Here is the full list of all 8 Motorbike trophies - there are 3 bronze, 3 silver and 2 gold.
You conquered 100 Online tracks.
You completed 10 Online tracks.
You mastered 10 Exclusive tracks.
You reached the finish line of your first Exclusive track.
You finished your first Online track.
You dominated all Original tracks.
You are now a graduated Motorbiker.
You made it through your first Original track.