Once each level is completed for the first time you will recive a bronze medal and if you try at the level again you will be required to race silva instead of bronzen. Beating silva is more difficult than bronzen due to the racer being faster. However if you go to the bottom of the pick track screen you will see silver shown. This can be changed to bronze by pressing b. When this is selected you will be racing for a silver medal only against bronzen. The only thing that will not change is the number of tricks required for a silver/gold medal. Therefore you will have to be good at your tricks to advance and not racing faster racers!