At the northwest corner of Downtown is a dirt track, and parked to the southwest corner of it is a Sanchez dirt bike, and a Landstalker SUV. Get into one of them to begin either "Trial By Dirt" or "Test Drive".
They are simple checkpoint courses around the dirt track. For 100% completion, you need to only beat both of them once, which is not hard with a cautious drive around it. However, the reward will get bigger upon recompletion, but you have to deal with issues such as rain, barrels and Haitians attacking you in these instances.
Upon your first try and completion of the trials, you are rewarded $100. Although I have not gone back to retry these, the reward is to supposedly double each time.
