Mercedes-Benz introduced the W08 lineup in 1928, and it was the first car offered by the German carmaker with an inline-eight powerplant, and the Sport Roadster was a one-of-a-kind example.
While it is not precisely how such versions of the W08 were produced, there are few things clearly known: it was designed by no other than Ferdinand Porsche, and two vehicles appeared in 1929 on the Alpine Rally and on the 8-hour ADAC (the German Automobile Club) race. These were driven by the famous Rudolf Caracciola and Otto Merz. These cars were not shown in the carmaker's brochure nor offered for sale.
Designed on a shortened version of the W08's chassis, the Sport Roadster was a race car built with one purpose: to win races. Thus, the carmaker decided to make it around the engine compartment. At the front, it sported the big radiator protected by an additional mesh and placed the headlamps in a way that they didn't block the cooling area. Since it was not intended to be used on public roads with open traffic, it didn't feature a front or a rear bumper. Unlike the rest of the W08 range, the Sport Roadster featured wired wheels instead of wooden (artillery) ones.
The cockpit was tailored around the drivers, and they offered just two seats, so it could pass the mandatory race specs. Moreover, the seat was fixed on the floor. In front of the driver, a four-spoke steering wheel dominated the driver's side, while the dials were placed in the middle of the dashboard.
Under the hood, Mercedes-Benz installed a 4.6-liter inline-eight fed by carburetors, and it offered the same power as the rest of the W08 range: 80 PS (79 hp). Power was sent to the rear wheels via a four-speed manual transmission.