In cycling races all riders wear race numbers for easier identification. Are there som rules or traditions which decide which team gets which set of numbers?
By looking on some races, it looks that number 1 is assigned to the past winner, if they start again this year. But I am not sure how it works with higher numbers. I am also not sure what happens if the last year's winners does not start. Also, does it depend on the cyclist who won last year or on the team who won the previous edition of the race? If there are rules about this, are they different for stage races and one-day race?
For example, looking at 2016 Tour of Flanders startlist, the winner from last year was wearing number 1. But the rider who was the 2nd last year was wearing 25. The 2015 winner John Degenkolb could not race in 2016 Paris–Roubaix due to injuries. But his team still received the first numbers in the 2016 startlist.
The defending champion Nairo Quintana did not race at this year's Tirreno-Adriatico. In the startlist, the first race numbers were assigned to Tinkoff team and then it seems to continue alphabetically.