Written by Tim Huber.

Unlike most creative mediums, custom motorcycle building isn’t taught in classrooms, and is instead of a mishmash of semi-related skills, often acquired over many years in other careers before being applied to one-off two-wheelers. For Tossa R’s owner, Tudor Dunev, that training and preparation came in the form of an illustrious four-wheeled motorsport career of building — and piloting — championship-winning drift and rally cars.

The Bulgarian racer’s accolades include a VW Lupo Cup championship, five consecutive Bulgarian Touring Car championship titles, and the title of 2010 European Drift King, among many others, the most recent of which being the 2019 Bulgarian Eco Rally which Dunev also took first in. So, after spending years churning out highly-competitive race cars engineered to take on extended abuse in some of the world’s toughest environments, Tudor has applied his skill-sets to running a successful customs shop with a proven history of quality and craftsmanship.

Tudor’s operations are split into two separate divisions: there’s Top Drift Services which repairs, tunes, and preps drift and race cars; and Tossa R, which focuses exclusively on custom motorcycles. Since the shop’s inception, it’s completed a variety of BMW-based bikes, all of which bare a similar theme but are each distinctly different. And Tossa’s latest Bavarian-based build is this lovely K100RS.

Though the donor bike looked to be a fairly decent shape, its age and extensive milage ultimately prompted Tossa to call on a full engine rebuild, tearing the lump apart, replacing the lion’s share of the internals with refreshed items and bestowing the mill with new gaskets and seals throughout. Once pieced back together, the engine’s exterior was hit with a coat of fresh black paint.

The stock respiratory bits are no more, with air now being sucked through an aggressive-looking forward-facing, cruiser-style pod filter that hangs on a custom extension piece. In place of the factory exhaust is a bespoke set of four-into-one pipes feeding back into a carbon fiber muffler that pokes out on the right side from underneath the single-sided swing-arm.

An elaborate custom subframe was drawn up before being reproduced with new tubular stock, along with a thick seat-pan-esque piece. The new framework cleans up the aft end of the build, provides support for the rider’s seat, and acts as the mounting point for the BMW’s revised rear suspension setup. Though the original swing-arm remains in play, it’s been reinforced via a new supplementary tubular structure that links to a non-offset modern, adjustable mono-shock arrangement.

Completing the rolling chassis is a beefy set of contemporary upside-down gold forks slotted in custom triples. On top of the improved handling, the build also sees its stopping power upgraded in the form of a modern dual-disc setup bit by four-pot calipers. Later model, split five-spoke rims and Pirelli Diablo Rosso rubber also help to bring the Beemer’s performance prowess into 2020.

The K-series now affords a markedly more attack-ready riding position, with a new hunched-forward triangle resulting from new clip-ons and a set of black-anodized adjustable rear-sets. The cockpit has also been treated to new Barracuda grips, modern switchgear, bar-end mirrors, new levers, and a round analogue tach/digital speedo combo. Perfectly following the contours of the new seat-pan and subframe is a minimalistic, ultra-low-profile, bobber-meets-scrambler-style seat adorned in gold accent stitching running up the center of the saddle and outlining the edges of the leather.

Like the powertrain, the frame, modified swing-arm, subframe, and wheels have all been powder-coated or painted in a gloss black. The bulk of the stock tank wears the same dark glossy hue, though the knee dent areas now boast a metallic gray, separated from the rest of the black via gold accent striping and gold “007” script that add a dash of color to the mix and compliments the build’s new inverted front-end. There’s also a new set of monochrome Roundels, furthering the build’s murdered-out theme.

With 95% of the build completed, the Tossa crew set out about polishing off the finishing touches. This included relocating the battery to custom housing that now rests just above the swing-arm pivot and installing top-shelf Rizoma-style reservoirs. There’s also new lighting across the board: out front a classic round headlight bucket houses a modern bulb, while front turn signal duties go to a pair of Motogadget m-Blaze pin indicators. Out in back, small circular taillights cap off either end of the back of the one-off subframe, serving double duty as turn signals and utilizing the new framework, back tire, and bottom of the new seat-pan to illuminate light off the red LEDs, creating a unique glowing effect.

The completed RS wonderfully demonstrates Tossa R’s proclivity for breathing new life into tired old Bavarian bikes. Looking at the shop’s earlier works, it becomes abundantly clear that lessons have been taken away from each project, all of which have now been applied to this latest work. The level of sheer craftsmanship and engineering on display doesn’t hurt either. Whether he’s getting sideways on four-wheels or organizing another bespoke two-wheeled project, we’re looking forward to seeing what Tudor has got in store next.