The Adler M200 was introduced at the Frankfurt show in 1951. It was a twin cylinder with alloy heads, helical gears connecting the primary drive to the gearbox, a wet clutch, and an innovative approach to sealing the crankcase. The M200 was well regarded by the press, but just 2 years later, Adler bumped the displacement up to 250cc, and created a real star. The perfectly square bore and stroke created a smooth engine, and a more rigid frame enhanced handling.
In 1954, sporting versions of the 250 run by privateers managed multiple top ten finishes. Those RS250 versions reached top speeds of 120mph. A few of them added water cooling to maintain full performance as the engine got hotter. By 1955, this began to change top tens into podiums and victories. However, the timing was bad. Adler was battling the rapid decline in motorcycle sales as cheap cars became available. They had also absorbed a struggling TWN in 1956, exacerbating the decline. They eventually were absorbed by Grundig, who only wanted the typewriter portion of the business and ceased motorcycle production in 1958.
But that is not the end of the story. Amazingly, tuners and privateers continued to campaign the RS250. Men such as Dieter Falk, and Willi Klee pushed performance and created more top tens in the Isle of Mann TT, and the 250cc world championship. For more on Adler see Flight of the Adler.