What is the relationship between a cart's load-bearing capacity and its wheel material?

The Core Relationship Between a Trolley's Load-Bearing Capacity and Wheel Material

 

A cart's load-bearing capacity isn't solely determined by the frame. The wheel material's physical properties (compression resistance, deformation resistance, and fatigue resistance) directly constrain the wheel's load-bearing capacity, which in turn affects the vehicle's overall load-bearing capacity.

 

This relationship can be explored from three perspectives: "Material performance determines the load-bearing foundation," "Application scenario adaptation influences actual load-bearing capacity," and "Structural coordination amplifies load-bearing effects." The core differences still lie in the two mainstream materials, nylon and polyurethane:

 

1. Core Logic: The "Three Load-Bearing Elements" of a Material Determine the Wheel's Load-Bearing Limit
The wheel is the "ultimate load-bearing end" of the cart's load, simultaneously bearing vertical pressure (the weight of the cargo) and horizontal friction (ground resistance during pushing). The material's compressive strength, creep resistance, and impact resistance are key factors in determining the wheel's maximum load-bearing capacity:
Compressive strength refers to the material's ability to resist crushing and directly determines the maximum vertical pressure a wheel can withstand.

 

Nylon has a higher compressive strength (typically 60-80 MPa), allowing a single wheel to typically bear a load of 150-200 kg (such as the wheels of supermarket delivery trolleys). Polyurethane has a slightly weaker compressive strength (typically 40-60 MPa), allowing a single wheel to typically bear a load of 100-150 kg (such as the wheels of supermarket shopping trolleys). If the compressive strength limit of the material is exceeded, nylon wheels may crack, while polyurethane wheels will simply collapse and deform.

 

Creep resistance refers to a material's ability to resist gradual deformation under long-term, sustained loads, affecting its load-bearing stability.

Nylon's creep resistance is far superior to polyurethane: under long-term loads (such as a fully loaded trolley left stationary for several hours), nylon wheels deform only 1/3-1/2 of that of polyurethane wheels, preventing wheel eccentricity or wheel jamming due to deformation. However, polyurethane wheels, under prolonged heavy loads, are prone to flattening due to creep, which not only reduces load-bearing capacity but also increases pushing resistance. Impact resistance refers to a material's ability to withstand sudden impacts (such as when a fully loaded cart is suddenly pushed, braked, or passes over a raised surface).

 

Nylon is rigid but generally tough. If a sudden impact exceeds a threshold (such as a fully loaded 200kg cart suddenly hitting a step), the wheel rim can easily crack. Polyurethane, with its excellent elasticity (elongation at break can reach 400%-600%), can cushion sudden impacts and is less susceptible to direct damage even when overloaded by 10%-15%. However, frequent and prolonged impacts can accelerate wheel aging.

 

2. Scenario Adaptation: Material Properties Determine the Difference Between "Actual Load Capacity" and "Theoretical Load Capacity"
The environmental adaptability of the wheel material can reduce the theoretical load capacity in actual use, thereby affecting the effective load capacity of the cart:
Temperature Impact:

 

Nylon becomes brittle below 0°C, with compressive strength decreasing by 30%-40% (e.g., in outdoor supermarket use in winter). A wheel rated for 200kg would need to be reduced to 120-140kg, otherwise it would crack.

 

Polyurethane softens above 50°C, with compressive strength decreasing by 20%-30% (e.g., near supermarket ovens or heaters). A wheel rated for 150kg would need to be reduced to 105-120kg to prevent collapse. Impact of the floor environment:

 

Rough surfaces (such as emery floors and non-slip tiles in fresh produce areas) can increase localized stress on the wheels. Nylon wheels, due to their high hardness, are less likely to deform under localized pressure, allowing actual load-bearing capacity to approach the theoretical value.

 

Polyurethane wheels, however, are more elastic and tend to dig into floor texture, leading to localized pressure concentrations. Therefore, actual load-bearing capacity should be reduced by 10%-15% compared to the theoretical value. Otherwise, the wheel surface can easily wear out and crack.

 

3. Structural Coordination: Material and Wheel Design Together Determine Overall Vehicle Load Capacity
A cart's overall load capacity isn't simply a sum of "single-wheel load capacity x number of wheels." The wheel structure must be designed based on the material's characteristics to maximize load capacity:

 

Nylon wheels: Due to their high rigidity and minimal deformation, they are often paired with a "thick hub + narrow tread" structure (e.g., a hub thickness of 8-10mm). This reduces material usage and distributes pressure through the rigid structure. Overall vehicle load capacity (4 wheels) can reach 500-800kg (e.g., heavy-duty supermarket delivery trucks).

 

Polyurethane wheels: Due to their high elasticity and ease of deformation, they require a "thin hub + wide tread" structure (tread width of 50-60mm). This widens the contact area to reduce pressure per unit area and prevent wheel deformation. Overall vehicle load capacity (4 wheels) is typically 300-500kg (e.g., lightweight supermarket shopping carts). In summary: Material selection must match "load requirements + usage scenarios."

 

If the cart is used for heavy loads (such as transporting goods or stacking) and is on a hard surface at room temperature, nylon wheels are preferred. Their high compressive and creep resistance ensures long-term stable load-bearing.

 

If the cart is used for light loads (such as shopping) and requires both comfortable handling (vibration cushioning), polyurethane wheels are preferred. Their elasticity improves the user experience, but the load-bearing capacity should be limited to no more than 80% of the theoretical value to avoid accelerated aging.

 

In short, the wheel material sets the "basic threshold" for the cart's load-bearing capacity. Discussing load-bearing capacity without considering the material's properties can easily lead to premature wheel damage or safety hazards.