Suggested

Choose your own car number

I dont need to explain this one in that much detail. Numbers 2-99 available, when teams get promoted and there are clashes the higher team picks their number first. Add the option of No.1 for champions too.

EDIT: for ideas of how to settle 'same number choice' debates, see the 3rd post on this page.

How about also making it, so that if you had a number, 87 for example, you get relegated and somebody else, new into elite, also choses 87, then when you promote back up, the first person to have chosen that number gets that number and ither racers get numbers that have not already been taken and are closest to 87?

Do not forget here that car number 87 is a random example.

I don't know really Tim. In general if there is a conflict of numbers, this could be sorted in many different ways, with some suggestions below:

-by the people themselves, over messages, in a mature way
-by an automatic random selection, the loser being awarded the next pick of numbers
-by rewarding managers higher in league standings with first picks
-by everyone new to the tier/wishing to change number entering a list of 3 or 4 chosen numbers in order of preference
-by the league host

(I would personally prefer the 4th option)
Also, there must be a choice to change or not, so there must be some kind of tick box form to confirm this, for example a notification given in the last 5 races of the previous season asking whether a number switch is wanted or not. It saves time for those who do not want to switch.
The time for re-allocating numbers could be in between seasons, or decided by the final round of the previous season, doesn't really matter. If polling is missed by an offline manager, they could be given a randomly selected number left when all the active managers have chosen theirs.

Anyone feel free to tweak these ideas however you want.