Ripley wrote:
I guess you cannot start a race due to lack of riders. You can make all but one rider drop out on stage 1 and the one guy will be fine riding the rest alone.

So you probably have two concurrent races and can't start the second one. Without an editor the easiest option would be to load the last weekly save and make riders drop out of the other race so you have enough to start the new race.

With an editor you can do it on the same day, though I'm not sure how much you need to change. Might be enough to go to the table dyn_cyclist and change fkidrace to 0 and fkidcyclist_state to free until you have enough free riders for the new race. If somebody is injured you can change the injured state to free and remove the fkidinjury, set to 0.