Harley-Davidson models. In the late summer of 1929, Harley-Davidson introduced its 45 cubic inches (737 cm³) flathead V-Twin to compete with the Indian 101 Scout and the Excelsior Super X. This was the "D" model, produced from 1929 to 1931. Riders of Indian motorcycles derisively referred to this model as the "three cylinder Harley" because the generator was upright and parallel to the front cylinder. The Great Depression began a few months after the introduction of their 45 cubic inch (737 cm³) model. Harley-Davidson's sales fell from 21,000 in 1929 to 3,703 in 1933. Despite this, Harley-Davidson unveiled a new lineup
Harley-Davidson by the Davis Machine Company from 1917 to 1921, when Davis stopped manufacturing bicycles. By 1920, Harley-Davidson was the largest motorcycle manufacturer in the world, with 28,189 machines produced, and dealers in 67 countries. In 1921, a Harley-Davidson, ridden by Otto Walker, was the first motorcycle ever to win a race at an average speed greater than . During the 1920s, several improvements were put in place, such as a new 74 cubic inch (1,212.6 cm³) V-Twin, introduced in 1921, and the "teardrop" gas tank in 1925. A front brake was added in 1928 although notably only on the J/JD