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Class Act: A millimeter-perfect BMW airhead from Sinroja

Pure class: A BMW R100RS airhead custom from Sinroja
In just four years, Sinroja has become one of the most talked-about custom shops in England. As immaculately finished bikes set sail from the workshop run by brothers Rahul and Birju Sinroja, word on the street builds.

Life in the Midlands city of Leicester is a far cry from the small town in India where Rahul and Birju grew up. But that’s where the brothers learned their skills, playing with lathes in their father’s factory, before they moved to the UK.

Pure class: A BMW R100RS airhead custom from Sinroja
Like all good custom shops, Sinroja relies on word-of-mouth—and not just publicity on sites like EXIF. The commission for this exquisite BMW R100 RS airhead came from a client called David, a friend of the Dubai-based chap who bought Sinroja’s very first custom bike.

“David was impressed by our work, and when it came to having a dream bike built for himself, he came to us,” says Rahul.

Pure class: A BMW R100RS airhead custom from Sinroja
“He had a lovely vision of an old school BMW, but wanted someone to ‘see it through’—and so we did.”

David already had the donor bike, an R100RS imported from USA. “The condition was rather questionable and clearly it hadn’t been run in a decade,” says Rahul. “David had a mechanic working on the bike, but realized that it needed a complete strip down and redesign.”

Pure class: A BMW R100RS airhead custom from Sinroja
Sinroja aren’t fazed by heavy mechanical work: on all their ‘classic’ bike builds, they dismantle the entire drivetrain down to the bare cases. Then everything gets vapor blasted, to check out the damage down by time and weather.

After seeing everything in bare metal, they cleaned up the mess and rebuilt everything with brand new or better-than-original parts.

Pure class: A BMW R100RS airhead custom from Sinroja
The airhead engine will now run for another decade or longer, without much problem. (“We don’t compromise on the quality of the build, no matter what,” says Rahul. )

Once the mechanicals were back together, Sinroja decided to leave them all in bare meal—to add to that old school feel, and let the BMW age naturally.

Pure class: A BMW R100RS airhead custom from Sinroja
The engine has been treated to new stainless headers though, and classic megaphones tucked up tightly near the frame.

To get an equally old school bobber look, Sinroja have lowered the front end around 75 mm (just under three inches), and commissioned a pair of classic-style custom shocks from Hagon to work with the new weight and stance of the bike.

Pure class: A BMW R100RS airhead custom from Sinroja
With the rolling chassis hanging together nicely, they started on the frame. “We wanted it to flow nicely with the curvature of the rear wheel,” says Rahul. “We covered the classic TT rubber with full length fenders, which are rare items on our bikes—we like to keep them as minimal as possible.”

“Most custom bikes don’t get ridden in the rain because they’re a customer’s pride and joy, so we’ve never needed them.”

Pure class: A BMW R100RS airhead custom from Sinroja
In this case, fenders were essential for the style of the bike, so Sinroja hand-made a pair from aluminum, and left them with a bare, brushed finish to match the engine.

The rest of the BMW is an essay in simplicity, with classic touches all round. The brushed aluminum levers are from K-Tech, the grips and bars are from Renthal, and the tank has the classic BMW pinstripes over solid black paint. It was painted by Glenn at GD Design, and matches perfectly to the comfortable new leather seat.

Pure class: A BMW R100RS airhead custom from Sinroja
To ensure reliability, Richard at Motorcycle Wiring Specialists has made up a custom loom with state of art electronics from Motogadget, including an m.unit control box, switchgear and rear indicators. (The front blinkers are from Rizoma.)

There’s also a Motogadget speedo set into the big seven-inch headlight bucket, just like on the old /5 BMWs, and a tiny taillight to match.

Pure class: A BMW R100RS airhead custom from Sinroja
“The BMW sounds amazing, and it’s ready to become David’s pride and joy,” says Rahul.


If you’re feeling a twinge of jealousy, as we are, the next best thing is to see the this airhead in the metal. It’ll be on display at the Bike Shed show in London later this month.

Sinroja Motorcycles | Facebook | Instagram | Images by Wil Collins Photography

Pure class: A BMW R100RS airhead custom from Sinroja

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