Trackday Special A Custom Aprilia Rs 660 By 46works

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When Shiro Nakajima isn’t tinkering away in his workshop or storming the B-roads around the foothills of the Yatsugatake Mountains, you’ll find him at the track. He’s a regular face on Japan’s classic racing scene, and is just as happy piloting race bikes as he is building them. Even when he’s working on a classic café racer or restomod for a client, the man behind 46Works can’t help but imbue it with a sense of track-ready performance.
Nakajima-san typically uses older donor bikes for his projects, but he’s not opposed to spinning spanners on newer machines. So when the Japanese leather racing suit manufacturer Kushitani asked him to customize a 2023-model Aprilia RS 660, he jumped right in.

Picking an Aprilia for the project wasn’t random. Kushitani is a sponsor of the Japanese MotoGP racing star Ai Ogura, who competes aboard a Trackhouse Racing Aprilia RS-GP. The idea was for Ogura to ride the bike at a Kushitani-sponsored event at the iconic Motegi circuit.
Aside from that stipulation, Kushitani had no notes for Shiro—leaving him free to do whatever he wanted with the RS 660. “I rarely customize supersport bikes,” he says. “I built a custom bike based on a KTM RC8 before, but that was a completely different approach.”

With 100 hp and 67 Nm from its 659 cc parallel-twin motor, and weighing just 183 kilos [403 pounds] wet, the Aprilia RS 660 is no slouch. It also boasts an aluminum twin-spar frame, alloy wheels, adjustable suspension, Brembo brakes, and a smorgasbord of electronic rider aids.
Shiro typically upgrades the running gear on his builds to eke modern levels of performance from them, but that wasn’t necessary here. Instead, he focused on the Aprilia’s aesthetics, without losing any of the characteristics that make it such a good sportbike.

“The design of a supersport bike suits race tracks and winding roads, but feels a little out of place when riding to a café in the city,” Shiro explains. “It’s like how ski apparel looks great at a ski resort, but feels out of place in the city. The concept was to build a supersport bike that would suit the rider whether they ride on the circuit, on a winding road, or to a café in the city.”
Shiro’s first task was to test the RS 660 extensively on his local twisties. Once he had his head around the bike’s handling and ergonomics, a clear path forward began to form. “The shape of the tank is good for sporty riding, so I decided to use it as is—but the original fairing has a complex shape with sharp edges,” he says.

With everything but the tank stripped off the Aprilia’s frame, Shiro focused on the fairing first. He sourced an aftermarket unit with smoother lines and then proceeded to massage it even further. The RS 660’s broad array of headlights was traded for a single round projector—no easy feat, since the bike’s lighting is managed by its CAN bus system.
One notable change is the absence of the RS 660’s fairing-mounted mirrors. “I don’t like how the mirrors stick out from the fairing like an insect’s antennae,” Shiro quips. “I made mirror mounts to attach to the handlebars, and mounted a pair of Tanax 46Works mirrors on them.”

Moving to the rear end of the bike, Shiro fabricated a new tailpiece out of aluminum, while maintaining the original ergonomics. “The design is my interpretation of a fusion between 1980s sportbikes and modern MotoGP bikes,” he explains. “The finish was left as bare aluminum, giving it a prototype look.”
The seat pan was made out of fiber-reinforced polymer, and the Alcantara upholstery was executed by Razzle Dazzle. The back pad can be removed to reveal a small storage compartment inside the rear hump. Shiro echoed the front end’s design by embedding a round taillight in the back of the tail cowl, and installed tiny LED turn signals at both ends.

Another part worth keeping was the RS 660’s carbon fiber SC-Project muffler, but the OEM mounting position was at odds with the redesign. Shiro repositioned the end can, fabricated a titanium section to connect it to the headers, and made an aluminum hanger to support it.
Drops Design Work handled the livery, which is as simple as it is impactful. The blue sections mimic the color of Ogura’s Aprilia RS-GP, complemented by blue pinstripes on the upper fairing and fuel tank. Subtle 46Works x Kushitani logos, done in silver leaf, add extra panache.

Shiro got the bike buttoned up in time for Kushitani’s event, with Ai Ogura tearing up Motegi with it as planned. Since then, it’s been relegated to display duty at the brand’s various locations across Japan.
With any luck, it’ll return to the track soon.
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