When choosing caster wheels for transportation and material handling applications, wheel hardness is a crucial property you need to consider. Wheel hardness determines ideal surfaces and caster wheel longevity. To help you out with your decision, the team at Caster Central put together this wheel durometer guide. 

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What Is a Durometer?

Industrial equipment manufacturers need a standardized way to measure and report the hardness of the various materials they work with. A durometer is a special machine that measures material hardness — i.e., a material’s resistance to mechanical deformation. 

Durometers utilize a needle and precise spring to apply pressure to the material’s surface. The machine then assigns a hardness rating depending on how difficult it is for the needle to penetrate the surface. 

Durometer Readings

Durometer readings typically report a number on a scale between 0 and 100. Unlike other material measurements, such as tensile strength, durometer measurements don’t have units. The number is relative to the hardness of other materials. For instance, polyurethane tubing with an 80A measurement is harder than polyurethane with a 70A measurement. 

Manufacturing companies today use three main hardness scales for different categories of plastics and resins:

• Shore 00: The Shore 00 scale is reserved for the softest rubbers and gels. 
• Shore A: The Shore A scale is for semi-hard plastics and rubbers. 
• Shore D.: The Shore D scale is for the hardest plastics and rubbers

Harder materials, such as metals, typically use either the Rockwell or Brinell hardness scale. 

The structure of these scales means that the same numbers can represent different hardnesses, depending on the scale. For example, typical pencil eraser rubber is about an 80 on the 00 scale, while a construction site hardhat would mostly likely have a D80 hardness rating. 

As such, you need to be extra attentive to the hardness scale the manufacturers use when buying materials. You don’t want to buy a material if you misunderstand the hardness measurement it has. 

Why Do Durometer Measurements Matter?

Below are just some of the reasons you should pay attention to the hardness of wheels. 

Rollability

The hardness of the material determines whether the wheel can give a smooth ride. Harder materials tend to roll better on harder surfaces because they deform less, and there are fewer points of contact between the wheel and the ground. Mismatches between the hardness of the wheel and the hardness of the surface can negatively affect rolling performance. 

Durability

Wheel hardness can also affect durability. Despite what you may think, harder wheels are not always the most durable. Durability can be impacted by the surface you regularly roll on. For example, extremely hard wheels against an extremely hard floor might not last as long as a wheel that is softer because the extreme rigidity might cause the larger wheel to crack instead of properly absorbing force. 

Rolling Speed

All other things being equal, smaller and harder wheels roll faster than larger and softer wheels. Hard wheels minimize the point of impact between the floor and the wheel, allowing it to spin faster. Soft wheels deform when they hit the ground, so they create a larger flat surface at the point of contact. This increases friction and makes the wheel turn slower. 

Common Material Durometer Measurements

Wheel hardness is a crucial feature of caster wheel design. Below is a wheel durometer guide featuring some of the most common caster wheel materials and their respective durabilities. 

Rubber

Hardness: 70 – 75 shore A

Rubber is a common material that has several variations and modifications to make it flexible. Rubber wheels are durable, resistant to most chemicals, and also resistant to electricity and heat. Rubber caster wheels hare durable, but hard and rough surfaces, like concrete, can damage them. 

Polyolefin

Hardness: 65 – 75 shore D

Polyolefin is a type of durable polymer that features incredible hardness and chemical resistance. Polyolefin is non-marking, so it is suitable for many types of floor materials. The smooth material also means polyolefin wheels make relatively little noise when rolling over the floor. However, polyolefin can pick up debris from the flooring. 

Polyurethane

Hardness: 90 – 95 shore A

Polyurethane is a classic material for caster wheels, thanks to its balancing durability and softness. Polyurethane wheels roll excellently, can handle high load capacities, and work well on a wide range of surfaces. Polyurethane also won’t leave any markings and won’t pick up debris from the flooring. However, polyurethane is highly susceptible to water damage, making it unsuitable for many outdoor applications. 

Phenolic

Hardness: 90 – 95 shore D

Phenolic caster wheels are extremely hard and are commonly used for heavy-duty applications. Phenolic wheels are also relatively expensive, given their durability and robustness. They are resistant to heat and are a good option for rigid casters that don’t need to swivel. 

Nylon

Hardness: 80 – 85 shore D

Nylon is another hard synthetic polymer that features a very high hardness rating. Nylon is resistant to heat and also relatively cheap to make. Nylon is also practically waterproof, making it suitable for outdoor applications. The main downside is that nylon can leave marks on the floor, and it creates more noise than other materials. 

Metal

Hardness: 145 Brinell

Metal is another common material for caster wheels and provides an incredibly hard solution. Metal has a very high load capacity and shock-loading rating, making them useful for heavy-duty applications. However, metal wheels are so hard they can become brittle. Metals can also be susceptible to corrosion and rust. 

The Best Home and Business Caster Solutions

Hardness affects caster rollability, so it’s crucial you use this wheel durometer guide to find the right caster wheels for the job. Caster Central has over 150 years of experience providing industry-leading caster solutions around the world. Our precision engineering puts our caster products in a different league than competitors, and you can always count on us for the best solution for your needs. 

Send us a message online or reach out to us today at (800) 445-4082!