Each container caster is rated for a specific load – that’s the maximum weight it can carry on its own, regardless of whether it has one wheel or two.
We often get questions about this because some of our part numbers look similar but differ in wheel configuration. For reference, all our container casters fall under the AC49000A- series. Out of the 13 models (-2PA through -13PA), three have a single wheel, and the rest have two wheels. But again, capacity is per caster, not per wheel.
Why We Recommend a 3:1 Safety Factor
Your container’s total weight and its contents should not exceed three times the rated capacity of a single caster. A caster rated at 5,000 lbs would have a maximum total container weight of 15,000 lbs.
Weight is not always fully distributed. A common way to think about this issue is when you have a wobbly table at a restaurant. Not all contact points always sit perfectly flush with the ground.
With 4 casters, it’s very likely that at some point, one corner will carry more weight than another corner, especially on uneven surfaces or on bumps. The total weight may be within the rating of each respective caster, however, an instantaneous shift in weight could cause one caster to briefly carry more than its share. This is precisely why we recommend the 3:1 ratio as a safety margin.
Why Not a 2:1 Ratio?
Some customers ask why the recommendation isn’t 2:1. The reason is that physics rarely allows load to concentrate evenly across just two casters. It’s much more likely to be spread across three or four, even with uneven conditions. So 3:1 provides a more realistic safety buffer for real-world scenarios.
Common Misconception: More Wheels = More Load?
A common misconception is that more wheels means more capacity, and that’s not the case. The listed rating applies to the entire caster assembly, not to each wheel. A dual-wheel pneumatic caster rated for 10,000 lbs still has a 10,000 lb rating, just like a single-wheel urethane-on-iron caster.
Why the Safety Factor Matters
On a perfectly smooth warehouse floor, you might think you can load right up to the total rating of four casters. But the moment one wheel hits a crack or ramp, the load could shift more of the container’s weight onto one caster. Without a 3:1 margin of safety, that caster could exceed its capacity and lead to equipment damage or a safety hazard.
This recommendation applies across all container caster types, whether it’s urethane-on-iron or air-filled pneumatic wheels. Physics is physics – the same principles apply regardless of wheel material or application.
When to Retire a Caster
There’s no set expiration date for casters. Lifespan depends on a lot of factors, like use, terrain, and load. If you see cracks, bent hardware, worn bearings, or other visible damage, it’s most likely time to get it checked out. Send photos or videos to your account manager or call us at 1-252-447-7155, and our engineering team will review and advise on repair or replacement.
Quick Guidelines for Caster Selection
- Check the capacity per caster, not per wheel.
- Keep container weight ≤ 3x the capacity of one caster.
- Choose wheel material based on your surface (urethane for smooth floors, pneumatic for rougher terrain, Nylon for specific height/capacity needs).
- Lock the rear wheels and allow the front wheels to swivel freely for better maneuverability.
- Inspect regularly and contact us if damage appears.
All in all, stick to the 3:1 safety factor and don’t assume more wheels mean more capacity. Inspect your casters, pay attention to wear, and always reach out if something looks off. These things may be able to take a beating, but like anything, they have their limits.
Contact us today and we'll help you choose the right caster or take a look if something’s not working right.
