There is a pretty strong culture in bike racing of making deals like this and sticking to them, because in a break like this, if two people work together, they have almost literally twice as good a chance of winning.
For example, Lance Armstrong and Marco Pantani on the famous Alpe d'Huez in the Tour de France: Lance offered him the stage win if he would work with him so he could make time on his rivals for the overall 23 day race general classification:
In top level professional riding, if you renege on a deal like this, you will have a seriously hard time making another deal like this in the future and that will seriously impair your professional prospects, because these deals are everywhere because of the multi-goaled nature (stage vs. overall vs. mountain points vs. sprint points) of the sport.
For example, Lance Armstrong and Marco Pantani on the famous Alpe d'Huez in the Tour de France: Lance offered him the stage win if he would work with him so he could make time on his rivals for the overall 23 day race general classification:
http://www.cyclingnews.com/features/armstrong-if-i-was-the-c...
In top level professional riding, if you renege on a deal like this, you will have a seriously hard time making another deal like this in the future and that will seriously impair your professional prospects, because these deals are everywhere because of the multi-goaled nature (stage vs. overall vs. mountain points vs. sprint points) of the sport.