Why can’t the load capacity be simply multiplied by four when all four casters are used together?

Time：Apr 30,2026

When selecting casters, many people have a very straightforward assumption: if a single caster can support 100 kilograms, then using four casters together should logically handle 400 kilograms, right? While this calculation seems sound on paper, in real-world applications the total load capacity of a caster system cannot be simply determined by multiplying the single-caster capacity by four. The more common industry practice is to base the overall vehicle load rating on three casters, which is both safer and better aligned with actual operating conditions.

I. Why can’t we simply calculate it as four times?

The reason is that, in actual use, the four casters of the equipment are seldom subjected to uniformly distributed loads. The floor may be uneven, the equipment’s center of gravity may be offset, and there may be inaccuracies in installation. Whether the equipment is stationary or moving, one caster typically bears a greater load, while another may experience a significantly reduced load—or even become nearly suspended—for brief periods. Consequently, the four casters do not share the weight evenly, and the total load capacity cannot be simply assumed to be four times the theoretical value.

II. Uneven load distribution is the most common cause.

The weight of the equipment is not automatically distributed evenly across all casters. For example, if the load is skewed to one side, or if the equipment’s motor, housing, and support structure are concentrated in a particular area, the center of gravity will shift. Once the center of gravity is off-center, the casters closest to the center of gravity will bear a greater portion of the load. In other words, even with four casters installed, it is often only two or three that actually carry the majority of the weight.

III. During dynamic use, stress variations become more pronounced.

Casters do not operate solely in a stationary state; they are frequently subjected to pushing, steering, and traversing thresholds or floor joints. During these operations, the applied loads continuously vary. When equipment starts, brakes, or turns, localized impact forces increase significantly, and the instantaneous load on a particular caster may exceed its static capacity. If casters are still selected based on the “single-caster load × 4” rule, they will easily be kept at or near their overload limit for extended periods, which can compromise their service life and operational safety.

IV. The structure of the casters themselves must also be considered as a whole.

The load-carrying capacity of casters depends not only on the wheel material itself, but also on factors such as bracket thickness, bearing design, mounting method, and turntable strength. Load ratings obtained under laboratory conditions for individual casters do not necessarily reflect the actual performance of an entire caster system in complex operating environments. In particular, for equipment that is frequently moved, subjected to heavy loads, or operated on poor road surfaces, it is essential to provide ample safety margins for the casters.

V. Why is the industry often calculated based on three casters?

This is because calculating based on three casters more accurately accounts for uneven surfaces, eccentric loading, and dynamic impacts. For example, if the total weight of the equipment plus any additional load is 300 kilograms, then with three casters each should be capable of supporting at least 100 kilograms—rather than selecting a model rated for only 75 kilograms per caster when divided equally among four. Choosing casters in this way ensures greater reliability and helps prevent issues such as deformation, jamming, or damage down the line.

VI. What other factors should be considered during selection?

In addition to assessing load capacity, it is essential to consider wheel diameter, material, frequency of use, and floor conditions. For instance, when the floor surface is rough, the wheel diameter and load margin should be appropriately increased; if the equipment needs to be pushed over long distances, rolling resistance must also be taken into account; and if the equipment frequently traverses ramps, thresholds, or encounters impact loads, the safety factor should be raised accordingly. Only by comprehensively evaluating all these factors can the selection of casters be made more reliable.

Summary

When all four casters are used simultaneously, the total load capacity cannot simply be calculated by multiplying the rated load of a single caster by four. The primary reason is that the actual load distribution under operating conditions is often uneven, and the equipment may experience impact and eccentric loading during movement. To ensure safety and durability, caster selection should typically be based on a three-caster load rating, with careful consideration given to the equipment’s weight, center of gravity, floor conditions, and mode of use. Proper selection results in smoother operation and longer caster service life.