The BMX Challenge is one of many side activities you can do in the game, and is accessible from pretty much the beginning of the game.
How to Unlock the BMX Challenge
In order to unlock the BMX Challenge, you will first need to complete the Big Smoke mission at the beginning of the game. Of course, it isn’t as simple as that, as you will need at least a Cycling Skill of 20% in order to actually begin the challenge. However, it is highly recommended that you have a Cycling Skill of 100% before attempting it, as some of the things you have to collect are a bit out of reach and this makes things much, much easier. To actually begin the BMX Challenge, head to Glen Park in Los Santos and look for the lone BMX sitting by one of the halfpipes.
How to Complete the BMX Challenge
The BMX Challenge is started upon climbing onto the bicycle at the specified location. This will cause 19 little red rings to appear in the park, and you need to collect them all before the timer expires. You start the challenge with 15 seconds on the clock and an additional 15 seconds is added for each checkpoint you collect. One strategy for this challenge is to collect all of the easy ones first, which will give you a larger clock, allowing you more time to grab the more difficult checkpoints. One of the more useful techniques during this challenge will be the Bunny Hop.
The Bunny Hop technique that you can do with the BMX is going to be your bread and butter in getting some of the coronas. To perform this, hold down the L1/LB/L button, depending on your platform of choice, until CJ squats down on the bike, then release it for a hop. Your Cycling Skill will dictate how high you can jump. At 100% Cycling Skill, your bunny hop will be the maximum height you can achieve. This is the sole reason you will want 100% Cycling Skill before attempting this challenge, since some of the checkpoints are much easier to grab with a max Bunny Hop.
Reward for BMX Challenge
For collecting all 19 checkpoints in time, you will be given $1,000 and also progress towards 100% Completion.