Figuring out your load capacity is vital when deciding what casters to purchase for your application. In this section we will share how to calculate your load capacity before you purchase.
The first step is to take the total load weight and divide it by the number of casters. Here is an example, for a 4-wheel material-handling cart that must support 3,000 lbs., dividing 3,000 by 4 gives a minimum load capacity of 750 lbs. per caster. Although, it doesn't end there.
Ideally, those 3,000 lbs. would be balanced equally on each caster. However, that can not be expected at all times in a working environment with a cart that is in motion, 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 the weight supported momentarily on only two wheels.
For these reasons, it's important to consider a safety factor when selecting casters that can bear the extra load imposed upon when equipment is unevenly loaded, shifts, or impacts objects. When figuring out the additional safety factor that needs to be added, we recommend adding a 33% addition to the total weight of the load. Continuing with the example above, for a 4-wheel cart that must support 3,000 lbs., the safety factor would be 990 lbs., totaling 3,990 lbs. Dividing this weight by the 4-wheels, gives the caster a rating of 1,000 lbs. per caster, which would be the recommended load capacity.
Once you have a result for load capacity, it's time to choose a caster!
Signs it's time to replace your caster.
Caster wheels can become damaged or worn when exposed to harsh environments including: overloading, changing temperatures, chemicals, uneven flooring, and more. If you've noticed your equipment hasn't been performing like it used to, it may be time to replace your caster. Here are eight common signs that it's time to replace your caster:
Soft rubber wheels are great for delivering a smooth ride but they are more likely to wear out over time, especially if used on rough surfaces. Signs of worn tread are uneven rolling and difficulty controlling when cornering. If your caster has reached this point, it may be time to replace the wheels. Although, if you find you're replacing the wheel too frequently, you may need to consider a different tread material that would better suit the application.
Similar to car tires, the wheels on casters can develop flat spots over time. Polyurethane wheels are more likely to develop flat spots. Some causes include equipment that is heavily loaded and left stationary for long periods of time, or the wheel came in contact with a liquid or chemical that caused internal softening of the wheel's material. A flat spot on a wheel may cause the equipment to be difficult to roll and hard to push once in motion. If this is a reoccurring issue, consider replacing the wheel with a compatible load capacity, or one that will withstand any chemicals or liquids it may come in contact with.
Some wheels are prone to cracking especially used in the wrong circumstances. If left too long outdoors and exposed to the elements, soft rubber wheels can become brittle and crack. If this is something that happens to you, consider switching to a caster that is designed for outdoor use. Overloaded Polyurethane wheels are also subject to cracking. Make sure you purchase a wheel compound that is appropriate for the load and application of the caster.
Chipped Tread or Chunks Missing
Over time, some wheel materials can begin to chip or lose chunks in the surface. This is mainly caused by sudden blows to the wheel. Each time a crack in the pavement or an obstruction on the floor is encountered, damage can be a result. If this is a reoccurring issue, consider using steel wheels instead since steel has more resilience, and will resist chipping.
Debris Accumulated on Tread
If you find yourself in a situation where you are rolling casters across debris covered floors, there are certain wheels that have the ability to reject debris and not collect on the surface of the wheels. If you have a wheel without this ability, debris like metal shavings can accumulate in the tread and eventually destroy the wheel. If you notice a heavy buildup in the tread, it may be time to replace the wheel. When replacing, consider purchasing a polyurethane material that will keep the debris from collecting.
Noisy when Rolling
Depending on the floor surface, some casters may be noisy from the start. Although, if you find that your caster once rolled quiet and has become loud, it may be time to replace it.
Many caster wheels are formed by lamination, including polyurethane wheels. The tread is attached to the substrate through an adhesive process. Occasionally, the tread can become separated from the wheel or hub and cause delamination. There are various causes for delamination including, exposure to liquids or chemicals, overheating the wheel, or improper application. If there is delamination occurring on your caster, it is time to replace the wheel.
When you hear the sounds of metal-on-metal occur with your caster, it can be a sign that your bearings need to be lubricated. If you find that lubricating the bearings no longer silences the squeaking, it may be time to replace the bearings entirely.
How to measure your casters.
Measuring the Top Plate of the Caster.
The top plate is the flat surface at the top of the caster assembly that fastens it to the desired object. To get the size, measure its overall length and width. There are various sizes available so make sure you measure correctly. When purchasing a new caster, make sure you measure the area you will be fastening the caster to. If you are replacing a caster, measure the existing caster's top plate to ensure the same size.
Measure the Bolt Hole Spacing.
To get this spacing, measure the distance between bolt holes, starting from the center of each holes. In most cases, you can't change the bolt hole spacing of the object or the caster itself. That is why it is important to measure before you purchase.
Measure the Wheel Size of the Caster.
This step involves two measurements: the width and the diameter.
In order to get the width, hold the wheel upright and measure one side of the wheel to the other, including the top plate.
To get the diameter, lay the caster flat on its side and measure the wheel from one side to the other, without the metal attachments.
Measuring the wheel size is crucial and often overlooked. Using the wrong wheel size will create problems that could have been avoided including difficulty rolling or constantly moving.
Measure the Swivel Radius of the Caster.
In order to get the swivel radius, lay the caster down flat on its side and measure from the middle of the top plate (the kingpin) to the outside edge of the wheel.
This is an important measurement if you are using the casters to carry heavy loads. When using the right swivel radius, this improves ergonomics and safety by reducing the required force to move and turn your equipment.
Measure the Overall Height of the Caster.
You can determine a caster's overall height by measuring the distance between the top plate and the bottom of the wheel.
This is a very important measurement if you have limited storage or if you are replacing a caster in a set.
Need a Little Extra Help?
You have measured the following: top plate, bolt hole spacing, wheel size, swivel radius, and overall height. Now what? This will guarantee that your caster will serve you and your company well. If you need some help measuring your caster, give us a call and our caster expert will be able to help (509) 535-1776.