Caster Load Ratings: Reading Static, Dynamic and Shock Capacity, Sizing Per Caster, and Choosing the Wheel Bearing

Why the Headline Number Is Not the Procurement Number

Every caster carries three ratings, and each governs a different failure. Static capacity is the load it holds at rest without permanent deformation.

Dynamic capacity is the load it rolls under repeatedly at a reference speed without premature bearing or tread failure; shock capacity is the momentary peak before the rig or wheel deforms¹⁶. Catalogs normally lead with the static figure.

That is why a caster marketed as 1,000 lb can carry a dynamic rating of only 600–700 lb at the 3 mph reference speed in one supplier's guidance^16,18.

For any application that moves, the dynamic rating is the service-life number and the basis for procurement; static numbers belong to stationary equipment such as machine bases and fixed stands^16,18.

The same split holds at the bearing level: the dynamic rating C covers rolling fatigue, while the static rating C0 covers very slow rotation, oscillation and long static loading^2,15,20.

Ask the supplier for the dynamic rating at your duty-cycle speed, and confirm whether the published figure is per caster or per wheel — no source in this set settles that labeling question.

Converting Total Load into a Required Per-Caster Rating

Start from the total moving load: payload plus the weight of the cart or equipment itself. On uneven or worn industrial floors, frame racking or floor slope routinely lifts one of four casters off the ground, so the three remaining casters carry the full load¹⁸.

That source treats dividing by 3 as the procurement-safe assumption and dividing by 4 as optimistic math that leads to early failure¹⁸. The general shape of the calculation is then total load ÷ number of loaded casters × safety factor, giving the required per-caster rating you compare against the catalog dynamic capacity.

Multiplying by a safety factor is standard bearing-sizing practice, but the sources supply no validated caster safety-factor value, so that multiplier has to come from the manufacturer or a governing standard^2,18.

Check your own floor condition before adopting the divide-by-3 rule — the caster-specific numbers behind it come from a single supplier publisher and lack independent corroboration.

Derating for Speed Before Comparing to Any Catalog Table

Dynamic ratings are quoted at a 3 mph reference speed, and tow speeds break the table¹⁸. Standard polyurethane wheels lose roughly 25% of dynamic capacity per mph above 3 mph¹⁸.

So the 1,000 lb-rated example falls to about 750 lb at 4 mph and about 560 lb at 5 mph per the same supplier source¹⁸. Past 5 mph, that source states the standard rating table no longer applies and you should specify high-speed or AGV-grade precision bearings rated at higher reference speeds¹⁸.

Before you request a quote, fix your real operating speed and ask the supplier to state the dynamic capacity at that speed, not just at 3 mph¹⁸. Published ratings assume laboratory conditions, and the caster-level guidance here de-rates only for speed and floor condition¹⁸.

Temperature is quantified at the bearing level. The size-selection guide divides the required load by an operating-temperature factor fT: 1 at 150 °C, 0.9 at 200 °C, 0.75 at 250 °C, 0.6 at 300 °C and 0.45 at 350 °C².

The margin a room-temperature calculation leaves can therefore shrink by half or more in oven-adjacent duty. The caster-level temperature derate is not in these sources; confirm it with the wheel supplier before you size a hot application.

When the Static Rating Governs Instead: Shock, Dwell and Very Slow Duty

Some duty cycles never reach the dynamic calculation at all. Bearing manufacturers direct you to the basic static load rating C0 when the bearing rotates below 10 rpm, oscillates very slowly, or sits stationary under load for extended periods².

Impact or excessive static load at very low rotation causes permanent deformation of the rolling elements and raceways. And once that deformation passes a limit, smooth rotation is hindered — that is the failure C0 exists to prevent²⁰.

This mirrors the caster-level shock rating, which governs momentary peaks before permanent deformation of the rig or wheel¹⁶. A heavily shock-loaded or indexing application can therefore exceed C0 well before it approaches the dynamic rating, so check the static figure against your peak and dwell loads¹⁰.

The sources provide no numeric shock or impact multiplier for caster duty; ask the manufacturer how their shock rating was tested and what peak load it permits.

Ball or Roller Bearings: How Type Moves the Capacity–Speed Envelope

Inside the same bore and outer diameter, bearing type sets the ceiling on capacity and speed. Roller bearings carry a higher basic dynamic load rating than ball bearings of identical boundary dimensions, because line contact spreads stress over a larger area than point contact.

That extra capacity either extends calculated life at a given load or raises the load a bearing can carry for the same target life¹⁰. Ball bearings are the other side of the trade: they are normally more suitable than roller bearings for high-speed applications²³.

A practical rule of thumb from a bearing supplier: light loads favor ball bearings, heavy loads favor rollers, then narrow by whether the load is radial, axial or combined¹⁰. For your caster spec, that means heavy or shock-prone duty pushes toward roller-element wheels and high-frequency, faster duty pushes toward ball bearings.

But the caster-specific wheel bearing options themselves are absent from the sources, so ask each supplier which bearing type sits behind their rated capacity and at what reference speed. For background on the families, see Ball vs Roller Bearings.

Sealing and Lubrication: What Decides Whether the Rating Survives

Capacity math means little if contamination eats the lubricant. Bearing service life is closely tied to the effectiveness and cleanliness of the lubricant, which makes the seal a key component in the system¹².

The selection logic splits on environment: metal shields suit low-contamination duty with speed and temperature limits set by the cage and grease rather than the shield, while contact seals protect in harsh environments at the cost of speed and temperature limited by the cage, grease and seal lip material¹².

Conditions such as contamination, exterior vibration and poor lubrication push the life-adjustment factor below 1, meaning the laboratory-derived dynamic capacity no longer applies at face value²⁵. Grease life also falls as speed rises toward grease limits, shortening relubrication intervals⁴.

So when you compare caster wheels, ask what seal type the bearing carries and whether the quoted rating assumed clean indoor floors or your actual environment. See Sealed (2RS) vs Open Bearings in Dusty or Wet Environments.

Checking That the Rating Is Auditable Before You Sign

Compliance with a test standard is what separates an auditable rating from a marketing number. ANSI MH28.3, as described by one supplier, establishes calibrated test procedures, pass/fail criteria, labeling requirements and standardized terminology, so "dynamic capacity" means the same thing across compliant manufacturers²⁷.

Related references include ANSI MH31.1 caster dimensional and performance testing, the ICWM dynamic load rating methodology, and ISO 22883 for casters up to 1.1 m/s²⁶.

• ✓Ask which standard backs the rating: ANSI MH31.1, ANSI MH28.3, ICWM methodology or ISO 22883.
• ✓Ask for the dynamic capacity at your actual duty-cycle speed, not only the 3 mph reference.
• ✓Ask whether published capacity is per caster or per wheel, and whether swivel and rigid variants carry the same rating.
• ✓Ask how the shock rating was tested and what momentary peak load it permits.
• ✓Confirm the bearing type and seal arrangement behind the rated capacity, and the duty environment they assume.

What the Sources Leave Unsettled — and What to Verify at the Point of Purchase

Four numbers you need at purchase cannot be settled from the evidence. The supplier sources cite different members of the test-standard family without explaining how they relate^26,27.

The divide-by-3 divisor rests on a single tier-unknown publisher¹⁸. No source delivers a validated caster safety factor; bearing-level guidance such as the Sreq table does not transfer to caster duty².

The commercial side of upsizing is addressed by no source in this set at all: no price delta across capacity classes or bearing options, no availability, no lead time. Treat cost and delivery as open procurement questions to quote, not assumptions carried over from a smaller caster.

Treat all of these as supplier questions, not assumptions.

Before you request a quote

• The evidence leaves this open — put it to the supplier: no source states whether published caster ratings are per caster or per wheel — ask the manufacturer to define the rating basis in writing.
• The evidence leaves this open — put it to the supplier: no source provides a validated caster safety-factor value; even whether 2x is adequate is left unanswered in the evidence.
• The evidence leaves this open — put it to the supplier: no numeric shock or impact multipliers or derate thresholds exist for drops, thresholds, potholes or powered towing — request the shock test basis from the supplier.
• The evidence leaves this open — put it to the supplier: caster-specific wheel bearing options (plain bore, bushing, sealed precision ball) and their capacity, speed or life differences for the same wheel are absent from the sources.
• The evidence leaves this open — put it to the supplier: no caster duty-cycle or distance-life ratings per bearing type, and no caster-level maintenance intervals, appear in the evidence.
• The evidence leaves this open — put it to the supplier: floor-surface, washdown, corrosion and swivel-vs-rigid effects on rated capacity are absent from the sources; temperature de-rating is established only at the bearing level (the fT factor) — no source gives a caster-level temperature derate.
• Request a written quote with price basis, MOQ, tooling, payment terms and production lead time.
• The evidence leaves this open — put it to the supplier: the governing standards (ANSI MH31.1, MH28.3, ICWM methodology, ISO 22883) are cited only by commercial blogs; the standard texts are not in evidence and their relationship is unclear.
• The evidence leaves this open — put it to the supplier: key quantitative claims — dynamic at 60–75% of static, ~25%/mph speed derate, divide-by-3 rule — come from a single tier-unknown publisher and lack independent corroboration.