Modern skateboarding wheels are available in an array of sizes, shapes, colors, and hardness or softness. Many companies make skateboarding wheels for specific purposes such as street skating, cruising, and tricks or stunts. Yet, all durable skateboarding wheels comprise one principal material.
Modern skateboarding wheels are made of a type of polymer or plastic material called polyurethane. Unlike most materials used in manufacturing, polyurethane isn’t one particular substance with a specific physical or chemical composition. Technically, polyurethane is neither plastic nor rubber.
All manufacturers have their takes on polyurethane; thus your skateboarding wheels could be flawless masterpieces that may last decades or duds. Polyurethane’s versatility is a boon and a bane. This guide reveals everything you must know about polyurethane skateboarding wheels.
So let’s dive into it.
Why Is Polyurethane Used To Make Skateboarding Wheels?
Polyurethane can be as flexible as moldable plastic that melts in hot water. Also, it can be as rigid as rubber. Some varieties are more durable, resilient, and abrasion or tear-resistant than the strongest rubbers.
Unsurprisingly, polyurethane has been the numero uno choice of manufacturers to make skateboarding wheels since the 1970s.
Polyurethane is used to make skateboarding wheels because it’s:
- Resilient against impact
- Resistive against abrasion
- Resistant against tear
- Relatively compressible
- Reliably durable
Furthermore, polyurethane’s versatility empowers manufacturers to attain varying levels of hardness and softness, measured by a durometer. During manufacturing, its flexibility enables companies to tinker with the shapes or forms, colors, and other design elements.
However, the eventual characteristics depend on the composition, manufacturing, and quality of polyurethane.
Flexible polyurethane is used to make cushions and mattresses. It’s also used in insulations, such as those in refrigerators or freezers. The material is also used in a plethora of adhesives, coatings, composite wooden panels, and even automobile parts.
Polyurethane’s resilience against constant abrasion due to frequent use and impact makes it ideal for shoe soles and a variety of sportswear. The polyurethane used to make tires, rollers, and skateboarding wheels is, of course, different from the flexible, slender, and cushiony variants.
If you are interested in learning about how wheel hardness and size affect your riding, check out my complete guide here.
What Is Polyurethane?
Polyurethane is a polymer, a macromolecule formed by multiple binding monomers or molecules. The monomer, which is the starting material, is fused with other molecules through urethane bonds. However, urethane is neither the starting monomer nor the principal component of polyurethane.
Polyurethane is so named because it’s a polymerized substance bound by urethane links. Urethane, a type of carbamate, is an organic material. However, what’s commonly known or referred to as urethane, ethyl carbamate, isn’t used in polyurethane.
Instead, a group of carbamates or more are used to form the bonds among the monomers in polyurethane. The term ‘urethane’ implies the polymerization process using carbamates and not the starting or the finished material.
Polyurethane is a unique case in the world of polymers. Most other polymers have a particular starting monomer.
The best example is the most common type of plastic the world knows of, polyethylene or polythene. Polyethylene has a specific starting monomer, ethylene. Likewise, polystyrene has a particular starting molecule, styrene.
Neither these two nor other common polymers have nomenclature implying the bonding process of the monomers.
Hence, you wouldn’t know the base monomer in the polyurethane polymer used to make a particular variety of skateboarding wheels. You have to rely on the brand or manufacturer. Some companies offer a warranty against all manufacturing defects. These brands are confident of their polyurethane.
What Were Skateboarding Wheels Made of Before Polyurethane?
The oldest mass-manufactured skateboarding wheels were made of steel. The alloy dominated the market for around five decades before clay’s unsuccessful foray in the 1950s. Neither steel nor clay had or has the grip, compressibility, rebound, or cushioning effect of polyurethane.
How Are Skateboarding Wheels Made From Polyurethane?
Skateboarding wheels are made from polyurethane by:
- Heating and mixing monomers with urethane.
- Adding dyes or pigments, optional.
- Pouring the mix into a mold.
- Cooling the molding polyurethane in a pressure-controlled setting.
- Shaping the wheel using a lathe or other machine.
Almost all modern skateboarding wheels are mass-produced using assembly lines. The manufacturing process typically involves heating and mixing liquid polyurethane, then using an aluminum mold to shape the material into a desired form, size, and design.
Some companies add dyes or pigments before molding for color and style. A few companies use the hand-pouring method to mold liquid polyurethane.
The molding is allowed to cool using different cooling methods. Assembly lines regulate both temperature and pressure during the casting process. Hence, the polyurethane is cast flawlessly.
Unregulated or uncontrolled environments may not lead to perfect casting. The eventual wheel cast out of the mold may have air bubbles or pockets. Also, the material may deform if the mold or cast is subjected to undue pressure or temperature fluctuations during hardening.
Finally, the mold is removed, and polyurethane wheels are cut, sliced, and shaped using a lathe to attain the predetermined specifications.
If you want to nerd out with some interesting trivia (including wheel history), check out my list of 25 surprising longboarding facts.
How To Compare Polyurethane Skateboarding Wheels
The most important attributes of polyurethane skateboarding wheels are composition and color. The composition is subject to the materials used, temperature, pressure, and the specifications of the metering machine. The presence or absence of color depends on the optional use of dye or pigment.
All other attributes, such as diameter and hardness or softness, are configurable while ensuring the highest standards for the two quintessential elements. The combined significance of composition, heat, mixing, and natural color cannot be overstated.
The melting point of polyurethane depends on the starting monomer and the characteristics of the resulting polymer. A particular polyurethane variety should be heated beyond its melting point to liquefy sufficiently.
Urethane or ethyl carbamate melts at 120°F (48.89°C). The specific carbamate group used by a manufacturer may not be ethyl carbamate. Nonetheless, the urethane should also be heated beyond its melting point.
Higher heat facilitates a more effective mixing of the monomers fusing through urethane bonds, in this case, to form the required polyurethane. The mixing depends on the metering machine, too.
Thus, manufacturers ensuring only the minimum temperatures required to melt and fuse the monomers and urethane may not produce the most resilient polyurethane skateboarding wheels.
The Metering Machine
A metering machine serves several crucial functions: controlling pressure and temperature, mixing or blending, and dispensing. Additionally, the system may also be responsible for mixing the optional dye or pigment added to the liquid polyurethane.
The specifications of the metering machine determine how well polyurethane is heated and mixed. Hence, the composition of the liquid, including the urethane bonding of the monomers, is decided by the prowess of the machine.
Furthermore, the metering machine influences the mixing of dye or pigment for color and the subsequent dispensing of polyurethane in an appropriate moldable form.
Here’s a YouTube video of a high-pressure metering machine:
Users have little say in the heat and metering machine specifications. At best, consumers can choose brands that have the best manufacturing standards and are known for the quality of their polyurethane skateboarding wheels.
However, what you can decide is the color of your wheels. Urethane is white. Monomers and polymers may have natural colors depending on the material used by a manufacturer. Resins, elastomers, and polymers, in general, can have natural colors.
Natural or organic colors aren’t an issue. Dyes or pigments are a cause for concern. Since urethane is white, the polyurethane skateboarding wheels will have a whitish hue. When manufacturers add dyes or pigments for color, they effectively dilute or replace the polyurethane in the final product.
The dyes or pigments can’t add weight or volume to the predesigned wheels. Thus, the substitution effect is on either the monomers or the urethane bonds. Both are equally undesirable, and you’ll have a poorer quality skateboard wheel.
Replacing or diluting urethane bonds when the polyurethane is in the molten state affects the integrity of the monomers in the polymer. Diluting the polymer itself is self-defeating as the final product will never be as strong as intended.
Leading brands selling colored skateboarding wheels take this into account. Some of them manage to strike a fine balance to ensure expected durability and desirable design. However, some companies may fail to accomplish this.
There’s a reason why so many skateboarding wheels are white. Also, the adverse effects of dyes and pigments in the polyurethane composition, thus quality, are why professionals don’t prefer colored wheels.
If you must choose polyurethane skateboarding wheels sporting an added color, find out if it’s a dye or a pigment. Generally, dyes tend to be thinner or lighter than pigments. The latter tends to cause more changes to the integrity of polyurethane and the eventual quality.
Can You Make Polyurethane Skateboard Wheels at Home?
DIY methods are riddled with challenges. You can buy polyurethane resin and casting molds to make wheels. However, durable skateboarding wheels require industrial-grade polyurethane, not just any resin. Besides, you need a metering machine, heat and pressure regulators, lathe, and other tools.
Challenges of DIY Polyurethane Skateboard Wheels
You need the following to make polyurethane skateboarding wheels at home:
- Polyurethane, or monomers, urethane, and other components.
- Liquid polyurethane mix or a metering machine.
- A ready-made mold or a bespoke model created by a 3D printer.
- A vacuum degasser or a pressurizing system.
- Lathe and post-production tools.
Preparing the Polyurethane Mix
DIY enthusiasts usually mix polyurethane at room temperature. There are two fundamental problems in this approach.
First, most DIY methods involve stirring a polyurethane mix. Stirring isn’t the equivalent of mixing in an industrial metering machine. Urethane bonds must have a uniform and comprehensive presence within the polymer to be the polyurethane needed for skateboard wheels.
Polyurethane isn’t in its rigid form when you use a ready-made mix already in a liquid state. A molten state effectively means the urethane is yet to bond and solidify the liquid monomers into a hardened polymer after casting.
Second, heat is a prerequisite for thorough mixing. Uniformity and consistency are easier to obtain when all components are mixed in an expanding liquid than in its denser form or semisolid paste. The absence of heat inevitably leads to inferior-grade polyurethane, irrespective of the quality of the chosen primary components.
Curing and Shaping Polyurethane Wheels
Polyurethane, including its elastomers and sealants, needs thermal curing. Room-temperature curing is possible, but only when there are catalysts and other agents to facilitate the process.
Thus, you won’t have industrial-grade polyurethane. The variant will be a blend of many materials. You can read more about such a step-polymerization process here.
The essential handheld tools to shape and work on molded wheels may be available. You may or may not have a lathe. The humble tool is pivotal when you work on shaping printed, molded, or cast objects.
In this case, you need to cut, slice, and shape a wheel, which is geometrically a spherical structure. Lathes are quintessential while working on such shapes. While a lathe may be managed, a metering machine or a vacuum degasser is harder to obtain if you don’t have one already.
Molding and Casting Issues
You may allow molten polyurethane, preferably not mixed with any dye or pigment, to cool naturally and be cast onto the mold. Unfortunately, the liquid mixture may have air pockets inside.
The air bubbles or pockets will ruin your DIY project. You need some kind of pressurizing system or a vacuum degasser to extract these air pockets from the polyurethane before it casts and hardens into its solid form.
Molds are another challenge, albeit manageable. You can buy ready-made molds or make a few. 3D printed molds aren’t always flawless. You may have to spend more money on mold prototypes, printing materials, polyurethane mixes, and other resources than what you would spare for a set of wheels at the store.
Risks of DIY Polyurethane Skateboard Wheels
Even if someone manages to overcome all the challenges of making polyurethane skateboarding wheels at home, there are a few risks to contemplate. The specific risks depend on the entire setting, types of equipment, and individual skillset. One risk applies to everyone.
Polyurethane is a versatile polymer. Heating polyurethane exudes fumes. It’s impractical to presume the safety or toxicity of those fumes unless the components in the mix are known. You need a completely controlled setting if you’re heating polyurethane or any such material.
Here’s a hazardous substance fact sheet about urethane published by the New Jersey Department of Health.
Urethane wheels can be hard and struggle with rolling over small debris. If you hate little sidewalk pebbles with a passion, check out my post on why pebbles suck and how to avoid them.
Polyurethane skateboarding wheels aren’t exceptionally expensive, except for a few brands. Choose a suitable diameter and width, durometer, and colored or not to shortlist the best options.
Always choose skateboarding wheels depending on your skills and the purpose. Some options are good for more than one purpose.
For instance, you can use a set of longboard wheels for a standard skateboard, but not a small and hard quartet meant for the latter with the former.
Anyway, thanks for reading, and look out for more content from Board and Wheels.