They run the race course, before the actual race, hence the word Pre. They are trying to learn the course before raceday. They use a lesser modified vehicle than the race car or truck, but these vehicles must be capable of the terrain to a certain point, just not as fast and usually not as expensive. These are called ''pre-runners''.
OR.........The fastest immigrants. They run for the border first and attract the attention of immigration officers so the rest can slip by......pre-runners!