Records from the era are not complete, but Harroun contested at least sixty American Automobile Association-sanctioned races that were the predecessors of modern Indy car racing. In fact, Harroun won no fewer than seven shorter races at the Indianapolis Motor Speedway prior to his famous triumph in the first Indianapolis 500. In 1927, the AAA retroactively named Harroun its 1910 National Driving Champion.
Only a part-time racer, Harroun worked for the Marmon Motor Car Company, an Indianapolis-based automobile manufacturer that produced cars from 1902-1933. From the very start of the project, he was directly involved with the racing car that became known as the Wasp due to its distinctive yellow and black paint scheme.
One key feature of the Wasp that Harroun was given credit for is the development of the rear-view mirror, a device he successfully used in his Indianapolis win that eliminated the need for a riding mechanic and spotter. The creative solution to traffic management was something Harroun had seen on a horse-drawn taxi several years earlier when he served as a chauffer in Chicago.