RCM-632, Unveiled: Kawasaki Z900RS Restomod

Z900RS built to AC Sanctuary’s tastes…   

In 2017, Kawasaki introduced the Z900RS, a 109-hp naked retro that recalls the storied air-cooled inline-four Zeds of the 1970s.

“You remember the 1970s, when things were simple, like frames that flexed, disc brakes that didn’t work in the wet, suspension that didn’t work in the dry, and tyres that didn’t work in either. Life was so much better then.” –Bennetts

While the Z900RS screams 70s classic on the outside, it’s actually a thoroughly modern machine beneath the retro guise. The running gear comes straight from the regular Z900 and includes a 948cc liquid-cooled 16-valve inline four tuned for better midrange and low end power, 41mm fully adjustable forks, 2x300mm front discs, traction control, ABS, and more.

In comparison to retro offerings from Triumph and BMW, the Z900RS is more performance-oriented — as it should be, given the original Z1 ethos — and the fit and finish is superb.

“A big Zed is as bulletproof as a tank and the attention to detail here borders on the obsessive. The Z900RS is more like a one-off special than a high volume production bike…with an apocalyptic exhaust raw on the throttle and a blood-spitting gurgle on the overrun.” –MCN

The modern master of Zed modification has to be Hiroyuki Nakamura of AC Sanctuary, whose RCM (Radical Custom Manufacture) builds transform aging warhorses into modernized restomods that channel their big-bore analog fury into weapons that can strike fear into modern sports bikes…and look absolutely incredible while doing so.

Nakamura’s restomods seek to address and overcome those well-known 70s shortcomings from as flexy frames, insufficient brakes, and primitive suspension and tire technology. Almost always, AC Sanctuary RCM projects are tailored to a specific client…but what if Nakamura-san built a modern Zed to his own tastes?

That’s the very special Z900RS you see here, unveiled just last week at the Tokyo Motorcycle Show. Says Nakamura-san:

“Since the machine doesn’t have an owner, I guess the concept is: ‘it was built for Nakamura’s hobby’ (lol).”

This is RCM-632, and it’s the second Z900RS to roll out of the Japanese master’s workshop after the RCM-534 build of 2023. Nakamura took inspiration from World Superbike and MotoGP to create a machine boasting the very best in suspension and braking technology from companies around the world.

“As I always say, we focus on items from top racing manufacturers that are popular around the world, rather than aftermarket manufacturer parts that are unique to Japan. We only use top brand manufacturers that combine performance and reliability, including OZ Racing wheels, Öhlins suspension, and Brembo brakes.”

But this Z900RS is much more than an assemblage of bolt-on top-spec parts. Nakamura has been honing his expertise for years, and many of the parts are designed, developed, and manufactured in-house:

“Planning → Measuring → 2D CAD → 3D Modeling → Prototype → Depending on the product, it’s a really long process from test drive to mass production…”

Highlights include the Sculpture swingarm CNC-cut from solid aluminum, the billet rearsets, and the 300mm Nitro Racing titanium silencer.  Nakamura says he chose a shorter exhaust to accentuate the length of the suspension and wheels in relation to the bike’s bodywork.

“This is a sense of balance that is often seen on custom motorcycles in Europe and America, where other parts such as the body are made to look as short as possible from front to back relative to the suspension.”

Even more interesting, you may have noticed the billet subframe that encases the engine. These are part of a Nitro Racing aluminum subframe kit developed in-house.

“The lower side of the engine is equipped with a Nitro Racing aluminum downtube, and a reinforced member for the upper side of the engine can be added there. The subframe kit strengthens the rigidity of the engine hanger at the rear of the cylinder head and connects it to the front engine mount.”

Another unique addition to the build includes the oversized Sunstar front discs developed to attach directly to the hubs of OZ Racing Wheels.

This eliminates the three-piece attachment typically required for mounting discs on aftermarket forged wheels. Nakamura finished out the brakes with the Sholto stainless line system from Italian company Allegri.

The result is one incredible modern Zed built to the tastes and desires of one of the great modern masters of the Japanese superbike. We can’t wait to see what rolls out of the AC Sanctuary workshop next.

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Website: www.ac-sanctuary.co.jp
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