Which driver won the Indianapolis 500 with the lowest average speed?

Ray Harroun won the Indianapolis 500 with the lowest winning average speed, completing the 1911 race at 74.602 mph.

The inaugural Indianapolis 500 covered 500 miles, or 200 laps, around the newly built Indianapolis Motor Speedway. Harroun drove a Marmon Wasp and finished in 6 hours, 42 minutes, and 8 seconds. The relatively slow average reflects the era’s early racing machinery, rougher track conditions, frequent mechanical problems, and long pit stops.

Harroun’s victory is famous for another innovation: he raced without the riding mechanic commonly carried by competitors. Instead, he used a small rear-view mirror, allowing him to monitor traffic behind the car. The device was considered unusual enough that officials initially questioned whether it was safe.

The question concerns winning average speed, not the slowest speed recorded by any finisher or the slowest qualifying run. Later winners, including Joe Dawson in 1912 and Louis Meyer in 1928, completed the race at substantially higher average speeds.