Radial load acts perpendicular to a shaft’s axis. Axial load acts parallel to it and is also called thrust load. The difference is direction relative to the shaft, not whether the force points up, down, or sideways on the page.
A bearing may carry radial load, axial load, or both. Its geometry and mounting arrangement determine which directions it can support. Start by identifying the shaft axis, then check the load at each bearing position.
Radial vs. Axial Load: The Key Differences
| Feature | Radial load | Axial load |
|---|---|---|
| Direction | Perpendicular to the shaft axis | Parallel to the shaft axis |
| Common symbol | Fr | Fa |
| Typical sources | Belt pull, gear forces, or weight on a horizontal shaft | Impeller thrust, helical-gear thrust, or weight on a vertical shaft |
| Simple example | A belt pulling across a pulley shaft | A screw-drive reaction pushing along its shaft |
| Selection question | Which bearing carries the radial reaction, and how large is it? | Which bearing locates the shaft, and must it resist thrust in one or both directions? |
What Is Radial Load?
Radial load is the force component acting at right angles to the shaft axis. A belt pulling on a pulley and the weight of a rotor on a horizontal shaft are familiar sources. Radial load can exist while the shaft is stationary; it is not another name for centrifugal force.
In a rolling bearing, force passes between the rings through the rolling elements and their contact with the raceways. Under radial loading, the rolling elements in the loaded zone carry different forces. Equal loading around the full circumference is not the normal requirement.
For a closer look at motor applications, see our guide to radial load and motor bearing sizing.
What Is Axial Load?
Axial load, or thrust load, acts along the shaft axis. It may push or pull in either direction. Typical sources include a pump impeller, a helical gear, a screw drive, and the weight of a vertical shaft assembly.
Thermal expansion can also create axial force if the shaft’s growth is restrained. A suitable locating and non-locating bearing arrangement allows the required thermal movement instead of forcing both supports to resist it.
Our bearing axial load guide covers axial loading in more detail.
Practical Examples: Identify the Axis First
| Application | Load direction | What to check |
|---|---|---|
| Horizontal pulley shaft | Belt pull is radial when it acts across the shaft | Belt forces, pulley position, and bearing spacing determine support reactions. |
| Vertical shaft assembly | The assembly’s weight acts axially along the shaft | The locating support must carry the applicable weight and process thrust. |
| Helical gearbox | Gear mesh can generate both radial and axial components | Calculate gear-force components and determine thrust direction for each operating condition. |
| Vehicle wheel hub | Vehicle weight produces radial loading; cornering can add axial loading | Assess the complete load case, including moments and load transfer. |
The same gravity force changes classification when the shaft orientation changes. On a horizontal shaft, the weight of a centered rotor acts radially. On a vertical shaft, that weight acts axially. “Vertical” and “axial” are not interchangeable terms.
Radial Bearings vs. Axial Bearings
A radial bearing is designed primarily for loads perpendicular to its axis. A thrust bearing, also called an axial bearing, is designed primarily for loads along its axis. These names describe the main load direction; they do not establish every bearing’s complete load capability.
Standard deep groove ball bearings can accommodate radial and axial loads in both directions. Their allowable axial load depends on the specific design and operating conditions. Conventional thrust ball bearings carry axial load and should not be selected to carry radial load.
Which Bearings Handle Radial and Axial Loads?
Use the following table to narrow the bearing family. Final selection still requires the exact model’s load data, speed limits, internal clearance or preload, lubrication requirements, and mounting details.
| Bearing type | Typical load capability | Important limitation |
|---|---|---|
| Deep groove ball bearing | Radial load plus axial load in either direction | Do not assume one universal allowable axial-to-radial load percentage. Filling-slot designs need particular care. |
| Single-row angular contact ball bearing | Combined radial load and axial load in one direction | Reverse thrust requires a suitable opposed arrangement or another appropriate bearing design. |
| Single-row tapered roller bearing | Combined radial load and axial load in one direction | Opposed arrangements support reverse thrust; setting and induced axial forces must be considered. |
| Cylindrical roller bearing | High radial capability; axial capability varies by flange design | N and NU designs do not locate the shaft axially. NJ and NUP arrangements require model-specific axial-load checks. |
| Conventional thrust ball bearing | Axial load only | Single-direction and double-direction designs differ. Radial support must be provided separately. |
| Spherical roller bearing | Radial and axial loads, with misalignment capability | Check the actual load ratio and operating limits. It is not a universal solution for pure thrust. |
“Combined loading” means radial and axial forces act together. It does not mean that a combined guide roller is required. Guide-rail combined bearings are a specific product family; many conventional bearing arrangements also support combined loads.
Calculation Example: Resolve a Force into Two Components
Assume a 1,000 N force acts at 30° to the shaft axis. This is a teaching example of force resolution, not a measured application or a bearing recommendation. With the angle measured from the axis:
Axial component: Fa = F × cos θ = 1,000 × cos 30° ≈ 866 N
Radial component: Fr = F × sin θ = 1,000 × sin 30° = 500 N
These are components of the applied force. They are not automatically the loads on each bearing. Calculate support reactions from the force location, bearing spacing, moments, and locating arrangement. Two bearings do not necessarily share either component equally.
Load Ratings and Bearing Life: What to Check
Basic dynamic load rating C and basic static load rating C0 are reference ratings for different calculations. They are not general maximum working-load limits. Radial and thrust bearing catalogs may use subscripts to identify the rating direction. An axial rating is not interchangeable with a manufacturer’s allowable axial operating load.
For many radial rolling bearings under combined loading, equivalent dynamic load is calculated using P = XFr + YFa. The applicable equation, factors X and Y, and any threshold conditions come from the specific bearing’s catalog. Do not substitute the vector resultant or assume X = Y = 1.
The basic rating-life framework is covered by ISO 281:2007. Basic rating life corresponds to 90% reliability under its stated assumptions; it is not a guarantee of service life. Wear, corrosion, and electrical erosion are outside that life model’s scope.
For the distinction between ratings and actual loads, see static vs. dynamic load in bearings.
A Practical Bearing Selection Checklist
Before choosing a part number, confirm these five items:
1. Load at each support: calculate radial and axial reactions for normal operation, starting, stopping, and peak events.
2. Thrust direction: identify whether it stays in one direction, reverses, or changes with the operating mode.
3. Locating arrangement: decide which support locates the shaft and where thermal expansion can be accommodated.
4. Operating conditions: check speed, lubrication, temperature, contamination, misalignment, and required stiffness.
5. Model verification: check equivalent dynamic and static loads, life requirements, allowable axial load, and any minimum-load requirement.
To discuss a selection, contact us with the shaft and housing dimensions, bearing spacing, force locations, load directions, speed, and operating conditions. Include a sketch if the force path is unclear.
Frequently Asked Questions
Does an axial load always cause visible axial movement?
No. A properly restrained shaft can carry axial force without noticeable travel. Movement depends on the arrangement’s clearance, stiffness, preload, and support conditions. Do not infer load magnitude from visible movement alone.
Do both bearings carry half the shaft’s axial load?
Not necessarily. In a locating and non-locating arrangement, the locating support generally carries external thrust. In opposed bearing arrangements, load sharing depends on direction, stiffness, clearance or preload, and the bearing geometry.
Is a moment load the same as an axial load?
No. A moment is a turning effect, measured in N·m, while axial force is measured in N. An offset force creates a moment, so its point of application matters when calculating the loads at the supports.
Does a larger load rating guarantee a better bearing choice?
No. A larger rating does not establish compatibility with the load direction, speed, mounting space, or thermal movement. Some bearings also need a minimum load for satisfactory rolling behavior. Check the complete operating case.
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