Thanks Remi for your help. But a friend of mine(also a racer) said me that if you use a board like 80 or 87, and if the wind stops during the race, the 80 or 87 won't be the one. He said me that I couldn't take the risk in the race. He also said that I am 16 years old so I will grow and put on weight so 87 or 80 will cause a problem. He said 90 is the one.