In Dragon Mines there are mine cart tracks that are zig zagging through the map. The very first one that crosses the road is shortly after the cave with the giant dragon on the right side and the pool of water on the left. For further reference it is also before the wooden spiral of road that goes up a giant right turn.
When you reach the tracks, slightly pause and take a right down the track following the mine cart. You will lose speed but go fast enough to escape the tunnel before you're run over for the trophy.