DiRT

If you're completing every tier before moving up to the next one, you'll unlock this following the Tier 7 Crossover race.

Crossover is a rally type in which 2 racers compete against each other in a cross race. They both start on the same track, one at the original starting line and one at exactly the middle. This way the cars won't get near each other, but it's still very competetive and much harder than most rally types.

Crossover is a much played rally type, to check which tier crossover ends, just check every race of every tier and the rally mode shall be revealed.

There are seven Crossover events in career mode (final one being the third event of Tier 7). Win all of these on any difficulty and the achievement will unlock.