Caster Speed Ratings and Duty-Cycle Derating for AGV and Conveyor Duty: What the Evidence Settles

A quoted load rating is only valid at its reference speed and duty

A catalogue load number is a laboratory figure taken at a low reference speed, not a statement about your AGV or conveyor. Most heavy-duty caster load ratings are established at 2-3 mph walking speed 22 , and the ICWM dynamic rating is cited at 3 mph as the industry-standard procurement reference 1 .

European scope points the same way: BS EN 12532 covers industrial wheels and castors for applications up to 1.1 m/s, about 4 km/h 13 . Dynamic capacity is also materially below static capacity, so a headline static number overstates what the caster carries once it rolls.

One source puts dynamic at 60-75% of static 1 ; another describes dynamic as about half of static or lower 10 . The ratio is not fixed, which is why you read the actual dynamic figure rather than derive one.

One published wheel shows how far the two diverge with speed. A 5.91 in polyurethane-tread wheel with an aluminum body and precision ball bearing carries a 2,204.62 lb static rating, but only 1,102.31 lb dynamic at 2.49 mph and 881.85 lb dynamic at 3.73 mph 12 .

Same wheel, same load, different speed basis. Before you compare anything else, ask the supplier for the dynamic rating at your operating speed and the basis on which it was measured 13 .

A rating quoted without a speed basis is not a number you can put against your application.

How much to derate for your actual operating speed

Above the reference speed, the tread generates hysteresis heat and dynamic capacity falls. For standard polyurethane, one source gives roughly 25% dynamic capacity loss per mph above 3 mph: a caster rated 1,000 lb at 3 mph is about 750 lb at 4 mph and about 560 lb at 5 mph 1 .

That same source states the standard rating table does not apply past 5 mph, where high-speed or AGV-grade precision bearings rated at higher reference speeds are specified instead 1 .

A second source frames the same problem for powered towing: a caster rated 1,000 lb at 3 mph is not rated for 1,000 lb at 6 mph, because bearing friction, tread heat buildup and centrifugal forces on the swivel all rise with speed 22 .

Its guidance for powered towing at 5+ mph is to derate by 20-30% or move to a higher-capacity unit 22 . Treat that as one supplier's figure, not a standard-required value.

The two positions differ in form. The per-mph loss is a worked example for standard polyurethane only and is not shown to apply to other tread materials 1 ; the 20-30% band is a single supplier's towing guidance 22 .

Neither is a published derating curve, and no source in this set provides one. What you can do is fix the speed band first.

If your platform runs at 2-4 mph sustained, as AGV/AMR platforms are described 3 , you are at or just above the reference point and the derate is small. If you are towing at 5+ mph, the standard table is stated not to apply and the decision shifts to bearing grade rather than a percentage.

Intermittent or continuous duty: the margin the duty cycle requires

Standard ratings assume a caster that rests between jobs. AGV and AMR platforms are described as running 16-24 hours per day at 2-4 mph sustained 3 , which is outside that assumption.

Continuous duty accumulates bearing heat, tread wear and swivel raceway fatigue, so the same load that lasts in a tool crib does not last on a production line 22 . The sources agree on the direction and disagree on the figure.

One source says continuous duty (24/7 or three-shift) needs 25-50% added to the required rating, or a step up of one stocked size 6 . Another states that ratings assuming intermittent service should be derated 25-33% for 24/7 use 16 .

A third says to specify casters one full size above what the load calculation suggests for 24/7 operations 22 . Those are three different ways of buying the same margin, and none is presented as a standard requirement.

The practical move is to decide which side of the intermittent/continuous line your duty falls on, then ask the supplier what margin their own duty-cycle data supports rather than adopting one of the three figures as settled.

If your duty is genuinely continuous, the margin is not optional in the sense that the base rating was never written for it. But the size of the margin is a supplier conversation, not a table lookup.

Bearing family: what the speed and duty require

The bearing controls how much of the rated capacity you can actually use in motion, and it is described as the lifespan variable rather than the wheel 2 .

A wheel rated 1,200 lb static with a plain bore may carry only 600 lb dynamic at 3 mph, while the same wheel size with sealed precision ball bearings can run the full 1,200 lb dynamic 2 . The families sort by duty.

Plain bore is for light, slow, indoor, intermittent use 2 , 9 . Roller bearing is the industrial workhorse with good dynamic capacity for frequently transported heavier loads 2 , 9 .

Precision ball bearing is required for tow and AGV duty, and the sealed precision version is maintenance-free and washdown-friendly 2 . One supplier reports per-wheel ceilings of up to 1,200 lb plain, up to 3,500 lb roller and up to 2,200 lb precision sealed ball 19 ; treat those as that supplier's figures, not industry limits.

For a continuously moving platform, the bearing question is not only load. A plain bore on a wet floor is stated to seize in months where a sealed precision bearing runs years 2 .

If your application runs a shift or more per day, the bearing family is the first specification to fix, and the load rating follows from it. Ask what bearing family is fitted and what load it is rated to carry at your speed 19 .

No source in this set gives a bearing rated speed or an L10 life method, so bearing life at a given speed and load cannot be calculated from this evidence.

Swivel and raceway precision at speed

At AGV speeds the swivel becomes a precision component, not a bracket. Standard raceways are reported to develop axial play within 6-12 months that causes measurable shimmy at AGV speeds 5 .

Caster flutter is stated to add 10-40 mm of positional noise against docking targets of ±5-20 mm 3 . The specification difference is measurable.

Standard industrial swivel bearings are described at Rockwell 55-58 HRC raceway hardness, ball grade 25-50, initial axial play of 0.005-0.015 in, stamped or formed raceways, and swivel torque varying ±30% 5 .

The AGV precision counterpart is described at 60-62 HRC, ball grade 10-16, axial play of 0.002 in or less, forged or machined raceways, and swivel torque controlled to ±10% 5 . The stated effects are 2-3x longer raceway life, lower stick-slip, no initial shimmy at speed and predictable cornering response 5 .

If your platform docks to a repeatability target, the axial play figure is the one to write into the specification. One source advises specifying initial axial play of 0.002 in or less at purchase, because raceway tolerance drift in service is described as the biggest driver of AGV shimmy and docking-alignment problems 5 .

A standard-raceway quote can look adequate on load and still fail on alignment. Check the raceway type and axial play before you accept it.

Wheel core and tread under sustained speed

Heat is the mechanism that links speed and duty to wheel degradation. Standard urethane develops hysteresis heat at 2-4 mph sustained and loses dimensional stability over a shift 3 .

In high-frequency AGV cycles, plastic wheel cores are stated to expand under heat, which causes the tread to separate from the core and jam the drive train. Metal cores, typically aluminum or cast iron, are described as the reliable option for continuous-duty robotic applications 21 .

This is where a wheel that passes a load check can still be the wrong part. The failure is not overload but heat-driven separation, and it shows up as a drive-train problem rather than a wheel problem.

If your duty is continuous, the core material belongs in the specification alongside the bearing. Polyurethane is described as the material that rates highest across wear resistance, noise, floor protection, shock absorption and rolling resistance for AGV applications 21 .

That is a material-fit statement, not a speed rating, and no source in this set gives a numeric wheel temperature limit or a heat-buildup model at speed. Ask the supplier what core material their wheel uses and whether they have duty-cycle data at your speed.

The sources establish the mechanism but not the threshold.

Confirm the speed band and get the test report

Standards are organised by speed band rather than by a single caster speed rating, so the first check is which band your application falls into. BS EN 12532 covers industrial wheels and castors up to 1.1 m/s, about 4 km/h, with dynamic, fatigue, performance and load capacity testing in scope 13 .

DIN EN 12533 covers heavy-duty wheels and castors for mechanical or power-driven applications at 1.1-4.4 m/s (4-16 km/h), and explicitly excludes drive wheels and pneumatic-tire wheels 27 . A compliance statement is not the same as a test report.

One manufacturer describes a dynamic load test cycling at 5 km/h for more than 100,000 cycles to check axle and bracket fatigue 14 ; that is one manufacturer's described method, not a standard requirement.

• ✓Confirm which speed band your application falls into: up to 1.1 m/s (EN 12532) or 1.1-4.4 m/s (DIN EN 12533)
• ✓Check whether the standard cited excludes your wheel type — DIN EN 12533 excludes drive wheels and pneumatic-tire wheels
• ✓Ask which standard supports the rating, and whether the value is static or dynamic
• ✓Ask at what speed the rating applies, and which wheel and bearing configuration was tested
• ✓Request the actual test report referencing standard clause numbers, not a compliance statement
• ✓Ask whether the complete castor or only the wheel received the rating

When standard casters are the wrong component

Three independent publishers converge on the position that standard industrial casters are not adequate for sustained AGV/AMR duty, with the stated failure modes being swivel axial play and shimmy, rolling-resistance inconsistency. And heat-driven core and tread degradation 3 , 5 , 21 .

Standard industrial casters are described as missing on swivel precision, rolling-resistance consistency and docking-alignment stability, and even premium manual-cart casters are said to typically lack the precision raceway and bearing tolerances AGV platforms require 3 . That convergence is qualitative.

No source quantifies the speed or duty threshold at which a standard caster becomes unacceptable, and none provides a test result comparing standard and AGV-grade casters under the same duty cycle 3 , 5 , 21 . So the decision is not a threshold you can look up; it is a specification stack you either meet or do not.

For AGV or motorized tugger duty, one source's guidance is to specify kingpinless and step up one size, with sealed precision bearings on both wheel and swivel 6 .

The AGV-grade stack is described as precision swivel bearings, forged or machined raceways, high-durometer polyurethane or polyamide treads, sealed IP67 bearings, and dual-wheel load distribution on heavier vehicles 3 . If your application needs sustained speed, continuous duty and docking repeatability, the specification is a specialty one rather than a catalogue selection.

The sources do not provide powered-equipment caster ratings to compare against passive casters, so the move away from standard casters is a specification decision, not a like-for-like swap.

Where the sources disagree on the margin

The sources give different figures for the same continuous-duty decision, so treat the margin as a range to confirm against the supplier's own duty-cycle data rather than a number to adopt.

What the sources do not establish

• No published maximum operating speed rating for a named caster series, with a continuous-versus-intermittent qualifier.
• No complete load-capacity derating curve or table as a function of speed and/or duty cycle.
• No bearing rated speed or L10 life calculation method for any bearing family, so bearing life at a given speed and load cannot be computed from these sources.
• No quantitative duty-cycle definition (percent time in motion, starts/stops per hour) or required rest period.
• No numeric wheel temperature limits or heat-buildup model at speed.
• No trail values or numeric shimmy speed limit for swivel and rig performance.
• No speed, load and duty ratings for powered-equipment casters (drive wheels, motorized casters) to compare against passive casters; DIN EN 12533 explicitly excludes drive wheels from its scope.
• No standard text or certification requirement establishing a mandatory derating or grade for continuous duty; the standards are described only by scope.
• No independent test data comparing standard and AGV-grade casters under the same speed and duty cycle.