Trial By Dirt is a side mission in Grand Theft Auto: Vice City which is triggered when jumping on the parked Sanchez on the dirt track in Downtown. It is a checkpoint mission, but it has no time limit. To complete this mission, the player must clear each checkpoint without destroying their bike or dismounting too long from it. There is a health pickup nearby on the track, in case Tommy falls off and gets injured. If the player enters the Landstalker instead, a similar mission entitled Test Track will start, the reverse of this mission but is a bit harder since it will fail if Tommy flips the car or bail.
The player can keep playing this mission once they've completed it. Each time they beat their time record, they receive a higher monetary reward.
Due to a bug in the game, the initial scores of both Trial By Dirt and Test Track will have the same time results once both scores are listed in stats. Once both missions are played again and each time is beaten, the scores will be individual as they should be.