How long is the longest Tour de France stage ever to have been cycled?

Explanation

The longest Tour de France stage ever was the 5th stage in the 1920 edition of the race. 482 km long, the stage went from Les Sables d'Olonne to Bayonne. It was won by Firmin Lambot in 19 hours and 44 seconds. That year, the race was made up of 15 stages, making up 5,503 km altogether. The riders had an average speed of 24.072 km/h.