From Wikipedia: “A succession of doping scandals in the 1960s, culminating in the death of Tom Simpson in 1967, led the Union Cycliste Internationale to limit daily and overall distances and to impose rest days.”

Meanwhile, wow, average speeds increased between 1903 to the present? You don’t say! The Tour must be getting easier! What about race cars, have those gotten faster too? If so, it can only be due to the tracks getting easier.

Interesting infographic, stupid label.

The dip around 2005 corresponding to the crackdowon on doping is significant. Most of the rest of the speed increase can be attributed to improvements in design, technology and training.