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 8 > 9: 30 Natura Magus orbs x2 (6hrs)
Lap 13 > 14: Heroic orbs chest x2 (8hrs)
Lap 17 > 18: 40 High Druid orbs x2 (8hrs)
Lap 19 > 20: 50 L Joker orbs chest x2 (8hrs)
Lap 20 > 21: 120 Natura Magus orbs x2 (8hrs)
Lap 24 > 25: 50 H Joker orbs chest x2 (8hrs)