Fast Answer
Load ratings are typically based on controlled test conditions. Real-world conditions include turning scrub, impacts, debris, slopes, and uneven loading.
If you size only from rated capacity, you often under-spec the caster. That creates downtime, premature wear, and higher push force.
What Load Ratings Represent
- Controlled load applied under defined conditions
- Performance that assumes correct installation and load distribution
- Results that do not include your floor, your duty cycle, or your operators
If compliance and documentation matter for your application, review: Caster Compliance and Liability Risks.
Duty Cycle Variables That Change Capacity
These factors commonly reduce real capacity below the rated number:
- Continuous operation versus intermittent moves
- High-speed travel or frequent starts and stops
- Long-distance pushing that increases heat and wear
- High-turn environments that increase scrub forces
Automation and AGV duty cycles usually require higher safety factors. The tolerance for variability is lower.
Shock Loading and Uneven Load Sharing
Real-world carts and fixtures rarely share load evenly. Floor joints, debris, and deflection create momentary overload conditions.
- Expansion joints create impact spikes
- Debris increases rolling resistance and heat
- Frames flex and shift load across wheels
- Turning increases side loading on swivels
Many failures are not caused by exceeding the average load. They are caused by repeated overload spikes over time.
Floor condition is a major driver of shock loading. Use: Floor Conditions.
Load Rating vs Real-World Selection Factors
| Factor | What it changes | Typical outcome |
|---|---|---|
| Duty cycle | Heat, wear, bearing life | Higher spec required |
| Turning frequency | Scrub forces, swivel stress | Stronger swivel required |
| Floor joints and debris | Impact and rolling resistance | Larger diameter required |
| Uneven load sharing | Peak overload spikes | Safety factor required |
| Maintenance reality | Performance over time | Maintenance-free often wins |
A Simple Sizing Process
- Start with total loaded weight including payload, fixture, and accessories
- Assume uneven load sharing and apply a safety factor
- Choose wheel diameter based on floor joints and debris
- Select a wheel material that matches the floor and duty cycle
- Decide on maintenance-free versus greasable based on reality
If you need continuous operation and reduced maintenance, start here: Maintenance-Free Casters. For greasable options with zerks, start here: Greasable Casters.