Why can motion be more demanding?
When a wheel crosses a floor joint or threshold, vertical and horizontal forces change quickly. The caster fork, swivel bearing, axle, wheel and mounting all respond. Turning also shifts load between casters and introduces side forces that are absent in a simple stationary calculation.
How should ratings be compared?
Ask what the rating represents: test speed, obstacle size, test duration, floor, failure criteria and mounting arrangement. Two equal numbers can represent different tests. Where a relevant application standard applies, use its definitions and verify that the supplier’s declaration uses compatible conditions.
Design implication
Calculate nominal load as a starting point, then evaluate uneven floors, center-of-gravity position, shock, braking and duty cycle. The final equipment requires validation as a system.