There’s something special about Shiro Nakajima’s work, and it’s painted all over the elegant lines of this custom KTM 690 Duke. Nakajima-san’s creations show a clear affinity to vintage race bikes but look like they’d be more at home on twisty B-roads. They are brutally mechanical yet graceful; retro and modern at the same time.
Shiro’s signature style is a byproduct of his considerable experience. He trained as an engineer, before rising to prominence as the boss of the legendary Japanese restomod house, Ritmo Sereno. He operates as 46Works now, working on furniture, motorcycles, and cars from his beautiful wooden home at the foot of the Yatsugatake Mountains.
Most of the Shiro’s custom builds are big twins, but he has a soft spot for thumpers. “In the late 1990s, the first motorcycle I acquired was a Yamaha SR400,” he explains. “It was the heyday of race replicas—but here I was, riding around on that SR400, fully banked on the mountain passes.”
“It was popular in Japan at the time for some enthusiasts to race single-cylinder bikes. The majority raced tuned Yamaha SR and SRXes, and the Suzuki Goose also participated in later years. So a big single is not a mere object of nostalgia to me, but a sportbike.”
Thanks to those memories, Shiro’s always had an itch to create his version of a single-cylinder racer. When the time came to bring his dream to life, he settled on a 2017-model KTM 690 Duke as the starting point. With 74 hp and 74 Nm on hand, aggressive geometry, WP Suspension components, and a dry weight of 149 kilos [328 lbs], it’s primed for maximum hooliganism.
“About 15 years ago, I test-rode a KTM Duke for a magazine,” Shiro recalls, “and was very impressed with the LC4 engine, which felt like a tuned single-cylinder racer. When this project began, I tested the 2017 KTM 690 Duke I had purchased in its fully original condition.”
“I rode it on city streets and mountain passes, and I also tested it on the race track at full throttle. I realized that I preferred the more flexible handling created by the rich suspension stroke, so I decided to create a road sport motorcycle without changing the body posture, ride height, or suspension.”
Shiro’s plan involved keeping the 690 Duke’s suspension, swingarm, and Brembo brakes. But it also meant fabricating new bodywork—which, in turn, called for a new subframe.
The Duke’s subframe is a bolt-on affair, so Shiro removed the original and built a new unit to attach to the original mounting points. The new subframe boasts a delightful trellis design, with a curve on the back edge that adds an organic feel to the typically angular Duke. The drilled brackets that support the structure at the front are the sort of quirky details that we’ve come to expect from 46Works.
Held inside the trellised structure is a handmade aluminum box that serves multiple purposes. Shiro repackaged the OEM electronics inside it and made space for the air filter, with a sneaky air duct at the front to channel air in. It follows the curve of the subframe flawlessly, acting as a rear fender, with a tidy indentation underneath it that matches the arc of the rear tire.
All-new handcrafted aluminum bodywork sits up top—every piece flowing seamlessly into the next to create an impossibly clean bone line. The fuel tank is slightly reminiscent of the iconic Benelli Mojave, with the width of its knee indents matched perfectly to the width of the café racer-style tail section.
The headlight nacelle wraps fluidly around the fork tubes, while the custom fender hugs the front wheel. Out back, the tail bump sports a tiny flared bit that houses the bike’s taillight. A generous aftermarket carbon fiber belly pan completes the set.
The new seat stands tall, wrapped in fresh upholstery from Razzle Dazzle. And although the ergonomics appear to be more back-breaking than a stock KTM 690 Duke, Shiro’s gone to great lengths to keep the bike supremely rideable. To that end, he’s fitted the forks with a custom-milled top yoke, designed to accommodate a set of raised Battle Factory clip-ons.
“The stock Duke has the waist-high styling of an off-road bike,” Shiro tells us. “But I designed it to express low, compact sportbike styling—without lowering the suspension and without lowering the riding position.”
“There’s no good reason to lower a bike, other than to improve your footing, in my opinion. The lower you make it, the more boring its handling becomes. Lowering is one of the easiest ways to make a bike look cool, but I’m always thinking about how to make the bike look cool without doing it.”
Other bits and pieces on Shiro’s custom KTM 690 Duke include handmade rear-set foot controls, Kijima turn signals, and a custom titanium exhaust muffler. The OEM speedo is still in play, but it’s been moved lower down, courtesy of the new top yoke. The 17” spoked wheels are from a different KTM and are shod with Pirelli Diablo Supercorsa tires.
The KTM’s single rear-view mirror is another simple detail with a lot of consideration behind it. One of Shiro’s many pet peeves is the way that mirrors can ruin the look of a high-end custom motorcycle. So he’s gotten into the habit of making his own for each build.
His tasteful designs have sparked interest, so he’s partnered with the Japanese mirror manufacturer, Tanax, to put his designs into production.
46Works machines usually wear subdued liveries, but Shiro decided to shake things up this time around. The zest lime green paint is a homage to the green hue that some early Duke models came in and a nod to the bike’s cheeky nature. Executed by Drops Design Works, it’s adorned with slick pin-striping; a detail that’s echoed on the carbon belly pan.
“These days, in Japan today, earthy and vintage colors are in vogue, and are often used on new models released by automobile manufacturers,” Shiro explains. “This is the antithesis of those colors.”
Shiro’s already faced some backlash for this bold choice, but he’s unfazed. And given his prowess as a custom motorcycle builder, why wouldn’t he be?
“Doing something unusual can cause rejection,” he adds, “but it doesn’t bother me and I move on.”
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