Caster Capacity Calculation: A Comprehensive Guide

Introduction: 

Caster capacity is a crucial factor to consider when selecting the right mobility solution for your needs. In many industries, the performance and functionality of a wide range of equipment and machinery often comes down to whether or not the right casters were selected in the design process. Understanding how caster capacity is calculated can be very helpful for manufacturers, engineers, and anyone involved in the design and selection of casters to ensure they provide the safest product to their employees or customers. In this blog post, we'll delve into the intricacies of caster capacity calculation, shedding light on the key factors that contribute to this crucial specification, which will give you a better understanding during your caster shopping experience. 

Definition of Caster Capacity: 

Caster capacity refers to the maximum working load that a single caster can safely carry while maintaining optimal performance. It is a fundamental parameter that guides the selection and use of casters in diverse applications, such as material handling carts, industrial equipment, and furniture. 

Components of Caster Capacity: 

Various factors influence a caster’s published capacity, and it important to note that not all caster manufacturers or distributors of caster products understand this or had a standard that they adhered to set the capacity. That is why all of Caster Specialists casters are tested to ANSI ICWM test standards (detailed more below) to ensure our casters will safely perform at the issued capacity. Key components we will discuss include: 

1. Dynamic Load: Dynamic load refers to the weight supported by a caster while in motion. It considers factors such as acceleration, deceleration, and abrupt changes in direction.
2. Impact: When carts or equipment are loaded with the goods or materials they were designed to move, the casters must be able to handle the additional shock and impact realized in that process. Impact stresses different parts of the casters than just rolling and why it is important to consider this. 
3. Static Load: Static load is the weight a caster supports when stationary. This is important in scenarios where equipment remains stationary for extended periods. The static load rating ensures that the caster can withstand the load without deformation or failure. 

Caster Capacity Calculation: 

To properly set the caster capacity calculation of a specific caster, a target load rating is designated based on the materials and caster design, and then it tested to ensure it can achieve or exceed the testing requirements. The test requirements, outlined in ANSI ICWM standards, involve controlled and repeatable tests to all of the previously mentioned key components: dynamic load, impact, and static load. The tests are detailed in the next section. 

ANSI ICWM Testing: Ensuring Reliable Capacity Ratings 

All casters sold on Caster Specialists have been tested and capacity rated according to the ANSI ICWM standards by experienced and trained engineering and test lab professionals. These tests, which not only confirm capacity, but reinforce reliability and safety, set our casters apart from those who don’t utilize ANSI standards, create their own testing standards, or just set their load ratings to be competitive in the marketplace. We do this to ensure that what we tell you about our casters is true, not just an assumption or target based on what our competitors list their products for. We take safety seriously, and we encourage our customers to as well. The main tests involved in setting a load capacity are listed below (other tests, such as brake fatigue testing, are also set in ANSI ICWM standards to ensure quality, reliability, and safety are maintained):  

Dynamic Test 6.8: 

This test involves an expected lifetime evaluation of the caster at the target capacity. Conducted with tens of thousands of rolling cycles over smooth flooring, metal barriers, and intermittent rests, it replicates real-life conditions that any caster could face, allowing materials to heat up and cool just like they would in real application. This dynamic test ensures the caster's resilience in diverse operational scenarios. 

Impact Test 6.10 (for casters) and 6.11 (for wheels only): 

This test involves subjecting the caster to 2 times the target capacity, dropping the weight vertically onto the caster as you would find it mounted to equipment or a cart. It aims to identify any failure points that may occur when loading your equipment or cart, ensuring the caster's reliability and stability. The higher weight is used to simulate lifetime application, the caster is not itself rated for continuous shock or load impacting at this weight. The test assesses the caster's and wheel's ability to withstand repeated impacts at the designated capacity, ensuring durability and safety.  

Static Test 6.7: 

This test involves placing a static weight of 4 times the target capacity on top of the caster in a static (non-moving) position as you would find it mounted to equipment or a cart. It aims to identify any failure points that may occur when the equipment or cart is stationary for periods of time and ensures a safety factor exists when not in motion. 

Applying Caster Capacity to Carts & Equipment in 5 Steps 

Step 1: Do a Total Weight Assessment 

Gain a comprehensive understanding of the total weight the equipment must support. This includes both the equipment's weight and the load it will carry. Total weight serves as the foundation for weight capacity calculations. 

Step 2: Consider Various Load Distribution Strategies 

Recognize that loads may not be evenly distributed across caster-equipped carts. Consider how weight is distributed among casters to prevent uneven loading, fostering stability and prolonging caster life. Optimal weight distribution ensures that each caster bears its share of the load. This might mean that the placement or number of casters used may be unconventional or unique to the cart or equipment being designed. It could also require you to select a higher rated caster to ensure that the area bearing the most weight is properly supported. 

Step 3: Caster Quantity and Type 

The number of casters and the type (rig and wheel selection of the caster) significantly impacts weight capacity. Typically, the wheel type of the caster will dictate how much capacity you will get out of a single caster. Softer wheels typically have less load capacity than harder wheels, and the larger caster, the more weight it typically will handle. These are general guidelines, and the individual needs of the application and floor need to be assessed to ensure proper specification. Increasing the number of casters can enhance load distribution and allow you to use softer wheels (if desired), but the arrangement is equally crucial. Understanding the optimal caster configuration for a specific application maximizes weight capacity. The number calculated from your Total Weight Assessment and the desired type of caster and wheel will be the driving factor behind how many casters are needed. 

Step 4: Caster Spacing and Alignment 

The spacing and alignment of casters play a pivotal role in weight distribution and stability. Ensure proper caster spacing evenly supports the load and minimize the risk of overloading specific casters. Consider both longitudinal and lateral spacing. 

Step 5:  Application Influences & Safety Calculation 

Various factors should also be considered to ensure the proper caster is selected for safe operation and long caster life.  Please consider and take into account the following scenarios and contact us for professional support regarding these applications: 

Floor Surface Conditions 

The condition of your flooring may require you to build in additional safety factor into your caster selection. If you will be regularly hitting larger barriers, gouges in your floor, or traveling over uneven surfaces, it would also be recommended to consider increasing the safety factor in your selection. Below you will see a common calculation that builds in a standard safety factor, but if you are getting into higher capacities and rougher flooring applications, additional safety factor may be required. If you are dealing with heavy loads, we are here to help figure this out. We take safety very seriously and have experienced professionals ready to assist. 

Unusual Conditions  

Extreme humidity, heat, and the presence of acids, chemicals, oils, and other unusual conditions can cause degradation and earlier than expected failure in certain wheel types. Even though the appropriate capacity caster may have been selected, these conditions will prevent you from taking advantage of lasting and safe mobility when failure occurs. Don’t worry though, we have wheel solutions for just about every application. It is all about making sure the right one was specified for your specific application. 

Weight Capacity Calculation for Carts and Equipment 

Determine the necessary capacity rating of your casters by determining the total working (moving) load of the cart of equipment, and then divide that by (the total of casters being used minus 1). The basic formula is: 

Caster Capacity Rating (per caster) = Total Working Load / ( Number of Casters -1) 

We subtract one from our number of casters because we want to account for times when the ground may not be level. In the event you are rolling on uneven ground, we want to consider that one of your casters may not be touching the ground, and if it’s not touching the ground, it's not supporting any weight. This is also referred to as building in the “Safety Factor” into your calculations. 

Consideration of Environmental Factors: 

In addition to load-related factors, environmental conditions play a crucial role in caster capacity. Factors such as temperature, humidity, and exposure to corrosive substances can impact the performance and longevity of casters. Manufacturers often provide guidelines on environmental considerations to ensure optimal caster performance. Please contact Caster Specialists for information regarding this, we are happy to help and ensure you have the correct wheel selected. 

Conclusion: 

Understanding how caster capacity is calculated is essential for making informed decisions in the selection and application of casters. Manufacturers and engineers must carefully consider load ratings, dynamic and static loads, and environmental factors to ensure that their casters operate effectively and safely in diverse settings. Effectively optimizing weight capacity for caster-equipped equipment is essential for safety and longevity. By understanding total weight, strategically distributing loads, configuring casters optimally, and considering influencing factors, users can confidently assess weight capacity. This step-by-step guide empowers individuals to make informed decisions, contributing to the optimal performance of caster-equipped equipment across diverse applications. By better understanding the caster capacity calculation, we empower individuals and businesses to make informed choices in optimizing the performance of their equipment and machinery.