Grand prix racing had been around for nearly half a century before the arrival of Formula 1. The inaugural world championship in 1950 is often used as a starting point, but there had been plenty of brilliant machines and epic races already. The rules were modified regularly from the inaugural French GP in 1906 to the outbreak of the Second World War. It was a period of huge change and innovation, creating a wide variety of eclectic machines – and some milestone ones. For this list, we’ve considered the success of each car that competed in major GP events between 1906 and 1939, and the impact they had on motorsport.…