Why does cc matter in a dirt bike?

CC refers to the engine displacement or in other words how big the motor is. Larger cc engines produce more power then a low cc engine can. When racing dirt bikes they require the engine size to be near the same size so that everyone has an equal chance in the race. For example: Racing a 125cc bike against a 500cc bike would be a one sided race. The 125cc bike would not have a chance against the power a 500cc bike puts out.