The BMW 309 was introduced in 1934 as the successor to the BMW 3/20 PS. It adopted the technically advanced tubular frame from the BMW 303 and combined this with the revised four-cylinder engine that powered the BMW 3/20 PS. By comparison with its predecessor, the bore of the BMW 309 was enlarged by 2 mm in order to achieve slightly more displacement and therefore more power. A total of 2,860 sedans (including a roll-top sedan) had been manufactured by the end of the production run in 1936.