Roehr RV1250sc Supercharged All-American Superbike - The American Alternative

American engineer Walter Roehrich thinks outside the norms-which is why his company is launching the world's first supercharged American superbike using the Porsche-designed V-twin engine from a Harley-Davidson V-Rod. This new all-American superbike joins the Australian-built Vee Two Super Squalo in bringing the supercharger system of forced induction to the two-wheel marketplace. But instead of the Super Squalo's format of converting an existing bike and clothing the result with streetfighter bodywork, Roehr is producing a complete from-the-ground-up product that-while also powered by a proprietary engine-also uses a different form of supercharging, housed in his own chassis design.

The Roehr RV1250sc builds on the promise of the prototype V-Roehr 1130 that I tested a year ago. That proof-of-concept model looked sharp, handled well, and had torque worthy of a sportcruiser, but with just 120 horsepower at the rear wheel in a package weighing 425 pounds dry, it simply lacked the requisite engine performance for a sportbike.

Roehrich solved this issue by attaching a Danish-made Rotrex centrifugal supercharger to the latest 5mm-overbore 1250cc version of the V-Rod motor, and modifying the chassis to suit. The outcome is substantially increased horsepower and torque, with a claimed 168 horsepower at 9100 rpm now on tap at the wheel, matched to 99.6 ft/lb of torque at 7600 rpm. All this is housed in a unique chassis that sports top-shelf equipment such as sleek carbon fibre bodywork, a single-sided swingarm, Ohlins suspension, Brembo radial brakes, forged aluminium Marchesini wheels, and Termignoni silencers. But the assemblage of parts doesn't come close to describing what a unique ride the RV1250sc really is.

Unlikely Beginnings
Roehrich originally had planned to build a sportbike using the light and compact 936cc 60-degree V-twin from Swedish off-road manufacturer Highland, but when supplies for that engine dried up he went looking for another powerplant, and the 60-degree V-Rod engine fit the bill. "I went to the Harley dealership and took measurements of the V-Rod engine," says Roehrich. "Everyone said it was too heavy, it wasn't suitable for a sport bike, and it was too big. But I was optimistic I could get it to work. It's actually not quite as long as a Ducati motor, for instance. So I bought a used V-Rod, and took it from there."

Creating a compact, light sportbike powered by a cruiser engine represented an engineering challenge. "Motorcycles almost design themselves, to some extent, based on the engine you're using," says Roehrich. "I knew wheelbase would be an issue, because although the V-Rod motor is a 60-degree Vee, it's still long. But it's possible to put it in exactly the right spot in the chassis to optimize weight distribution, while still retaining a long enough swingarm for good traction."

Roehrich accomplished this by positioning the V-Rod engine (converted to chain final drive, thus dispensing with the heavy belt pulley and cover) as close to the front wheel as possible. There's still 6mm tire clearance at full bottom on the 125mm (4.9 in.) front suspension stroke, while yielding a handy 1422mm (56 in.) wheelbase-8mm less than a Ducati 1098. The fully adjustable 43mm TiN-coated Ohlins inverted fork is set at a 23.5-degree rake, with 89mm of trail, and a 54/46-per cent forward weight bias on a motorcycle weighing 430 pounds.

An unusual blend of materials is used to create the Roehr's hybrid chassis. Manufactured to Roehrich's design by Union, Illinois-based chassis specialists Framecrafters, the frame uses a pair of CNC-machined 6061 billet-aluminum swingarm pivot plates epoxy-bonded and bolted to rectangular-section 4130 chrome-moly steel main frame spars. Roehrich believes his design combines the rigidity of an aluminium deltabox frame with the responsiveness of a tubular steel chassis. "To provide space for the supercharger installation, I had to widen the frame an inch each side," he reveals. "I didn't want the supercharger to be obtrusive, to have the belt sticking up out of the frame, so I'm pleased with the way it turned out. It looks nice and clean." The single-sided swingarm is likewise a steel fabrication made from chrome-moly sheet, the same weight as a Ducati's comparable cast aluminium unit and working a fully adjustable Ohlins shock via a rising-rate link; wheel travel is 4.5 inches.