Find the man standing on the sidewalk in El Corona (a red marker will appear in front of him when you're on foot). Approach him and he'll ask if you're looking for the lowrider competition. Respond positively and he'll direct you to the nearby parking lot.
You will have a minute or so to get to the competition location or it will disperse. This is why it's better to get the low-rider before you start the challenge.
Once you get to the competition location, you will challenge a banger as you did in the Cesar Vialpando mission. When the music starts, move the hydraulics in the indicated direction in time to the beat.
Synchronization and correct movements add to your score. You must get a better score than your opponent to win the bet.
Some people turn down the sound and focus on the arrows to get the proper synchronicity.
Cash: whatever you bet.
Completion of this challenge (apart from the Cesar Vialpando mission) is not required for 100% completion.