When industrial equipment is fitted with four or even six casters, many people naturally assume that the equipment’s weight will be distributed fairly evenly across each wheel.

However, in practical use, a common phenomenon arises: even when the same equipment, the same batch of casters, and the same duration of service are involved, one or two of them are already noticeably worn, while the others remain in excellent condition.

At this point, in addition to checking whether the equipment is overloaded, there’s another issue that’s all too easy to overlook— Does the equipment frame itself have sufficient rigidity?

It may appear that “all four wheels are on the ground at the same time,” but that doesn’t mean the four casters are always bearing roughly equal loads.

I. Casters bear loads—this is far more than a simple division.

During the equipment design phase, it is common to first estimate the overall machine weight and then select appropriate casters based on the number of wheels required.

This method can serve as a baseline reference, but real-world devices are not perfectly rigid geometric bodies.

The frame consists of profiles, sheet metal, welded assemblies, and various equipment components. As the load varies, the structure may undergo a certain degree of elastic deformation.

If the equipment base frame lacks sufficient rigidity, some casters may bear a greater load, while others experience relatively less stress.

Therefore, “equipping it with four wheels” does not automatically mean that “the four wheels are operating at the same rate.”

II. Why does the vehicle perform normally when empty, but encounter problems after loading?

This is an important clue for assessing the frame’s stiffness.

When the equipment is unloaded, its weight is relatively light, and frame deformation is not noticeable; all four casters appear to make normal contact with the floor.

After loading, the vehicle frame is subjected to greater stresses, and even minor structural differences may be amplified.

After a slight subsidence occurs at a particular corner, the caster at that location may bear a greater load; meanwhile, the other caster may even experience a reduction in its ground contact.

As a result, a very strange phenomenon emerges:

At rest, no abnormalities are apparent; however, once the equipment is loaded and in operation, one particular caster consistently proves more prone to failure.

III. Long frames deserve particular attention for “mid‑section deformation.”

For material carts, tooling carts, and large equipment bases with extended body lengths, the issue does not necessarily occur at all four corners.

If the structure has a large span, the midspan region may experience some deflection under load.

This is also why some large mobile platforms employ six wheels or even more.

However, increasing the number of casters does not automatically resolve the issue.

If the frame structure and wheel‑set arrangement are not properly coordinated, some casters may bear the primary load while others contribute only a limited share.

The more wheels there are, the greater the need to consider the relationship between the equipment’s structure and its support points.

4. Frame distortion can also cause the casters to operate in a “suspended” state.

There is also a situation arising from manufacturing and assembly.

After machining, a large welded frame may develop slight warping if the mounting positions for the casters are not kept in proper alignment.

After being placed on the ground, some casters make full contact, while others do not achieve optimal contact.

When the vehicle is empty, pushing it by hand may not feel very noticeable.

However, as the load increases, the differences in stress distribution among the support points may become even more pronounced.

Therefore, before installing casters on large mobile equipment, it is essential not only to ensure the accuracy of the caster base mounting holes but also to verify the overall alignment and relationship among the mounting surfaces of all the casters.

V. Why is the “two opposite corners” problem always more severe?

If the casters on a piece of equipment consistently exhibit noticeable diagonal misalignment, it is worth checking whether the frame has become twisted.

For example, one set of diagonal casters shows significant wear, while the other set exhibits relatively minor wear, which may indicate that the actual load distribution across the support points is uneven.

Of course, the cause cannot be determined directly based solely on the wear morphology.

The ground, the equipment’s center of gravity, the operating route, and the installation condition all need to be inspected together.

However, the obvious inconsistency among the casters itself is a signal worth further investigation.

6. Increasing the number of casters does not necessarily enhance the effective load capacity.

This is a common pitfall in equipment design.

Four aren’t enough, so we’ll increase it to six; if six still isn’t reassuring, we’ll go up to eight.

However, if the frame itself cannot provide adequate support for these casters, the additional wheels may not distribute the load as intended.

In particular, for fixed multi‑wheel configurations, a holistic assessment should be conducted, taking into account the equipment’s length, the undercarriage’s structural rigidity, and the actual ground conditions.

Otherwise, the theoretically envisioned “multi‑round burden‑sharing” may differ from the actual on‑site conditions.

VII. How to conduct a preliminary on-site investigation?

You can start with a few simple phenomena.

Under no-load and full-load conditions, observe whether there are any noticeable changes in the grounding status of each caster.

Inspect the wheel tread wear of different casters to determine whether there are any abnormal discrepancies.

Inspect the equipment base frame for any obvious deflection or distortion.

If casters at a fixed location fail prematurely, the corresponding frame structure at that location should be further inspected.

When necessary, the equipment’s actual loading condition should also be inspected, rather than merely checking an empty vehicle.

Written at the end

Many malfunctions of casters do not necessarily originate from the casters themselves.

The load capacity of a caster depends not only on the equipment’s weight but also on its center of gravity, the frame’s rigidity, the installation configuration, and the spatial relationship among the support points.

Therefore, when the service life of casters on the same piece of equipment varies markedly, it may be worth shifting your focus slightly upward from the wheels.

Casters serve as the connection points between the equipment and the floor, while the frame determines how the load is transmitted to these connection points.

Choosing the right casters is crucial, and ensuring that each caster operates under optimal conditions is equally important.