 At age eighteen, he began to drive in support events for the car races of the time.He was a mechanic, but sought to be a race car driver and signed on with the Duesenberg brothers after World War I. Hartz made his debut at the 1921 Indianapolis 500 race as Eddie Hearne's riding mechanic.The following year, Hartz was behind the wheel of the Duesenberg and finished in second place.