I remember hearing about this too.
Any one try explaining what you need to do ?
I heard about this for DTR 2 as well.
www.ign.com/cheats/games/dirt-track-racing-pc-12874
"Easy Win
When the race starts go a lap and wait beside the white line. Don’t go through it stay just close to it. Wait on the side and when it brings up the one more lap flag go through the white line. PS: If you needed nine laps and only did one, this will still work.
"