Whether you are selecting casters for a new piece of equipment designing, or searching for replacement casters for equipment you already have, the issue of weight limits for caster wheels is important, and should be considered in every phase of your selection process.
One of the first steps to take is to calculate the load each caster must bear. This is a more complicated process than simply dividing the total load by 4, as we’ll discuss below.
Once you have an idea of what load capacity is required, the next step is to pick a caster that can support that load. Here you will have many choices for light or medium loads, and fewer choices for heavy loads. Operating conditions will affect your selection: is floor protection important? How about humidity, sunlight or corrosive chemicals? Conditions such as these limit your caster choices, which will have an effect on how many models from which you can choose.
Caster manufacturers combine many components – wheels, bearings, a housing etc. when creating a caster. They then publish weight limits for that caster. Because it’s not always obvious how they arrived at those weight limits, or the way in which load capacity is dependent upon things like wheel material or bearing style, we’ll look at individual caster components, and describe how each affects the caster’s weight limit.
Calculating Load Capacity
The first step in figuring out how much each caster must support is to divide the total load by the number of casters. For a 4-wheel material-handling cart that must support 1,000 lbs., for example, dividing 1,000 by 4 gives a minimum load capacity of 250 lbs. per caster. But we can’t stop here!
In an ideal world, those 1000 lbs. would be balanced equally on each caster. In the real world, however, with a cart that’s in motion and rocking back and forth, at times the weight might be balanced on three wheels. The situation can be even worse if the moving cart impacts a crack in the floor or a doorway threshold – the cart might tip forward, with all of the weight supported momentarily on only two wheels.
For these reasons, it’s important to use a safety factor, and select casters that can bear the extra load imposed when equipment is unevenly loaded, shifts, or impacts objects. Once you have a result for load capacity, it’s time to choose a caster.
Factors That Affect Caster Wheel Weight Limits
Casters are made from many components, each of which will affect the load capacity. Understanding the effects of size, width, profile and wheel materials will help you navigate through the many caster models from which you may choose.
- Wheel Diameter – In general, caster wheels can support more weight as their diameter becomes larger. Let’s look at Colson’s Moldon Polyurethane wheel on a cast iron core, for example. A 6” diameter wheel has a load capacity of 2,000 lbs. 8” wheels can support 2,500 lbs., 10” wheels can support 2,900 lbs., and 12” wheels can support 3,500 lbs.
While you may be only looking for wheels with load capacities of 75 or 100 lbs. each, the principle remains the same – larger diameter wheels can support heavier loads. (Larger diameters also have the advantage of rolling easier, and are better at handling obstructions like rough pavement or debris.)
- Tread Width – Wheels with wide treads can support more weight than wheels with narrower treads. The Colson examples above are for wheels with 3” tread widths. Decreasing the width to 2.5” also decreases the load capacity for each diameter wheel. With 2.5” tread widths, 6” wheels are rated for 1,600 lbs. rather than 2,000, and 10” wheels are rated for 2,500 lbs. rather than 2,900 lbs.
If you need wheels that must support more weight, but your equipment’s height limits won’t allow you to increase wheel diameter, try increasing tread width.
- Tread Profile – Many caster wheels are available in either a flat profile or rounded profile. Each has its advantages. Rounded treads tend to roll easier and be more maneuverable, while flat treads often last longer and wear better. The tread profile also affects weight limits of the wheel. Wheels with flat treads distribute the weight over a larger surface area, and can support more weight than identical wheels with rounded treads.
Consider Colson’s very popular Performa wheel, which is available with either flat or rounded treads. A 5 Series wheel, 6” in diameter with a rounded tread, is rated for a load capacity of 450 lbs. Switching the same wheel to a flat tread increases the load capacity to 600 lbs.
- Soft Wheels vs. Hard Wheels – We’ve saved one of the biggest considerations for last. Wheels with extremely high load capacities are usually made from very hard materials such as steel, cast iron or phenolic resins. Many of Colson’s metal wheels, for example, are rated for load capacities up to 6,000 lbs.
Softer wheel materials have the advantages of offering quieter operation and floor protection, but are usually not rated for as high a load capacity as harder materials. For example, most of Colson’s rubber tread, Performa and polyurethane tread wheels have load capacities well below 2,000 lbs.
Concerned about Weight Limits? Contact Douglas Equipment for Solutions!
Picking the best caster for your unique application involves balancing many competing requirements. It can be tough to find a caster that has the performance characteristics you want, is suitable for your environmental conditions, fits in the space available on your equipment – and can support the weight of your load. That’s where Douglas Equipment comes in! Our customer service team has tremendous in-depth knowledge of casters, and understand the way that varying each caster component will affect overall load capacity. For quick answers to weight limit questions, please contact our team today at 800-451-0030, or online through our contact form. We look forward to helping!