear can experience:

• Radial gear force
• Axial gear force

The bearing therefore needs to accommodate both components.

SKF explains that combined loads can be handled by bearing types such as angular-contact ball bearings and tapered roller bearings, while deep-groove ball bearings and spherical roller bearings may also be suitable depending on the axial component.

Moment Load

A moment load occurs when the load acts at a distance from the bearing or bearing centerline, creating a tilting effect.

This can happen when:

• A long shaft carries an eccentric load
• A pulley is located far from the bearing
• A cantilevered component creates a bending moment
• A machine component is mounted away from the bearing support

Moment loading can cause uneven bearing loading and must be considered during bearing arrangement design.

SKF notes that double-row bearings can accommodate tilting moments, while paired angular-contact or tapered roller bearing arrangements can be more suitable for certain moment-load applications.

3. Radial vs Axial vs Combined Load

Load Type	Force Direction	Typical Application	Common Bearing Choices
Radial	Perpendicular to shaft	Motors, rollers, fans	Deep-groove, cylindrical roller, spherical roller
Axial	Parallel to shaft	Thrust, screws, pumps	Thrust ball, thrust roller
Combined	Radial + axial	Gears, pumps, transmissions	Angular contact, tapered roller, deep groove
Moment	Creates tilting effect	Overhung shafts, eccentric loads	Double-row or paired bearings

This table is a general guide. Actual bearing selection should always be checked against the manufacturer’s load ratings, speed, mounting arrangement and application conditions.

4. How to Determine the Type of Load

Step 1: Identify the Shaft Direction

First identify the shaft centerline.

Imagine a horizontal shaft.

A force pushing downward on that shaft is generally radial.

A force pushing along the shaft toward its end is axial.

This simple visualization makes the first classification easier.

Step 2: Identify All External Forces

Do not consider only the machine’s weight.

Look for:

• Gear forces
• Belt tension
• Chain tension
• Coupling forces
• Rotor weight
• Fan forces
• Pump forces
• External process loads

A shaft can have multiple forces acting at the same time.

Step 3: Resolve the Forces

If the force is angled, separate it into components.

For example:

Radial component = Fr

Axial component = Fa

The combined load is determined from these components.

The exact calculation method depends on bearing type and manufacturer factors.

For many radial bearings, NTN gives the dynamic equivalent radial load in the form:

P = XFr + YFa

where Fr is the radial load, Fa is the axial load, and X and Y are bearing-specific factors.

Do not use generic X and Y values without checking the particular bearing manufacturer’s catalog.

5. Determine Whether the Load Is Constant or Variable

Load direction alone is not enough.

You should also determine whether the load is:

• Constant
• Alternating
• Fluctuating
• Shock loading
• Impact loading

SKF distinguishes between constant-direction and alternating-direction loads, as well as static and dynamic loading conditions.

Constant Load

The load magnitude and direction remain approximately constant.

Example:

A conveyor roller operating with a relatively stable product load.

Variable Load

The load changes during operation.

Example:

A machine that starts with a light load and later operates under heavy load.

Alternating Load

The direction changes repeatedly.

Example:

A mechanism where forces reverse during each operating cycle.

Shock Load

A sudden force is applied to the bearing.

Examples include:

• Impact machinery
• Crushers
• Heavy conveyors
• Drop loads
• Poorly aligned machinery

Shock loads require special attention because the peak force may be much greater than the normal operating force.

6. Determine the Magnitude of the Load

After identifying the load direction, determine its magnitude.

Use appropriate units such as:

• Newton (N)
• Kilonewton (kN)
• Pound-force (lbf)

For example:

Suppose a shaft bearing experiences:

Radial load = 5 kN

Axial load = 2 kN

This is not a pure radial application. It is a combined-load application.

The bearing’s actual equivalent load must then be calculated using the manufacturer’s prescribed method.

For variable loading, the operating cycle may also need to be converted into an equivalent or mean load. NTN provides load-calculation methods for fluctuating and stepped loads and uses different exponents for ball and roller bearings in its calculation methods.

7. Bearing Selection According to Load Type

For Mainly Radial Loads

Common options include:

• Deep-groove ball bearings
• Cylindrical roller bearings
• Spherical roller bearings
• Needle roller bearings

Roller bearings are generally advantageous when heavier radial loads must be supported because roller bearings can accommodate higher loads than similarly sized ball bearings.

For Mainly Axial Loads

Possible choices include:

• Thrust ball bearings
• Cylindrical roller thrust bearings
• Tapered roller thrust bearings
• Spherical roller thrust bearings

The exact selection depends on load magnitude, direction, speed and whether radial load is also present.

For Combined Loads

Possible choices include:

• Deep-groove ball bearings
• Angular-contact ball bearings
• Tapered roller bearings
• Spherical roller bearings

As the axial component becomes more significant, bearing types with greater axial load capability may become more appropriate. SKF specifically notes angular-contact ball bearings and tapered roller bearings for higher axial components in combined loading.

8. Contact Angle and Load Direction

Contact angle is an important concept when select bearings for combined loading.

A bearing with a larger contact angle generally has greater axial load-carrying capability.

SKF explains that increasing contact angle increases axial load capability, while the direction of the combined load is determined by the ratio between radial and axial components.

This creates a practical trade-off.

Smaller Contact Angle

Advantages:

• Better suitability for predominantly radial loads
• Generally favorable for higher-speed applications

Disadvantages:

• Lower axial load capability

Larger Contact Angle

Advantages:

• Better axial load capacity
• Better suitability for combined loads with significant axial force

Disadvantages:

• May involve different speed and friction characteristics depending on bearing design

Therefore, do not select a contact angle simply because “larger is stronger.” The complete application must be considered.

9. Comparison: Ball Bearings vs Roller Bearings

Feature	Ball Bearing	Roller Bearing
Radial load	Light to moderate applications	Moderate to heavy applications
Axial capability	Depends on design	Depends strongly on design
Speed	Often excellent	Depends on type
Friction	Generally low	Depends on roller design
Heavy-load capability	Moderate	Generally higher
Typical use	Motors, fans, general machinery	Gearboxes, heavy machinery, industrial equipment

SKF states that roller bearings generally accommodate heavier loads than similarly sized ball bearings.

10. Advantages of Correct Load Identification

Correct load identification provides several benefits.

1. Longer Bearing Life

Selecting a bearing according to actual loading reduces the risk of overloading.

2. Better Reliability

The bearing is less likely to experience premature fatigue, excessive vibration or overheating.

3. Better Machine Performance

Correct bearing selection helps maintain shaft positioning and machine accuracy.

4. Better Lubrication Decisions

Load, speed and temperature influence lubricant selection and relubrication requirements.

5. Lower Maintenance Cost

A properly selected bearing can reduce unplanned downtime and replacement frequency.

11. Disadvantages of Incorrect Load Identification

Undersized Bearing

An undersized bearing may experience:

• Excessive stress
• Raceway fatigue
• Overheating
• Vibration
• Premature failure

Wrong Bearing Type

A bearing selected for radial loading may be unsuitable for a large axial component.

Ignoring Moment Loads

An eccentric load can produce additional stress that is not obvious if only the vertical or horizontal force is considered.

Ignoring Shock Loads

Using only the average load can underestimate the actual operating severity.

Ignoring Variable Loading

A machine with changing loads requires more detailed analysis than a machine operating at one constant load.

12. How to Improve Bearing Load Selection

Follow this practical process:

Improvement 1: Create a Load Diagram

Draw the shaft, bearings and all external forces.

Mark:

Fr = radial force

Fa = axial force

M = moment

Improvement 2: Measure Actual Operating Conditions

Where possible, use:

• Load cells
• Torque sensors
• Vibration measurements
• Speed measurements
• Temperature monitoring

Improvement 3: Consider the Worst Operating Condition

Do not select the bearing only according to normal average load.

Consider:

• Startup
• Shutdown
• Maximum load
• Shock load
• Emergency conditions

Improvement 4: Use Manufacturer Calculations

Use the exact manufacturer’s bearing data.

Important parameters include:

• Dynamic load rating
• Static load rating
• X factor
• Y factor
• Limiting speed
• Contact angle
• Internal clearance

NTN’s technical handbook specifically provides equivalent-load equations and manufacturer-specific factors for combined radial and axial loading.

Improvement 5: Check the Complete System

Bearing selection should also consider:

• Shaft diameter
• Housing
• Fit
• Alignment
• Lubrication
• Temperature
• Contamination
• Speed
• Required life

Load is critical, but it is not the only selection criterion.

13. Practical Example

Consider a gearbox shaft.

Suppose the shaft experiences:

• Radial load: 8 kN
• Axial load: 3 kN
• Rotational speed: 1,500 RPM

Because both radial and axial forces are present, this is a combined-load application.

The next step is not simply to select a bearing with an 8 kN radial rating.

Instead:

1. Determine the bearing type.
2. Obtain the manufacturer’s X and Y factors.
3. Calculate the equivalent dynamic bearing load.
4. Check the dynamic load rating.
5. Check static load conditions.
6. Calculate or verify bearing life.
7. Check speed and temperature.
8. Confirm lubrication and mounting conditions.

This method is much more reliable than selecting a bearing only from its bore diameter.

14. Quick Load-Identification Checklist

Before purchasing a bearing, answer these questions:

1. Is the load radial?
2. Is the load axial?
3. Is it a combined load?
4. Is there a moment load?
5. What is the maximum load?
6. What is the normal operating load?
7. Is the load constant or variable?
8. Does the load direction change?
9. Is there shock or impact?
10. What is the shaft speed?
11. What temperature will the bearing experience?
12. What lubrication will be used?
13. What bearing life is required?
14. What are the manufacturer’s dynamic and static load ratings?

If these questions are answered correctly, bearing selection becomes considerably more systematic.

Conclusion

Determining the type of load is one of the most important steps in bearing selection. A bearing does not simply carry “weight”; it experiences forces with specific directions, magnitudes and operating patterns.

The four major load categories are radial, axial, combined and moment loads. Radial loads act perpendicular to the shaft, axial loads act parallel to the shaft, combined loads contain both radial and axial components, while moment loads create a tilting effect.

For light or moderate combined loads, a deep-groove ball bearing may be suitable in many applications. When the axial component becomes larger, angular-contact or tapered roller bearings may be more appropriate. Heavy radial applications may favor roller bearings because of their generally higher load-carrying capability.

The most important principle is simple:

Do not choose a bearing only by shaft size. Determine the actual load type, direction, magnitude, speed and operating conditions first.A proper load analysis can improve bearing life, machine reliability, maintenance planning and overall equipment performance.

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