New Hard Cores

Urethane makers reinvent the wheel.

In skateboarding, as in modern art, everything that is touted as “new” can be traced to something that’s come before. New novels, new paintings, and new tricks are all variations of something that’s already been done. The difference is that the new incarnation is somehow improved, repackaged, or modernized.

This isn’t a bad thing; good ideas can get old, and to survive they need to be reinterpreted to remain fresh. Skateboard products are good examples of things constantly reinterpreted. New lines are rarely really new, but different shapes and graphics attract consumers to them season after season.

Since skateboard wheels adopted urethane in 1972 (Cadillac) and the 608 precision bearing in 1974 (Road Rider II) as standards, many experiments in sizes, shapes, and formulas have led to the white, double-radiused, urethane doughnut that most skaters use today.

In the late 70s, a wheel called the Gyro was made popular because it featured an aluminum hub, around which a double-conical urethane skin was poured. Also known as cores or inserts, these stiff bearing seats have become standard in large gummy wheels, like those found on today’s longboards. Made from materials like plastic or nylon, the original inserts bonded poorly with the surrounding material. With the advent of the modern urethane insert, tight chemical bonds between the two parts are now possible, and a new generation of “dual-durometer,” or urethane-core wheels is being developed.

Proponents of dual-durometer wheels suggest that the tight bearing seat and less-flexible center creates a wheel that accelerates more quickly and better retains its speed. “The main thing is that the wheel just seems to keep on rolling,” says Darkstar Owner Chet Thomas. “You don’t have to push quite as much.”

Thomas founded Darkstar two years ago. Working closely with chemists at Elasco Manufacturing, he’s helped develop the formulas used in the Darkstar line, including the company’s new Dualdurometer series. “The goal was to make a wheel that’s stiff, yet maintains grip and is abrasion-resistant, with increased rollability – which means less drag,” he says, alluding to abstract physical principles that basically translate to a wheel that does what he wants it to – roll really fast.

Darkstar Dualdurometers feature closed, or solid, cores with the softer outer urethane wrapping around the front of the wheel, hiding the core and providing a full printing surface. The hard core is only visible on the back of the wheel, and the Darkstar Dualdurometers offer the performance of a core wheel with full front graphics.

The extreme hardness of the core urethanes require that they be measured on the polymer D scale, which encompasses hardnesses higher than those on the standard A scale. Elasco COO Darryl Readshaw says that while skateboarders are accustomed to the A scale, it is only accurate to about 97. After that, the D scale picks up at about 45, with a gray area in between that is usually marked as 100A. “No one’s bothered to educate the consumer about the difference between the measurements,” he says. The Darkstar Dualdurometers, for instance, feature 70D cores with either a 97A or a slightly harder 54D outer material.

Critics of core wheels contest that the vibration a wheel is subjected to is transmitted straight through the stiff hubs and absorbed by the bearings. But Bryan Hansen of Creative Urethanes OEM suggests that standard bearings are capable of withstanding just about anything a skateboarder can subject them to. “For the type of service a 608 bearing is designed for, it’s still well within the realm of normal service,” he says. “I still maintain that the only thing that’s gonna kill a bearing is dirt.”

Creative has been prototyping versions of dual-durometer wheels since last year. Their latest version features a visible, open core with holes molded through it. Hansen says that the greatest benefit of a core wheel is the weight reduction and more accurate bearing alignment.

Creative’s core wheels are available for OEM in sizes starting at 55mm. Hansen believes that because of the extreme hardness of the core, this type of wheel is best suited for the smoother surfaces of vert ramps or skateparks, but he realizes that street skaters might appreciate the speed a stiff core facilitates: “Even though that stuff is pretty hard, it’s still a polymer – it’ll still stretch 125 percent of its original size and return to normal. They do ride firm, but maybe not as firm as people expect. It’s the same family of stuff that we’re using for mono-urethane wheels; it’s still really lively.”

Unlike many of their predecessors, the modern core wheels are actually pure urethane. The two parts have different properties that control their respective hardnesses, but their common base allows them to form a strong molecular bond in the mold, fusing them into a single unit. “In a lab, the actual urethane will fail before the bond will,” says Hansen.

Previous core-wheel designs that featured nylon or aluminum hubs relied on bonding agents or mechanical interlocks molded into the core surface. Many new dual-durometer wheels still feature these gear-like protrusions in their cores. Livewire released its X Wheel last February with this feature, which tightens the interface in the wheel’s materials. The latest dual-durometer wheel from Livewire, the Centerline, features H-Lock – a single wide groove along the core surface that the outer urethane sits in. While the X Wheel is only available in sizes starting at 56mm, the Centerline design accommodates a 52mm model.

Marty Jiminez and manufacturer Bravo Corporation designed the Livewire cores to be lighter, and injection molding gave them more latitude in appearance and materials than other cast-urethane cores. Their open-face design and cavities eliminate much of the center-wheel mass, and the tough glass-reinforced Estalok material can withstand much more force than standard urethanes. Having tested them himself, Jiminez says that their goal was to design a better-performing wheel. “The main benefit is that they make my board lighter, and they feel solid and fast,” he says.

The recent proliferation of core wheels represents the first visible change in wheel technology in some time. “So many of the things we do can’t be seen,” says Hansen. “Like, I’ve got this new bitchen formula that I’ve been preaching for the last six months. You put it up next to the old formula, and it looks the same. It’s tough to sell stuff like that. This core-wheel technology is something that you don’t even need to be a skateboarder to look at and say, ‘Wow, that’s really cool.'”

World Industries is banking on the visual appeal of the open-core design to attract buyers, and the enhanced performance to keep them. Having designed a custom injection-molded core with devil-head-shaped cavities, World has heavily invested in the tooling necessary to give their Hellholes wheels a cosmetic advantage. World Industries Sales Manager Vince Krause says that although sets of Hellholes cost about six dollars more at retail, the company can justify the higher price because core wheels tend to hold their shape better and last longer than mono-urethanes. “In the past, core wheels started out as a good idea, but they ended up being gimmicky,” he says. “But these days people are putting more emphasis on quality.”

Since releasing the Hellholes line in May, Krause says that they’ve accounted for about four percent of total World wheel sales. If response and demand continues to be good, he says World will expand the line. At present, an A-Team line of closed-core dual-durometer wheels is being planned in sizes 50—56mm. Similar to the Darkstar line, it will lack the mechanical interlock of the larger-sized Hellholes line.

Hansen sees about the same interest in Creative’s core wheel. While it accounts for only about six percent of Creative’s wheel sales, he believes that core/insert/dual-durometer wheels will become a lasting alternati
ve to mono-urethane: “I do think it’s a viable niche. If we can get the pricing in-line through volume, that will help.”

Jiminez believes that the market is ready for core wheels and improvements in other skateboard components: “Thanks to the fact that skateboard shoes have become teched-out, now kids can relate to further advancement in technology with their actual skateboard hardgoods. So I think there’s gonna be some even newer things happening with wheels.”

Core wheels require two stages of manufacturing – casting or injecting the inserts, and casting the riding surface around that. “The way we’re doing it, it’s about like making a wheel twice,” says Hansen of the Creative core wheel. “After you cast the insert, you’ve gotta go back, finish trim, degrease, then place it in a tool and pour again. So it just requires a lot of handwork, which is why at the OEM level, they’re about 25 to 30 percent more than a regular wheel.”

The extra steps required to make core wheels convinced Spitfire to discontinue its original Hard Core line of closed-core Dual-durometer wheels a few years ago. Increased production capabilities at its factory and a renewed interest in core wheels has allowed the company to release its new Power Cored series, which features outer urethanes as soft as 92A. The smaller Power Cored insert facilitates a stable bearing seat, while the wheel has the feel of a mono-urethane. Mounted, the wheel’s core is invisible.

The future of core wheels may belong to open-faced designs, primarily because they’re lighter and because urethane is an expensive material, and open-faced cores use less of it. Long-term, if core-wheel sales continue to increase, even the costly tooling of injection-molded cores can be offset, bringing the retail price for core wheels much closer to mono-urethanes. But like most new products, Hansen says that the market will first have to accept core wheels as a viable category, and not just a passing fancy. “A lot of this stuff is real subjective,” he says. “We just put it out there, take skater feedback, and apply what we know technically and try and improve it. You can test until you’re blue in the face, but ultimately someone’s gotta skate it and like it. That’s the proof in the pudding.”

– Miki Vuckovich