In daily life and industrial production, casters serve as the "mobile joints" of various equipment and furniture, silently bearing the important roles of supporting weight and assisting movement. The load capacity of casters, as a core indicator of their performance, directly relates to usage safety and equipment lifespan. So, what exactly does the load capacity of casters refer to? What factors influence it? How to choose the right caster based on actual needs? This article will provide a detailed analysis around these key questions.

1. Clarify the Concept: The Core Definition of Caster Load Capacity

The load capacity of a caster, simply put, refers to the maximum weight that the caster can safely and stably bear , also known as the rated load of the caster. This indicator is not arbitrarily set but is a safety threshold determined by manufacturers through professional mechanical testing — within this weight range, the caster can maintain normal rotation performance and structural stability without issues such as wheel body cracking, bracket deformation, or bearing damage; exceeding this weight may not only cause immediate caster damage but also lead to safety accidents like equipment tipping or items falling. Therefore, strict adherence to the caster's load standards is essential during use and selection.

It should be noted that the load capacity usually refers to the "rated load of a single caster," but in actual applications, equipment or furniture often uses multiple casters (e.g., carts typically have 4 casters). In this case, the total load must be evenly distributed across each caster, with a safety margin of 10%-20% reserved (for example, for 4 casters each rated at 100kg, the total recommended load should not exceed 320-360kg) to avoid overloading a single caster due to uneven weight distribution.

2. Breakdown of Key Factors: Core Factors Affecting Caster Load Capacity

The load capacity of casters is not determined by a single parameter but is influenced by multiple factors such as material, size, and structure. Different factors affect load performance through different mechanisms, which can be categorized as follows:

(1) Material: The "Basic Framework" Determining Caster Load Capacity

The material of the caster (including the wheel body and bracket materials) is the primary factor affecting load capacity. The hardness, strength, and toughness of the material directly determine whether the caster can withstand heavy loads without damage:

1. Wheel Body Material Different wheel body materials have significant differences in load limits. Metal wheels (such as cast iron or stainless steel) generally have a rated load exceeding 500kg due to the high hardness and compressive strength of metal, meeting the needs of industrial heavy equipment (like machine tools and storage racks); rubber wheels (such as natural rubber or polyurethane) combine elasticity with certain load capacity, typically rated between 100-300kg, suitable for shock absorption and noise reduction scenarios (like medical carts and office furniture); plastic wheels (such as nylon or PP) are low cost and lightweight but have weaker load capacity, generally rated between 50-150kg, often used for light furniture (like storage cabinets and small carts) or household settings. Additionally, the thickness of the wheel body material also affects load capacity — with the same material, thicker wheel walls provide stronger compression resistance and higher load limits.
2. Bracket Material The bracket, as the "bridge" connecting the wheel body to the equipment, also critically depends on material strength. Industrial-grade caster brackets often use thickened steel plates (3-5mm thick) reinforced by stamping and welding, capable of withstanding large vertical pressure and lateral tension; household light-duty caster brackets are usually thin steel plates (1-2mm thick) or high-strength plastic, sufficient for daily light loads but unable to bear heavy pressure. If the bracket material strength is insufficient, even if the wheel body meets load standards, the bracket may bend or break, causing overall load failure.

(2) Size: The "Physical Dimension" Affecting Load and Stability

The size of the caster (including diameter and wheel width) is positively correlated with load capacity. Reasonable size design can effectively distribute weight and reduce pressure per unit area, thereby improving load performance:

1. Diameter The larger the caster diameter, the stronger the load capacity usually is. On one hand, a larger diameter wheel has a relatively bigger contact area with the ground (especially when rolling), which disperses weight over a larger contact area, reducing local pressure on the wheel and ground and lowering the risk of wheel deformation; on the other hand, a larger diameter wheel rim (the metal or plastic frame of the wheel) is longer, better supporting the internal bearings and fillers, enhancing overall structural stability. For example, a 50mm diameter plastic caster is rated for about 50kg, while a 100mm diameter caster of the same material can have a rated load of 100-120kg; industrial heavy-duty casters can have diameters exceeding 200mm to meet load demands of several tons.
2. Wheel Width Wheel width refers to the width of the wheel's contact area with the ground. The wider the wheel, the stronger the load capacity and stability. A wider wheel further increases the contact area with the ground, reducing pressure per unit area — for example, a caster with a 20mm wide wheel has a contact area of about 10cm², while a 40mm wide wheel's contact area can increase to 20cm². Under the same weight, the pressure per unit area of the latter is only half that of the former, greatly reducing wheel wear and damage probability. Additionally, wider wheels provide better stability on uneven surfaces, reducing caster tilting and jamming, indirectly protecting the load-bearing structure.

(3) Structure: "Design Details" Optimizing Load Performance

Whether the caster's structural design is reasonable directly affects the efficiency of weight distribution and the structure's resistance to deformation. Excellent structural design can further increase load limits under the same material and size conditions:

1. Wheel Body Structure Some casters use a "hollow ribbed" design — the wheel body is not solid inside but reinforced with radial or ring ribs, which reduces weight while enhancing compressive strength; some heavy-duty casters use a "multi-spoke" design, where the rim and hub are connected by multiple metal spokes, forming a stable structure similar to a "wheel," evenly distributing weight across the wheel body and avoiding local stress concentration that could cause cracking. For example, nylon wheels with 3-4 ring ribs have over 30% higher load capacity than same-sized nylon wheels without ribs.
2. Bracket Structure The structural design of the bracket is equally critical. Some caster brackets use a "double bearing" design, with a bearing installed on each side of the wheel body, which reduces friction resistance during wheel rotation and disperses axial pressure, enhancing load-bearing stability; some brackets add a "reinforcement plate" at the connection point with the equipment or use a "rounded transition" design at the bracket corners to avoid stress concentration at sharp angles, reducing the risk of bracket bending or breaking. Additionally, the universal joint structure of swivel casters (casters with universal joints) also affects load-bearing — high-quality universal joints use thickened metal shells and precision ball bearings to withstand greater lateral tension and longitudinal pressure, while inferior universal joints tend to jam or break, causing the caster to malfunction.

(4) Easily Overlooked "Hidden Factors"

Besides the core factors mentioned above, there are two hidden factors that affect the actual load-bearing capacity of casters, which require special attention during selection and use:

1. Installation Method and Supporting Components The load-bearing capacity of casters must be achieved through the combined effect of "wheel body + bracket + mounting screws." If the screws used during installation are undersized (e.g., using M4 screws instead of the required M6), if the screws are not tightened sufficiently, or if the connection surface between the bracket and equipment is uneven, the weight cannot be evenly distributed, causing excessive local stress and reducing overall load capacity. Additionally, some casters require "brake devices," and the material and design of the brake structure also affect load-bearing — high-quality brake devices use metal brake pads and reinforced springs to lock the caster securely under load, while inferior brakes tend to break or fail under load.
2. Usage Environment and Working Conditions The actual load-bearing capacity of casters fluctuates with changes in the usage environment. Uneven floors or sharp debris can cause excessive local stress on the caster, accelerating wheel wear and lowering the load limit; high temperatures (such as in hot workshops) may cause plastic or rubber wheels to soften or deform, significantly reducing load capacity; frequent swiveling, braking, or use on slopes increases additional stress loads, so the actual load capacity should be appropriately reduced (a safety margin of 20%-30% is recommended).

3. Practical Guide: How to Choose Casters with Suitable Load Capacity Based on Needs

After understanding the factors affecting caster load capacity, how to select suitable casters based on actual needs? The key lies in "accurate weight calculation + matching the usage scenario," following these steps:

Step 1: Calculate the "Actual Required Load Capacity"

First, determine the "total weight" of the equipment or furniture (including the weight of the equipment itself and any possible load), then calculate the "required load per caster" based on the number of casters, leaving a 10%-20% safety margin. The formula is as follows:

Required rated load per caster = (Total equipment weight + maximum load weight) ÷ number of casters × (1 + 10%~20%)

For example, a medical cart weighing 200kg in total, planned to be equipped with 4 casters, with a maximum load of 100kg, then the required rated load per caster = (200 + 100) ÷ 4 × 1.2 = 90kg. In this case, casters with a rated load of no less than 90kg should be selected (it is recommended to choose 100kg or above to further enhance safety).

Step 2: Match "Material and Structure" According to the Scenario

• Home / Office Scenarios (such as storage cabinets, office chairs, small carts): total weight usually ranges from 50-200kg. Plastic wheels (nylon, PP) or rubber wheels can be chosen, with diameters of 50-80mm and wheel widths of 20-30mm. Brackets can be thin steel plates or high-strength plastic. There is no need to pursue heavy-duty structures excessively; focus on quietness and shock absorption performance.
• Commercial Scenarios (such as supermarket shopping carts, catering carts, medical carts): total weight 200-500kg, requiring rubber wheels (polyurethane rubber preferred for wear resistance and quietness) or medium-sized metal wheels, diameter 80-120mm, wheel width 30-40mm, brackets made of thickened steel plates (2-3mm thick), with double bearings and reliable brake devices.
• Industrial Scenarios (such as warehouse racks, machine tools, heavy-duty handling equipment): total weight above 500kg, requiring heavy-duty metal wheels (cast iron, stainless steel), diameter 120-200mm, wheel width 40-60mm, brackets made of thickened steel plates (3-5mm thick), with multi-spoke structure, double bearings, and reinforced universal joints to ensure stable operation under heavy loads.

Step 3: Verify Parameters and Test

When purchasing, carefully check the "rated load" parameter in the product manual to ensure it meets the calculated requirements. Also pay attention to details such as material, size, and structure (e.g., whether the wheel body has reinforcing ribs, whether the bracket is made of thickened steel plate). If conditions permit, perform a simple test — place a weight slightly above the rated load (not exceeding 10%) on the caster, leave it static for 1-2 hours, observe whether the wheel body and bracket deform or crack, and check if rotation is smooth to ensure load-bearing performance meets standards.

4. Summary

The load-bearing capacity of casters is a comprehensive indicator influenced by multiple factors, from the basic strength of materials to the physical advantages of size, and the optimization of structural design. Every aspect directly affects the safe load limit. In practical applications, it is necessary not only to accurately calculate the required load based on total weight but also to match appropriate materials and structures according to the usage scenario, while paying attention to hidden factors such as installation methods and usage environment. Only then can casters that are "both safe and durable" be selected. Whether for small furniture at home or heavy equipment in industry, only by valuing the load-bearing capacity of casters can safety and stability during movement and use be ensured, avoiding various problems caused by caster failure.