Fred and his brother, August "Augie" Duesenberg, began building and racing bicycles in Iowa in the 1890s. They also began experimenting with gasoline-powered, internal combustion engines. The brothers designed one of their own engines around 1900, as well as building motorcycles. After working at a garage in Des Moines, Iowa, Fred and Augie had a bicycle repair shop in Rockford, but the business went bankrupt in 1903. A short time later the brothers established another shop in Garner, Iowa, but Fred left the business in 1903 to work for the Thomas B. Jeffery Company, a manufacturer of Rambler bicycles and early automobiles in Kenosha, Wisconsin. Fred returned to Iowa a year later to work as a machinist in a Des Moines auto supply company before opening a garage with Cheney Prouty and working as a sales agent for Rambler.