Rewards can be seen in the game.
Race tips can be found here.
To get any reward you have to finish lap 4 to qualify. If you win and reach lap 15 you will still only get one heroic dragon when the race ends.
Lap 5 > 6: 250k Food x2 (9hrs)
Lap 7 > 8: 750k Food x2 (9hrs)
Lap 12 > 13: 30 Betrayer orbs x4 (10hrs)
Lap 17 > 18: 1k Random Tokens x6 (11hrs)
Lap 19 > 20: 40 Betrayer orbs x5 (11hrs)
Lap 20 > 21: 2m Food x2 (11hrs)
Lap 24 > 25: 3m Food x2 (11hrs)
Lap 30 > 31: 4m Food x2 (12hrs)
Lap 32 > 33: 5m Food x2 (12hrs)
Lap 34 > 35: 5m Food x2 (13hrs)
Lap 36 > 37: 6m Food x2 (13hrs)
Lap 38 > 39: 6m Food x2 (13hrs)
Lap 40 > 41: 6m Food x2 (14hrs)
Lap 42 > 43: 6m Food x2 (14hrs)
Lap 44 > 45: 6m Food x2 (14hrs)
EDIT: New announcement showing you get the Heroic from lap 15 AFTER the race ends.
EDIT @: It doesn't get clearer than this, I LOVE IT!!