The BMX Challenge is a side mission in Grand Theft Auto: San Andreas. The mission is started by entering a parked BMX in a skate park in Glen Park with a cycling skill of more than 20%. The goal of the mission is to collect 19 floating coronas around the skate park before the countdown timer runs out of time. The timer starts when the cutscene finishes. Each corona will add 10 seconds to the timer. The reward for completing this mission is $1,000 and a step closer to 100%.
If you have a low cycling skill it will be basically impossible to complete the challange. Therefore you will need to do "super bunny hops" in order to get the highest corona, which is right above another low corana in the west side of the skate park. To do the super bunny hop you will need to be wielding a Sub Machine Gun like the TEC 9 and do a bunny hop and right after, you shoot. You do not actually have to shoot but to hold the gun up, if the timing is fast enough you will jump much higher but that requires some practice.